The prevention of heart failure--a new agenda

Natural history of idiopathic dilated cardiomyopathy: effect of referral bias and secular trend

OBJECTIVES

The current study was designed to determine the effect of secular trend and referral bias on the natural history of idiopathic dilated cardiomyopathy.

BACKGROUND

In a previous study of 104 patients with idiopathic dilated cardiomyopathy conducted in a referral population at the Mayo Clinic between 1960 and 1973, the 1- and 5-year mortality rates were 31% and 64%, respectively. A recent study of 40 patients with idiopathic dilated cardiomyopathy conducted in a population-based cohort at the Mayo Clinic between 1975 and 1984 reported 1- and 5-year mortality rates of 5% and 20%, respectively. We hypothesized that improvements in diagnosis and therapy have occurred since the original referral cohort was described and that these improvements have altered the apparent natural history of the disease. We refer to this effect as secular trend. Alternatively, the presence of more advanced disease in the referral population (referral bias) may also contribute to the differences in survival.

METHODS

Two sequential referral populations with idiopathic dilated cardiomyopathy seen at the Mayo Clinic between 1976 and 81 (n = 85) and 1982 and 1987 (n = 137) were identified. Outcome was compared between these cohorts and the 1960-1973 referral cohort to examine the effect of secular trend. Outcomes were compared with that of the population-based cohort to examine the effect of referral bias.

RESULTS

Survival in the 1976-1981 referral cohort did not differ from that in the 1960-1973 referral cohort, suggesting little impact of secular trend during these time periods. Survival in the more recent 1982-1987 referral cohort was significantly better than that in the earlier referral cohorts, suggesting that improvements in diagnosis and treatment in the 1980s altered the natural history of idiopathic dilated cardiomyopathy. Survival in the 1982-1987 referral cohort was still worse than that of the population-based cohort, suggesting an effect of referral bias on studies of the natural history of idiopathic dilated cardiomyopathy.

CONCLUSIONS

The current study demonstrates that secular trend and referral bias affect the apparent natural history of idiopathic dilated cardiomyopathy. Survival in referral patients with this disease is significantly better than previously described.

Temporal evolution of endothelial dysfunction in a rat model of chronic heart failure

OBJECTIVES

The goal of this study was to investigate the evolution of endothelial dysfunction and plasma renin activity in a rat model of heart failure.

BACKGROUND

Endothelial dysfunction has been demonstrated in heart failure and may play a significant role in this pathophysiologic process. Studies have also suggested a physiologic interaction between the renin-angiotensin system and endothelium-derived relaxing factor. However, the evolution of endothelial dysfunction and plasma renin activity in heart failure has not been studied to date.

METHODS

Endothelium-dependent and -independent relaxations were studied at 1, 4 and 16 weeks after coronary artery ligation in a rat model of heart failure. Thoracic aortic rings were placed in isolated organ baths and acetylcholine and sodium nitroprusside concentration response curves were generated. Plasma renin activity was assessed at each time point.

RESULTS

Aortic rings from rats with heart failure demonstrated no evidence of endothelial dysfunction at week 1, although progressive rightward shifts in the acetylcholine curves and decreasing maximal relaxation over time compared with findings in sham-operated control rats were evident at weeks 4 and 16. The sodium nitroprusside curves were not different between rats with heart failure and sham-operated rats. Plasma renin activity was elevated at week 1 and progressively increased through week 16, even though it correlated poorly with endothelial dysfunction.

CONCLUSIONS

This study suggests that endothelial dysfunction in heart failure is a progressive time-dependent process that probably plays a minor role early in heart failure. Although plasma renin activity increased significantly in rats with heart failure, it was poorly predictive of endothelial dysfunction.

Effect of angiotensin-converting enzyme inhibitors on ventricular remodeling and survival following myocardial infarction

OBJECTIVE

To discuss the effects of angiotensin-converting enzyme (ACE) inhibitors on ventricular remodeling and survival after acute myocardial infarction (AMI). An overview is provided of the pathophysiologic changes produced by AMI and the ventricular remodeling process. ACE inhibitors have been studied for their use in the prevention of ventricular remodeling and reduction in postinfarction mortality. Trials in humans and animals are reviewed, including study methods, results, and limitations.

DATA SOURCES

MEDLINE searches identified applicable literature, including experimental trials and review articles.

STUDY SELECTION

All clinical trials of ACE inhibitors following AMI were reviewed.

DATA EXTRACTION

Morbidity and mortality data evaluating the effect of postinfarction ventricular remodeling are rare. At the time of publication, all available clinical trials studying the effects of ACE inhibitors on postinfarction ventricular remodeling were included, regardless of whether morbidity and mortality were assessed. Data from the Survival and Ventricular Enlargement (SAVE) and Cooperative New Scandinavian Enalapril Survival Study II (CONSENSUS II) trials include almost 10,000 patients. Data were extracted by two independent observers. Data quality and validity were assessed based on sample size, stratification of study population, and statistical power of the studies.

DATA SYNTHESIS

ACE inhibitors may prevent the deleterious consequences of AMI, including ventricular remodeling and neurohumoral activation. Ventricular hypertrophy begins acutely following infarction, an early physiologic response to myocardial injury. Hemodynamic benefits from the initial phase of left ventricular hypertrophy include increased ventricular working capacity, normalized systolic wall stress, and maintenance of stroke volume. Although acute dilatation may delay hemodynamic deterioration for six to eight months, it also results in reduced coronary reserve, decreased ventricular compliance, and altered myocardial contractility. With chronic dilatation, the beneficial effects reach a plateau, stroke volume decreases, contractility is reduced, and cardiac failure may ensue. Ventricular hypertrophy is associated with worsened prognosis following infarction and may be the most important single determinant of late prognosis. Ventricular hypertrophy contributes to postinfarction heart failure, angina, and sudden death. Clinical trials show a beneficial effect of the ACE inhibitor captopril on the prevention of left ventricular dysfunction. Although captopril therapy significantly improved survival and myocardial function following AMI in the SAVE trial, these results cannot be generalized to all patient subpopulations. The CONSENSUS II trial demonstrated a decreased survival rate when enalapril was administered within 24 hours of AMI, indicating that timing of therapy may be an important consideration. Captopril therapy may positively affect outcome when initiated 3-16 days following infarction in patients with ejection fractions below 40 percent and who have no signs of ischemia or heart failure. Based on the CONSENSUS II results, enalapril therapy immediately following AMI cannot be recommended.

CONCLUSIONS

Clinical trials have demonstrated that ACE inhibitors can limit ventricular hypertrophy following AMI, resulting in clinical benefit and improved survival. These effects may be secondary to modulation of neurohumoral activation or the antiischemic effect of ACE inhibitors, which may also reduce the incidence of reinfarction. Early intervention with ACE inhibitors (within 3-16 days of infarction) can slow the progression of cardiovascular disease and improve the survival rate.

Progressive left ventricular dysfunction and remodeling after myocardial infarction. Potential mechanisms and early predictors

BACKGROUND

Left ventricular enlargement and the development of chronic heart failure are potent predictors of survival in patients after myocardial infarction. Prospective studies relating progressive ventricular enlargement in individual patients to global and regional cardiac dysfunction and the onset of late chronic heart failure are not available. It was the aim of this study to define the relation between left ventricular dilatation and global and regional cardiac dysfunction and to identify early predictors of enlargement and chronic heart failure in patients after myocardial infarction.

METHODS AND RESULTS

Left ventricular volumes, regional area shrinkage fraction in 18 predefined sectors (gated single photon emission computed tomography), global ejection fraction, and hemodynamics at rest and during exercise (supine bicycle, 50 W, 4 minutes, Swan-Ganz catheter) were assessed prospectively 4 days, 4 weeks, 6 months, and 1.5 and 3 years after first myocardial infarction. Seventy patients were assigned to groups with progressive, limited, or no dilatation. Patients without dilatation (n = 38) maintained normal volumes and hemodynamics until 3 years. With limited dilatation (n = 18), left ventricular volume increased up to 4 weeks after infarction and stabilized thereafter; depressed stroke volume was restored 4 weeks after infarction and then remained stable at rest. Wedge pressure during exercise, however, progressively increased. With progressive dilatation (n = 14), depressed cardiac and stroke indexes were also restored by 4 weeks but progressively deteriorated thereafter. Area shrinkage fraction as an estimate of regional left ventricular function in normokinetic sectors at 4 days gradually deteriorated during 3 years, but hypokinetic and dyskinetic sectors remained unchanged. Global ejection fraction fell after 1.5 years, whereas right atrial pressure, wedge pressure, and systemic vascular resistance increased. By multivariate analysis, ejection fraction and stroke index at 4 days, ventriculographic infarct size, infarct location, and Thrombolysis in Myocardial Infarction trial grade of infarct artery perfusion were significant predictors of progressive ventricular enlargement and chronic dysfunction.

CONCLUSIONS

Almost 26% of patients may develop limited left ventricular dilatation within 4 weeks after first infarction, which helps to restore cardiac index and stroke index at rest and to preserve exercise performance and therefore remains compensatory. A somewhat smaller group (20%) develops progressive structural left ventricular dilatation, which is compensatory at first, then progresses to noncompensatory dilatation, and finally results in severe global left ventricular dysfunction. In these patients, depression of global ejection fraction probably results from impairment of function of initially normally contracting myocardium. Early predictors from multivariate analysis allow identification of patients at high risk for progressive left ventricular dilatation and chronic ventricular dysfunction within 4 weeks after acute infarction.

Pathophysiology of heart failure and the renin-angiotensin-system

For more than a decade, the inhibition of the renin-angiotensin system in heart failure has been regarded as pure vasodilator therapy. Consequently, the role of the renin-angiotension system has been seen as contributing to hemodynamic overload by vasoconstriction and volume retention. Meanwhile, clinical experience was indicated that important additional aspects of ACE-inhibition in heart failure are attenuation of the enhanced neuroendocrine activity and reversal or prevention of inappropriate trophic reactions of the overloaded myocardium. In overloaded hearts there is enhanced intracardiac formation of angiotensin due to enhanced expression of angiotensinogen and ACE, and due to accumulation of circulating, nephrogenic active renin. In human hearts, a mast-cell-derived chymase, which is not blocked by ACE-inhibition, contributes to intracardiac angiotensin formation. The enhanced intracardiac angiotensin-II formation in overloaded hearts is involved in coronary constriction, impairment of diastolic relaxation, myocyte enlargement and interstitial fibrosis, which aggravate the diastolic impairment. The major problem in overloaded, hypertrophied cardiocytes is the dedifferentiation with instabilization of Ca(++)-homeostasis due to an altered program of gene expression. Dedifferentiated cardiocytes have a reduced expression of sarcoplasmic reticulum Ca(++)-ATPase and an enhanced expression of the sarcolemmal Na+/Ca(++)-exchanger, resulting in an attenuation of active diastole (Ca(++)-reaccumulation into the sarcoplasmic reticulum), a depressed force-frequency relation, and an enhanced susceptibility for fatal arrhythmias. Furthermore, an enhanced local renin-angiotensin system in distensible coronary and systemic arteries seems to contribute to a reduced releasability of endothelium-derived relaxing factor, probably by reducing bradykinin availability. This modulation of endothelial function appears to contribute to the localization and progression of atheroma development in presence of risks factors for atherosclerosis.