Doppler echocardiographic estimation of left ventricular end-diastolic pressure after MI in rats

Percutaneous intracoronary delivery of SERCA gene increases myocardial function: a tissue Doppler imaging echocardiographic study

The aim of this study was to examine the efficiency of adenovirus-mediated overexpression of sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA1a) gene in a realistic model based on percutaneous intracoronary delivery and on noninvasive functional monitoring. Catheter-based selective coronary delivery of saline or adenoviruses (Ad.CMV.SERCA1a or Ad.CMV.lacZ, 10(10) plaque-forming units) was performed in the circumflex artery of rabbits. Effects were assessed and compared by using serial Doppler echocardiography, hemodynamics, and measurements of SERCA protein and Ca(2+) uptake activity. On day 3, a 21% increase in SERCA proteins and a 37% increase in the maximal rate of Ca(2+) uptake were observed in the transfected left ventricular (LV) walls of Ad.CMV.SERCA1a rabbits. Baseline hemodynamics and conventional echographic measurements of global LV function were poorly affected. In contrast, tissue Doppler imaging (TDI) was able to assess a strong increase in the baseline function of transfected LV walls, as assessed with maximal wall velocities (+32% and +43%, respectively) and strain rates (+18% and +30%, respectively). TDI parameters were closely related to the maximal rate of Ca(2+) uptake (r(2) = 0.68 for the systolic strain rate). Serial TDI analysis during follow-up showed that the effects lasted for 7 days and were no longer detectable 15 days after adenoviruses injection. In conclusion, LV function can be increased by adenovirus-mediated overexpression of SERCA in a clinically relevant model, and TDI provides an accurate and noninvasive tool for monitoring effects on global as well as regional myocardial function.

Serial magnetic resonance imaging based assessment of the early effects of an ACE inhibitor on postinfarction left ventricular remodeling in rats

In vivo assessment of treatment efficacy on postinfarct left ventricular (LV) remodeling is crucial for experimental studies. We examined the technical feasibility of serial magnetic resonance imaging (MRI) for monitoring early postinfarct remodeling in rats. MRI studies were performed with a 7-Tesla unit, 1, 3, 8, 15, and 30 days after myocardial infarction (MI) or sham operation, to measure LV mass, volume, and the ejection fraction (EF). Three groups of animals were analyzed: sham-operated rats (n = 6), MI rats receiving lisinopril (n = 11), and MI rats receiving placebo (n = 8). LV dilation occurred on day 3 in both MI groups. LV end-systolic and end-diastolic volumes were significantly lower in lisinopril-treated rats than in placebo-treated rats at days 15 and 30. EF was lower in both MI groups than in the sham group at all time points, and did not differ between the MI groups during follow-up. Less LV hypertrophy was observed in rats receiving lisinopril than in rats receiving placebo at days 15 and 30. We found acceptable within- and between-observer agreement and an excellent correlation between MRI and ex vivo LV mass (r = 0.96; p < 0.001). We demonstrated the ability of MRI to detect the early beneficial impact of angiotensin-converting enzyme (ACE) inhibitors on LV remodeling. Accurate and noninvasive, MRI is the tool of choice to document response to treatment targeting postinfarction LV remodeling in rats.

Temporally controlled onset of dilated cardiomyopathy through disruption of the SRF gene in adult heart

BACKGROUND

Serum response factor (SRF) is a cardiac transcription factor involved in cell growth and differentiation. We have shown, using the Cre/loxP system, that cardiac-specific disruption of SRF gene in the embryonic heart results in lethal cardiac defects. The role of SRF in adult heart is unknown.

METHODS AND RESULTS

We disrupted SRF in the adult heart using a heart-specific tamoxifen-inducible Cre recombinase. This disruption led to impaired left ventricular function with reduced contractility, subsequently progressing to dilated cardiomyopathy, as demonstrated by serial echocardiography, including tissue Doppler imaging. The cytoarchitecture of cardiomyocytes was altered in the intercalated disks. All mutant mice died from heart failure 10 weeks after treatment. These functional and structural defects were preceded by early alterations in the cardiac gene expression program: major decreases in mRNA levels for cardiac alpha-actin, muscle creatine kinase, and calcium-handling genes.

CONCLUSIONS

SRF is crucial for adult cardiac function and integrity. We suggest that the rapid progression to heart failure in SRF mutant mice results primarily from decreased expression of proteins involved in force generation and transmission, low levels of polymerized actin, and changes in cytoarchitecture, without hypertrophic compensation. These cardiac-specific SRF-deficient mice have the morphological and clinical features of acquired dilated cardiomyopathy in humans and may therefore be used as an inducible model of this disorder.

Spironolactone reduces fibrosis of dilated atria during heart failure in rats with myocardial infarction

AIMS

Congestive heart failure (CHF) is associated with severe structural changes of atria, contributing to impaired atrial function and the risk of arrhythmia. This study investigated the effects of CHF treatments on atrial remodelling.

METHODS AND RESULTS

Three months after myocardial infarction (MI), rats were treated for 1 month with spironolactone, lisinopril, or atenolol alone or in combination. Echocardiography-Doppler tissue imaging, haemodynamic measurements, and 24-h Holter monitoring were used to characterize the cardiomyopathy. Atrial fibrosis was quantified with Picrosirius Red staining. Left atrial diameter was increased (5.8+/-0.6 mm in MI vs. 3.6+/-0.3 mm in sham; P<0.0001), as was atrial fibrosis (26.7+/-3.8% in MI vs. 10.5+/-2.2% in sham; P<0.0001), which correlated with left ventricular (LV) dysfunction after 3 months of MI. P-wave duration was also increased and premature atrial beats were frequent on the 24-h electrocardiogram. Similar improvements in LV dysfunction were observed after 1 month of spironolactone, ACE-inhibitor, or beta-blocker therapy alone or in combination. Atrial hyperexcitability was reduced by all the treatments, but only spironolactone attenuated atrial fibrosis and reduced P-wave duration.

CONCLUSION

Atrial fibrosis caused by chronic CHF is reduced by spironolactone.

Validation of echocardiographic and Doppler indexes of left ventricular relaxation in adult hypertensive and normotensive rats

This study was performed to validate echocardiographic and Doppler techniques for the assessment of left ventricular (LV) diastolic function in spontaneously hypertensive rats (SHR) and normotensive Wistar rats. In 11 Wistar rats and 20 SHR, we compared 51 sets of invasive and Doppler LV diastolic indexes. Noninvasive indexes of LV relaxation were related to the minimal rate of pressure decline (−dP/d tmin), particularly isovolumic relaxation time (IVRT), the Tei index, the early velocity of the mitral annulus ( Em) using Doppler tissue imaging, and early mitral flow propagation velocity using M-mode color ( r = 0.28–0.56 and P < 0.05–0.0001). When the role of systolic load was considered, the correlation between Doppler indexes of LV diastolic function and relaxation rate [(−dP/d tmin)/LV systolic pressure] improved ( r = 0.48–0.86 and P = 0.004–0.0001, respectively). Similarly, Doppler indexes of LV diastolic function and the time constant of isovolumic LV relaxation (τ) correlated well ( r = 0.50–0.84 and P = 0.0002–0.0001, respectively). In addition, eight SHR and eight Wistar rats were compared; their LV end-diastolic diameters were similar, whereas the SHR LV mass was greater. Furthermore, IVRT and Tei index were significantly higher and Em was lower in SHR. Moreover, τ was higher in SHR, demonstrating impaired LV relaxation. In conclusion, LV relaxation can be assessed reliably using echocardiographic and Doppler techniques, and, using these indexes, impaired relaxation was demonstrated in SHR.

Left ventricular SERCA2a gene down-regulation does not parallel ANP gene up-regulation during post-MI remodelling in rats

BACKGROUND

In most animal models of chronic hemodynamic overload of the left ventricle (LV) as well as in human end stage heart failure, the sarcoplasmic reticulum (SR) Ca2+-ATPase (SERCA2a) mRNA levels are decreased in parallel with increased atrial natriuretic peptide (ANP) mRNA levels. The situation in the remote myocardium following myocardial infarction (MI) is unclear.

AIMS

(1) To examine SERCA2a mRNA levels in the non-infarcted LV myocardium of rats at the chronic stage of experimental MI and (2) To examine whether a negative linear correlation exists between SERCA2a and ANP mRNA levels in this model.

METHODS

Anesthetized adult male Wistar rats underwent left coronary artery ligation or sham operation. Three months later, the rats were divided into three groups: sham-operated rats (sham, n=21), HF-free rats with MI (non-failing (NF)-MI, n=29) and rats with both MI and HF (congestive heart failure (CHF)-MI, n=14). LV remodelling and function were assessed by echocardiography and hemodynamic measurements. SERCA2a and ANP mRNA levels were determined by Northern and dot blot analysis with specific cDNA probes.

RESULTS

LV SERCA2a mRNA levels varied markedly in sham-operated rats (0.9-1.8). Mean ANP mRNA level increased markedly and mean SERCA2a mRNA level decreased moderately in the remote myocardium. In some NF-MI rats, SERCA2a mRNA levels were higher than those in some sham controls. Whereas ANP mRNA levels correlated well with MI severity (r2=0.79, p<0.001), this was not the case for SERCA2a mRNA levels (r2=0.42, p<0.01). We found no negative correlation between ANP and SERCA2a mRNA levels.

CONCLUSION

SERCA2a gene down-regulation in the non-infarcted myocardium of rats with MI does not correlate with ANP gene up-regulation, suggesting that the two genes are not antithetically regulated.

Evolution of expression of cardiac phenotypes over a 4-year period in the beta-myosin heavy chain-Q403 transgenic rabbit model of human hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM), the most common cause of sudden cardiac death in the young, is characterized by a diverse array of cardiac phenotypes evolving over several decades. We have developed transgenic rabbits that fully recapitulate the phenotype of human HCM and provide for the opportunity to delineate the sequence of evolution of cardiac phenotypes, and thus, the pathogenesis of HCM. We determined evolution of biochemical, molecular, histological, structural and functional phenotypes at 4 age-periods in 47 beta-myosin heavy chain-glutamine (MyHC-Q)-403 transgenic rabbits. Ca(+2) sensitivity of myofibrillar ATPase activity was reduced very early and in the absence of other discernible phenotypes. Myocyte disarray also occurred early, prior to, and independent of hypertrophy and fibrosis. The latter phenotypes evolved predominantly during puberty in conjunction with activation of stress-related signaling kinases. Myocardial contraction and relaxation velocities were decreased early despite normal global cardiac function and in the absence of histological phenotype. Global cardiac function declined with aging, while left atrial size was increased along with Doppler indices of left ventricular filling pressure. Thus, Ca(+2) sensitivity of myofibrillar ATPase activity is a primary phenotype expressed early and independent of the ensuing phenotypes. Pathogenesis of myocyte disarray, which exhibits age-independent penetrance, differs from those of hypertrophy and fibrosis, which show age-dependent expression. Myocardial dysfunction is an early marker that predicts subsequent development of hypertrophy. These findings in an animal model that recapitulates the phenotype of human HCM, implicate involvement of multiple independent mechanisms in the pathogenesis of cardiac phenotypes in HCM.

Validation of echocardiographic methods for assessing left ventricular dysfunction in rats with myocardial infarction

The rat infarct model is widely used in heart failure research, but few echocardiographic indexes of left ventricular (LV) function are validated in this model. Accordingly, the objective of this study was to validate a 13-segment LV wall motion score index (WMSI) and the myocardial performance index (MPI) in infarcted rats. Twenty-nine male Wistar rats underwent left coronary artery ligation or sham operation and were evaluated with two-dimensional and Doppler flow echocardiography 8 wk later. After echocardiography, invasive indexes were obtained using a high-fidelity catheter. WMSI and MPI were correlated with the invasive and noninvasive measurements of LV function. WMSI and MPI significantly correlated directly with end-diastolic pressure (r=0.72 and 0.42 for WMSI and MPI, respectively) and the time constant of isovolumic relaxation (r=0.68 and 0.48) and inversely with peak rate of rise of LV pressure (+dP/dt; r=-0.68 and -0.50), peak rate of decline in LV pressure (r=-0.57 and -0.44), LV developed pressure (r=-0.58 and -0.42), area fractional shortening (r=-0.85 and -0.53), and cardiac index (r=-0.74 and -0.74). Stepwise linear regression analyses revealed that LV end-diastolic pressure, +dP/dt, area fractional shortening, and cardiac index were independent determinants of WMSI (r=0.994) and that cardiac index and +dP/dt were independent determinants of MPI (r=0.781). We conclude that the 13-segment WMSI and MPI are reproducible and correlate strongly with established echocardiographic and invasive indexes of systolic and diastolic function. These findings support the use of WMSI and MPI as indexes of global LV function in the rat infarction model of heart failure.

Constitutive Cardiac Overexpression of Sarcoplasmic/Endoplasmic Reticulum Ca 2+ -ATPase Delays Myocardial Failure After Myocardial Infarction in Rats at a Cost of Increased Acute Arrhythmias

Background— Heart failure often complicates myocardial infarction (MI), and sarcoplasmic/endoplasmic reticulum Ca 2+ -ATPase (SERCA2a) is underexpressed in the failing myocardium. We examined the effect of preexisting cardiac SERCA2a protein overexpression on rat survival and left ventricular (LV) remodeling after MI.

Methods and Results— Baseline myocardial SERCA2a expression was 37% higher in transgenic (TG) rats than in their wild-type (WT) controls, consistent with enhanced myocardial function. The mortality rate of TG rats during the 24 hours after surgical MI was higher than that of WT rats (71% versus 35%, P <0.001), associated with a higher frequency of ventricular arrhythmias, and was normalized by lidocaine treatment. The increased acute-phase mortality in TG rats was not accompanied by increased 6-month mortality. Function of the noninfarcted myocardium, as assessed by tissue Doppler imaging, was higher in TG rats than in WT rats for up to 1 month after MI, a beneficial effect no longer observed at 3 months. LV remodeling and global function were similar in TG and WT rats. No difference in papillary muscle function was found at 6 months.

Conclusions— Constitutive cardiac SERCA2a overexpression has a transient beneficial effect on remote myocardium function in rat MI, with no improvement in LV global function or prevention of LV remodeling and failure. This benefit is associated with a higher risk of acute mortality, which is prevented by lidocaine treatment.

Long-term left ventricular echocardiographic follow-up of SHR and WKY rats: effects of hypertension and age

Long-term follow-up of left ventricular (LV) function using echocardiography has not been reported and, in this study, was carried out in normotensive (WKY) rats and spontaneously hypertensive rats (SHR). In 10 WKY rats and SHR, LV diastolic and systolic diameter (LVEDD and LVSD), shortening fraction (SF), and weight (LVW) were determined at 8, 15, 20, 35, and 80 wk of age. The ratio of early to late mitral flow and mitral annulus velocity (VE/VA and Em/Am), isovolumic relaxation time (IVRT), deceleration time of the E wave (DTE), Tei index, and mitral flow propagation velocity (Vp) were measured. No difference in LVEDD was found between SHR and WKY rats; however, LVEDD was increased at 80 wk in both strains. SF decreased slightly in old WKY rats. LVW progressively increased from 20 to 80 wk in both strains and was greater in SHR. VE/VA and Em/Am decreased at 80 wk in WKY rats. LV relaxation (IVRT, Tei index, and Vp) was progressively impaired in SHR compared with WKY rats. LV compliance (DTE) was altered in old SHR. Echocardiography permitted a long follow-up of LV function in SHR and WKY rats. Ventricular relaxation was impaired early in the life of SHR and progressed with aging. Furthermore, LV compliance was altered, but systolic function remained unchanged, in old SHR. In contrast, relaxation and SF were only slightly altered in old WKY rats, suggesting that pressure-related changes in LV function were the dominant features in the SHR.

Pulmonary endothelium as a site of synthesis and storage of interleukin-6 in experimental congestive heart failure

BACKGROUND

Pulmonary endothelium is an early upstream hemodynamic target of left ventricular dysfunction. Interleukin 6 (IL-6) is a pro-inflammatory cytokine reported to increase in congestive heart failure (CHF) patients.

AIMS

We sought to determine the origin of IL-6, IL-6 receptor (IL-6R) and gp130 in experimental CHF.

METHODS

We used rats with coronary artery ligation as an experimental model of either compensated or decompensated heart failure. Lung and aorta samples were analysed by RT-PCR, ELISA and immunohistochemistry for IL-6 and its receptors.

RESULTS

IL-6 mRNA expression increased in the lung of rats with decompensated heart failure and was positively correlated with infarct severity whereas IL-6R mRNA decreased in the lung of myocardial infarction rats and gp130 mRNA remained unchanged. In contrast, there were no changes in IL-6 mRNA expression in the aorta and left ventricular myocardium. IL-6 peptide content as determined by ELISA and Western Blot in lung tissue was 2-fold higher in decompensated heart failure as compared to control rats. These data were confirmed by immunohistochemistry showing a preferential endothelial localization of IL-6 in the CHF lung. IL-6 peptide was also present in the pleural effusion of decompensated heart failure and was positively correlated with IL-6 mRNA expression in the lungs of decompensated HF rats. Pulmonary IL-6 overexpression was associated with nuclear translocation of NF-kappaB and cytosolic degradation of IkappaB.

CONCLUSION

Dysfunctional pulmonary endothelium is a source of synthesis and storage of IL-6 in an experimental model of CHF.

Fibrosis of the left atria during progression of heart failure is associated with increased matrix metalloproteinases in the rat

OBJECTIVES

The purpose of this study was to determine the pathogenic factors and molecular mechanisms involved in fibrosis of the atria.

BACKGROUND

Fibrosis is an important component of the pathophysiology of atrial fibrillation, especially when the arrhythmia is associated with heart failure (HF) or atrial dilation.

METHODS

We used a rat model of myocardial infarction (MI) complicated by various degrees of left ventricular dysfunction and atrial dilation to study fibrosis and matrix metalloproteinase (MMP) activity in the left atrial (LA) myocardium by means of histologic, Western blot, zymographic, and immunohistologic techniques.

RESULTS

Three months after surgical ligature of the left coronary artery, 27 rats had a large MI, 12 were in mild HF, and 15 in severe HF. Both groups had LA enlargement at the echocardiography. Masson's trichrome and picrosirius staining of tissue sections revealed marked fibrosis at the periphery of trabeculae and also surrounding myolytic myocytes, in both mild and severe HF. In mild HF, the activity and expression of the matrilysin MMP-7 were increased (122%), whereas in severe HF, both MMP-7 (211%) and the gelatinase MMP-2 (187%) were up-regulated. There were no changes in the expression or activity of MMP inhibitors, TIMP-1, -2, and -4. Immunostaining of cryosections showed that MMP-2 was present in the interstitial spaces, whereas MMP-7 accumulated in myolytic myocytes.

CONCLUSIONS

Hemodynamic overload of the atria is an important pathogenic factor of fibrosis; MMP-7 appears to be involved in the early stage of this tissue remodeling process.

Left ventricular response to sustained volume overload from chronic aortic valve regurgitation in rats

OBJECTIVES

Aortic regurgitation (AR) induces left ventricular (LV) eccentric hypertrophy in response to chronic volume overload. Patients suffering from this disease often remain asymptomatic for decades before progressive LV dysfunction develops silently. Because of this slow evolution, large clinical trials with long-term follow-up on subjects with chronic AR are hard to perform. To overcome this problem, animal models have been developed in the past but results were very heterogeneous.

METHODS

Helped by echocardiography, we refined a known technique to induce homogeneous degrees of severe AR in Wistar-Kyoto rats. The effects on LV function without treatment and with nifedipine (25 mg/kg daily) (a drug currently recommended in humans with chronic AR) were evaluated by echocardiography.

RESULTS

Over 6 months, nontreated animals developed progressive LV dilatation and eccentric hypertrophy, characteristic of chronic LV volume overload. The animals also developed progressive LV systolic dysfunction, mimicking closely the evolution of the disease in humans. Abnormal filling parameters were also detected in the majority of animals. Systolic and diastolic abnormalities were prevented but only partially in the group treated with nifedipine.

CONCLUSION

This model can be used to study chronic AR and LV dysfunction associated with the disease. Nifedipine seems to protect the LV against chronic volume overload but only partially. Treatment strategies currently used in humans deserve further investigation.

Increased systolic performance with diastolic dysfunction in adult spontaneously hypertensive rats

Hypertensive heart disease is characterized by early development of hypertrophy and fibrosis that leads to heart failure (HF). HF develops in spontaneously hypertensive rats (SHR) after 18 months; however, it is not clear whether hypertrophy leads to altered cardiac performance at an earlier age in these rats. We studied cardiac performance in 10- to 11-month-old SHR and age-matched Wistar-Kyoto rats (WKY), using presssure-volume (PV) conductance catheter system to evaluate systolic and diastolic function in vivo at different preloads, including preload recruitable stroke work (PRSW), +dP/dt, and its relation to end-diastolic volume (+dP/dt-EDV) and preload-adjusted maximal power (PWR(max)-EDV(2)) as well as the time constant of left ventricular pressure decay, tau (tau), as an index of relaxation. The slope of the end-diastolic pressure-volume relation (EDPVR) and the ex vivo PV relation, both indexes of stiffness, were also calculated for each heart, and the Doppler E/A ratio was determined. In addition, plasma samples were obtained to assess B-type natriuretic peptide levels (BNP). We found that PRSW was higher in SHR than in WKY (174.5+/-15.6 versus 92.6+/-18.9 mm Hg; P<0.01). +dP/dt and +dP/dt-EDV were also enhanced in SHR versus WKY (9125+/-662 versus 6633+/-392 mm Hg/sec, P<0.01, and 28.14+/-4.35 versus 12.7+/-2.8 mm Hg/s per micro L, P<0.02). In addition, PWR-EDV(2) was elevated in SHR (7.3+/-1.5 versus 3.1+/-0.6 mW/ micro L(2)). Tau was prolonged in SHR (14.5+/-1 ms versus 10.8+/-0.8 for WKY, P<0.02) and EDPVR was significantly greater in SHR than in WKY (0.01+/-0.005 versus 0.004+/-0.001, P<0.05). The ex vivo pressure-volume relation was also steeper for SHR and the E/A ratio was 2.53+/-0.15 for SHR versus 1.67+/-0.08 for WKY (P<0.02). BNP was 45+/-2.5 pg/mL for SHR and 33.3+/-1.8 pg/mL for WKY (P<0.02). Taken together, these data suggest that at 10 to 11 months of age, before HF develops, SHR have increased systolic performance accompanied by delayed relaxation and increased diastolic stiffness.