Biologically derived epicardial patch induces macrophage mediated pathophysiologic repair in chronically infarcted swine hearts

There are nearly 65 million people with chronic heart failure (CHF) globally, with no treatment directed at the pathologic cause of the disease, the loss of functioning cardiomyocytes. We have an allogeneic cardiac patch comprised of cardiomyocytes and human fibroblasts on a bioresorbable matrix. This patch increases blood flow to the damaged heart and improves left ventricular (LV) function in an immune competent rat model of ischemic CHF. After 6 months of treatment in an immune competent Yucatan mini swine ischemic CHF model, this patch restores LV contractility without constrictive physiology, partially reversing maladaptive LV and right ventricular remodeling, increases exercise tolerance, without inducing any cardiac arrhythmias or a change in myocardial oxygen consumption. Digital spatial profiling in mice with patch placement 3 weeks after a myocardial infarction shows that the patch induces a CD45pos immune cell response that results in an infiltration of dendritic cells and macrophages with high expression of macrophages polarization to the anti-inflammatory reparative M2 phenotype. Leveraging the host native immune system allows for the potential use of immunomodulatory therapies for treatment of chronic inflammatory diseases not limited to ischemic CHF.

A comprehensive study of the incremental prognostic value of novel biomarkers in PARADIGM-HF (Bio-PREDICT-HF)

Background

Although multiple novel biomarkers have individually been shown to predict outcomes in patients with HFrEF, the value of these over and above conventional clinical and laboratory variables, plus natriuretic peptides, is uncertain.

Purpose

To test the incremental predictive value of 11 novel biomarkers added to a recent prognostic model 1 (PREDICT-HF) derived in PARADIGM-HF and validated in ATMOSPHERE and the Swedish heart failure registry. The PREDICT-HF model includes clinical variables, standard laboratory variables, and BNP or NT-proBNP.

Methods

1559 participants enrolled in PARADIGM-HF had all 11 biomarkers of interest measured. These reflected different pathophysiological pathways: (i) myocyte injury (high sensitivity cardiac troponin T), (ii) cardiac remodelling and inflammation (growth stimulation expressed gene 2, growth differentiation factor-15 and galectin-3), (iii) extracellular matrix remodelling (matrix metalloproteinase-2, matrix metalloproteinase-9, tissue inhibitor of metalloproteinase-1), (iv) neurohormonal pathways (aldosterone) and (v) renal dysfunction and injury (cystatin C, kidney injury molecule-1 and urinary albumin to creatinine ratio). The incremental prognostic value of these biomarkers was evaluated using Harrell's C statistic.

Results

The mean age of participants studied was 67.3 (SD 9.9) years, 1254 (80%) were men and 1103 (71%) were in NYHA class II. During a median follow-up of 31 months, 197 patients died and 300 experienced the primary composite outcome (cardiovascular death or heart failure hospitalization).

When each candidate biomarker (log unit) was added individually to the PREDICT-HF base model, GDF-15, ST2, TIMP1, cystatin C, hsTnT and UACR were independent predictors of all-cause mortality (Table 1). GDF-15, TIMP1, hs-TnT and cystatin C consistently increased the risk of both all-cause mortality and the primary outcome. Individuals who had all 4 biomarkers elevated (compared to none elevated) had the highest risk: HR for all-cause mortality 3.65 (2.01–6.64), p<0.0001. Adding these 4 biomarkers to the baseline PREDICT HF model improved the C statistic for all-cause mortality from 0.726 to 0.745.

Conclusion

Several novel biomarkers provide meaningful additional prognostic information in patients with HFrEF. A multimarker approach incorporating biomarkers reflecting different pathophysiological pathways added most information. This approach may be useful in refining risk and targeting treatment.

Funding Acknowledgement

Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): The PARADIGM-HF trial was funded by Novartis.J.J.V.M is supported by a British Heart Foundation Centre of Excellence Grant

History of stroke in patients with heart failure: prevalence, baseline characteristics and clinical outcomes

Background

Stroke is an important but neglected comorbidity in patients with heart failure (HF). Little is known about the characteristics and outcomes of HF patients with a history of stroke.

Purpose

To examine the prevalence of prior stroke in patients with HF and reduced ejection fraction (HFrEF) and HF with preserved ejection fraction (HFpEF), the clinical characteristics of patients with a history of stroke, and the clinical outcomes in patients with prior stroke compared to those without.

Methods

Individual patient data analysis using three recent HFrEF trials (ATMOSPHERE, PARADIGM-HF, and DAPA-HF) and HFpEF trials (CHARM-Preserved, I-Preserve, TOPCAT-Americas, and PARAGON-HF). Cox regression was used to analyze clinical outcomes.

Results

Among 20159 HFrEF patients enrolled, 1683 (8.3%) had a history of stroke and among the 13252 patients with HFpEF 1287 (9.7%) had a prior stroke. Compared to patients without stroke, those with stroke were slightly older and more likely to have a history of hypertension, myocardial infarction, atrial fibrillation, diabetes, carotid artery disease, and peripheral artery disease (for both HFrEF and HFpEF). Patients with a history of stroke had worse NYHA class and KCCQ scores, and a higher rate of fatigue; they also had a higher median NT-proBNP level and lower eGFR than those without prior stroke (whether HFrEF or HFpEF). Systolic BP, pulse pressure and LVEF did not differ susbtantialy between patients with and without a history of stroke. The table shows outcomes according to history of stroke or not, stratified by LVEF phenotype. During follow-up, all fatal and non-fatal outcomes were significantly more common in patients with a history of stroke. The augmentation of risk tended to be greater in patients with HFpEF than HFrEF, but was not statistically different.

Conclusion

Approximately 1 in 11 patients in recent HF trials had a history of stroke and these patients were at higher risk of fatal and non-fatal events than those without prior stroke. HF hospitalization as well as atherothrombotic events (myocardial infarction and stroke) were more common among patients with prior stroke – patients with prior stroke had at least 30% higher risk of all events examined, regardless of LVEF, and more than double incidence of repeat stroke.

Funding Acknowledgement

Type of funding sources: Other.

Stroke in patients with heart failure and reduced ejection fraction without atrial fibrillation: external validation of a risk model

Background

Heart failure (HF) ranks only second to atrial fibrillation (AF) as a cause of cardio-embolic stroke. Although anticoagulation reduces this risk in HF patients not in AF, the risk/benefit profile in relatively unselected populations is not favourable. Identification of patients at high risk of stroke may allow targeted and safer use of prophylactic anticoagulant therapy. Previously, we proposed a simple risk model for stroke in patients with HF and reduced ejection fraction (HFrEF). However, this model was derived from the two older trials (published in 2007/2008) and was not externally validated.

Purpose

We aimed to evaluate the current incidence of stroke in patients with HFrEF not in AF receiving modern pharmacological therapy and to validate our stroke prediction model.

Methods

We examined patient-level data from the PARADIGM-HF, ATMOSPHERE, and DAPA-HF trials. The risk score was calculated following: 7.39×(insulin-treated diabetes) + 6.53×(previous stroke) + 2.80×[ln(NT-proBNP (pg/ml)) × 0.1182]). According to the tertile of risk score, we divided the patients into three groups. Patients with AF were defined as those with either AF on an ECG or a history of AF.

Results

Of the total of 20,159 patients (who experienced 590 strokes) enrolled in the three trials, 12,751 patients did not have AF at baseline. Of those, 1,143 patients (9%) had insulin-treated diabetes, 873 patients (6.8%) had a history of the previous stroke, and the median value of NT-proBNP was 1,243 pg/ml. During a median follow-up of 2.0 years, 346 (2.7%) experienced a stroke (11.7 per 1000 patient-years). Figure 1 shows cumulative incidence function plots for stroke according to the tertile of risk score in 12,331 patients whose risk score can be calculated. The number of strokes in tertile 1, 2 and 3 were 80, 102 and 149, respectively. The 3-year cumulative incidence function rates of stroke were 2.0 (95% CI: 1.5–2.5) % in tertile 1, 2.6 (95% CI: 2.1–3.2) % in tertile 2, and 4.3 (95% CI: 3.6–5.2) % in tertile 3, respectively. In patients with tertile 3, the stroke rate was 18.1 per 1000 patient-years (compared to 20.1 per 1000 patient-years in patients with AF not receiving anticoagulation). In the Cox model, risk for stroke increased according to the elevation in the risk score (tertile 2: HR 1.47 (95% CI 1.09–1.97), tertile 3: HR 2.53 (95% CI 1.92–3.33), with tertile 1 as reference). Figure 2 shows calibration plots by comparing observed and predicted probabilities of stroke at 1 to 3 years. Discrimination evaluated using the overall c-index 0.84 (95% CI: 0.75–0.91) was good.

Conclusions

These findings validate a previously described predictive model and confirm that it is possible to identify a subset of HFrEF patients without AF who have a risk of stroke that approximates to that in patients with AF. In these patients, the risk/benefit balance might justify the use of prophylactic anticoagulation, but this hypothesis needs to be tested prospectively.

Funding Acknowledgement

Type of funding sources: Foundation.

Prevalent and incident anaemia in PARADIGM-HF and effect of sacubitril/valsartan

Background

Anaemia is common in patients with HFrEF and is associated with poor clinical outcomes. Although they reduce rates of mortality and heart failure hospitalization, renin-angiotensin (RAS) blockers lower haemoglobin and may induce anaemia. Concomitant neprilysin inhibition might ameliorate this effect of RAS blockers.

Purpose

We investigated the effect of sacubitril/valsartan compared with enalapril on clinical outcomes, according to anaemia status, and on haemoglobin levels in PARADIGM-HF.

Methods

Patient characteristics and clinical outcomes were compared between patients with and without anaemia (defined as haemoglobin <120 g/L in women and <130 g/L in men) at baseline. We investigated the effect of randomized treatment (sacubitril/valsartan or enalapril) on clinical outcomes according to anaemia status at screening. We also examined the effect of treatment on change in haemoglobin from baseline and on the incidence of anaemia. The primary endpoint in PARADIGM-HF was the composite of heart failure hospitalization or cardiovascular death.

Results

Of 8239 participants with a baseline haemoglobin measurement, 1677 (20.4%) were anaemic. Compared to those without anaemia, patients with anaemia had a more severe heart failure profile, worse kidney function, greater neurohormonal derangement and worse clinical outcomes. Sacubitril/valsartan, compared to enalapril, reduced the risk of the primary endpoint similarly in patients with anaemia (HR 0.84, 95% CI 0.71–1.00) and without anaemia (HR 0.78, 95% CI 0.71–0.87), p-value for interaction=0.478. Between baseline and 12 months, haemoglobin decreased by 1.5 (95% CI 1.7 to 1.2) g/L with sacubitril/valsartan compared with 2.3 (2.6 to 2.0) g/L with enalapril group: mean difference 0.8 (95% CI 0.5 to 1.2) g/L, p<0.001. The between-treatment difference apparent by 12 months, persisted up to 36 months. Patients assigned to sacubitril/valsartan were less likely to develop new anaemia at 12 months [321 of 2806 (11.4%)] compared to patients randomized to enalapril [440 of 2384 (15.6%)], odds ratio 0.70 (95% CI 0.60–0.81), p<0.001.

Conclusions

Compared to enalapril, sacubitril/valsartan reduced mortality and hospitalization in HFrEF patients with and without anaemia. Haemoglobin decreased less with sacubitril/valsartan and the incidence of new anaemia was lower in the sacubitril/valsartan group compared with the enalapril group.

Funding Acknowledgement

Type of funding sources: Private company. Main funding source(s): PARADIGM-HF was funded by Novartis.

Implications of the 2021 CKD-EPI cystatin C/creatinine eGFR equation for eligibility for therapy in HFrEF: insights from PARADIGM-HF

Background

Estimated glomerular filtration rate (eGFR) is a key determinant of eligibility for many life-saving therapies in HFrEF. Recently, the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) provided new equations based on creatinine (CKD-EPIcr), cystatin C (CKD-EPIcys) or both (CKD-EPIcyscr) that do not include race. These new equations may reclassify individuals, irrespective of race, from one eGFR category to another, with implications for eligibility for HFrEF treatments.

Purpose

To assess the difference between eGFR estimation using the 2021 CKD-EPIcyscr equation and the 2009 CKD-EPIcr and Modification of Diet in Renal Disease Study (MDRD)-4 equations which are still standard in many European laboratories.

Methods

We included patients from PARADIGM-HF with cystatin C and creatinine values available at the time of randomization. For each patient, baseline eGFRs were calculated using the 3 equations described. Our focus was on patients with chronic kidney disease (CKD) stages III–V.

Results

Overall, 1910 patients were eligible. Mean age was 67.3 (10.1) year and 385 (18.7%) were female. Using 2009 CKD-EPIcr, 779 patients were in CKD stages 3–5, of which 233 (30%) were reclassified to a better CKD stage (higher eGFR) with the 2021 CKD-EPIcyscr equation (Table 1). Similar reclassification was seen when comparing MDRD-4 with the 2021 CKD-EPIcyscr equation: 277 (33%) of 831 patients in CKD stages 3–5 were reclassified to a better CKD stage (Figure 1).

Conclusions

The 2021 CKD-EPIcyscr equation favourably reclassified CKD stage in a large percentage of patients with HFrEF and a low eGFR, potentially increasing the proportion of these patients considered eligible for guideline-recommended therapies.

Funding Acknowledgement

Type of funding sources: None.

Myocardial Mechanisms Causing Heart Failure Early After Cardiac Transplantation

Early after heart transplantation, some patients have heart failure (HF) with preserved left ventricular ejection fraction (LVEF), in the absence of rejection. The purpose of this study was to define the mechanisms causing HF early after transplantation and to determine whether these mechanisms involve changes that occur in active or passive myocardial properties. Eleven consecutive patients 1 week after heart transplantation underwent right heart catheterization and echocardiography with an endomyocardial biopsy. Hemodynamic measurements were obtained at spontaneous heart rate, and then were repeated at three atrially paced rates increased in 20-bpm increments above spontaneous heart rate. At baseline, 5 patients (group 1) had clinical HF and a pulmonary capillary wedge pressure (PCWP) > or = 16 mmHg, and 6 patients (group 2) had no clinical evidence of HF and a PCWP < 16 mmHg. LVEF was normal in all 11 patients. The relationships between cardiac index versus heart rate (HR) and PCWP versus HR were normal in all 11 patients. These normal function-versus-frequency relationships suggested that there were no significant abnormalities in the active myocardial processes of contraction or relaxation. In group 1 patients, the PCWP was significantly increased but the left ventricular end diastolic dimension was normal, suggestive of diastolic stiffness. Early after transplantation, there was a significant increase in LV wall thickness in group 1 patients as compared with preexplantation values despite myocardial biopsies in all 11 patients, showing no evidence of rejection, cardiomyocyte hypertrophy, or interstitial fibrosis thus suggestive of myocardial edema.

Diastolic heart failure. Diagnosis, prognosis, treatment

It is now abundantly clear that congestive heart failure caused by a predominant abnormality in diastolic function (i.e., diastolic heart failure) is common and causes a significant increase in morbidity and mortality. However, there is continued controversy surrounding the terminology used to describe patients with heart failure and the criteria used to make the diagnosis of diastolic heart failure. As a result, clinical therapeutic trials have been slow to develop and difficult to design. Fortunately, these controversies are yielding to an emerging consensus. Recent clinical studies have provided sufficient data to develop standardized diagnostic criteria to define diastolic heart failure. Experimental studies have provided increased insight into the mechanisms causing diastolic heart failure. Together, these clinical and experimental studies are being used to design targeted clinical trials to test effective treatments for diastolic heart failure. The purpose of this review is to describe the criteria used to diagnose diastolic heart failure, the effects of diastolic heart failure on prognosis, and approaches to treatment.

Heart failure with a normal ejection fraction: is measurement of diastolic function necessary to make the diagnosis of diastolic heart failure?

BACKGROUND

The diagnosis of diastolic heart failure is generally made in patients who have the signs and symptoms of heart failure and a normal left ventricular (LV) ejection fraction. Whether the diagnosis also requires an objective measurement of parameters that reflect the diastolic properties of the ventricle has not been established.

METHODS AND RESULTS

We hypothesized that the vast majority of patients with heart failure and a normal ejection fraction exhibit abnormal LV diastolic function. We tested this hypothesis by prospectively identifying 63 patients with a history of heart failure and an echocardiogram suggesting LV hypertrophy and a normal ejection fraction; we then assessed LV diastolic function during cardiac catheterization. All 63 patients had standard hemodynamic measurements; 47 underwent detailed micromanometer and echocardiographic-Doppler studies. The LV end-diastolic pressure was >16 mm Hg in 58 of the 63 patients; thus, 92% had elevated end-diastolic pressure (average, 24+/-8 mm Hg). The time constant of LV relaxation (average, 51+/-15 ms) was abnormal in 79% of the patients. The E/A ratio was abnormal in 48% of the patients. The E-wave deceleration time (average, 349+/-140 ms) was abnormal in 64% of the patients. One or more of the indexes of diastolic function were abnormal in every patient.

CONCLUSIONS

Objective measurement of LV diastolic function serves to confirm rather than establish the diagnosis of diastolic heart failure. The diagnosis of diastolic heart failure can be made without the measurement of parameters that reflect LV diastolic function.

beta-Adrenergic and endothelin receptor interaction in dilated human cardiomyopathic myocardium

BACKGROUND

Although end-stage dilated cardiomyopathy (DCM) is characterized by defects in beta-adrenergic receptor (beta-AR) activity and increased endothelin-1 (ET-1), possible interactions between these 2 systems remain to be defined. Accordingly, the goal of this study was to determine the effects of ET receptor activation on beta-AR signaling through measurement of cyclic adenosine monophosphate (cAMP) in normal and DCM myocardium.

METHODS AND RESULTS

Myocardial sarcolemmal preparations were prepared from normal human (n = 6), dilated cardiomyopathic (n = 10), and ischemic cardiomyopathic (ICM, n = 10) tissue. Basal cAMP production was measured in the presence of ET-1 alone (10(-6) to 0(-9) mol/L) as well as after (-)isoproterenol (10(-6) to 10(-2) mol/L) or forskolin (0.05 to 30.0 micromol/L) stimulation. beta-AR and ET receptor profiles were determined by radiolabeled ligand assays. ET-1 inhibited basal cAMP production in all preparations in a concentration-dependent manner. However, beta-AR-stimulated cAMP production by either isoproterenol or forskolin was not significantly affected by ET-1. beta-AR receptor density was reduced, and a selective reduction of the ET(B) receptor occurred in both forms of DCM.

CONCLUSIONS

Under basal conditions, ET receptor stimulation reduced cAMP levels, which may influence contractility, particularly with DCM.

Diastolic heart failure: diagnosis and treatment

The most frequent hospital diagnosis-related group is congestive heart failure (CHF). CHF increases dramatically with age, making it an important problem in our aging population. CHF is caused by a primary abnormality in diastolic function (diastolic heart failure [DHF]) in 50% of patients with CHF who are > 70 years of age. Mortality rates in patients with DHF are comparable to those of patients with systolic heart failure, approaching 50% over 5 years. Successful therapy of DHF requires making a correct diagnosis, identifying the underlying cause, and applying specific and individualized treatment.

Cardiocyte cytoskeleton in patients with left ventricular pressure overload hypertrophy

OBJECTIVES

We sought to determine whether the cardiocyte microtubule network densification characteristic of animal models of severe pressure overload cardiac hypertrophy occurs in human patients.

BACKGROUND

In animal models of clinical entities causative of severe right and left ventricular (LV) pressure overload hypertrophy, increased density of the cellular microtubule network, through viscous loading of active myofilaments, causes contractile dysfunction that is normalized by microtubule depolymerization. These linked contractile and cytoskeletal abnormalities, based on augmented tubulin synthesis and microtubule stability, progress during the transition to heart failure.

METHODS

Thirteen patients with symptomatic aortic stenosis (AS) (aortic valve area = 0.6 +/- 0.1 cm2) and two control patients without AS were studied. No patient had aortic insufficiency, significant coronary artery disease or abnormal segmental LV wall motion. Left ventricular function was assessed by echocardiography and cardiac catheterization before aortic valve replacement. Left ventricular biopsies obtained at surgery before cardioplegia were separated into free and polymerized tubulin fractions before analysis. Midwall LV fractional shortening versus mean LV wall stress in the AS patients was compared with that in 84 normal patients.

RESULTS

Four AS patients had normal LV function and microtubule protein concentration; six had decreased LV function and increased microtubule protein concentration, and three had borderline LV function and microtubule protein concentration, such that there was an inverse relationship of midwall LV fractional shortening to microtubule protein.

CONCLUSIONS

In patients, as in animal models of severe LV pressure overload hypertrophy, myocardial dysfunction is associated with increased microtubules, suggesting that this may be one mechanism contributing to the development of congestive heart failure in patients with AS.

Normal myocardial function in severe right ventricular volume overload hypertrophy

Severe left ventricular volume overloading causes myocardial and cellular contractile dysfunction. Whether this is also true for severe right ventricular volume overloading was unknown. We therefore created severe tricuspid regurgitation percutaneously in seven dogs and then observed them for 3.5-4.0 yr. All five surviving operated dogs had severe tricuspid regurgitation and right heart failure, including massive ascites, but they did not have left heart failure. Right ventricular cardiocytes were isolated from these and from normal dogs, and sarcomere mechanics were assessed via laser diffraction. Right ventricular cardiocytes from the tricuspid regurgitation dogs were 20% longer than control cells, but neither the extent (0.171 +/- 0.005 microm) nor the velocity (2.92 +/- 0.12 microm/s) of sarcomere shortening differed from controls (0.179 +/- 0.005 microm and 3.09 +/- 0.11 microm/s, respectively). Thus, despite massive tricuspid regurgitation causing overt right heart failure, intrinsic right ventricular contractile function was normal. This finding for the severely volume-overloaded right ventricle stands in distinct contrast to our finding for the left ventricle severely volume overloaded by mitral regurgitation, wherein intrinsic contractile function is depressed.

Preliminary report on high thoracic epidural analgesia: relationship between its therapeutic effects and myocardial blood flow as assessed by stress thallium distribution

OBJECTIVES

To extend the duration of high thoracic epidural analgesia (HTEA) treatment compared with the authors' previous studies, to test the hypothesis that the mechanism by which HTEA reduces angina during long-term treatment includes an improvement in myocardial blood flow distribution and a reduction in stress-induced ischemia, and to show that new myocardial infarctions are not masked or missed in patients receiving HTEA.

DESIGN

Prospective consecutive study.

SETTING

Department of Veteran's Affairs medical center and university-affiliated hospital.

PARTICIPANTS

Six consenting adult patients.

INTERVENTIONS

Patients were evaluated before HTEA catheter insertion and >2 months after HTEA catheter insertion with stress thallium tests.

MEASUREMENTS AND MAIN RESULTS

Two of 6 patients had improvement but not resolution of stress-induced ischemia at 8 and 12 months. The remaining 4 patients had no change in stress-induced ischemia. None of the 6 patients had any new areas of ischemia or infarction as determined by stress thallium tests.

CONCLUSIONS

The authors previously showed that HTEA is safe and effective in relieving refractory angina pectoris. The current study shows that this therapeutic effect persists and does not appear to be related to a change in myocardial blood flow; rather the improvement in symptoms probably results, in part, from an anesthetic effect. HTEA does not mask the development of new myocardial infarctions.

Integrin activation and focal complex formation in cardiac hypertrophy

Cardiac hypertrophy is characterized by both remodeling of the extracellular matrix (ECM) and hypertrophic growth of the cardiocytes. Here we show increased expression and cytoskeletal association of the ECM proteins fibronectin and vitronectin in pressure-overloaded feline myocardium. These changes are accompanied by cytoskeletal binding and phosphorylation of focal adhesion kinase (FAK) at Tyr-397 and Tyr-925, c-Src at Tyr-416, recruitment of the adapter proteins p130(Cas), Shc, and Nck, and activation of the extracellular-regulated kinases ERK1/2. A synthetic peptide containing the Arg-Gly-Asp (RGD) motif of fibronectin and vitronectin was used to stimulate adult feline cardiomyocytes cultured on laminin or within a type-I collagen matrix. Whereas cardiocytes under both conditions showed RGD-stimulated ERK1/2 activation, only collagen-embedded cells exhibited cytoskeletal assembly of FAK, c-Src, Nck, and Shc. In RGD-stimulated collagen-embedded cells, FAK was phosphorylated only at Tyr-397 and c-Src association occurred without Tyr-416 phosphorylation and p130(Cas) association. Therefore, c-Src activation is not required for its cytoskeletal binding but may be important for additional phosphorylation of FAK. Overall, our study suggests that multiple signaling pathways originate in pressure-overloaded heart following integrin engagement with ECM proteins, including focal complex formation and ERK1/2 activation, and many of these pathways can be activated in cardiomyocytes via RGD-stimulated integrin activation.

Diastolic Heart Failure

The diagnosis of diastolic heart failure (DHF) can be made when a patient has both symptoms and signs on physical exam of congestive heart failure (CHF), and normal left ventricular volume and ejection fraction. Documentation of abnormal diastolic function is confirmatory but not mandatory. Diastolic heart failure is a frequent cause of CHF (prevalence is 35% to 50%) and has a significant effect on mortality (5-year mortality rate is 25% to 35%) and morbidity (1-year readmission rate is 50%). Treatment should be targeted at symptoms, causal clinical disease, and underlying basic mechanisms. Symptom-targeted therapy: decrease pulmonary venous pressure using diuretics and long-acting nitrates, maintain atrial contraction and atrial ventricular synchrony, reduce heart rate using beta-adrenergic blockers and calcium channel blockers; increase exercise tolerance by reducing exercise- induced increases in blood pressure and heart rate using angiotensin-converting enzyme (ACE) inhibitors, angiotensin II receptor blockers, and calcium channel blockers. Disease-targeted therapy: prevent or treat myocardial ischemia, prevent or regress left ventricular hypertrophy. Mechanism-targeted therapy (future directions): modify neurohumoral activation using renin, angiotensin, and aldosterone system antagonists (ACE inhibitors, angiotensin II receptor blockade, aldosterone and renin antagonist); endothelin antagonists; nitric oxide agonists; and atrial natruretic peptide agonists; alter intracellular mechanisms; alter extracellular matrix structures.

Microtubule depolymerization normalizes in vivo myocardial contractile function in dogs with pressure-overload left ventricular hypertrophy

BACKGROUND

Because initially compensatory myocardial hypertrophy in response to pressure overloading may eventually decompensate to myocardial failure, mechanisms responsible for this transition have long been sought. One such mechanism established in vitro is densification of the cellular microtubule network, which imposes a viscous load that inhibits cardiocyte contraction.

METHODS AND RESULTS

In the present study, we extended this in vitro finding to the in vivo level and tested the hypothesis that this cytoskeletal abnormality is important in the in vivo contractile dysfunction that occurs in experimental aortic stenosis in the adult dog. In 8 dogs in which gradual stenosis of the ascending aorta had caused severe left ventricular (LV) pressure overloading (gradient, 152+/-16 mm Hg) with contractile dysfunction, LV function was measured at baseline and 1 hour after the intravenous administration of colchicine. Cardiocytes obtained by biopsy before and after in vivo colchicine administration were examined in tandem. Microtubule depolymerization restored LV contractile function both in vivo and in vitro.

CONCLUSIONS

These and additional corroborative data show that increased cardiocyte microtubule network density is an important mechanism for the ventricular contractile dysfunction that develops in large mammals with adult-onset pressure-overload-induced cardiac hypertrophy.

Effects of gene deletion of the tissue inhibitor of the matrix metalloproteinase-type 1 (TIMP-1) on left ventricular geometry and function in mice

Alterations in the expression and activity of the matrix metalloproteinases (MMPs) and the tissue inhibitors of the MMPs (TIMPs) have been implicated in tissue remodeling in a number of disease states. One of the better characterized TIMPs, TIMP-1, has been shown to bind to active MMPs and to regulate the MMP activational process. The goal of this study was to determine whether deletion of the TIMP-1 gene in mice, which in turn would remove TIMP-1 expression in LV myocardium, would produce time-dependent effects on LV geometry and function. Age-matched sibling mice (129Sv) deficient in the TIMP-1 gene (TIMP-1 knock-out (TIMP-1 KO), n=10) and wild-type mice (n=10) underwent comparative echocardiographic studies at 1 and 4 months of age. LV catheterization studies were performed at 4 months and the LV harvested for histomorphometric studies. LV end-diastolic volume and mass increased (18+/-4 and 38+/-3%, respectively, P<0.05) at 4 months in the TIMP-1 KO group; a significant increase compared to wild-type controls (P<0.05). At 4 months, LV and end-diastolic wall stress was increased by over two-fold in the TIMP-1 KO compared to wild type (P<0.05). However, LV systolic pressure and ejection performance were unchanged in the two groups of mice. LV myocyte cross-sectional area was unchanged in the TIMP-1 KO mice compared to controls, but myocardial fibrillar collagen content was reduced. Changes in LV geometry occurred in TIMP-1 deficient mice and these results suggest that constitutive TIMP-1 expression participates in the maintenance of normal LV myocardial structure.

Randomized trial of partial versus complete chordal preservation methods of mitral valve replacement: A preliminary report

BACKGROUND

The merits of retaining the subvalvular apparatus during mitral valve replacement for chronic mitral regurgitation have been demonstrated in numerous clinical and laboratory investigations. In this preliminary report, we analyzed the early effects of complete versus partial chordal preservation on left ventricular mechanics.

METHODS AND RESULTS

Fifty patients undergoing isolated surgical correction of mitral insufficiency were prospectively randomized to either total or partial chordal-sparing mitral valve replacement. Of the first 19 patients studied, 8 had preservation of the posterior leaflet only, and 11 had complete preservation of all chordal structures. A comparison group consisted of 6 patients who had primary mitral valve repair. Echocardiography was performed preoperatively and at discharge from the hospital to determine dimensions, wall stress, and ejection fraction. Preservation of the posterior leaflet only resulted in a reduction in end-diastolic volume, an increase in end-systolic volume (P=0.058), a rising trend in end-systolic stress, a decrease in long-axis fractional shortening, and a fall in ejection fraction from 0.68+/-0.16 to 0. 46+/-0.19 (P=0.001). Although patients who had preservation of all chordal structures also had decreased end-diastolic volume, long-axis fractional shortening, and ejection fraction (0.60+/-0.13 to 0.52+/-0.07, P=0.01), end-systolic stress fell and end-systolic volume decreased instead of increased. Compared with the posterior leaflet preservation group, those in the group with completely preserved chordal structures had a larger decline in end-diastolic volume and smaller decreases in long-axis fractional shortening and ejection fraction. Changes in end-systolic volume and stress were also statistically different between the 2 cohorts. No differences were detected between the group with total preserved chordal structures and the mitral repair group in any of the measured parameters.

CONCLUSIONS

Compared with posterior chordal preservation only, complete retention of the subvalvular apparatus during mitral valve replacement resulted in improved ejection performance and smaller chamber volumes due to reduced systolic wall stress. These hemodynamic advantages are comparable to those observed with primary mitral reconstruction.

Angiotensin-converting enzyme and matrix metalloproteinase inhibition with developing heart failure: comparative effects on left ventricular function and geometry

The progression of congestive heart failure (CHF) is left ventricular (LV) myocardial remodeling. The matrix metalloproteinases (MMPs) contribute to tissue remodeling and therefore MMP inhibition may serve as a useful therapeutic target in CHF. Angiotensin converting enzyme (ACE) inhibition favorably affects LV myocardial remodeling in CHF. This study examined the effects of specific MMP inhibition, ACE inhibition, and combined treatment on LV systolic and diastolic function in a model of CHF. Pigs were randomly assigned to five groups: 1) rapid atrial pacing (240 beats/min) for 3 weeks (n = 8); 2) ACE inhibition (fosinopril, 2.5 mg/kg b.i.d. orally) and rapid pacing (n = 8); 3) MMP inhibition (PD166793 2 mg/kg/day p.o.) and rapid pacing (n = 8); 4) combined ACE and MMP inhibition (2.5 mg/kg b.i.d. and 2 mg/kg/day, respectively) and rapid pacing (n = 8); and 5) controls (n = 9). LV peak wall stress increased by 2-fold with rapid pacing and was reduced in all treatment groups. LV fractional shortening fell by nearly 2-fold with rapid pacing and increased in all treatment groups. The circumferential fiber shortening-systolic stress relation was reduced with rapid pacing and increased in the ACE inhibition and combination groups. LV myocardial stiffness constant was unchanged in the rapid pacing group, increased nearly 2-fold in the MMP inhibition group, and was normalized in the ACE inhibition and combination treatment groups. Increased MMP activation contributes to the LV dilation and increased wall stress with pacing CHF and a contributory downstream mechanism of ACE inhibition is an effect on MMP activity.

Matrix metalloproteinase inhibition during the development of congestive heart failure : effects on left ventricular dimensions and function

The development of congestive heart failure (CHF) is associated with left ventricle (LV) dilation and myocardial remodeling. The matrix metalloproteinases (MMPs) play a significant role in extracellular remodeling, and recent studies have demonstrated increased MMP expression and activity with CHF. Whether increased MMP activity directly contributes to the LV remodeling with CHF remains unknown. Accordingly, this study examined the effects of chronic MMP inhibition (MMPi) on LV size and function during the progression of CHF. Pigs were assigned to the following groups: (1) CHF, rapid pacing for 3 weeks at 240 bpm (n=12); (2) CHF/MMPi, rapid pacing and concomitant MMPi (PD166793, 20 mg/kg per day [n=10]), and (3) control (n=11). With pacing CHF, LV fractional shortening was reduced (19+/-1 versus 45+/-1%), and end-diastolic dimension increased (5.67+/-0.11 versus 3.55+/-0.05 cm), compared with baseline values (P<0.05). In the CHF/MMPi group, LV endocardial shortening increased (25+/-2%) and the end-diastolic dimension was reduced (4.92+/-0.17 cm) compared with CHF-only values (P<0.05). LV midwall shortening was reduced to a comparable degree in the CHF-only and CHF/MMPi groups. LV peak wall stress increased 3-fold with pacing CHF compared with controls and was significantly reduced in the CHF/MMPi group. LV myocardial stiffness was unchanged with CHF but was increased in the CHF/MMPi group. LV myocyte length was increased with pacing CHF compared with controls (180+/-3 versus 125+/-4 microm, P<0.05) and was reduced in the CHF/MMPi group (169+/-4 microm, P<0.05). Basal-state myocyte shortening velocity was reduced with pacing CHF compared with controls (33+/-2 versus 66+/-1 microm/s, P<0.05) and was unchanged in the CHF/MMPi group (31+/-2 microm/s). Using an ex vivo assay system, myocardial MMP activity was increased with pacing CHF and was reduced with chronic MMPi. In summary, concomitant MMPi with developing CHF limited LV dilation and reduced wall stress. These results suggest that increased myocardial MMP activity contributes to LV myocardial remodeling in developing CHF.

Beta3-integrin-mediated focal adhesion complex formation: adult cardiocytes embedded in three-dimensional polymer matrices

In vivo studies show that beta3-integrin-mediated focal adhesion formation (FAF) causes recruitment of nonreceptor tyrosine kinases to the cytoskeleton in pressure-overloaded myocardium. To define the mechanism of beta3-integrin-mediated signaling, we developed a cell culture model (adult feline cardiocytes embedded in a 3-dimensional matrix of native type 1 collagen, fibronectin, and vitronectin) wherein beta3-integrin-mediated focal adhesion kinase occurs. Focal adhesion kinase was analyzed immunocytochemically using confocal microscopy. Initial studies suggested that cardiocytes cultured in a 3-dimensional matrix formed focal adhesions consisting of both beta3-integrin and the muscle-specific isoform, beta1-integrin (beta1D). The focal adhesions were associated with focal adhesion kinase on both costameres and intercalated disks. To determine the cause of beta1D-integrin-mediated focal adhesion kinase in this model, time course studies were done. Beta3-integrin-mediated focal adhesion kinase occurred within 30 minutes after embedding cardiocytes and persisted for >24 hours, whereas beta1D-integrin-mediated focal adhesion kinase was present from the outset. Because confocal microscopy showed that laminin was present on the surface of freshly isolated cardiocytes, we hypothesized that this was causative of beta1D-integrin-mediated focal adhesion kinase. Freshly isolated cardiocytes washed with acidic medium (2 minutes, pH 3.0) to remove laminin and then embedded in a 3-dimensional matrix showed complete absence of beta1D-integrin-mediated focal adhesion kinase, but beta3-integrin-mediated focal adhesion kinase occurred with a time course similar to that seen in cultured, unwashed cardiocytes. Acid washing did not alter the binding ability of beta1D-integrin, because acid-washed cardiocytes in the presence of laminin showed beta1D-integrin-mediated focal adhesion kinase. Thus, cardiocytes embedded in a 3-dimensional matrix show beta3-integrin-mediated focal adhesion kinase and provide an in vitro model to study beta3-integrin-mediated signaling in response to hemodynamic cardiac loading.

Hypertrophic response to hemodynamic overload: role of load vs. renin-angiotensin system activation

Myocardial hypertrophy is one of the basic mechanisms by which the heart compensates for hemodynamic overload. The mechanisms by which hemodynamic overload is transduced by the cardiac muscle cell and translated into cardiac hypertrophy are not completely understood. Candidates include activation of the renin-angiotensin system (RAS) and angiotensin II receptor (AT1) stimulation. In this study, we tested the hypothesis that load, independent of the RAS, is sufficient to stimulate cardiac growth. Four groups of cats were studied: 14 normal controls, 20 pulmonary artery-banded (PAB) cats, 7 PAB cats in whom the AT1 was concomitantly and continuously blocked with losartan, and 8 PAB cats in whom the angiotensin-converting enzyme (ACE) was concomitantly and continuously blocked with captopril. Losartan cats had at least a one-log order increase in the ED50 of the blood pressure response to angiotensin II infusion. Right ventricular (RV) hypertrophy was assessed using the RV mass-to-body weight ratio and ventricular cardiocyte size. RV hemodynamic overload was assessed by measuring RV systolic and diastolic pressures. Neither the extent of RV pressure overload nor RV hypertrophy that resulted from PAB was affected by AT1 blockade with losartan or ACE inhibition with captopril. RV systolic pressure was increased from 21 +/- 3 mmHg in normals to 68 +/- 4 mmHg in PAB, 65 +/- 5 mmHg in PAB plus losartan and 62 +/- 3 mmHg in PAB plus captopril. RV-to-body weight ratio increased from 0.52 +/- 0.04 g/kg in normals to 1.11 +/- 0.06 g/kg in PAB, 1.06 +/- 0.06 g/kg in PAB plus losartan and 1.06 +/- 0.06 g/kg in PAB plus captopril. Thus 1) pharmacological modulation of the RAS with losartan and captopril did not change the extent of the hemodynamic overload or the hypertrophic response induced by PAB; 2) neither RAS activation nor angiotensin II receptor stimulation is an obligatory and necessary component of the signaling pathway that acts as an intermediary coupling load to the hypertrophic response; and 3) load, independent of the RAS, is capable of stimulating cardiac growth.

Role of microtubules in the contractile dysfunction of hypertrophied myocardium

OBJECTIVES

We sought to determine whether the ameliorative effects of microtubule depolymerization on cellular contractile dysfunction in pressure overload cardiac hypertrophy apply at the tissue level.

BACKGROUND

A selective and persistent increase in microtubule density causes decreased contractile function of cardiocytes from cats with hypertrophy produced by chronic right ventricular (RV) pressure overloading. Microtubule depolymerization by colchicine normalizes contractility in these isolated cardiocytes. However, whether these changes in cellular function might contribute to changes in function at the more highly integrated and complex cardiac tissue level was unknown.

METHODS

Accordingly, RV papillary muscles were isolated from 25 cats with RV pressure overload hypertrophy induced by pulmonary artery banding (PAB) for 4 weeks and 25 control cats. Contractile state was measured using physiologically sequenced contractions before and 90 min after treatment with 10(-5) mol/liter colchicine.

RESULTS

The PAB significantly increased RV systolic pressure and the RV weight/body weight ratio in PAB; it significantly decreased developed tension from 59+/-3 mN/mm2 in control to 25+/-4 mN/mm2 in PAB, shortening extent from 0.21+/-0.01 muscle lengths (ML) in control to 0.12+/-0.01 ML in PAB, and shortening rate from 1.12+/-0.07 ML/s in control to 0.55+/-0.03 ML/s in PAB. Indirect immunofluorescence confocal microscopy showed that PAB muscles had a selective increase in microtubule density and that colchicine caused complete microtubule depolymerization in both control and PAB papillary muscles. Microtubule depolymerization normalized myocardial contractility in papillary muscles of PAB cats but did not alter contractility in control muscles.

CONCLUSIONS

Excess microtubule density, therefore, is equally important to both cellular and to myocardial contractile dysfunction caused by chronic, severe pressure-overload cardiac hypertrophy.

Constitutive properties of adult mammalian cardiac muscle cells

BACKGROUND

The purpose of this study was to determine whether changes in the constitutive properties of the cardiac muscle cell play a causative role in the development of diastolic dysfunction.

METHODS AND RESULTS

Cardiocytes from normal and pressure-hypertrophied cats were embedded in an agarose gel, placed on a stretching device, and subjected to a change in stress (sigma), and resultant changes in cell strain (epsilon) were measured. These measurements were used to examine the passive elastic spring, viscous damping, and myofilament activation. The passive elastic spring was assessed in protocol A by increasing the sigma on the agarose gel at a constant rate to define the cardiocyte sigma-versus-epsilon relationship. Viscous damping was assessed in protocol B from the loop area between the cardiocyte sigma-versus-epsilon relationship during an increase and then a decrease in sigma. In both protocols, myofilament activation was minimized by a reduction in [Ca2+]i. Myofilament activation effects were assessed in protocol C by defining cardiocyte sigma versus epsilon during an increase in sigma with physiological [Ca2+]i. In protocol A, the cardiocyte sigma-versus-epsilon relationship was similar in normal and hypertrophied cells. In protocol B, the loop area was greater in hypertrophied than normal cardiocytes. In protocol C, the sigma-versus-epsilon relation in hypertrophied cardiocytes was shifted to the left compared with normal cells.

CONCLUSIONS

Changes in viscous damping and myofilament activation in combination may cause pressure-hypertrophied cardiocytes to resist changes in shape during diastole and contribute to diastolic dysfunction.

Mechanisms of cardiac hypertrophy in canine volume overload

This study tested whether the modest hypertrophy that develops in dogs in response to mitral regurgitation is due to a relatively small change in the rate of protein synthesis or, alternatively, is due to a decreased rate of protein degradation. After 3 mo of severe experimental mitral regurgitation, the left ventricular (LV) mass-to-body weight ratio increased by 23% compared with baseline values. This increase in LV mass occurred with a small, but not statistically significant, increase in the fractional rate of myosin heavy chain (MHC) synthesis (Ks), as measured using continuous infusion with [3H]leucine in dogs at 2 wk, 4 wk, and 3 mo after creation of severe mitral regurgitation. Translational efficiency was unaffected by mitral regurgitation as measured by the distribution of MHC mRNA in polysome gradients. Furthermore, there was no detectable increase in translational capacity as measured by either total RNA content or the rate of ribosome formation. These data indicate that translational mechanisms that accelerate the rate of cardiac protein synthesis are not responsive to the stimulus of mitral regurgitation. Most of the growth after mitral regurgitation was accounted for by a decrease in the fractional rate of protein degradation, calculated by subtracting fractional rates of protein accumulation at each time point from the corresponding Ks values. We conclude that 1) volume overload produced by severe mitral regurgitation does not trigger substantial increases in the rate of protein synthesis and 2) the modest increase in LV mass results primarily from a decrease in the rate of protein degradation.

Gel stretch method: a new method to measure constitutive properties of cardiac muscle cells

Diastolic dysfunction is an important cause of congestive heart failure; however, the basic mechanisms causing diastolic congestive heart failure are not fully understood, especially the role of the cardiac muscle cell, or cardiocyte, in this process. Before the role of the cardiocyte in this pathophysiology can be defined, methods for measuring cardiocyte constitutive properties must be developed and validated. Thus this study was designed to evaluate a new method to characterize cardiocyte constitutive properties, the gel stretch method. Cardiocytes were isolated enzymatically from normal feline hearts and embedded in a 2% agarose gel containing HEPES-Krebs buffer and laminin. This gel was cast in a shape that allowed it to be placed in a stretching device. The ends of the gel were held between a movable roller and fixed plates that acted as mandibles. Distance between the right and left mandibles was increased using a stepper motor system. The force applied to the gel was measured by a force transducer. The resultant cardiocyte strain was determined by imaging the cells with a microscope, capturing the images with a CCD camera, and measuring cardiocyte and sarcomere length changes. Cardiocyte stress was characterized with a finite-element method. These measurements of cardiocyte stress and strain were used to determine cardiocyte stiffness. Two variables affecting cardiocyte stiffness were measured, the passive elastic spring and viscous damping. The passive spring was assessed by increasing the force on the gel at 1 g/min, modeling the resultant stress vs. strain relationship as an exponential [sigma = A/k(ekepsilon - 1)]. In normal cardiocytes, A = 23.0 kN/m2 and k = 16. Viscous damping was assessed by examining the loop area between the stress vs. strain relationship during 1 g/min increases and decreases in force. Normal cardiocytes had a finite loop area = 1.39 kN/m2, indicating the presence of viscous damping. Thus the gel stretch method provided accurate measurements of cardiocyte constitutive properties. These measurements have allowed the first quantitative assessment of passive elastic spring properties and viscous damping in normal mammalian cardiocytes.

Cytoskeletal role in the transition from compensated to decompensated hypertrophy during adult canine left ventricular pressure overloading

Increased microtubule density causes cardiocyte contractile dysfunction in right ventricular (RV) pressure-overload hypertrophy, and these linked phenotypic and contractile abnormalities persist and progress during the transition to failure. Although more severe in cells from failing than hypertrophied RVs, the mechanical defects are normalized in each case by microtubule depolymerization. To define the role of increased microtubule density in left ventricular (LV) pressure-overload hypertrophy and failure, in a given LV we examined ventricular mechanics, sarcomere mechanics, and free tubulin and microtubule levels in control dogs and in dogs with aortic stenosis both with LV hypertrophy alone and with initially compensated hypertrophy that had progressed to LV muscle failure. In comparing initial values with those at study 8 weeks later, dogs with hypertrophy alone had a very substantial increase in LV mass but preservation of a normal ejection fraction and mean systolic wall stress. Dogs with hypertrophy and associated failure had a substantial but lesser increase in LV mass and a reduction in ejection fraction, as well as a marked increase in mean systolic wall stress. Cardiocyte contractile function was equivalent, and unaffected by microtubule depolymerization, in cells from control LVs and those with compensated hypertrophy. In contrast, cardiocyte contractile function in cells from failing LVs was quite depressed but was normalized by microtubule depolymerization. Microtubules were increased only in failing LVs. These contractile and cytoskeletal changes, when assayed longitudinally in a given dog by biopsy, appeared in failing ventricles only when wall stress began to increase and function began to decrease. Thus, the microtubule-based cardiocyte contractile dysfunction characteristic of pressure-hypertrophied myocardium, originally described in the RV, obtains equally in the LV but is shown here to have a specific association with increased wall stress.

Pressure-overload hypertrophy is unabated in mice devoid of AT1A receptors

Mechanisms controlling cardiac growth are under intense investigation. Among these, the renin-angiotensin system has received great interest. In the current study, we tested the hypothesis that the renin-angiotensin system was not an obligate factor in cardiac hypertrophy. We examined the left ventricular hypertrophic response to a pressure overload in mice devoid of the AT1A receptor, the putative major effector of the growth response of the renin-angiotensin system. Aortic banding produced similar transband gradients in wild-type and AT1A knockout mice. The left ventricular mass-to-body weight ratio increased from 3.44 +/- 0.08 to 5.62 +/- 0.25 in wild-type ascending aortic-banded mice. The response in the knockout mice was not different (from 2.97 +/- 0.13 to 5.24 +/- 0.37). We conclude that the magnitude of cardiac hypertrophy is not affected by the absence of the AT1A receptor and its signaling pathway and that this component of the renin-angiotensin system is not necessary in cardiac hypertrophy.

Left ventricular length-force-shortening relations before and after surgical correction of chronic mitral regurgitation

OBJECTIVES

We tested the hypothesis that postoperative left ventricular (LV) systolic wall stress can be predicted from the change in LV diastolic dimension and ejection fraction (EF) after surgical correction of chronic mitral regurgitation (MR). We used a simple mathematic model to predict postoperative systolic stress from end-diastolic dimension and EF. The validity of this model was assessed using data from 21 patients undergoing mitral valve replacement (MVR) for chronic MR.

BACKGROUND

The decline in EF after MVR for chronic MR is traditionally thought to be a consequence of a postoperative increase in afterload, caused by closure of a low resistance runoff into the left atrium. However, consideration of the Laplace relation suggests that afterload does not necessarily increase after the operation.

METHODS

A spherical mathematical model of the left ventricle was used to define the relations between LV end-diastolic dimension, systolic wall stress and EF. To test the validity of this model, clinical and echocardiographic data were obtained from 21 patients with chronic MR before and 10 to 14 days after MVR. These echocardiographic data were examined with reference to plots derived from the mathematical model.

RESULTS

Patients were categorized as those in whom end-diastolic dimension declined after the operation (group I, n = 15) and those with no reduction in end-diastolic dimension (group II, n = 6). Group I patients were subclassified into those undergoing MVR with chordal preservation (group Ia) and those undergoing MVR with chordal transection (group Ib). In groups Ib and II, there were significant reductions in EF (56 +/- 3% to 48 +/- 3% in group Ib and 50 +/- 2% to 40 +/- 3% in group II, both p < 0.05), but the changes in end-diastolic dimension and wall stress differed. In group Ib, end-diastolic dimension decreased and systolic wall stress was unchanged; in group II, end-diastolic dimension was unchanged and wall stress increased. In contrast, group Ia patients experienced a substantial reduction in end-diastolic dimension, no change in EF and a reduction in stress. The corresponding length-force-shortening coordinates closely approximate those predicted from a mathematic model relating end-diastolic dimension to EF and systolic wall stress.

CONCLUSIONS

Concordant echocardiographic and mathematical model results indicate that postoperative changes in systolic stress are directly related to changes in chamber size and that LV afterload may fall when chordal preservation techniques are used in combination with MVR.

Treatment of medically and surgically refractory angina pectoris with high thoracic epidural analgesia: initial clinical experience

Surgical sympathectomy can relieve symptoms of angina in patients with refractory angina. However, in these high-risk patients this thoracic surgery may result in significant morbidity and mortality rates. Similar sympathetic blockade can now be produced with high thoracic epidural analgesia (HTEA). From September 1995 to August 1996, we treated 10 consecutive patients with HTEA. These eight men and two women, aged 58 +/- 5 years, with extensive three-vessel coronary disease and ejection fractions of 40% +/- 5%, had New York Heart Association (NYHA) class IV angina despite medical therapy, including nitrates, beta-blockade, calcium channel blockade, and narcotics. HTEA was performed at the T1 through T4 levels with a catheter placed either percutaneously or surgically, with radiographic confirmation of catheter placement with an epidurogram or computed tomography scan. Bupivacaine (0.25% to 0.5%), an amide local anesthetic, was given as a bolus through the epidural catheter and then maintained either as a continuous infusion or an intermittent rebolus. The epidural catheter remained in place for 7 days in four patients, 14 days in three patients, and > or =90 days in three patients. Before consideration for HTEA, each patient was deemed unsuitable for or refused coronary bypass surgery and percutaneous coronary angioplasty and had NYHA class IV symptoms of angina. Seven of 10 patients required intravenous nitroglycerin and heparin and were unable to be discharged from the intensive care unit because of anginal symptoms. Two of these seven patients also required an intraaortic balloon pump for symptom control. After HTEA, all 10 patients had improved symptoms, with five patients improving to NYHA class II symptoms and five improving to NYHA class III. All seven patients receiving intravenous nitroglycerin, heparin, or intraaortic balloon pump support had these modalities discontinued. Six of these seven patients were subsequently discharged from the hospital. One patient died from a non-HTEA related cause. There were no HTEA-related deaths. There were three catheter-related complications necessitating catheter removal during 12 months of HTEA use. Local infection developed in one patient, one had catheter occlusion caused by fibrosis, and one patient had chronic back pain exacerbation from a paraspinous muscle spasm. No patient had a myocardial infarction or a significant arrhythmia. In patients with otherwise intractable angina pectoris, HTEA is an effective modality that produces symptomatic relief of angina pectoris and allows increased activity level.

Premorbid determinants of left ventricular dysfunction in a novel model of gradually induced pressure overload in the adult canine

BACKGROUND

When a pressure overload is placed on the left ventricle, some patients develop relatively modest hypertrophy whereas others develop extensive hypertrophy. Likewise, the occurrence of contractile dysfunction also is variable. The cause of this heterogeneity is not well understood.

METHODS AND RESULTS

We recently developed a model of gradual proximal aortic constriction in the adult canine that mimicked the heterogeneity of the hypertrophic response seen in humans. We hypothesized that differences in outcome were related to differences present before banding. Fifteen animals were studied initially. Ten developed left ventricular dysfunction (dys group). Five dogs maintained normal function (nl group). At baseline, the nl group had a lower mean systolic wall stress (96 +/- 9 kdyne/cm2; dys group, 156 +/- 7 kdyne/cm2; P < .0002) and greater relative left ventricular mass (left ventricular weight [g]/body wt [kg], 5.1 +/- 0.36; dys group, 3.9 +/- 0.26; P < .02). On the basis of differences in mean systolic wall stress at baseline, we predicted outcome in the next 28 dogs by using a cutoff of 115 kdyne/cm2. Eighteen of 20 dogs with baseline mean systolic stress > 115 kdyne/cm2 developed dysfunction whereas 6 of 8 dogs with resting stress < or = 115 kdyne/cm2 maintained normal function.

CONCLUSIONS

We conclude that this canine model mimicked the heterogeneous hypertrophic response seen in humans. In the group that eventually developed dysfunction there was less cardiac mass despite 60% higher wall stress at baseline, suggesting a different set point for regulating myocardial growth in the two groups.

Cytoskeletal mechanics in pressure-overload cardiac hypertrophy

We have shown that the cellular contractile dysfunction characteristic of pressure-overload cardiac hypertrophy results not from an abnormality intrinsic to the myofilament portion of the cardiocyte cytoskeleton but rather from an increased density of the microtubule component of the extramyofilament portion of the cardiocyte cytoskeleton. To determine how, in physical terms, this increased microtubule density mechanically overloads the contractile apparatus at the cellular level, we measured cytoskeletal stiffness and apparent viscosity in isolated cardiocytes via magnetic twisting cytometry, a technique by which magnetically induced force is applied directly to the cytoskeleton through integrin-coupled ferromagnetic beads coated with Arg-Gly-Asp (RGD) peptide. Measurements were made in two groups of cardiocytes from cats with right ventricular (RV) hypertrophy induced by pulmonary artery banding: (1) those from the pressure-overloaded RV and (2) those from the normally loaded same-animal control left ventricle (LV). Cytoskeletal stiffness increased almost twofold, from 8.53 +/- 0.77 dyne/cm2 in the normally loaded LV cardiocytes to 16.46 +/- 1.32 dyne/cm2 in the hypertrophied RV cardiocytes. Cytoskeletal apparent viscosity increased almost fourfold, from 20.97 +/- 1.92 poise in the normally loaded LV cardiocytes to 87.85 +/- 6.95 poise in the hypertrophied RV cardiocytes. In addition to these baseline data showing differing stiffness and, especially, apparent viscosity in the two groups of cardiocytes, microtubule depolymerization by colchicine was found to return both the stiffness and the apparent viscosity of the pressure overload-hypertrophied RV cells fully to normal. Conversely, microtubule hyperpolymerization by taxol increased the stiffness and apparent viscosity values of normally loaded LV cardiocytes to the abnormal values given above for pressure-hypertrophied RV cardiocytes. Thus, increased microtubule density constitutes primarily a viscous load on the cardiocyte contractile apparatus in pressure-overload cardiac hypertrophy.

Effects of pressure- or volume-overload hypertrophy on passive stiffness in isolated adult cardiac muscle cells

It has been hypothesized that the changes in myocardial stiffness induced by chronic hemodynamic overloading are dependent on changes in the passive stiffness of the cardiac muscle cell (cardiocyte). However, no previous studies have examined the passive constitutive properties of cardiocytes isolated from animals with myocardial hypertrophy. Accordingly, changes in relative passive stiffness of cardiocytes isolated from animals with chronic pressure- or volume-overload hypertrophy were determined by examining the effects of anisosmotic stress on cardiocyte size. Anisosmotic stress was produced by altering superfusate osmolarity. Hypertrophied cardiocytes were enzymatically isolated from 16 adult cats with right ventricular (RV) pressure-overload hypertrophy induced by pulmonary artery banding (PAB) and from 6 adult cats with RV volume-overload hypertrophy induced by creating an atrial septal defect (ASD). Left ventricular (LV) cardiocytes from each cat served as nonhypertrophied, normally loaded, same-animal controls. Superfusate osmolarity was decreased from 305 +/- 3 to 135 +/- 5 mosM and increased to 645 +/- 4 mosM. During anisosmotic stress, there were no significant differences between hypertrophied RV and normal LV cardiocytes in pressure overload PAB cats with respect to percent change in cardiocyte area (47 +/- 2% in RV vs. 48 +/- 2% in LV), diameter (46 +/- 3% in RV vs. 48 +/- 2% in LV), or length (2.4 +/- 0.2% in RV vs. 2.0 +/- 0.3% in LV), or sarcomere length (1.5 +/- 0.1% in RV vs. 1.3 +/- 0.3% in LV). Likewise, there were no significant differences in cardiocyte strain between hypertrophied RV and normal LV cardiocytes from ASD cats. In conclusion, chronic pressure-overload hypertrophy and chronic volume-overload hypertrophy did not alter the cardiocyte response to anisosmotic stress. Thus chronic overload hypertrophy did not alter relative passive cardiocyte stiffness.

Comparative effects of contraction and angiotensin II on growth of adult feline cardiocytes in primary culture

The purposes of this study were 1) to determine whether angiotensin II causes growth of adult feline cardiocytes in long-term culture, 2) to compare the growth effects of angiotensin II with those resulting from electrically stimulated contraction, and 3) to determine whether the anabolic effects of contraction are exerted via the angiotensin type 1 receptor. Adult feline cardiocytes were cultured on laminin-coated trays in a serum-free medium. Cardiocytes were either electrically stimulated to contract (1 Hz, 5-ms pulse duration, alternating polarity) or were nonstimulated and quiescent. Quiescent cells were studied as controls and after treatment with angiotensin II (10(-8) M), losartan (10(-6) M; an angiotensin type 1-receptor antagonist), or angiotensin II plus losartan. Contracting cells were studied in the presence and absence of angiotensin II or losartan. In quiescent cardiocytes, angiotensin II treatment on day 7 significantly increased protein synthesis rates by 22% and protein content per cell by 17%. The effects of angiotensin II were completely blocked by losartan. Electrically stimulated contraction on days 4 and 7 in culture significantly increased protein synthesis rate by 18 and 38% and protein content per cell by 19 and 46%, respectively. Angiotensin II treatment did not further increase protein synthesis rate or protein content in contracting cardiocytes. Furthermore, losartan did not block the anabolic effects of contraction on protein synthesis rates or protein content. In conclusion, angiotensin II can exert a modest anabolic effect on adult feline cardiocytes in culture. In contracting feline cardiocytes, angiotensin II has no effect on growth. Growth caused by electrically stimulated contraction occurs more rapidly and is greater in magnitude than that caused by angiotensin II. Growth of contracting adult feline cardiocytes is not dependent on activation of the angiotensin receptor.

Effects of anisosmotic stress on cardiac muscle cell length, diameter, area, and sarcomere length

The purpose of this study was to examine the effects of anisosmotic stress on adult mammalian cardiac muscle cell (cardiocyte) size. Cardiocyte size and sarcomere length were measured in cardiocytes isolated from 10 normal rats and 10 normal cats. Superfusate osmolarity was decreased from 300 +/- 6 to 130 +/- 5 mosM and increased to 630 +/- 8 mosM. Cardiocyte size and sarcomere length increased progressively when osmolarity was decreased, and there were no significant differences between cat and rat cardiocytes with respect to percent change in cardiocyte area or diameter; however, there were significant differences in cardiocyte length (2.8 +/- 0.3% in cat vs. 6.1 +/- 0.3% in rat, P < 0.05) and sarcomere length (3.3 +/- 0.3% in cat vs. 6.1 +/- 0.3% in rat, P < 0.05). To determine whether these species-dependent differences in length were related to diastolic interaction of the contractile elements or differences in relative passive stiffness, cardiocytes were subjected to the osmolarity gradient 1) during treatment with 7 mM 2,3-butanedione monoxime (BDM), which inhibits cross-bridge interaction, or 2) after pretreatment with 1 mM ethylene glycol-bis(beta-aminoethyl ether)-N, N,N',N'-tetraacetic acid (EGTA), a bivalent Ca2+ chelator. Treatment with EGTA or BDM abolished the differences between cat and rat cardiocytes. Species-dependent differences therefore appeared to be related to the degree of diastolic cross-bridge association and not differences in relative passive stiffness. In conclusion, the osmolarity vs. cell size relation is useful in assessing the cardiocyte response to anisosmotic stress and may in future studies be useful in assessing changes in relative passive cardiocyte stiffness produced by pathological processes.

Inhibition of collagen cross-linking: effects on fibrillar collagen and ventricular diastolic function

The fibrillar collagen network is postulated to be a primary determinant of left ventricular diastolic stiffness. This hypothesis was tested by examining the structural and physiological effects of a reduction in fibrillar collagen content and cross-linking in the intact left ventricle. Collagen cross-linking was inhibited by treating five normal adult pigs with beta-aminopropionitrile (BAPN; 10 g/day po) for 6 wk; five normal untreated pigs served as controls. Left ventricular volume, mass, and function were determined by simultaneous echocardiography and catheterization. Chamber stiffness, defined by pressure vs. volume data, and myocardial stiffness, defined by stress vs. dimension data, were determined from variably loaded beats during dextran infusion. Collagen distribution (% area) and integrity (% confluence) were determined by light microscopy. Collagen content was measured by hydroxyproline assay, and collagen cross-linking was measured by salt extraction. BAPN decreased collagen distribution (% area decreased from 12 +/- 1% in control to 7 +/- 1% in BAPN, P < 0.05), collagen integrity (% confluence decreased from 8 +/- 1% in control to 4 +/- 1% in BAPN, P < 0.05), collagen content (from 36 +/- 2 mg/g dry wt in control to 27 +/- 2 mg/g dry wt in BAPN, P < 0.05), and collagen cross-linking (extractable collagen increased from 21 +/- 2% in control to 28 +/- 2% in BAPN, P < 0.05). BAPN decreased chamber stiffness (0.13 +/- 0.02 in control to 0.06 +/- 0.01 in BAPN, P < 0.05) and myocardial stiffness (10.4 +/- 0.5 in control to 6.6 +/- 0.5 in BAPN, P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Growth effects of electrically stimulated contraction on adult feline cardiocytes in primary culture

The purpose of this study was to determine effects of long-term electrical stimulation of cardiocyte contraction on protein synthesis rates and total protein content. Adult feline cardiocytes were plated on laminin-coated culture trays and maintained in a serum-free medium consisting of M199 supplemented with ascorbate, bovine serum albumin, creatine, carnitine, taurine, and 10(-7) M recombinant insulin. Cardiocytes were electrically stimulated to contract with use of continuous electrical pulses of alternating polarity at a frequency of 1 Hz and pulse duration of 5 ms. Nonstimulated cardiocytes are normally quiescent and were used as the control group. In control quiescent cardiocytes, protein synthesis rate decreased by 14% between days 1 and 4 in culture and then remained stable through day 7. In electrically stimulated cardiocytes, protein synthesis rates increased by 19% between days 1 and 7. Protein synthesis rates were 18% higher on day 4 and 43% higher on day 7 in electrically stimulated than in quiescent cardiocytes. Protein content per cell was determined by measuring total fluorescence per cell by use of confocal microscopy of fluorescein isothiocyanate-stained cells. Electrical stimulation significantly increased cellular protein content by 52% after 7 days compared with controls. Quiescent and electrically stimulated cardiocytes remained rod shaped, retained their myofibrillar architecture, and were responsive to electrical stimulation over the 7-day period. These data demonstrated that electrically stimulated contraction of adult cardiocytes resulted in cell growth, as assessed by an increase in protein content per cell over 7 days in culture. This increase was due, at least in part, to an acceleration of steady-state protein synthesis rates.

Effects of chronic supraventricular pacing tachycardia on relaxation rate in isolated cardiac muscle cells

Chronic supraventricular pacing tachycardia (SVT) causes abnormalities in both ventricular and cellular relaxation. The mechanisms causing these abnormalities have not been fully determined. To examine two of the possible mechanisms, a decrease in restoring force or an impairment of the intrinsic myocardial relaxation process, cardiocytes were enzymatically isolated from the left ventricle of pigs subjected to left atrial pacing at 240 beats/min for 3 wk and normal control pigs. SVT caused a decrease in the extent of cardiocyte shortening and the velocity of cardiocyte lengthening. To determine whether the changes in the relaxation velocity merely reflected a concomitant decrease in the extent of cardiocyte shortening (and a resultant decrease in restoring forces) or, in addition, reflected impairment in intrinsic relaxation properties, the relation between cardiocyte relaxation velocity and cardiocyte shortening extent was examined. There was a direct relation between relaxation velocity and shortening extent in both control and SVT cardiocytes. However, SVT decreased the relaxation velocity at any common extent of shortening and decreased the slope of the direct relation (slope 5.91 in control vs. 3.51 s-1 in SVT, P < 0.05). Therefore, these data suggested that SVT caused a primary impairment in the intrinsic myocardial relaxation process independently of a decrease in restoring force.

Load effects on gene expression during cardiac hypertrophy

Hemodynamic load is a primary regulator of cardiac mass. A potential proximal event in this regulatory pathway is thought to be the induction of immediate early genes, and markers of this process include the re-expression of genes for fetal sarcomeric proteins and the ventricular expression of atrial natriuretic factor (ANF). Previous in vivo models which have examined these questions have often neither quantified myocardial loading nor accounted for covariables which may affect gene expression such as the renin-angiotensin-aldosterone system, the sympathetic nervous system, or baroreceptors. Thus, whether load alone is sufficient to induce immediate early genes, which may ultimately result in cardiac hypertrophy, remains unknown. In the present study two models of right ventricular (RV) pressure overload were created by partially occluding the pulmonary artery (PA), either with a balloon catheter for 1 or 4 h, or with a surgically placed PA band for 12, 24, or 48 h. Serum catecholamine concentrations were determined in a subset of RV pressure overload cats at basal state, after 5 min of balloon inflation, and after 1 h of balloon inflation to examine the effects of this systemic trophic factor on IEG induction. Northern blot analysis for c-fos, egr-1, alpha-skeletal actin, and ANF from paired RV and left ventricular (LV) RNA allowed the effect of load (selectively increased in the RV) to be separated from other systemic variables (present in both ventricles). The relative signal intensities of the optical density of RV and LV mRNA autoradiograms were determined from northern blots, alternate lanes of which were loaded with 7.5 micrograms of total RNA from RV and LV tissue from the same cat. Partial PA occlusion caused RV systolic pressure to increase from a control value of 22 +/- 1 mmHg to 57 +/- 6 mmHg after 1 h, 59 +/- 5 mmHg after 4 h, and 58 +/- 5 mmHg after 48 h of RV pressure overload (RVPO). Serum norepinephrine and epinephrine levels at both 5 and 60 min of RVPO were not significantly different from basal levels. The RV/LV ratios of mRNA for both egr-1 and c-fos were equal in control and 48 h PA banded animals, but were increased in the 1 and 4 h balloon RVPO cats. The RV/LV ratio of mRNA for alpha-skeletal actin was equal in the basal state and did not increase after 12, 24, or 48 h of RVPO. After 48 h of RVPO, total RNA was increased in the RV compared with the LV (1.9 +/- 0.1 v 1.1 +/- 0.1 micrograms/g tissue, P < 0.05). ANF expression was present in the RV after 48 h of RVPO, but absent in same-animal LV and all control ventricles. Thus, while increased load alone did not alter the expression of alpha-skeletal actin, it was sufficient both to induce increased expression of two distinct classes of immediate early genes, as well as ANF, and to increase total RNA, indicating hypertrophic growth initiation.

Direct effects of acute administration of 3, 5, 3' triiodo-L-thyronine on myocyte function

Recent studies have suggested that acute administration of 3, 5, 3' triiodo-L-thyronine (T3) may increase ventricular performance; however, the direct cellular effects of acute T3 administration are not understood. The objectives of this study were to determine (1) whether T3 acts directly on the cardiac muscle cell (myocyte) itself, and (2) whether T3 acts independently of the myocyte beta-adrenergic receptor. Accordingly, isolated myocyte function was examined using video-microscopy in normal porcine myocytes (n = 60) in the control state and in the presence of increasing T3 concentrations (10 to 500 pmol/L). T3 caused myocyte shortening extent, shortening velocity, and lengthening velocity to increase in a dose-dependent manner. For example, shortening velocity increased from 49.2 +/- 4.3 microns/s at baseline to 66.5 +/- 6.1 microns/s with 100 pmol/L T3 (p < 0.05). beta-Adrenergic stimulation with 25 nmol/L isoproterenol increased shortening velocity to 97.6 +/- 5.7 microns/s; isoproterenol with T3 increased shortening velocity further to 168.5 +/- 10.9 microns/s. Analysis of variance revealed that this increase with T3 was independent of and additive to the beta-adrenergic receptor system. In summary, T3 caused a dose-dependent increase in myocyte contractile performance, and these effects were independent of and additive to beta-adrenergic receptor stimulation. Thus, acute T3 administration may provide a novel modality to improve left ventricular contractile function independent of the beta-adrenergic receptor system.

Cellular and molecular alterations in the beta adrenergic system with cardiomyopathy induced by tachycardia

OBJECTIVE

The aim was to examine the relationship between changes in myocyte function to changes in protein and mRNA content of components of the beta adrenergic system with tachycardia induced cardiomyopathy.

METHODS

Contractile function and beta adrenergic responsiveness were measured in isolated myocytes from control pigs (n = 6) and in pigs subjected to three weeks of pacing induced supraventricular tachycardia (n = 6). beta Receptor density and affinity, the relative content of the stimulatory (Gs) and inhibitory (Gi) subunits of the G protein complex, and adenylate cyclase activity were determined from sarcolemmal preparations. In order to determine whether these changes were accompanied by alterations in steady state mRNA levels for specific components of the beta adrenergic system, mRNA content for the beta 1 adrenergic receptor and the G alpha s and G alpha i2 subunits of the G protein complex was measured.

RESULTS

Chronic supraventricular tachycardia caused a 36% increase in left ventricular end diastolic dimension and a 61% decrease in left ventricular fractional shortening compared to controls. The velocity of isolated myocyte shortening was 50% lower in myocytes from hearts with tachycardia cardiomyopathy than in control myocytes. In the presence of 50 nM isoprenaline or 2 microM forskolin, the velocity of myocyte shortening was 65% lower in the myopathic myocytes than in the controls. With the development of tachycardic cardiomyopathy, beta adrenergic receptor density fell by 25% with no change in affinity, Gs decreased by 35%, and Gi increased by over 50% compared to controls. Basal adenylate cyclase activity and isoprenaline and forskolin stimulated adenylate cyclase activity fell by over 50% with supraventricular tachycardia compared to controls. The relative content of G alpha i2 mRNA increased threefold with the development of tachycardic cardiomyopathy with no change in the relative abundance of mRNA for the beta 1 receptor or G alpha s when compared with controls.

CONCLUSIONS

The changes in myocyte beta adrenergic responsiveness with the development of tachycardic cardiomyopathy are due to alterations in cellular mechanisms (decreased beta receptor and Gs density, increased Gi) and in molecular mechanisms (increased Gi mRNA content).

Effects of protamine on myocyte contractile function and beta-adrenergic responsiveness

The use of protamine sulfate in patients has been associated with severe circulatory collapse and myocardial failure. However, the exact mechanisms responsible for these reactions to protamine remain unclear. Accordingly, we examined the effect of protamine on isolated myocyte contractile function. Indexes of isolated myocyte contractile function, percent shortening, and velocity of shortening were examined using videomicroscopy. Porcine cardiocytes (n = 75) were studied at baseline and in the presence of 80 micrograms/mL protamine. In addition, myocyte function was examined sequentially, first during treatment with 8 IU/mL heparin and then after the addition of a protamine dose sufficient to completely bind the heparin. The binding of heparin and protamine resulted in the formation of a heparin-protamine complex. The protamine concentration of 80 micrograms/mL is approximately equal to the serum concentration of protamine obtained in patients when administered in a dose of 5 mg/kg. In the presence of 80 micrograms/mL protamine, both percent shortening and velocity of shortening fell by more than 32% from baseline values (p < 0.05). The presence of either heparin alone or the heparin-protamine complex resulted in no change in baseline myocyte contractile measurements. Furthermore, to examine the effect of protamine on myocyte beta-adrenergic responsiveness a second series of experiments were performed. Myocyte contractile function was measured when 25 nmol/L isoproterenol was added to each of the protocols above. The presence of 80 micrograms/mL protamine resulted in a significant blunting of myocyte beta-adrenergic responsiveness. The presence of either heparin alone or the heparin-protamine complex resulted in no change in myocyte beta-adrenergic responsiveness.(ABSTRACT TRUNCATED AT 250 WORDS)

Native beta-adrenergic support for left ventricular dysfunction in experimental mitral regurgitation normalizes indexes of pump and contractile function

BACKGROUND

It is generally accepted that the adrenergic nervous system provides inotropic support for the failing heart. However, the magnitude of this support has never been studied extensively. The present study was performed to test the hypothesis that the adrenergic nervous system is capable of maintaining indexes of pump and contractile function in the normal range despite significant innate myocardial depression.

METHODS AND RESULTS

We used our model of experimental canine mitral regurgitation, which produces left ventricular dysfunction after 3 months of volume overload. We studied indexes of contractile function on and off beta-blockade at baseline and again on and off beta-blockade 3 months after chronic mitral regurgitation had induced significant contractile dysfunction. At baseline, acute beta-blockade caused insignificant reductions in the mass-corrected slope of the end-ejection stress-volume relation (EESVR), the end-systolic stiffness constant, and the ejection fraction-end-systolic stress and the mean velocity of circumferential fiber shortening (VCF)-end-systolic stress relations. After 3 months of chronic mitral regurgitation, all indexes of contractile function were normal in the unblocked state except for the VCF-stress relation, which was mildly reduced. However, after acute beta-blockade after 3 months of chronic mitral regurgitation, the EESVR fell to 303 +/- 27 versus 443 +/- 24 during acute beta-blockade before mitral regurgitation was created (P < .05), and the end-systolic stiffness constant was reduced to 2.54 +/- 0.15 versus 3.27 +/- 0.11 (P < .05). Only after beta-blockade was the ejection fraction-stress relation significantly reduced for dogs with chronic mitral regurgitation. The VCF-stress relation became markedly more abnormal. The viscosity-velocity relation of myocytes isolated from the ventricles of the dogs with mitral regurgitation confirmed that substantial innate contractile depression was present.

CONCLUSIONS

After 3 months of chronic mitral regurgitation, the adrenergic nervous system was able to maintain most indexes of contractile function in the normal range despite significant depression in innate contractile function. Thus, in the absence of beta-blockade, significant innate contractile depression may be obscured by adrenergic support.

The effects of complete versus incomplete mitral valve repair in experimental mitral regurgitation

Severe mitral regurgitation (regurgitant fraction 0.75 +/- 0.02) was created in eight dogs by our closed-chest chordal rupture technique. After 3 months of chronic mitral regurgitation all indices of contractile function were depressed. Mitral valve repair was then attempted. Postoperative regurgitant fraction was reduced compared with the preoperative value in all eight dogs. Concomitantly, forward cardiac output increased in all dogs and pulmonary capillary wedge pressure fell in all dogs. However, in some dogs, significant regurgitation persisted despite repair. Postoperative regurgitant fraction ranged from 0% to 60%. Postoperative residual regurgitant fraction was related significantly to postoperative cardiac output (r = 0.99), pulmonary capillary wedge pressure (r = 0.77), ejection fraction (r = 0.75), and two indices of contractile function--the mass-corrected end-systolic stress volume relationship (r = 0.87) and end-systolic stiffness (r = 0.93). In general, these parameters returned to their normal values before mitral regurgitation when postoperative regurgitant fraction was less than 30%. Myocytes isolated from the ventricles at the end of study also demonstrated normal contractile function when regurgitant fraction was less than 30%.

Effect of catheter positioning on the variability of measured gradient in aortic stenosis

The purpose of this study was to quantify the variation in measured aortic valve gradient and calculated aortic valve area when different techniques of cardiac catheterization were utilized. Hemodynamic assessment of aortic stenosis severity requires an accurately determined pressure gradient. In aortic stenosis, the presence of intraventricular pressure gradients and downstream pressure recovery within the aorta means that a range of aortic valve gradients could be measured in a given patient depending upon catheter position and measurement technique. To quantify the degree of variation in measured gradient and calculated aortic valve area, we generated transvalvular gradients by nine different techniques in 15 patients (11 men, 4 women; 29-86 years old). Patients were divided into those with severe aortic stenosis (aortic valve area < or = 0.6 cm2, n = 6) and those with moderately severe aortic stenosis (aortic valve area 0.61-0.90 cm2, n = 9). Considerable variation in measured gradient and calculated aortic valve area was observed. The maximum variation in gradient was similar in severe and moderately severe aortic stenosis groups (33 mm Hg. vs. 32 mm Hg., p = NS). However, the variation in gradient as a percent of maximum gradient was greater (P < 0.05) in the moderately severe aortic stenosis group. The maximum variation in calculated aortic valve area was 0.1 cm2 in the severe group and 0.3 cm2 in the moderately severe group (P < 0.01). An intraventricular gradient, present in 13 of 15 (87%) patients, was partially responsible for the variation in pressure gradient measurement and calculated aortic valve area.(ABSTRACT TRUNCATED AT 250 WORDS)

The cellular basis for the blunted response to beta-adrenergic stimulation in supraventricular tachycardia-induced cardiomyopathy

Chronic tachycardia-induced dilated cardiomyopathy causes increased plasma catecholamines and alterations in beta-adrenergic responsiveness in vivo. However, whether isolated myocyte contractile response to beta-stimulation is directly affected by the development of cardiomyopathy and how these changes are related to alterations in the beta-adrenergic receptor system remain unclear. Accordingly, isolated myocyte function and beta-adrenergic responsiveness were examined in two groups of 12 pigs each: sham controls, and with supraventricular tachycardia induced cardiomyopathy (SVT; pace: 240 beats/min, 3 weeks). Isolated LV myocyte percent and velocity of shortening were examined at baseline, with isoproterenol (2-100 nM), and forskolin (0.1-4 microM). Baseline percent and velocity of shortening were significantly reduced with SVT compared to controls (1.6 +/- 0.1 vs 5.4 +/- 0.2%, 56 +/- 3 vs 25 +/- 1 micron/s, respectively, P < 0.05). The maximal increase in the percent and velocity of shortening with isoproterenol was significantly blunted in the SVT myocytes compared with controls (3.2 +/- 0.4 vs 9.7 +/- 1.0%, 48.0 +/- 5.3 vs 122.6 +/- 15.5 micron/s, respectively, P < 0.05). Similarly, maximal increase in the percent and velocity of shortening with forskolin were reduced with SVT compared to controls (3.3 +/- 0.4 vs 10.5 +/- 0.6%, 50.7 +/- 6.4 vs 120.1 +/- 9.7 micron/s, respectively, P < 0.05). In order to determine the cellular basis for these changes in beta-adrenergic response, myocyte structure, sarcolemmal beta-receptor density and affinity, and adenylate cyclase activity were examined. There was a 25% reduction in beta-receptor number with SVT (P < 0.05) but no change in affinity. Basal adenylate cyclase activity was lower with SVT compared to control (46 +/- 3 vs 77 +/- 10 pmol cyclic AMP/mg/min, P < 0.05), and exhibited a blunted response with both isoproterenol (1 mM; 106 +/- 19 vs 203 +/- 26 pmol cyclic AMP/mg/min, P < 0.05) and forskolin (100 microns: 209 +/- 35 vs 378 +/- 58 pmol cyclic AMP/mg/min, P < 0.05). Finally, myofibrillar content within SVT myocytes was significantly reduced from controls (43 +/- 7 vs 63 +/- 4%, P < 0.05). In summary, the cellular basis for the depressed myocyte contractile response to beta-stimulation with tachycardia induced SVT are probably due to several factors which include: decreased expression of beta-receptors, alterations in beta-receptor transduction, reduced adenylate cyclase activity, and decreased myocyte contractile protein content.

Effects of chronic mitral regurgitation on diastolic function in isolated cardiocytes

We have previously shown that chronic mitral regurgitation (MR) increases the rate of left ventricular early diastolic filling. These changes in chamber diastolic function were felt to be secondary to alterations in left ventricular loading conditions. Therefore, cellular diastolic function measured in cardiac muscle cells (cardiocytes) isolated from animals with chronic MR (absent alterations in loading conditions) was expected to be normal. However, chronic MR caused a decrease in sarcomere lengthening rate. The purpose of the current study was to define the mechanisms causing this decreased sarcomere lengthening rate in chronic MR cardiocytes and to explain the apparent dichotomy between chamber and cellular diastolic properties. Accordingly, sarcomere motion was measured using laser diffraction techniques in enzymatically isolated cardiocytes from seven control dogs and 11 dogs with chronic MR (produced by closed-chest transection of the mitral chordae). In the MR cardiocytes, there were abnormalities in cellular systolic function (decreased extent and velocity of shortening) and in cellular diastolic function (decreased velocity of sarcomere lengthening). Because studies in papillary muscles have shown that there is a direct relation between abnormal diastolic function (decreased velocity of muscle lengthening) and abnormal systolic function (decreased extent of muscle shortening), it was unclear whether the changes in cellular relaxation rate observed in chronic MR merely reflected a concomitant decrease in the extent of shortening or instead reflected an impairment in intrinsic relaxation properties. To make this distinction, the relation between relaxation velocity (measured as peak sarcomere lengthening rate) and sarcomere shortening extent was examined in MR cardiocytes and compared with that in control cardiocytes. There was a direct relation between sarcomere relaxation velocity and sarcomere shortening extent in both control and MR cardiocytes. Over a wide range of shortening extent, the slopes and y intercepts of this relation were similar in control and MR cardiocytes (slope, 27.7 sec-1 in control cells versus 28.1 sec-1 in MR cells; y intercept, -1.1 microns/sec in control cells versus -1.7 microns/sec in MR cells; p = NS). At any common shortening extent, relaxation velocity was the same in control and MR cardiocytes. To prove that this relation could detect abnormalities in the intrinsic myocardial relaxation process, interventions known to produce primary alterations in the intrinsic myocardial relaxation process were examined: the effects of hypothermia (30 degrees C) and isoproterenol (10(-6) M) on the relaxation velocity-shortening extent relation were studied in normal and MR cardiocytes.(ABSTRACT TRUNCATED AT 400 WORDS)

Changes in diastolic function during development and correction of chronic LV volume overload produced by mitral regurgitation

BACKGROUND

Mitral regurgitation (MR) causes an augmentation in left ventricular (LV) diastolic function, increasing early diastolic filling rate and decreasing LV stiffness. Whether these changes in diastolic function persist, return to normal, or become abnormal after mitral valve replacement (MVR) is unknown.

METHODS AND RESULTS

Simultaneous LV echocardiography and catheterization studies were performed in six dogs in the baseline state (baseline), 3 months after creation of MR (chronic MR), and 3 months after MVR. Chronic MR caused LV dilation (end-diastolic dimension increased from 4.5 +/- 0.1 cm in baseline to 5.8 +/- 0.1 cm in chronic MR, p < 0.05) and eccentric LV hypertrophy (LV-to-body weight ratio increased from 3.6 +/- 0.2 g/kg in baseline to 4.9 +/- 0.4 g/kg in chronic MR, p < 0.05). Chronic MR caused an increase in LV early diastolic filling rate (peak rate of increase in minor-axis dimension increased from 11 +/- 1 cm/sec in baseline to 18 +/- 1 cm/sec in chronic MR, p < 0.05), did not change the time constant of myocardial relaxation (tau was 31 +/- 4 msec in baseline and 30 +/- 2 msec in chronic MR), and caused a decrease in the modulus of regional chamber stiffness from 7.7 +/- 1.2 in baseline to 2.4 +/- 0.03 in chronic MR, p < 0.05. MVR caused the resolution of LV dilation (end-diastolic dimension returned to normal [4.8 +/- 0.2 cm]), but three months after MVR, regression of LV hypertrophy was incomplete (LV-to-body weight ratio remained elevated [4.4 +/- 0.5 g/kg]). After MVR, LV early diastolic filling rate (8 +/- 1 cm/sec), the relaxation time constant (31 +/- 2 msec), chamber stiffness (7.1 +/- 1.8), myocardial stiffness (11.2 +/- 3.1), and LV end-diastolic pressure (8 +/- 1 mm Hg) returned to normal.

CONCLUSIONS

The enhanced diastolic function seen in chronic MR returned to normal after correction of the chronic volume overload by MVR.

Contractile properties of isolated porcine ventricular myocytes

OBJECTIVE

The aim was to examine the structure, function, and inotropic responsiveness of isolated porcine myocytes.

METHODS

Left ventricular myocytes were harvested from six pigs with normal echocardiographic and pressure indices of left ventricular function: fractional shortening 30 (SEM 2)%, peak+dP/dt 1225(110) mm Hg.s-1, end diastolic pressure 7(2) mm Hg, and cardiac output 2.8(0.5) litres.min-1. Indices of myocyte contractility were examined using a computer assisted video edge detection system which included the percent and velocity of myocyte shortening. Myocyte contractions were recorded by alternating field stimulation at 1 Hz and measurements performed in the presence of 2-10 mM extracellular Ca2+. Contractile properties of isolated porcine myocytes were examined unattached (n = 20) or following attachment to a basement membrane substrate (n = 63).

RESULTS

Left ventricular myocytes were successfully obtained from all pigs with a 68% average yield of viable myocytes. Isolated myocyte length was 128(6) microns with an average profile surface area of 2226(51) microns 2 (coefficients of variation of 25% and 35% respectively). Electron microscopic examination showed normal cytoarchitecture with 62(4)% myofibrils by volume. Baseline extent and velocity of shortening for unattached myocytes was 6.2% and 77(10) microns.s-1 respectively. Baseline extent and velocity of shortening for myocytes adherent to a basement substrate were 4.9(0.4)% and 64(7) microns.s-1. These indices of myocyte contractile function increased from baseline values for both the unattached and attached cells with increased extracellular Ca2+.

CONCLUSIONS

Isolated porcine left ventricular myocytes retain normal cytoarchitecture and composition, respond to field stimulation, and are responsive to extracellular Ca2+. Myocytes adherent to a basement membrane substrate were capable of contracting against this resistive load.