The Physiopathology of Cardiorenal Syndrome: A Review of the Potential Contributions of Inflammation

Inter-organ crosstalk plays an essential role in the physiological homeostasis of the heart and other organs, and requires a complex interaction between a host of cellular, molecular, and neural factors. Derangements in these interactions can initiate multi-organ dysfunction. This is the case, for instance, in the heart or kidneys where a pathological alteration in one organ can unfavorably affect function in another distant organ; attention is currently being paid to understanding the physiopathological consequences of kidney dysfunction on cardiac performance that lead to cardiorenal syndrome. Different cardiorenal connectors (renin-angiotensin or sympathetic nervous system activation, inflammation, uremia, etc.) and non-traditional risk factors potentially contribute to multi-organ failure. Of these, inflammation may be crucial as inflammatory cells contribute to over-production of eicosanoids and lipid second messengers that activate intracellular signaling pathways involved in pathogenesis. Indeed, inflammation biomarkers are often elevated in patients with cardiac or renal dysfunction. Epigenetics, a dynamic process that regulates gene expression and function, is also recognized as an important player in single-organ disease. Principal epigenetic modifications occur at the level of DNA (i.e., methylation) and histone proteins; aberrant DNA methylation is associated with pathogenesis of organ dysfunction through a number of mechanisms (inflammation, nitric oxide bioavailability, endothelin, etc.). Herein, we focus on the potential contribution of inflammation in pathogenesis of cardiorenal syndrome.

Influence of cardiac nerve status on cardiovascular regulation and cardioprotection

Neural elements of the intrinsic cardiac nervous system transduce sensory inputs from the heart, blood vessels and other organs to ensure adequate cardiac function on a beat-to-beat basis. This inter-organ crosstalk is critical for normal function of the heart and other organs; derangements within the nervous system hierarchy contribute to pathogenesis of organ dysfunction. The role of intact cardiac nerves in development of, as well as protection against, ischemic injury is of current interest since it may involve recruitment of intrinsic cardiac ganglia. For instance, ischemic conditioning, a novel protection strategy against organ injury, and in particular remote conditioning, is likely mediated by activation of neural pathways or by endogenous cytoprotective blood-borne substances that stimulate different signalling pathways. This discovery reinforces the concept that inter-organ communication, and maintenance thereof, is key. As such, greater understanding of mechanisms and elucidation of treatment strategies is imperative to improve clinical outcomes particularly in patients with comorbidities. For instance, autonomic imbalance between sympathetic and parasympathetic nervous system regulation can initiate cardiovascular autonomic neuropathy that compromises cardiac stability and function. Neuromodulation therapies that directly target the intrinsic cardiac nervous system or other elements of the nervous system hierarchy are currently being investigated for treatment of different maladies in animal and human studies.

Renocardiac syndromes: physiopathology and treatment stratagems

Purpose of review

Bidirectional inter-organ interactions are essential for normal functioning of the human body; however, they may also promote adverse conditions in remote organs. This review provides a narrative summary of the epidemiology, physiopathological mechanisms and clinical management of patients with combined renal and cardiac disease (recently classified as type 3 and 4 cardiorenal syndrome). Findings are also discussed within the context of basic research in animal models with similar comorbidities.

Sources of information

Pertinent published articles were identified by literature search of PubMed, MEDLINE and Google Scholar. Additional data from studies in the author’s laboratory were also consulted.

Findings

The prevalence of renocardiac syndrome throughout the world is increasing in part due to an aging population and to other risk factors including hypertension, diabetes and dyslipidemia. Pathogenesis of this disorder involves multiple bidirectional interactions between the kidneys and heart; however, participation of other organs cannot be excluded. Our own work supports the hypothesis that the uremic milieu, caused by kidney dysfunction, produces major alterations in vasoregulatory control particularly at the level of the microvasculature that results in impaired oxygen delivery and blood perfusion.

Limitations

Recent clinical literature is replete with articles discussing the necessity to clearly define or characterize what constitutes cardiorenal syndrome in order to improve clinical management of affected patients. Patients are treated after onset of symptoms with limited available information regarding etiology. While understanding of mechanisms involved in pathogenesis of inter-organ crosstalk remains a challenging objective, basic research data remains limited partly because of the lack of animal models.

Implications

Preservation of microvascular integrity may be the most critical factor to limit progression of multi-organ disorders including renocardiac syndrome. More fundamental studies are needed to help elucidate physiopathological mechanisms and for development of treatments to improve clinical outcomes.

Nitric oxide bioavailability affects cardiovascular regulation dependent on cardiac nerve status

The sympathetic nervous system and nitric oxide (NO) contribute to regulation of vascular tone, blood flow regulation and cardiac function. Intrinsic cardiac neurons are tonically influenced by locally released NO and exogenous NO donors; however, the role of intact central neural connections remains controversial. We investigated the effects of S-nitroso-N-acetylpenicillamine (SNAP) administered into an intracoronary artery near the ventral interventricular ganglionated plexus (VIVGP) to evaluate distribution of myocardial blood flow (MBF) and ventricular function in normal and acute cardiac decentralized dogs. MBF was measured with microspheres during infusion of SNAP (100μM, IC) after systemic administration of 7-nitroindazole (nNOS blocker) followed by N(ω)-nitro-L-arginine methyl ester (LN; non-selective NOS blocker). Cardiac dynamics were not significantly affected by cardiac decentralization; several of these parameters (aortic systolic and diastolic pressures) were significantly increased after systemic administration of LN. Overall SNAP administered to the VIVGP increased blood flow in the anterior LV wall (vs. posterior LV wall) without affecting other cardiodynamic factors. In cardiac decentralized dogs subepicardial blood flow to the anterior LV wall during LN+SNAP was diminished resulting in a significantly higher inner:outer blood flow ratio (index of blood flow uniformity across the LV wall). LV function was not affected by acute cardiac decentralization; however, LV ejection fraction decreased markedly after LN (reduced NO bioavailability). These results validate earlier claims that reduced NO bioavailability imposes an upper limit on myocardial blood flow regulation and its transmural distribution. These effects are exacerbated after disconnection of intrinsic cardiac neurons from intact central neuron connections.

Impact of chronic kidney disease on myocardial blood flow regulation in dogs

BACKGROUND/AIMS

Chronic kidney disease (CKD) increases cardiovascular risk possibly due to coronary microvessel dysfunction and impaired myocardial flow reserve. This study investigated the effects of CKD on the regulation and transmural distribution of myocardial blood flow along with oxygen demand during intravenous dobutamine-induced increases in cardiac work.

METHODS

CKD was produced in dogs by a two-stage subtotal nephrectomy (kidney ablation-infarction model). Serum creatinine and blood urea nitrogen were evaluated during the development of CKD along with systemic blood pressure (tail-cuff plethysmography). After 5 weeks, the CKD dogs were staged according to the International Renal Interest Society staging system; all dogs were anesthetized and surgically prepared for blood flow studies. Data analyses were performed between sham control (CTR) and stage 1 and 2 CKD dogs.

RESULTS

At baseline, myocardial blood flow and diastolic aortic pressure were similar for all groups. During intravenous dobutamine, myocardial blood flow was markedly higher than CTR even though hematocrit levels declined with the severity of CKD. In the CTR dogs, myocardial blood flow increased in direct relation to cardiac work. However, in the CKD dogs (stage 1 and 2), maximum blood flow was achieved with low-dose dobutamine, indicating that coronary autoregulation is more readily exhausted with minimal increases in cardiac work during CKD.

CONCLUSION

We report that CKD markedly impairs coronary vascular reserve and myocardial blood flow regulation which could contribute to greater cardiovascular risk and poor clinical outcomes in CKD patients.

Role of the autonomic nervous system in cardioprotection by remote preconditioning in isoflurane-anaesthetized dogs

AIMS

Remote ischaemic preconditioning (rIPC) protects cardiac and non-cardiac tissues against ischaemic injury. Although there is increased demand to investigate its potential clinical applicability, fundamental mechanisms responsible for rIPC-mediated protection remain unresolved. We examined in isoflurane-anaesthetized dogs whether an intact cardiac nervous system was necessary to mediate rIPC protection against ischaemic injury.

METHODS AND RESULTS

Dogs were randomly allocated to six groups: 1, control (CON, no-rIPC); 2, rIPC (4 × 5 min renal artery occlusion/reperfusion); 3, autonomic ganglionic blockade with hexamethonium (HEX, no-rIPC; 20 mg/kg iv); 4, HEX + rIPC; 5, cardiac decentralization by surgical ablation of extracardiac nerves (DCN, no-rIPC); and 6, DCN + rIPC. All dogs underwent 60 min coronary occlusion and 180 min reperfusion; cardiac haemodynamic parameters were monitored. Regional blood flow (microspheres) in the heart and kidneys was assessed. Necrotic tissue was visualized using triphenyltetrazolium staining and related to anatomic risk zone size (area at risk; P = NS between groups) and coronary collateral blood flow. Infarct size (% AAR) was 29 ± 5 (mean ± 1 SD) in CON and 15 ± 4 in rIPC dogs (P = 0.001 vs. CON); 24 ± 3 in HEX vs. 12 ± 2 in HEX + rIPC (P = 0.001 vs. HEX); and 20 ± 2 in DCN vs. 12 ± 4 in DCN + rIPC (P = 0.001 vs. DCN). In CON dogs, infarct size was inversely related to coronary collateral flow; this relation was shifted downwards in all groups pre-treated with rIPC.

CONCLUSION

We report robust myocardial protection by rIPC against ischaemic injury in canines that was not abrogated by either pharmacological or surgical decentralization of cardiac nerves.

Coronary vasoregulation in health and disease

The present article reviews pertinent contributions from the Coronary Physiology Research Group at the Quebec Heart Institute to the understanding of coronary physiology in health and disease. Mechanisms that contribute to regulation of coronary blood flow and its distribution across the ventricular wall are discussed. Data from animal studies of ischemia-reperfusion injury are also presented and discussed in the context of current concepts regarding postischemic myocardial protection strategies. Future research directions regarding the cardiac nervous system and its importance in the regulation of coronary blood flow, cardiac function and myocyte injury during acute myocardial infarction are also discussed.

Influence of Acute Renal Failure on Coronary Vasoregulation in Dogs

Impaired renal function is associated with an increased risk for cardiovascular events and death, but the pathophysiology is poorly defined. The hypothesis that coronary blood flow regulation and distribution of ventricular blood flow could be compromised during acute renal failure (ARF) was tested. In two separate groups (n = 14 each) of dogs with ARF, (1) coronary autoregulation (pressure-flow relations), vascular reserve (reactive hyperemia), and myocardial blood flow distribution (microspheres) and (2) coronary vessel responses to intracoronary infusion of select endothelium-dependent and -independent vasodilators were evaluated. In addition, coronary pressure-flow relations and vascular reserve after inhibition of nitric oxide and prostaglandin release were evaluated. Under resting conditions, myocardial oxygen consumption increased in dogs with ARF compared with no renal failure (NRF; 11.8 +/- 9.2 versus 5.0 +/- 1.5 ml O(2)/min per 100 g; P = 0.01), and the autoregulatory break point of the coronary pressure-flow relation was shifted to higher diastolic coronary pressures (60 +/- 17 versus 52 +/- 8 mmHg in NRF; P = 0.003); the latter was shifted further rightward after inhibition of both nitric oxide and prostaglandin release. The endocardial/epicardial blood flow ratio was comparable for both groups, suggesting preserved ventricular distribution of blood flow. In dogs with ARF, coronary vascular conductance also was reduced (P = 0.001 versus NRF), but coronary zero-flow pressure was unchanged. Vessel reactivity to each endothelium-dependent/independent compound also was blunted significantly. In conclusion, under resting conditions, coronary vascular tone, reserve, and vessel reactivity are markedly diminished with ARF, suggesting impaired vascular function. Consequently, during ARF, small increases in myocardial oxygen demand would induce subendocardial ischemia as a result of a limited capacity to increase oxygen supply and thereby contribute to higher risk for adverse coronary events and mortality.

Comparison of Neutron Activated and Radiolabeled Microsphere Methods for Measurement of Transmural Myocardial Blood Flow in Dogs

BACKGROUND

The 'gold standard' radioactive microsphere (RM) technique for measurement of organ blood flow under various experimental conditions is inaccessible to many researchers due to increasing environmental concerns regarding safety and disposal of low-level radioactive waste materials. A new method using neutron activated microspheres (NAM) has recently been described.

METHODS

We compared regional myocardial blood flows using the new formulation STERIspheres (NAM; 15.0 +/- 0.1 [SD] microm; density 1.5 gr/mL) with RM (15.0 +/- 0.1 [SD] microm; density 1.5 gr/mL) under different experimental conditions during acute ischemia-reperfusion injury in dogs. Random paired combinations of four different RM and NAM were co-injected into the left atrium during autoregulation, coronary occlusion and flow-mediated hyperemia (reperfusion) in the same animal. The left ventricle was divided into non-ischemic and ischemic regions and further subdivided into endocardial, mid-myocardial and epicardial portions. After gamma-counting, blood and myocardial tissue samples (n = 180) were dried and then shipped to a core facility for neutron activation and analysis. NAM-RM blood flow data were directly compared by ANOVA and regression analysis; Bland and Altman analysis was also performed to assess mean differences in blood flow with NAM-RM.

RESULTS

A direct relation for blood flow between NAM-RM was observed; the slope of the relation (1.17 RM +/- 0.04 [SEE]) was different from unity but the intercept (0.06 +/- 0.06 [SEE]) was not different from the origin. Intermethod mean differences were minimal between NAM-RM in the low to normal range of blood flow and were increased at the higher blood flow levels the latter being of minor physiological consequence. A direct relation for endo/epicardial blood flow ratios between NAM-RM was also observed; the slope of the relation (0.98 RM +/- 0.04 [SEE]) and the intercept (0.03 +/- 0.06 [SEE]) were not different from unity or the origin, respectively.

CONCLUSIONS

RESULTS show that in addition to limiting production of radioactive waste materials, NAM accurately measure myocardial blood flow, endocardial/epicardial and ischemic/non-ischemic blood flow distributions over a wide range. We compared myocardial blood flows using paired combinations of neutron activated (NAM) and the 'gold standard' radiolabeled microspheres (RM) co-injected during autoregulation, coronary occlusion and flow-mediated hyperemia in an in situ canine ischemia-reperfusion preparation. A direct relation for blood flow and endo/epicardial blood flow ratios between NAM-RM was observed; intermethod mean differences between NAM-RM were minimal in the low to normal blood flow range but increased at higher blood flow levels. These results indicate that NAM accurately measure myocardial blood flow and its transmural distribution in addition to limiting unnecessary production of radioactive laboratory waste products.

Angiotensin inhibition and coronary autoregulation in a canine model of LV hypertrophy

In humans with hypertension and LV hypertrophy, beneficial effects of angiotensin inhibition may be associated with preserved autoregulatory capacity. We studied the effect of acute angiotensin converting enzyme (ACE) inhibition on coronary autoregulatory pressure-flow relations and transmural distribution of blood flow in sham and LV hypertrophy dogs. Heart/body weight ratio increased (p = 0.001) from 5.5 +/- 0.7 in sham to 6.9 +/- 0.5 in LV hypertrophy dogs. The lower coronary pressure limit (LPL) on the pressure-flow relation was 47 +/- 2 mmHg in sham and 57 +/- 6 mmHg (p = 0.001) in LV hypertrophy dogs; after acute ACE-inhibition the LPL was reduced to 40 +/- 5 mmHg and 49 +/- 6 mmHg (p = 0.001), respectively. Transmural distribution of blood flow was preserved at the LPL in both groups before and after acute ACE-inhibition. Concomitant blockade of prostaglandin and nitric oxide release and bradykinin catabolism had no additional effects on the LPL and distribution of blood flow. After acute ACE-inhibition in LV hypertrophy dogs, distribution of blood flow across the LV wall was preserved and subendocardial vascular reserve was maintained even though the LPL was significantly lower. Preservation of autoregulatory capacity by ACE inhibitors contributes to beneficial outcome in patients with hypertension and LV hypertrophy.

Right ventricular dysfunction and risk of heart failure and mortality after myocardial infarction

OBJECTIVES

The aim of this study was to determine the prognostic value of right ventricular (RV) function in patients after a myocardial infarction (MI).

BACKGROUND

Right ventricular function has been shown to predict exercise capacity, autonomic imbalance and survival in patients with advanced heart failure (HF).

METHODS

Two-dimensional echocardiograms were obtained in 416 patients with left ventricular (LV) dysfunction (ejection fraction [LVEF] < or = 40%) from the Survival And Ventricular Enlargement (SAVE) echocardiographic substudy (mean 11.1 +/- 3.2 days post infarction). Right ventricular function from the apical four-chamber view, assessed as the percent change in the cavity area from end diastole to end systole (fractional area change [FAC]), was related to clinical outcome.

RESULTS

Right ventricular function correlated only weakly with the LVEF (r = 0.12, p = 0.013). On univariate analyses, the RV FAC was a predictor of mortality, cardiovascular mortality and HF (p < 0.0001 for all) but not recurrent MI. After adjusting for age, gender, diabetes mellitus, hypertension, previous MI, LVEF, infarct size, cigarette smoking and treatment assignment, RV function remained an independent predictor of total mortality, cardiovascular mortality and HF. Each 5% decrease in the RV FAC was associated with a 16% increased odds of cardiovascular mortality (95% confidence interval 4.3% to 29.2%; p = 0.006).

CONCLUSIONS

Right ventricular function is an independent predictor of death and the development of HF in patients with LV dysfunction after MI.

Myocardial blood flow after chronic cardiac decentralization in anesthetized dogs: effects of ACE-inhibition

Coronary blood flow regulation was studied in dogs with an intact or chronically decentralized intrinsic cardiac nervous system. We also examined the effect of angiotensin-converting enzyme inhibition (ACEI) on coronary autoregulatory pressure-flow relations and distribution of blood flow since the renin-angiotensin system may play a critical role in vasoregulation. Myocardial oxygen demand was reduced in the chronic decentralized dogs compared to the control dogs. The lower pressure limit of the autoregulatory pressure-flow relation was similar for the control and chronic decentralized dogs (47+/-2 and 44+/-7 mm Hg, respectively; p = NS). After ACEI, the lower pressure limit shifted leftward to 40 mm Hg (p=0.001) in both groups. Concomitant blockade of cyclooxygenase, bradykinin catabolism and nitric oxide synthase had no further effect on the lower pressure limit. Total myocardial blood flow was lower (p=0.001) in the chronic decentralized dogs compared to the control dogs, while transmural distribution of blood flow was preserved in both groups. The results show that even though myocardial oxygen requirements are lower in the chronically decentralized heart compared to controls, coronary autoregulation is maintained at levels observed in normally innervated hearts. The present findings indicate that intrinsic cardiac neurons contribute to coronary autoregulatory control and myocardial blood flow distribution even in the absence of cardiac connections to the central nervous system. In addition, in the chronic decentralized dog, ACEI allows the heart to work at lower coronary perfusion pressures while myocardial blood flow distribution is preserved.

Effect of estrogen replacement therapy on distribution of myocardial blood flow in female anesthetized rabbits

Estrogen replacement therapy reduces risk of cardiovascular events by altering coronary vasoregulation and distribution of blood flow. Vessel reactivity and blood flow distribution were assessed in anesthetized female rabbits in the following groups: 1) sham, 2) ovariectomy, 3) ovariectomy + 17beta-estradiol, and 4) ovariectomy + dehydroepiandrosterone. After a 2-wk treatment, cardiac hemodynamics, vascular reserve, and blood flow were evaluated during the following infusions: 1) NaCl, or vehicle (0.5 ml/min), 2) acetylcholine (2 mg/kg), 3) isoproterenol (2 mg. kg(-1). min(-1)), and 4) chromonar (8 mg/kg). In hearts from ovariectomized rabbits, autoregulatory blood flow was preserved despite lower diastolic perfusion pressures (55 +/- 8 vs. 64 +/- 8 mmHg in sham) and rate-pressure product (14.4 +/- 0.8 vs. 19.3 +/- 0.8 beats/min. mmHg x 10(-3)). Estrogen replacement therapy restored coronary pressure and reserve, and all drugs increased vascular conductance. In conclusion, in hearts from ovariectomized rabbits, vascular reserve declined because coronary pressure was lower; however, blood flow was preserved at a higher level than expected for oxygen demand. Estrogen replacement therapy restores myocardial oxygen supply-demand indices and returns coronary pressure-flow data to levels observed in animals with intact ovaries.

Effect of angiotensin inhibition on the coronary artery lower pressure limit in anesthetized dogs

The renin-angiotensin system plays a critical role in regulating vasoconstriction and vasodilatation that can influence myocardial blood flow and its transmural distribution. We tested the hypothesis that angiotensin inhibition can induce a leftward shift of the coronary autoregulatory pressure-flow relation and preserve distribution of myocardial blood flow at lower coronary perfusion pressures. We established circumflex artery pressure-flow relations under baseline conditions and after intracoronary enalaprilat or losartan potassium. Thereafter, transmural myocardial blood flow was measured at baseline and at the lower coronary pressure limit (LPL). With enalaprilat, the LPL was shifted leftward from 48 +/- 6 mmHg at baseline to 43 +/- 3 mmHg (P = 0.026); with losartan, the LPL was shifted leftward from 48 +/- 10 mmHg at baseline to 41 +/- 5 mmHg (P = 0.027). The leftward shift occurred while cardiac hemodynamics and MVO2 were maintained at control levels. These results indicate that angiotensin inhibition extends the range of coronary autoregulation to lower LPL while preserving myocardial blood flow distribution, a physiologic effect that might explain the lower incidence of coronary events in treated patients.

Effect of angiotensin inhibition on the coronary artery lower pressure limit in anesthetized dogs

The renin-angiotensin system plays a critical role in regulating vasoconstriction and vasodilatation that can influence myocardial blood flow and its transmural distribution. We tested the hypothesis that angiotensin inhibition can induce a leftward shift of the coronary autoregulatory pressure-flow relation and preserve distribution of myocardial blood flow at lower coronary perfusion pressures. We established circumflex artery pressure-flow relations under baseline conditions and after intracoronary enalaprilat or losartan potassium. Thereafter, transmural myocardial blood flow was measured at baseline and at the lower coronary pressure limit (LPL). With enalaprilat, the LPL was shifted leftward from 48 ± 6 mmHg at baseline to 43 ± 3 mmHg (P = 0.026); with losartan, the LPL was shifted leftward from 48 ± 10 mmHg at baseline to 41 ± 5 mmHg (P = 0.027). The leftward shift occurred while cardiac hemodynamics and M[Formula: see text]O2 were maintained at control levels. These results indicate that angiotensin inhibition extends the range of coronary autoregulation to lower LPL while preserving myocardial blood flow distribution, a physiologic effect that might explain the lower incidence of coronary events in treated patients.Key words: angiotensin, microcirculation, microspheres, myocardium.

Myocardial blood flow regulation relative to left ventricle pressure and volume in anesthetized dogs

The influence of left ventricle pressure and volume changes on coronary blood flow was investigated in eight anesthetized dogs. Coronary artery pressure-flow relationships were determined at two levels of left ventricular pressure and volume. The distribution of blood flow within the myocardium was also determined when these relationships varied. Reducing left ventricle pressures and volumes increased heart rate. Rate-pressure product, diastolic coronary pressure, myocardial O2 consumption, total, subendocardial and subepicardial flow decreased. Hematocrit and blood gas data were unchanged. The pressure-flow relationships were shifted leftward (p = 0.001) but the range of autoregulation was not altered. At low left ventricle pressures and volumes, the lower coronary artery pressure limit was shifted leftward (from 75 to 45 mm Hg (1 mm Hg = 133.3 Pa)), while total, subendocardial, and subepicardial blood flow did not change compared with the control. Below the lower coronary artery pressure limit, subendocardial but not subepicardial flow decreased, resulting in maldistribution of flow across the left ventricular wall. When coronary pressure was reset between control and the lower coronary artery pressure limit, subendocardial flow was restored. These results show that the lower coronary artery pressure limit can be shifted leftward while the distribution of blood flow across the left ventricular wall is preserved.

Myocardial blood flow regulation relative to left ventricle pressure and volume in anesthetized dogs

The influence of left ventricle pressure and volume changes on coronary blood flow was investigated in eight anesthetized dogs. Coronary artery pressure-flow relationships were determined at two levels of left ventricular pressure and volume. The distribution of blood flow within the myocardium was also determined when these relationships varied. Reducing left ventricle pressures and volumes increased heart rate. Rate-pressure product, diastolic coronary pressure, myocardial O2 consumption, total, subendocardial and subepicardial flow decreased. Hematocrit and blood gas data were unchanged. The pressure-flow relationships were shifted leftward (p = 0.001) but the range of autoregulation was not altered. At low left ventricle pressures and volumes, the lower coronary artery pressure limit was shifted leftward (from 75 to 45 mmHg (1 mmHg = 133.3 Pa)), while total, subendocardial, and subepicardial blood flow did not change compared with the control. Below the lower coronary artery pressure limit, subendocardial but not subepicardial flow decreased, resulting in maldistribution of flow across the left ventricular wall. When coronary pressure was reset between control and the lower coronary artery pressure limit, subendocardial flow was restored. These results show that the lower coronary artery pressure limit can be shifted leftward while the distribution of blood flow across the left ventricular wall is preserved.Key words: autoregulation, coronary artery pressure-flow relations, myocardial blood flow distribution, left ventricular pressure, left ventricular volume.

Influence of baseline lipids on effectiveness of pravastatin in the CARE Trial. Cholesterol And Recurrent Events

OBJECTIVES

We sought to assess the influence of baseline lipid levels on coronary event rates and the effectiveness of pravastatin therapy in the Cholesterol And Recurrent Events (CARE) study.

BACKGROUND

The CARE study cohort provided a relatively unique opportunity to examine the relation between lipid levels and clinical events in a post-myocardial infarction (MI) population with relatively low cholesterol and low density lipoprotein (LDL) cholesterol values.

METHODS

There were 4,159 patients with a previous infarct and a total cholesterol level <240 mg/dl, LDL cholesterol level 115 to 174 mg/dl and triglyceride level <350 mg/dl randomly allocated to placebo (n=2,078) or pravastatin 40 mg/day (n=2,081). Time to either coronary death or nonfatal MI (primary end point) or to the secondary end point, which included undergoing a coronary revascularization procedure, was determined as a function of baseline lipids (total, LDL, high density lipoprotein [HDL] cholesterol and triglyceride levels).

RESULTS

Quartile analysis indicated important effects for LDL cholesterol, in which a higher LDL was associated with greater cardiac event rates (in the placebo group, every 25-mg/dl increment in LDL was associated with a 28% increased risk [5% to 56%, p=0.015]) in the primary event. The differential event rates with respect to baseline LDL cholesterol for placebo and pravastatin groups reduced the difference in clinical outcomes at lower LDL cholesterol levels. In both the placebo and pravastatin groups, an inverse relation between baseline HDL cholesterol and cardiac events was observed (10 mg/dl lower baseline HDL cholesterol level was associated with a 10% [0% to 19%, p=0.046] increase in coronary death or nonfatal MI).

CONCLUSIONS

Within the LDL cholesterol levels in CARE (115 to 174 mg/dl), baseline values influenced both the risk of events in the placebo group as well as the clinical effectiveness of pravastatin therapy.

A reappraisal of exercise electrocardiographic indexes of the severity of ischemic heart disease: angiographic and scintigraphic correlates

OBJECTIVES

We explored how the exercise electrocardiographic (ECG) indexes generally presumed to signify severe ischemic heart disease (IHD) correlate with coronary angiographic and scintigraphic myocardial perfusion findings.

BACKGROUND

In exercise testing, it is generally assumed that the early onset of ST segment depression and its occurrence at a low rate-pressure product (ischemic threshold); the amount of maximal ST segment depression; and a horizontal or downsloping ST segment and its prolonged recovery after exercise signify more severe IHD. However, the relation of these indexes to coronary angiographic and exercise myocardial perfusion findings in patients with IHD is unclear.

METHODS

We prospectively carried out a symptom-limited 12-lead Bruce protocol thallium-201 single-photon emission computed tomographic (SPECT) exercise test in 66 consecutive subjects with stable angina, > or = 70% stenosis of at least one coronary artery, normal rest ECG and left ventricular wall motion and a prior positive exercise ECG. The above ECG indexes, vessel disease (VD), a VD score and the quantitative thallium-SPECT measures of the extent, maximal deficit and redistribution gradient of the perfusion abnormality were characterized.

RESULTS

Maximal ST segment depression could not differentiate the number of diseased vessels; was not related to VD score, maximal thallium deficit or redistribution gradient; but was related to the extent of perfusion abnormality (r = 0.29, 95% confidence interval [CI] 0.08 to 0.52, p = 0.02). Time of onset of ST segment depression correlated inversely only with VD (r = -0.22, 95% CI -0.44 to -0.05, p < 0.05), whereas the ischemic threshold had low inverse correlation only with VD score (r = -0.25, 95% CI -0.47 to -0.01, p < 0.05) and the redistribution gradient (r = -0.33, 95% CI -0.53 to -0.10, p < 0.01). A horizontal or downsloping compared with an upsloping ST segment did not demonstrate more severe angiographic and scintigraphic disease. Recovery time did not correlate with angiographic and scintigraphic findings, and correlations between angiographic and scintigraphic findings were also low or absent.

CONCLUSIONS

In this homogeneous study group, the exercise ECG indexes did not necessarily signify more severe IHD by angiographic and scintigraphic criteria. Lack of concordance between the exercise ECG, angiography and myocardial scintigraphy suggests that these diagnostic modalities examine different facets of myocardial ischemia, underscoring the need for caution in the interpretation of their results.

Left ventricular intramyocardial pressure determination using two different solid-state micromanometric pressure sensors

Intramyocardial tissue pressure can influence distribution of ventricular blood flow and dynamics during the cardiac cycle. Left ventricular ventral wall subepicardial and subendocardial tissue pressures were measured simultaneously using two different types of solid-state micromanometers (5F Millar model SPR-230 and Konigsberg Instruments model P19 pressure transducers) and compared with left ventricular cavity pressure. Systolic pressures recorded by Millar and Konigsberg transducers were similar when the sensor surfaces faced the left ventricular cavity either in the endocardium or epicardium. Diastolic pressures in the epicardium were higher than left ventricular cavity pressure. When Millar and Konigsberg transducer were placed in the epicardium, with the pressure sensors facing epicardially, the output signal of the Millar transducer was out of phase with the signal of the Konigsberg transducer and left ventricular chamber pressure outputs. Results indicate that output signals for intramyocardial pressures vary depending on the direction of the Millar or Konigsberg pressure sensor in the left ventricular wall. Thus, pressure output signals vary depending on configuration of the sensor surface, relative flexibility of the connecting cables, and orientation of the sensor surface with respect to left ventricular anatomy.

Effect of 3-aminotriazole on hyperthermia-mediated cardioprotection in rabbits

Hyperthermia-induced cardioprotection during myocardial ischemia may involve increased activity of antioxidative enzymes. In this study we investigated the effects of 3-amino-1,2,4-triazole (3-AT), an irreversible catalase inhibitor, in heat-shocked (HS) rabbits subjected to ischemia-reperfusion injury. Rabbits underwent whole body hyperthermia at 42 degrees C for 15 min. Twenty-four hours later, rabbits were administered either saline vehicle or 3-AT (1 or 2 g/kg i.p.) 30 min before undergoing 30 min of regional coronary occlusion and 3 h reperfusion. Controls did not undergo whole body hyperthermia and were given either saline or 3-AT. Heart rate and left ventricular pressure were recorded continuously during these experiments. Infarct area (tetrazolium staining) was normalized to anatomic risk zone size (microsphere autoradiography). Expression of HSP 71 was verified using Western blot analysis; myocardial catalase activity was determined in tissue biopsies. Infarct size was significantly reduced in HS rabbits (25.1 +/- 2.8%, P = 0.2; means +/- SE) compared with controls (53.6 +/- 4.7%). Treatment with 1 g/kg 3-AT attenuated HS-mediated cardioprotection (36.9 +/- 4.9%, P = 0.063 vs. HS); protection was abolished with 2 g/kg 3-AT (48.9 +/- 6.6%). Myocardial catalase activities were higher in tissue biopsies from HS rabbits (47.0 +/- 4.5 U/mg protein, P < or = 0.02) compared with controls (33.4 +/- 1.9 U/mg protein); catalase activities were significantly reduced in rabbits treated with 3-AT. In conclusion, whole body hyperthermia increases expression levels of HSP 71; myocardial catalase activity is also significantly increased. Myocardial protection is HS rabbits subjected to ischemia-reperfusion injury was reversed with 3-AT. These data suggest that increased intracellular activities of catalase and possibly other antioxidant enzymes is an important mechanism for hyperthermia-mediated cellular protection.

Chemical modulation of in situ intrinsic cardiac neurones influences myocardial blood flow in the anaesthetised dog

OBJECTIVE

The aim was to determine whether modulation of intrinsic cardiac neurones influences the distribution of myocardial blood flow in canine anaesthetised open chest experimental preparations.

METHODS

Intrinsic cardiac neurones were modified by locally applied nicotine (100 micrograms) or bradykinin (50 micrograms) while changes were recorded in cardiac haemodynamics and myocardial blood flow (radiolabelled microspheres). Right and left ventricular intramyocardial tissue pressures were measured with high fidelity microtip transducers.

RESULTS

Control injections of saline (vehicle; 0.1 ml) into active loci did not produce cardiovascular responses. Nicotine modulation of intrinsic cardiac neurones did not change coronary artery conductance, but total myocardial blood flow [116(SEM 17) v 532(97) ml.min-1.100 g-1; p = 0.001 v baseline] and oxygen consumption [7.92(1.10) v 20.14(1.86) ml.min-1.100 g-1; p = 0.001] increased in direct relation to heart rate-blood pressure product changes. Locally administered bradykinin increased coronary artery conductance [2.62(0.39) v 4.71(1.07) ml.min-1.100 g-1.mm Hg-1], total myocardial blood flow, to 263(72) ml.min-1.100 g-1, and oxygen consumption, to 14.9(4.4) ml.min-1.100 g-1; however, heart rate-blood pressure product did not change.

CONCLUSIONS

These results support earlier findings that intrinsic neurones are involved in cardiac regulation. Furthermore, modification of intrinsic cardiac neurones by nicotine or bradykinin significantly alters the distribution of myocardial blood flow, possibly because of increased myocardial metabolism.

Prognostic value of neurohumoral activation in patients with an acute myocardial infarction: effect of captopril

OBJECTIVES

This study attempted to evaluate whether neurohumoral activation at the time of hospital discharge in postinfarction patients helps to predict long-term prognosis and whether long-term therapy with the angiotensin-converting enzyme inhibitor captopril modifies this relation.

BACKGROUND

Neurohumoral activation persists at the time of hospital discharge in a large number of postinfarction patients. The Survival and Ventricular Enlargement (SAVE) study demonstrated that the angiotensin-converting enzyme inhibitor captopril improves survival and decreases the development of severe heart failure in patients with left ventricular dysfunction (left ventricular ejection fraction < or = 40%) but no overt postinfarction heart failure.

METHODS

In 534 patients in the SAVE study, plasma neurohormone levels were measured a mean of 12 days after infarction. Patients were then randomized to receive captopril or placebo and were followed up for a mean (+/- SD) of 38 +/- 6 months (range 24 to 55). The association between activation of plasma neurohormones at baseline and subsequent cardiovascular mortality or the development of heart failure was assessed with and without adjustment for other important prognostic factors.

RESULTS

By univariate analysis, activation of plasma renin activity and aldosterone, norepinephrine, atrial natriuretic peptide and arginine vasopressin levels were related to subsequent cardiovascular events, whereas epinephrine and dopamine levels were not. By multivariate analysis, only plasma renin activity (relative risk 1.6, 95% confidence interval [CI] 1.0 to 2.5) and atrial natriuretic peptide (relative risk 2.2, 95% CI 1.3 to 3.8) were independently predictive of cardiovascular mortality, whereas the other neurohormones were not. Only plasma renin activity and aldosterone, atrial natriuretic peptide and arginine vasopressin were independent predictors of the combined end points of cardiovascular mortality, development of severe heart failure or recurrent myocardial infarction. Except for 1-year cardiovascular mortality, the use of captopril did not significantly modify these relations.

CONCLUSIONS

Neurohumoral activation at the time of hospital discharge in postinfarction patients is an independent sign of poor prognosis. This is particularly true for plasma renin activity and atrial natriuretic peptide. Except for 1-year cardiovascular mortality, captopril does not significantly modify these relations.

Timely administration of AICA riboside reduces reperfusion injury in rabbits

OBJECTIVE

Agents which promote increased interstitial adenosine levels may be cardioprotective. The aim of this study was to evaluate the ability of 5-amino-1-beta-D- ribofuranosylimidazole-4-carboxamide (AICAr), an adenosine regulating agent, to limit infarct size when given before ischaemia, before coronary reperfusion, or postreperfusion in a rabbit preparation of ischaemia-reperfusion injury.

METHODS

The left coronary artery was occluded for 30 min and subsequently the ischaemic bed was reperfused for 180 min. Infarct size and risk zone size were delineated by tetrazolium staining and microsphere autoradiography, respectively. Four groups were studied: controls (n = 13), AICAr (2.5 mg.kg-1.min-1 intravenously for 5 min followed by 0.5 mg.kg-1.min-1 for 60 min) beginning either 5 min before coronary occlusion (n = 11), 5 min before coronary reperfusion (n = 11), or at 25 min coronary reperfusion (n = 10). Lignocaine was not given in these experiments.

RESULTS

Infarct size, normalised to risk zone, was significantly reduced with AICAr given 5 min before coronary reperfusion, at 35.0(SEM 4.4)% v 51.8(3.9)% in controls; p = 0.03. Cardioprotection was not observed when AICAr was given either 5 min before coronary occlusion [44.2(4.8)%] or 25 min postreperfusion [45.9(3.2)%].

CONCLUSIONS

These findings support the hypothesis that adenosine regulating agents, such as AICAr, can modulate infarct size in this rabbit preparation of ischaemia-reperfusion injury.

Acute tamponade alters subendo- and subepicardial pressure-flow relations differently during vasodilation

Instantaneous diastolic left coronary artery pressure-flow relations (PFR) shift during acute tamponade as pressure surrounding the heart increases. Coronary pressure at zero flow (Pf = 0) on the linear portion of the PFR is the weighted mean of the different myocardial waterfall pressures, the distribution of which varies across the left ventricular wall during diastole. However, instantaneous PFR measured in large epicardial coronary arteries cannot be used to estimate Pf = 0 in the different myocardial tissue layers. During coronary vasodilatation in a capacitance-free model, myocardial PFR differs from subendocardium to subepicardium. Therefore, we studied the effects of acute tamponade during maximal pharmacology induced coronary vasodilatation on myocardial PFR in in situ anesthetized dogs. Tamponade reduced cardiac output, aortic pressure, and coronary blood flow. Results demonstrate that different mechanisms influence distribution of myocardial blood flow during tamponade. Subepicardial vascular resistance is unchanged and the extrapolated Pf = 0 is increased, thereby shifting PFR to a higher intercept on the pressure axis. Subendocardial vascular resistance is increased while the extrapolated Pf = 0 remains unchanged. Results indicate that in the setting of acute tamponade with coronary vasodilatation different mechanisms regulate the distribution of myocardial blood flow: in the subepicardium only outflow pressure increases, whereas in the subendocardium only vascular resistance increases.

Microsphere and dilution measurements of flow and interstitial space in dog heart

The effects of coronary flow on cardiac capillary permeability-surface area products and interstitial spaces were examined at rest and after hemodilution in the canine heart. Multiple-indicator-dilution experiments and left atrial injections of microspheres were carried out in closed-chest anesthetized animals at rest and after plasma expansion with dextran. Plasma expansion was utilized to produce a large increase in coronary perfusion compared with control conditions. Values for plasma flow per unit interstitial space, derived from analysis of the indicator-dilution data, were found to correlate closely with average vascular plasma flow per gram, calculated from the cardiac microsphere data; the one reflects the other. With an increase in flow, cardiac capillary permeability-surface area product values were found to increase substantially, whereas the average sucrose extravascular or cardiac interstitial spaces remained stable. Consequently the dilution parameter, flow per unit interstitial space, which is independent of tracer loss, provided a good reflection of flow per weight of tissue in the heart, without the additional requirement for a flow probe.

Myocardial tissue pressure and blood flow during coronary sinus pressure modulation in anesthetized dogs

To determine whether coronary sinus outflow pressure (Pcs) or intramyocardial tissue pressure (IMP) is the effective back pressure in the different layers of the left ventricular (LV) myocardium, we increased Pcs in 14 open-chest dogs under maximal coronary artery vasodilation. Circumflex arterial (flowmeter), LV total, and subendocardial and subepicardial (15-microns radioactive spheres) pressure-flow relationships (PFR) and IMP (needle-tip pressure transducers) were recorded during graded constriction of the artery at two diastolic Pcs levels (7 +/- 3 vs. 23 +/- 4 mmHg). At high Pcs, LV, aortic and diastolic circumflex arterial pressure, heart rate, myocardial oxygen consumption, and lactate extraction were unchanged; IMP in the subendocardium did not change (130/19 mmHg), whereas IMP in the subepicardium increased by 17 mmHg during systole and 10 mmHg during diastole (P < or = 0.001), independently of circumflex arterial pressure. Increasing Pcs did not change the slope of the PFR; however, coronary pressure at zero flow increased in the subepicardium (P < or = 0.008), whereas in the subendocardium it remained unchanged at 24 +/- 3 mmHg. Thus Pcs can regulate IMP independently of circumflex arterial pressure and consequently influence myocardial perfusion, especially in the subepicardial tissue layer of the LV.

Improved high-performance liquid chromatographic assay for the stereoselective determination of mexiletine in plasma

A simple and sensitive high-performance liquid chromatographic procedure for resolution of mexiletine enantiomers has been developed. Proteins from plasma samples containing RS-mexiletine were precipitated with a mixture of barium hydroxide and zinc sulphate before extraction under alkaline conditions with diethyl ether. Organic extracts were evaporated to dryness, and the residues reconstituted with 0.03 M hydrochloric acid (20 microliters). Derivatization with o-phthalaldehyde N-acetyl-L-cysteine reagent was performed after alkalinization with 0.1 M sodium borate. An aliquot of the resulting solution was injected onto a reversed-phase C18 column and resolution of mexiletine diastereoisomeric derivatives was achieved with a mobile phase consisting of methanol-50 mM sodium acetate (65:35), at a flow-rate of 1 ml/min. The retention times of S-(+)- and R-(-)-mexiletine diastereoisomeric peaks were 14 and 15 min, respectively. Product elution was monitored by fluorescence detection using excitation and emission wavelengths fixed at 350 and 445 nm, respectively. Calibration curves were linear over the concentration range 2.5-500 ng/ml for each enantiomer (r greater than 0.99). The assay is shown to be suitable for pharmacokinetic studies after administration of a single oral dose of 200 mg of RS-mexiletine hydrochloride to healthy volunteers.

Influence of debrisoquine phenotype and of quinidine on mexiletine disposition in man

Mexiletine is a low clearance drug which undergoes extensive metabolism in man. In vitro studies with human liver microsomes have suggested that major oxidation pathways of mexiletine are predominantly catalyzed by the genetically determined debrisoquine 4-hydroxylase (cytochrome P450IID6) activity. In this study, we investigated the role of debrisoquine polymorphism and the effects of low dose quinidine, a selective inhibitor of cytochrome P450IID6, on the disposition of mexiletine. Fourteen healthy volunteers, 10 with the extensive metabolizer (EM) and 4 with the poor metabolizer (PM) phenotype, received a single 200-mg dose of mexiletine hydrochloride orally on two occasions (1 week apart), once alone and once under steady-state conditions for quinidine (50 mg QID). During the phase mexiletine alone, total clearance, nonrenal clearance and partial metabolic clearance of mexiletine to hydroxymethylmexiletine, to m-hydroxymexiletine and to p-hydroxymexiletine were decreased in PM compared to EM (all P less than .05). In EM, quinidine decreased mexiletine total clearance from 621 +/- 298 to 471 +/- 214 ml/min (mean +/- S.D.; P less than .05) and mexiletine nonrenal clearance from 583 +/- 292 to 404 +/- 188 ml/min (P less than .05). Moreover, quinidine increased mexiletine elimination half-life in EM from 9 +/- 1 to 11 +/- 2 h (P less than .05). In these subjects, partial metabolic clearance to hydroxymethylmexiletine, m-hydroxymexiletine and p-hydroxymexiletine were decreased by quinidine coadministration 5-, 4- and 7-fold, respectively, whereas partial metabolic clearance to N-hydroxymexiletine was unaffected. Changes induced by quinidine in EM were correlated to their debrisoquine metabolic ratio. Thus, genetically determined or pharmacologically induced modulation of cytochrome P450IID6 activity represents a major determinant of mexiletine disposition.

Prognosis in patients with a strongly positive exercise electrocardiogram

In patients with a strongly positive exercise electro-cardiogram, the workload achieved during the test allows the identification of subsets with good or poor survival rates. To determine whether the same criteria also predict acute ischemic heart events such as unstable angina and myocardial infarction, fatal and nonfatal acute manifestations were documented in 241 patients medically treated during an 8-year follow-up. All patients had a Bruce protocol treadmill exercise test with ST-segment depression greater than or equal to 2 mm and coronary angiographic studies. There were 52 deaths; of these 44 were due to coronary artery disease. There were 41 episodes of unstable angina and 21 myocardial infarcts documented as first morbid events. As expected, survival improved with increased workload achieved; patients terminating their exercise at stage I (5.1 METs) had an 8-year survival rate of 45 +/- 9% while those reaching stage IV or more (10 METs) had a survival rate of 93 +/- 6%. In a multivariate analysis, the duration of exercise and the number of narrowed coronary arteries and of left ventricular segment abnormalities correlated significantly with survival. In contrast, nonfatal acute events occurred in about 20 to 35% of patients whatever the stage of the exercise test. Furthermore, neither variables during the exercise test nor angiographic findings predicted nonfatal events. Thus, although the workload achieved did identify patients with different mortality rates, it failed to predict subsets of patients with different morbid event rates.

Effect of N-acetylcysteine on tissue necrosis during acute myocardial infarction in rabbits

This study examined whether N-acetylcysteine, a low molecular weight compound used clinically to replenish glutathione, could limit tissue necrosis during acute myocardial infarction in hearts with minimal coronary collateral flow. Fifty rabbits underwent 45 mins ischemia with and without coronary reperfusion for 3h. Four groups were studied. Saline or N-acetylcysteine (140 mg/kg) was administered intravenously 10 mins before occlusion and continued for 35 mins after occlusion. The area at risk of necrosis was assessed with fluorescent particles and the area of tissue necrosis was defined using triphenyltetrazolium chloride staining. No differences were observed for tissue necrosis expressed as a percentage of the risk zone size (mean +/- SEM, 46.7 +/- 8.2% versus 46.3 +/- 8.2%) for saline and N-acetylcysteine treated rabbits subjected to 45 mins coronary occlusion. Tissue necrosis in rabbits with 45 mins ischemia followed by 3 h reperfusion was not significantly reduced with N-acetylcysteine treatment (36.4 +/- 5.1%) compared to untreated controls (36.5 +/- 6.4%). Risk zone size and hemodynamic parameters were similar between the treatment groups. Thus, treatment before and during short term coronary occlusion did not limit tissue necrosis during acute myocardial infarction.

Some applications of the P-V relation to the study of left ventricular performance

There is still controversy as to which characteristics of the pressure-volume relation should be used to define myocardial contractility. In the present study a mathematical model for the left ventricle as a two-dimensional cylinder contracting radially and symmetrically was used to establish a relation between a calculated intramyocardial pressure (Dh) and the P-V relation (PVR) at end-systole. Four new indices are introduced that allow a better assessment of change in inotropic state of the myocardium, namely the calculated intramyocardial pressure (Dh), the calculated resultant pressure across the inner surface of the myocardium (Dh-P) (P = cavity pressure), the work Wt related to the pressure (Dh) and the work Wd related to the pressure (Dh-P). A relation between Wt and Wd and different parts of the area under the PVR is established. Indices derived in this manner from the PVR to study changes in myocardial contractility appear to have a clear physical meaning.

Survival with painless strongly positive exercise electrocardiogram

To determine the prognosis of patients with painless strongly positive exercise electrocardiogram, the 6-year cumulative survival rate was computed for 298 medically treated patients who terminated their exercise test with or without angina. All had horizontal or downsloping ST depression greater than or equal to 2 mm during a treadmill exercise test according to the standardized multistage Bruce protocol. Of the 298 patients, 119 terminated the exercise test because of dyspnea or fatigue and 179 stopped because of angina. Among the 119 patients without angina, there were 18 deaths, 16 from coronary artery disease (CAD), of which 8 occurred suddenly. Among the 179 patients with exercise-induced angina, 36 died, 33 from CAD, of which 13 were sudden deaths. The overall 6-year survival rate was 85 +/- 3% for patients without angina and 80 +/- 3% in those with angina (p less than 0.05). However, patients without angina achieved a significantly longer duration of exercise and had higher maximal heart rate and systolic blood pressure during exercise. In both groups, survival decreased with decreasing duration of exercise. In patients without angina, the 6-year survival rate was 97 +/- 3% in those achieving stage IV (greater than or equal to 541 s), 87 +/- 4% in stage III (361 to 540 s), 64 +/- 13% in stage II (181 to 360 s) and 60 +/- 15% in stage I (less than or equal to 180 s).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of perfluorochemical hemodilution on coronary blood flow distribution in dogs

To determine the effect of perfluorocarbon (PFC) hemodilution on myocardial vessel capacity to autoregulate, circumflex coronary artery pressure-flow relations were studied in anesthetized dogs under three conditions: maximal vasodilatation before and after PFC; autoregulation before and after PFC with 100% oxygen supplemented with room air ventilation, and autoregulation with PFC hemodilution during either room air or 100% oxygen supplemented with room air ventilation. During coronary vasodilatation, PFC did not modify coronary conductance or zero-flow pressure. During autoregulation after PFC, the lower pressure limit of the autoregulatory pressure-flow relation was shifted leftward. This leftward shift occurred because endocardial blood flow was maintained at a lower coronary perfusion pressure with PFC while epicardial blood flow was unchanged. Endocardial blood flow was also preserved at 50% of control blood flow levels as evidenced by the higher endocardial-epicardial blood flow ratio with PFC. After PFC with 100% oxygen supplemented with room air ventilation, oxygen transport increased significantly when coronary perfusion pressure was below the lower pressure limit; the effect was most prominent in the endocardial tissue layer. Thus, PFC shifts the lower pressure limit to the left because of the increased ability of the endocardial vessel to autoregulate. Consequently, PFC can be considered a useful intervention for improving endocardial oxygen transport at low coronary perfusion pressures.

Effects of coronary sinus pressure elevation on coronary blood flow distribution in dogs with normal preload

Coronary sinus pressure (Pcs) elevation shifts the diastolic coronary pressure-flow relation (PFR) of the entire left ventricular myocardium to a higher pressure intercept. This finding suggests that Pcs is one determinant of zero-flow pressure (Pzf) and challenges the existence of a vascular waterfall mechanism in the coronary circulation. To determine whether coronary sinus or tissue pressure is the effective coronary back pressure in different layers of the left ventricular myocardium, the effect of increasing Pcs was studied while left ventricular preload was low. PFRs were determined experimentally by graded constriction of the circumflex coronary artery while measuring flow using a flowmeter. Transmural myocardial blood flow distribution was studied (15-micron radioactive spheres) at steady state, during maximal coronary artery vasodilatation at three points on the linear portion of the circumflex PFR both at low and high diastolic Pcs (7 +/- 3 vs. 22 +/- 5 mmHg; p less than 0.0001) (1 mmHg = 133.322 Pa). In the uninstrumented anterior wall the blood flow measurements were obtained in triplicate at the two Pcs levels. From low to high Pcs, mean aortic (98 +/- 23 mmHg) and left atrial (5 +/- 3 mmHg) pressure, percent diastolic time (49 +/- 7%), percent left ventricular wall thickening (32 +/- 4%), and percent myocardial lactate extraction (15 +/- 12%) were not significantly changed. Increasing Pcs did not alter the slope of the PFR; however, the Pzf increased in the subepicardial layer (p less than 0.0001), whereas in the subendocardial layer Pzf did not change significantly. Similar slopes and Pzf were observed for the PFR of both total myocardial mass and subepicardial region at low and high Pcs. Subendocardial:subepicardial blood flow ratios increased for each set of measurements when Pcs was elevated (p less than 0.0001), owing to a reduction of subepicardial blood flow; however, subendocardial blood flow remained unchanged, while starting in the subepicardium toward midmyocardium blood flow decreased at high Pcs. This pattern was similar for the uninstrumented anterior wall as well as in the posterior wall. Thus as Pcs increases it becomes the effective coronary back pressure with decreasing magnitude from the subepicardium toward the subendocardium of the left ventricle. Assuming that elevating Pcs results in transmural elevation in coronary venous pressure, these findings support the hypothesis of a differential intramyocardial waterfall mechanism with greater subendo- than subepi-cardial tissue pressure.

Coronary vasodilator reserve impairment distal to systolic coronary artery compression in dogs

To investigate the mechanism by which muscular coronary overbridging can cause myocardial ischaemia, we studied the effect of systolic compression (SC) of the proximal left circumflex coronary artery in ten anaesthetised dogs, with both intact autoregulation and maximally dilated coronary arteries. Systolic compression was produced by a mechanical device adjusted to interrupt circumflex coronary flow only during the aortic ejection period and we measured left ventricular, aortic and distal circumflex coronary pressures, phasic coronary blood flow, regional myocardial blood flow (RMBF), myocardial oxygen consumption (MVO2), and myocardial lactate extraction (MLE). During both autoregulation and maximal coronary vasodilatation, there was a diastolic time lag after SC to restart phasic circumflex coronary blood flow (34 +/- 3 vs 31 +/- 3 ms) and to increase distal circumflex coronary pressure (69 +/- 4 vs 79 +/- 6 ms). With autoregulation, SC reduced the diastolic circumflex coronary: systolic left ventricular pressure time ratio (DPTIc:SPTI) and there were no changes in the other measured variables. During maximal coronary vasodilatation and SC, the coronary vasodilator reserve, the DPTIc:SPTI ratio and the inner:outer myocardial blood flow distribution were decreased in the territory of the left circumflex coronary artery; a linear relationship was observed between the DPTIc:SPTI and the inner:outer myocardial blood flow ratio. Systolic compression during vasodilatation also produced a reduction in myocardial oxygen consumption of the whole heart and a production of lactate in the coronary sinus. These results suggest that myocardial ischaemia with a myocardial bridge is due to the combined effects of a diastolic time lag to repressurise the coronary vascular bed, of tachycardia and of coronary vasodilatation.

Survival of patients with a strongly positive exercise electrocardiogram

To assess the prognosis of patients with a strongly positive exercise ECG, the 5-year cumulative survival rate was computed for 220 medically treated patients. Of these patients, 107 had coronary angiograms (group A) and 113 did not (group B). All had horizontal or downsloping ST depression greater than or equal to 2 mm during a multistage Bruce protocol treadmill exercise test. In group A, the overall 5-year survival rate was 74 +/- 5%. Survival decreased with decreasing duration of exercise: All patients who achieved stage IV (541 seconds or more) survived, whereas the survival rate was 86 +/- 6% when the patients terminated their exercise during stage III (361 - 540 seconds), 73 +/- 7% when during stage II (181 - 360 seconds) and only 52 +/- 13% when during stage I (180 seconds or less). The mortality was associated with more severe coronary artery disease, and sudden death was the main cause of death. Patients in group B had a longer mean exercise duration than those in group A and, as expected, a higher survival rate (91 +/- 3%, p less than 0.01), which also varied according to the exercise duration. Among patients with a strongly positive exercise ECG, the duration of exercise identifies subsets that have different survival rates.

Free fatty acid as a determinant of myocardial oxygen consumption: a caveat

The present study was designed to determine whether the antilipolytic agent β-pyridylcarbinol modifies left ventricular blood flow distribution. It has been shown that the administration of this agent during isoproterenol infusion reduced both myocardial oxygen consumption and myocardial free fatty acid uptake. Although attributed to a decrease in myocardial free fatty acid uptake, the reduction in myocardial oxygen consumption might also be due to a modification in left ventricular blood flow distribution induced by β-pydidyiearbinol. To verify this possibility left ventricular blood flow distribution was measured with radioactive microspheres in 10 anesthetized dogs during control, during an infusion of isoproterenol (0.2 μg∙kg−1∙min−1) alone, and during an isoproterenol plus β-pyridylcarbinol infusion (0.1 mg∙kg−1∙min−1). In comparison with the control observations, isoproterenol infusion induced a significant increase of 37% in heart rate and of nearly 100% in myocardial free fatty acid uptake, myocardial oxygen consumption, and coronary blood flow, but did not affect the left ventricular blood flow distribution. The addition of β-pyridylcarbinol to the isoproterenol infusion did not cause any significant changes in left ventricular blood flow distribution, although it reduced myocardial free fatty acid uptake by 67% (p < 0.01). Despite this reduction, myocardial oxygen consumption did not change. However, in dogs with a myocardial oxygen uptake above 12.5 mL∙min−1∙100 g−1 during isoproterenol infusion, there was a reduction in myocardial oxygen consumption when β-pyridylcarbinol was added, without significant change in left ventricular blood flow distribution. The present findings reveal that β-pyridylcarbinol does not modify left ventricular blood flow distribution and that the determinant role of free fatty acids on myocardial oxygen consumption is restricted to conditions with increased myocardial demand.

Effects of metoprolol on effort angina during the postprandial state

To determine whether beta blockers prevent the more rapid onset of effort angina during the postprandial state, metoprolol 100 mg was given before and after an 800-calorie meal in 12 male patients with stable angina and coronary artery disease. Three graded treadmill exercise tests were done daily on 2 days. After an overnight fast the first test on each day was done after a placebo to detect day-to-day variations. The second test was done 90 min after metoprolol or placebo given orally in a double-blind randomized fashion. Immediately thereafter the patients ate their meal and did their third test 30 min later. There was no significant difference between the first test on each day. After placebo the postprandial state was associated with an earlier onset of effort angina (310 and 370 sec, p less than 0.01) and with greater heart rate and systolic blood pressure rises for any work load. After metoprolol, however, there was no significant difference between the pre- and postprandial findings. During the postprandial state metoprolol delayed the onset of angina more than placebo (385 and 310 sec) and positive electrocardiogram (310 and 228 sec) and induced lowering of maximal heart rate (120 and 144 bpm) and systolic blood pressure (157 and 187 mm Hg) (p less than 0.01). Metoprolol slowed the rapid onset of effort agina during the postprandial state.

The use of 201thallium for myocardial perfusion imaging in sarcoid heart disease

Cardiac dysfunction due to systemic sarcoidosis is most of ten due to severe restrictive pulmonary diseases. Although the diagnosis is frequently missed during life, direct granulomatous infiltration of the myocardium may occur with systemic sarcoidosis and, when present in the heart, is a major cause of death. To explore the possible use of radioactive 201thallium, a new agent for myocardial imaging, for improved clinical recognition of sarcoid heart disease, myocardial perfusion imaging with 201Tl was performed in six normal volunteers and in five patients with documented systemic sarcoidosis and clinically apparent cardiac dysfunction. Two of the patients with sarcoidosis had severe restrictive pulmonary disease. Their myocardial perfusion scans revealed relatively uniform uptake of 201Tl by the left ventricle, similar to that found in the normal volunteers; however, the right ventricular uptake of 201Tl and right ventricular thickness in these two patients with sarcoidosis was greater than normal. The other three patients with sarcoidosis had unexplained congestive heart failure, mitral regurgitation, or arrhythmias. Myocardial perfusion imaging in these patients revealed normal right ventricular uptake of radioactivity but segmental defects in the left ventricle compatible with an infiltrative disease of the myocardium. Segmental myocardial infiltration by sarcoid was confirmed by autopsy in one of these patients and at operation in another. Thus, myocardial imaging with 201Tl may provide a noninvasive technique for the improved clinical recognition of primary myocardial sarcoid and for distinguishing it from cardiac dysfunction secondary to pulmonary disease.

Thallium 201 myocardial imaging in patients with pulmonary hypertension

The appearance of the right ventricular myocardium on thallium 201 myocardial perfusion images was evaluated in patients with chronic pulmonary hypertension and compared to patients without pulmonary hypertension. Four groups of patients were studied: 1) eight normals, 2) five patients with angiographically documented coronary artery disease and normal pulmonary artery pressures, 3) ten patients with moderate to severe pulmonary parenchymal or vascular disease and documented pulmonary hypertension and 4) eight patients with chronic left ventricular dysfunction and pulmonary hypertension discovered during cardiac catheterization. The right ventricular free wall was visualized on the thallium 201 myocardial perfusion image in only one of eight normals (group 1) and in only one of the five patients with coronary artery disease (group 2) and measured 0.5 cm and 0.9 cm in thickness, respectively. In patients with documented pulmonary hypertension the right ventricle was visualized on low contrast thallium 201 myocardial perfusion image in all patients. The apparent right ventricular free wall thickness measured from the ungated thallium 201 myocardial perfusion images was 1.7 +/- 0.3 cm in group 3 and 1.5 +/- 0.2 cm in group 4. Right ventricular hypertrophy was detected by electrocardiography in only five of ten patients in group 3 and only one of eight patients in group 4. Thallium 201 myocardial perfusion imaging appears to be a useful technique for assessing the effects of chronic pulmonary hypertension on the right ventricular myocardium.

Reversal by phenylephrine of the beneficial effects of intravenous nitroglycerin in patients with acute myocardial infarction

Nitroglycerin has been shown to reduce ST-segment elevation during acute myocardial infarction, an effect potentiated in the dog by agents that reverse nitroglycerin-induced hypotension. Our study was designed to determine the effects of combined nitroglycerin and phenylephrine therapy. Ten patients with acute transmural myocardial infarctions received intravenous nitroglycerin, sufficient to reduce mean arterial pressure from 107 +/- 6 to 85 +/- 6 mm Hg (P less than 0.001), for 60 minutes. Left ventricular filling pressure decreased from 19 +/- 2 to 11 +/- 2 mm Hg (P less than 0.001). SigmaST, the sum of ST-segment elevations in 16 precordial leads, decreased (P less than 0.02) with intravenous nitroglycerin. Subsequent addition of phenylephrine infusion, sufficient to re-elevate mean arterial pressure to 106 +/- 4 mm Hg (P less than 0.001) for 30 minutes, increased left ventricular filling pressure to 17 +/- 2 mm Hg (P less than 0.05) and also significantly increased sigmaST (P less than 0.05). Our results suggest that addition of phenylephrine to nitroglycerin is not beneficial in the treatment of patients with acute myocardial infarction.