The role of third-generation beta-blocking agents in chronic heart failure

Third-generation beta-blocking agents developed for the hypertension market are proving useful in the treatment of chronic heart failure (HF). These compounds share the ancillary property of vasodilation, which improves acute tolerability by unloading the failing left ventricle at a time when beta-adrenergic withdrawal produces myocardial depression. In the case of carvedilol and bucindolol, this allows for the administration of nonselective beta blockade. Because of blockade of both beta 1 and beta 2 adrenergic receptors as well as other properties, these compounds possess a more comprehensive antiadrenergic profile than second-generation, beta 1-selective compounds. For this and potentially other reasons, third-generation beta-blocking agents have theoretical efficacy advantages that have yet to be demonstrated in large-scale trials. Ongoing trials with either second- or third-generation compounds and one trial directly comparing a compound from each class will provide the answer as to whether third-generation compounds have an advantage in the treatment of chronic HF.

Effect of baseline or changes in adrenergic activity on clinical outcomes in the beta-blocker evaluation of survival trial

BACKGROUND

Adrenergic activation is thought to be an important determinant of outcome in subjects with chronic heart failure (CHF), but baseline or serial changes in adrenergic activity have not been previously investigated in a large patient sample treated with a powerful antiadrenergic agent.

METHODS AND RESULTS

Systemic venous norepinephrine was measured at baseline, 3 months, and 12 months in the beta-Blocker Evaluation of Survival Trial (BEST), which compared placebo treatment with the beta-blocker/sympatholytic agent bucindolol. Baseline norepinephrine level was associated with a progressive increase in rates of death or death plus CHF hospitalization that was independent of treatment group. On multivariate analysis, baseline norepinephrine was also a highly significant (P<0.001) independent predictor of death. In contrast, the relation of the change in norepinephrine at 3 months to subsequent clinical outcomes was complex and treatment group-dependent. In the placebo-treated group but not in the bucindolol-treated group, marked norepinephrine increase at 3 months was associated with increased subsequent risks of death or death plus CHF hospitalization. In the bucindolol-treated group but not in the placebo-treated group, the 1st quartile of marked norepinephrine reduction was associated with an increased mortality risk. A likelihood-based method indicated that 18% of the bucindolol group but only 1% of the placebo group were at an increased risk for death related to marked reduction in norepinephrine at 3 months.

CONCLUSIONS

In BEST, a subset of patients treated with bucindolol had an increased risk of death as the result of sympatholysis, which compromised the efficacy of this third-generation beta-blocker.

Coordinate changes in Myosin heavy chain isoform gene expression are selectively associated with alterations in dilated cardiomyopathy phenotype

BACKGROUND

The most common cause of chronic heart failure in the US is secondary or primary dilated cardiomyopathy (DCM). The DCM phenotype exhibits changes in the expression of genes that regulate contractile function and pathologic hypertrophy. However, it is unclear if any of these alterations in gene expression are disease producing or modifying.

MATERIALS AND METHODS

One approach to providing evidence for cause-effect of a disease-influencing gene is to quantitatively compare changes in phenotype to changes in gene expression by employing serial measurements in a longitudinal experimental design. We investigated the quantitative relationships between changes in gene expression and phenotype n 47 patients with idiopathic DCM. In endomyocardial biopsies at baseline and 6 months later, we measured mRNA expression of genes regulating contractile function (beta-adrenergic receptors, sarcoplasmic reticulum Ca(2) + ATPase, and alpha- and beta-myosin heavy chain isoforms) or associated with pathologic hypertrophy (beta-myosin heavy chain and atrial natriuretic peptide), plus beta-adrenergic receptor protein expression. Left ventricular phenotype was assessed by radionuclide ejection fraction.

RESULTS

Improvement in DCM phenotype was directly related to a coordinate increase in alpha- and a decrease in beta-myosin heavy chain mRNA expression. In contrast, modification of phenotype was unrelated to changes in the expression of beta(1)- or beta(2)-adrenergic receptor mRNA or protein, or to the mRNA expression of sarcoplasmic reticulum Ca(2) + ATPase and atrial natriuretic peptide.

CONCLUSION

We conclude that in human DCM, phenotypic modification is selectively associated with myosin heavy chain isoform changes. These data support the hypothesis that myosin heavy chain isoform changes contribute to disease progression in human DCM.

Aspirin impairs reverse myocardial remodeling in patients with heart failure treated with beta-blockers

OBJECTIVES

We hypothesized that aspirin (ASA) might alter the beneficial effect of beta-blockers on left ventricular ejection fraction (LVEF) in patients with chronic heart failure.

BACKGROUND

Aspirin blunts the vasodilation caused by both angiotensin-converting enzyme (ACE) inhibitors and beta-blockers in hypertensive patients and in patients with heart failure. Several studies suggest that ASA also blunts some of beneficial effects of ACE inhibitors on mortality in patients with heart failure. To our knowledge, there have been no data evaluating the possible interaction of ASA and beta-blockers on left ventricular remodeling in patients with heart failure.

METHODS

We retrospectively evaluated patients entered into the Multicenter Oral Carvedilol Heart failure Assessment (MOCHA) trial, a 6-month, double-blind, randomized, placebo-controlled, multicenter, dose-response evaluation of carvedilol in patients with chronic stable symptomatic heart failure. Multivariate analysis was performed to determine if aspirin independently influenced the improvement in LVEF.

RESULTS

Over all randomized patients (n = 293), LVEF improved 8.2 +/- 0.8 ejection fraction (EF) units in ASA nonusers and 4.5 +/- 0.7 EF units in ASA users (p = 0.005). In subjects randomized to treatment with carvedilol (n = 231), LVEF improved 9.5 +/- 0.9 EF units in ASA nonusers and 5.8 +/- 0.8 EF units in ASA users (p = 0.02). In subjects randomized to treatment with placebo (n = 62), LVEF improved 2.8 +/- 1.2 EF units in ASA nonusers and 0.5 +/- 1.4 EF units in ASA users (p = 0.20). Aspirin did not significantly affect the heart rate or systolic blood pressure response in either the placebo or carvedilol groups. The effect of ASA became more significant on multivariate analysis. The change in LVEF was also influenced by carvedilol dose, etiology of heart failure, baseline heart rate, EF and coumadin use. The detrimental effect of ASA on the improvement in LVEF was dose-related and was present in both placebo and carvedilol groups, although the effect was statistically significant only in the much larger carvedilol group.

CONCLUSIONS

Aspirin significantly affects the changes in LVEF over time in patients with heart failure and systolic dysfunction treated with carvedilol. The specific mechanism(s) underlying this interaction are unknown and further studies are needed to provide additional understanding of the molecular basis of factors influencing reverse remodeling in patients with heart failure.

Milrinone versus dobutamine in heart failure subjects treated chronically with carvedilol

OBJECTIVE

To compare the efficacy of milrinone and dobutamine in patients chronically treated with carvedilol.

BACKGROUND

Milrinone and dobutamine are used to manage decompensated heart failure, but their efficacy in patients on beta-blocker therapy was unknown.

METHODS

Twenty patients with decompensated heart failure were prospectively enrolled. Inotropic responses to milrinone (12.5, 25 or 50 microg/kg bolus infusions) or dobutamine (5, 10, 15 or 20 microg/kg/min infusions) were evaluated by right-heart catheterization.

RESULTS

Milrinone increased cardiac index (2.0-2.6 l/min/m2, P=0.0001) without significantly altering heart rate (70-75 bpm, P=0.19). Milrinone decreased mean pulmonary artery pressure (36-29 mm Hg, P=0.0001), pulmonary capillary wedge pressure (24-18 mm Hg, P=0.0001) and mean arterial blood pressure (78-75 mm Hg, P=0.0002). Left ventricular stroke volume index increased in the milrinone group (31-35 ml/beat/m2, P=0.0001). Dobutamine produced an increase in cardiac index (2.4-3.3 l/min/m2, P=0.0001) only at doses that are not typically used to treat heart failure (15-20 microg/kg/min). At these doses, dobutamine increased heart rate (68-82 bpm, P=0.008), mean systemic pressure (90-117 mm Hg, P=0.0001) and mean pulmonary artery pressure (21-30 mm Hg, P=0.001). Dobutamine did not alter left ventricular stroke volume index or pulmonary capillary wedge pressure.

CONCLUSIONS

Dobutamine and milrinone have different hemodynamic effects in patients treated chronically with carvedilol. These differences should be considered when selecting inotropic therapy for decompensated heart failure.

Regulation of thyroid hormone receptor isoforms in physiological and pathological cardiac hypertrophy

Physiological and pathological cardiac hypertrophy have directionally opposite changes in transcription of thyroid hormone (TH)-responsive genes, including alpha- and beta-myosin heavy chain (MyHC) and sarcoplasmic reticulum Ca(2+)-ATPase (SERCA), and TH treatment can reverse molecular and functional abnormalities in pathological hypertrophy, such as pressure overload. These findings suggest relative hypothyroidism in pathological hypertrophy, but serum levels of TH are usually normal. We studied the regulation of TH receptors (TRs) beta1, alpha1, and alpha2 in pathological and physiological rat cardiac hypertrophy models with hypothyroid- and hyperthyroid-like changes in the TH target genes, alpha- and beta-MyHC and SERCA. All 3 TR subtypes in myocytes were downregulated in 2 hypertrophy models with a hypothyroid-like mRNA phenotype, phenylephrine in culture and pressure overload in vivo. Myocyte TRbeta1 was upregulated in models with a hyperthyroid-like phenotype, TH (triiodothyronine, T3), in culture and exercise in vivo. In myocyte culture, TR overexpression, or excess T3, reversed the effects of phenylephrine on TH-responsive mRNAs and promoters. In addition, TR cotransfection and treatment with the TRbeta1-selective agonist GC-1 suggested different functional coupling of the TR isoforms, TRbeta1 to transcription of beta-MyHC, SERCA, and TRbeta1, and TRalpha1 to alpha-MyHC transcription and increased myocyte size. We conclude that TR isoforms have distinct regulation and function in rat cardiac myocytes. Changes in myocyte TR levels can explain in part the characteristic molecular phenotypes in physiological and pathological cardiac hypertrophy.

Bucindolol, a nonselective beta 1- and beta 2-adrenergic receptor antagonist, decreases beta-adrenergic receptor density in cultured embryonic chick cardiac myocyte membranes

Bucindolol and carvedilol, nonselective beta1- and beta2-adrenergic receptor antagonists, have been widely used in clinical therapeutic trials of congestive heart failure. The aim of the current study was to investigate long-term effects of bucindolol or carvedilol on beta-adrenergic receptor protein and gene expression in cardiac myocytes. Embryonic chick cardiac myocytes were cultured and incubated with bucindolol (1 microM), carvedilol (1 microM), or norepinephrine (1 microM) for 24 h. 125I-iodocyanopindolol binding assays demonstrated that incubation with norepinephrine or bucindolol, but not carvedilol, significantly decreased beta-adrenergic receptor density in crude membranes prepared from the myocytes. Neither bucindolol nor carvedilol significantly stimulated adenylyl cyclase activity in membranes from drug-untreated cells. Unlike by norepinephrine, the receptor density reduction by bucindolol incubation was not accompanied by a change in beta1-adrenergic receptor messenger RNA abundance. A decrease in membrane beta-adrenergic receptor density without a change in cognate messenger RNA abundance was also observed in hamster DDT1 MF2 cell line incubated with bucindolol (1 microM, 24 h). We conclude that incubation with bucindolol, but not carvedilol, results in true reduction of beta-adrenergic receptor density in chick cardiac myocyte membranes by mechanisms that are distinct from those responsible for receptor density reduction by the agonist norepinephrine.

Inotropes and beta-blockers: is there a need for new guidelines?

Beta-adrenergic blocking agents are standard treatment for patients with mild-to-moderate heart failure. When patients receiving beta-blockers decompensate they often need treatment with a positive inotropic agent. The beta-agonist dobutamine may not produce much increase in cardiac output during full-dose beta-blocker treatment and may increase systemic vascular resistance via alpha-adrenergic stimulation. In contrast, phosphodiesterase inhibitors (PDEIs) such as milrinone or enoximone retain full hemodynamic effects during complete beta-blockade because the site of action of PDEIs is beyond the beta-adrenergic receptor and because beta-blockade reverses some of the desensitization phenomena that account for the attenuation of PDEI response in heart failure related to upregulation in G(alphai). Inotrope-requiring subjects with decompensated heart failure who are undergoing long-term therapy with beta-blocking agents should be treated with a type III-specific PDEI, not a beta-agonist such as dobutamine.

Race and the response to adrenergic blockade with carvedilol in patients with chronic heart failure

BACKGROUND

The benefits of angiotensin-converting-enzyme inhibitors and beta-blockers may be smaller in black patients than in patients of other races, but it is unknown whether race influences the response to carvedilol in patients with chronic heart failure.

METHODS

In the U.S. Carvedilol Heart Failure Trials Program, 217 black and 877 nonblack patients (in New York Heart Association class II, III, or IV and with a left ventricular ejection fraction of no more than 0.35) were randomly assigned to receive placebo or carvedilol (at doses of 6.25 to 50 mg twice daily) for up to 15 months. The effects of carvedilol on ejection fraction, clinical status, and major clinical events were retrospectively compared between black and nonblack patients.

RESULTS

As compared with placebo, carvedilol lowered the risk of death from any cause or hospitalization for any reason by 48 percent in black patients and by 30 percent in nonblack patients. Carvedilol reduced the risk of worsening heart failure (heart failure leading to death, hospitalization, or a sustained increase in medication) by 54 percent in black patients and by 51 percent in nonblack patients. The ratios of the relative risks associated with carvedilol for these two outcome variables in black as compared with nonblack patients were 0.74 (95 percent confidence interval, 0.42 to 1.34) and 0.94 (95 percent confidence interval, 0.43 to 2.05), respectively. Carvedilol also improved functional class, ejection fraction, and the patients' and physicians' global assessments in both the black patients and the nonblack patients. For all these measures of outcome and clinical status, carvedilol was superior to placebo within each racial cohort (P<0.05 in all analyses), and there was no significant interaction between race and treatment (P> 0.05 in all analyses).

CONCLUSIONS

The benefit of carvedilol was apparent and of similar magnitude in both black and nonblack patients with heart failure.

Influence of carvedilol on hospitalizations in heart failure: incidence, resource utilization and costs. U.S. Carvedilol Heart Failure Study Group

BACKGROUND

Carvedilol reduces disease progression in heart failure, but to our knowledge, its effects on hospitalizations and costs have not been evaluated.

OBJECTIVES

We examined the effects on hospitalization frequency and costs in the U.S. Carvedilol Heart Failure Trials Program. This program consisted of four concurrent, multicenter, double-blind, placebo-controlled studies involving 1,094 patients with New York Heart Association class II to IV heart failure, which treated patients with placebo or carvedilol for up to 15 months (median, 6.5 months).

METHODS

Detailed resource utilization data were collected for all hospitalizations occurring between randomization and the end of follow-up. In-patient care costs were estimated based on observed levels of resource use.

RESULTS

Compared with placebo, carvedilol reduced the risk of hospitalization for any reason by 29% (p = 0.009), cardiovascular hospitalizations by 28% (p = 0.034) and heart failure hospitalizations by 38% (p = 0.041). Carvedilol also decreased the mean number of hospitalizations per patient (for cardiovascular reasons 30% [p = 0.02], for heart failure 53% [p = 0.03]). Among hospitalized patients, carvedilol reduced severity of illness during hospital admission, as reflected by shorter length of stay and less frequent use of intensive care. For heart failure hospital admissions, carvedilol decreased mean length of stay by 37% (p = 0.03) and mean number of intensive care unit/coronary care unit days by 83% (p = 0.001), with similar effects on cardiovascular admissions. As a result, estimated inpatient care costs with carvedilol were 57% lower for cardiovascular admissions (p = 0.016) and 81% lower for heart failure admissions (p = 0.022).

CONCLUSIONS

Carvedilol added to angiotensin-converting enzyme inhibition reduces hospitalization risk as well as severity of illness and resource utilization during admission in patients with chronic heart failure.

Altered beta-adrenergic receptor gene regulation and signaling in chronic heart failure

J. D. Port and M. R. Bristow. Altered Beta-adrenergic Receptor Gene Regulation and Signaling in Chronic Heart Failure. Journal of Molecular and Cellular Cardiology (2001) 33, 887-905. Beta adrenergic receptors (beta -ARs) are critical regulators of cardiac function in both normal and pathophysiological states. Under normal conditions, beta -ARs and their signaling pathways modulate both the rate and force of myocardial contraction and relaxation, allowing individuals to respond appropriately to physiological stress or exercise. However, in chronic heart failure, sustained activation of the beta -AR signaling pathways can have overtly negative biological consequences. This notion is reinforced by the positive outcomes of a number of clinical trials demonstrating the usefulness of beta-blocker therapy in chronic congestive heart failure. During the last few years, significant progress has been made in understanding the molecular biological basis of beta -AR function, both at the biochemical and genetic levels. In this review, the biological basis of adrenergic signaling and how this changes in heart failure is discussed. Aspects of adrenergic receptor pharmacology relevant to heart failure are reviewed, including the recently emerging differences described for beta(1)- v beta(2)-AR signaling pathways. Highlighting these differences is recent evidence that over-stimulation of the beta(1)-AR pathway in cardiac myocytes appears to be pro-apoptotic, whereas stimulation of the beta(2)-AR pathway may be anti-apoptotic. Overview of beta -AR gene regulation, transgenic models of beta -AR overexpression, and beta -AR polymorphisms as they relate to heart failure progression are also discussed.

Low-level inotropic stimulation with type III phosphodiesterase inhibitors in patients with advanced symptomatic chronic heart failure receiving beta-blocking agents

beta-blocking agents are now well established as a cornerstone therapy in mild to moderate heart failure. Patients with more advanced heart failure depend on adrenergic activation to maintain adequate myocardial function. This leads to significant difficulties in using beta-blockers in advanced or severe heart failure. In addition, recent data indicate that adrenergic withdrawal might be detrimental in some of these patients. In higher doses, positive inotropic agents have been shown to increase mortality when used alone in subsets with advanced heart failure. Preliminary data suggest that the combination of low-dose phosphodiesterase inhibitors and a beta-blocker may be better tolerated and does not appear to be associated with the adverse effects of either therapy used alone. We discuss the theoretic underpinning of this approach and the supportive clinical data.

Alterations in cardiac adrenergic signaling and calcium cycling differentially affect the progression of cardiomyopathy

The medical treatment of chronic heart failure has undergone a dramatic transition in the past decade. Short-term approaches for altering hemodynamics have given way to long-term, reparative strategies, including beta-adrenergic receptor (betaAR) blockade. This was once viewed as counterintuitive, because acute administration causes myocardial depression. Cardiac myocytes from failing hearts show changes in betaAR signaling and excitation-contraction coupling that can impair cardiac contractility, but the role of these abnormalities in the progression of heart failure is controversial. We therefore tested the impact of different manipulations that increase contractility on the progression of cardiac dysfunction in a mouse model of hypertrophic cardiomyopathy. High-level overexpression of the beta(2)AR caused rapidly progressive cardiac failure in this model. In contrast, phospholamban ablation prevented systolic dysfunction and exercise intolerance, but not hypertrophy, in hypertrophic cardiomyopathy mice. Cardiac expression of a peptide inhibitor of the betaAR kinase 1 not only prevented systolic dysfunction and exercise intolerance but also decreased cardiac remodeling and hypertrophic gene expression. These three manipulations of cardiac contractility had distinct effects on disease progression, suggesting that selective modulation of particular aspects of betaAR signaling or excitation-contraction coupling can provide therapeutic benefit.

Current perspective new insights into the molecular basis of familial dilated cardiomyopathy

Genetic disease transmission has been identified in a significant proportion of patients with dilated cardiomyopathy (DCM). Variable clinical characteristics and patterns of inheritance, as well as recent molecular genetic data, indicate the existence of several genes causing the disease. Several distinct subtypes of familial DCM have been identified. Autosomal dominant DCM is the most frequent form (56% of our cases), and several candidate disease loci have been identified by linkage analysis. Three disease genes are presently known: the cardiac actin gene, the desmin gene, and the lamin A/C gene. This latter gene has recently been found to be responsible for both the autosomal dominant form of DCM with subclinical skeletal muscle disease (7.7% of cases) and the familial form with conduction defects (2.6% of cases) or the autosomal dominant variant of Emery-Dreifuss muscular dystrophy. The autosomal recessive form of DCM accounts for 16% of cases and is characterized by a worse prognosis. An X-linked form of DCM (10% of cases) manifests in the adult population and is due to mutations in the dystrophin gene. In the rare infantile form of DCM, mutations in the G4.5 gene have been identified. Finally, some of the rare unclassifiable forms (7.7% of cases) may be due to mitochondrial DNA mutations. Clinical and experimental evidence based on animal models suggest that, in a large number of cases, DCMs are diseases of the cytoskeleton. However, other causes, such as alterations in regulatory elements and in signaling molecules, are possible. Moreover, other genes called modifier genes can influence the severity, penetrance, and expression of the disease, and they will be a main objective of future investigations. Familial DCM is frequent, cannot be predicted on a clinical or morphological basis and requires family screening for identification. The advances in the genetics of familial DCM can allow improved diagnosis, prevention and genetic counseling, and represent the basis for the development of new therapies.

Predicting response to carvedilol for the treatment of heart failure: a multivariate retrospective analysis

BACKGROUND

Carvedilol has been shown to decrease the progression of heart failure and improve left ventricular function and survival in patients with a left ventricular ejection fraction (LVEF) less than 35%. However, not all patients respond uniformly to this therapy. We proposed to identify variables that could, potentially, be used to predict response to carvedilol therapy as measured by the change in LVEF after treatment (Delta LVEF), and to identify pretreatment variables associated with hospitalization for heart failure after carvedilol therapy.

METHODS AND RESULTS

A retrospective analysis of 98 patients treated with open-label carvedilol for a mean period of 16 months was performed by using bivariate and step-wise multivariate analyses. Bivariate analysis showed a positive correlation of Delta LVEF with heart rate at baseline (P =.001). There was a negative correlation of Delta LVEF with baseline LVEF (P <.01), diabetes mellitus (P =.04), and ischemic cardiomyopathy (P =.0002). Multivariate analysis showed a positive correlation of Delta LVEF with heart rate at baseline (P =.01) and a negative correlation with initial LVEF (P =.02) and ischemic cardiomyopathy (P =.006). Variables associated with hospitalization after initiation of carvedilol therapy were New York Heart Association (NYHA) classification (P =.001), lower extremity edema (P =.001), presence of an S3 (P =.02), hyponatremia (P =.02), elevated blood urea nitrogen (BUN) (P =.002), atrial fibrillation (P =.001), diabetes mellitus (P =.02), and obstructive sleep apnea (P =.009).

CONCLUSIONS

Heart failure patients with the lowest LVEF or the highest heart rate at baseline had the greatest gain in LVEF after treatment with carvedilol. Patients with ischemic cardiomyopathy derived less benefit. Patients with clinical evidence of decompensated heart failure were at greater risk for hospitalization after initiation of carvedilol therapy.

Signaling pathways responsible for fetal gene induction in the failing human heart: evidence for altered thyroid hormone receptor gene expression

BACKGROUND

We have previously demonstrated that changes in myosin heavy chain (MHC) isoforms that occur in failing human hearts resemble the pattern produced in rodent myocardium in response to hypothyroidism. Because thyroid hormone status is usually within normal limits in these patients, we hypothesized that failing/hypertrophied human myocardium might have a defect in thyroid hormone signaling due to alterations in expression of thyroid hormone receptors (TRs).

METHODS AND RESULTS

To examine this hypothesis, we used RNase protection assay to measure mRNA levels of TRs in failing left ventricles that exhibited a fetal pattern of gene expression, ie, decreased expression of alpha-MHC with increased beta-MHC expression compared with left ventricles from age-matched controls. We detected expression of TR-alpha(1), -alpha(2), and -beta(1) isoforms in human left ventricles. In failing left ventricles, TR-alpha(1) was downregulated, whereas TR-alpha(2), a splice variant that does not bind thyroid hormone but inhibits responses to liganded TRs, was increased. Expression levels of TR-beta(1) did not differ significantly between the 2 groups. According to linear regression analysis, expression levels of TR-alpha(1) and -alpha(2) were positively and negatively correlated with those of alpha-MHC, respectively.

CONCLUSIONS

We conclude that decreases in TR-alpha(1) and increases in TR-alpha(2) may lead to local attenuation of thyroid hormone signaling in the failing human heart and that the resulting tissue-specific hypothyroidism is a candidate for the molecular mechanism that induces fetal gene expression in the failing human ventricle.

Heart failure management using implantable devices for ventricular resynchronization: Comparison of Medical Therapy, Pacing, and Defibrillation in Chronic Heart Failure (COMPANION) trial. COMPANION Steering Committee and COMPANION Clinical Investigators

BACKGROUND

Although pharmacological therapy has ameliorated symptoms and improved the survival of patients with chronic heart failure (CHF), this chronic syndrome remains a progressive disease causing incremental morbidity and early mortality. A new therapy for the treatment of CHF should ideally decrease mortality, alleviate symptoms, and improve functional capacity. A growing body of evidence suggests that the use of implantable devices to resynchronize ventricular contraction may be a beneficial adjunct in the treatment of CHF.

METHODS

The Comparison of Medical Therapy, Pacing, and Defibrillation in Chronic Heart Failure (COMPANION) trial is a randomized, open-label, 3-arm study of patients in New York Heart Association class III or IV with an ejection fraction of 35% or less and a QRS duration of 120 milliseconds or less. The COMPANION study objectives are to determine whether optimal pharmacological therapy used with (1) ventricular resynchronization therapy alone or (2) ventricular resynchronization therapy combined with cardioverter-defibrillator capability is superior to optimal pharmacological therapy alone in reducing combined all-cause mortality and hospitalizations; reducing cardiac morbidity; improving functional capacity, cardiac performance, and quality of life; and increasing total survival.

Low-dose enoximone improves exercise capacity in chronic heart failure. Enoximone Study Group

OBJECTIVES

This study was designed to evaluate the effects of low-dose enoximone on exercise capacity.

BACKGROUND

At higher doses the phosphodiesterase inhibitor, enoximone, has been shown to increase exercise capacity and decrease symptoms in heart failure patients but also to increase mortality. The effects of lower doses of enoximone on exercise capacity and adverse events have not been evaluated.

METHODS

This is a prospective, double-blind, placebo-controlled, multicenter trial (nine U.S. centers) conducted in 105 patients with New York Heart Association class II to III, ischemic or nonischemic chronic heart failure (CHF). Patients were randomized to placebo or enoximone at 25 or 50 mg orally three times a day. Treadmill maximal exercise testing was done at baseline and after 4, 8 and 12 weeks of treatment, using a modified Naughton protocol. Patients were also evaluated for changes in quality of life and for increased arrhythmias by Holter monitoring.

RESULTS

By the protocol-specified method of statistical analysis (the last observation carried-forward method), enoximone at 50 mg three times a day improved exercise capacity by 117 s at 12 weeks (p = 0.003). Enoximone at 25 mg three times a day also improved exercise capacity at 12 weeks by 115 s (p = 0.013). No increases in ventricular arrhythmias were noted. There were four deaths in the placebo group and 2 and 0 deaths in the enoximone 25 mg three times a day and enoximone 50 mg three times a day groups, respectively. Effects on degree of dyspnea and patient and physician assessments of clinical status favored the enoximone groups.

CONCLUSIONS

Twelve weeks of treatment with low-dose enoximone improves exercise capacity in patients with CHF, without increasing adverse events.

Beta-blockade in adriamycin-induced cardiomyopathy

Beta-blockade consistently improves myocardial systolic function in patients with both nonischemic and ischemic cardiomyopathy. The effects of beta-blockade on Adriamycin-induced cardiomyopathy (ACM), however, are unknown. We retrospectively evaluated the effects of beta-blockade on patients with ACM by using a case-controlled design. The control group consisted of 16 consecutively chosen age- and sex-matched patients with idiopathic dilated cardiomyopathy (IDC) who were treated with beta-blockers. Patients with ACM had a baseline mean left ventricular ejection fraction (LVEF) of 28%, which improved to 41% (P = .041) after treatment with beta-blockers. The control group had a baseline mean LVEF of 26%, which improved to 32% (P = .015) after treatment. The mean duration of beta-blocker therapy in the Adriamycin and control groups was 8 and 9 months, respectively. The degree of improvement between the 2 groups was not significantly different. Beta-blockers have a beneficial effect on cardiac function in patients with ACM, which is at least comparable with other forms of heart failure with systolic dysfunction.

Mechanistic and clinical rationales for using beta-blockers in heart failure

In the 1980s and early 1990s, evidence suggesting a pivotal role for chronic neurohormonal stimulation in the pathophysiology of heart failure began to emerge, which has now produced a dramatic change in the way heart failure is viewed and treated. Preclinical data and results from clinical trials revealed that blocking the actions or generation of norepinephrine or angiotensin II positively affected the course of left ventricular dysfunction and myocardial failure, despite the fact that this inhibition had minimal or negative effects on hemodynamics. Angiotensin-converting enzyme (ACE) inhibitors have been used for heart failure for many years, but only recently have beta-blockers been recommended as part of standard treatment for heart failure. The negative inotropic effects of beta-blockers are well known; these agents must be used with caution in patients with heart failure. However, after several months of treatment, left ventricular ejection fraction (LVEF) gradually increases, and a reversal of the pathological remodeling associated with chronic heart failure occurs: left ventricular mass decreases, chamber shape becomes more elliptical, and mitral regurgitation decreases. Data from clinical trials have shown that long-term beta-adrenergic blockade halts the progression of pump dysfunction, substantially improves left ventricular function, and reduces morbidity and mortality rates in patients with mild-to-moderate heart failure. This article provides a detailed rationale for the use of beta-blockers in patients with chronic heart failure, based on the current understanding of pathophysiology and recent clinical trial data.

Myocardial-directed overexpression of the human beta(1)-adrenergic receptor in transgenic mice

The beta(1)-adrenergic receptor (AR) is the dominant subtype in non-failing and failing myocardium. beta(1)-AR signaling, by the endogenous neurotransmitter norepinephrine, is central to the regulation of myocardial contractility. In heart failure, the beta(1)-AR undergoes subtype-selective downregulation which may protect against the increased cardiac adrenergic drive associated with this pathophysiological state. To examine the hypothesis that chronically increased beta(1)-AR mediated signaling has adverse myocardial effects, transgenic mice overexpressing the human beta(1)-AR in a cardiac-selective context were produced, utilizing an alpha-myosin heavy chain (MHC) promoter. In these mice, beta(1)-AR protein abundance was approximately 24-46-fold (1-2 pmol/mg protein) that of wild-type mice. Histopathological examination of young (4 months old) and old (approximately 9 months old) transgenic mouse hearts consistently demonstrated large areas of interstitial replacement fibrosis, marked myocyte hypertrophy and myofibrilar disarray. In addition, increased expression of the pre-apoptotic marker, Bax, was observed coincident with regions of fibrosis accompanied by an increased apoptotic index, as measured by TUNEL assay. Older non-transgenic mice exhibited a slight tendency towards a decreased fractional shortening, whereas older beta(1)-AR transgenic mice had a marked reduction in fractional shortening (%FS approximately 30) as determined by echocardiography. Additionally, older beta(1)-AR transgenic mice had an increased left ventricular chamber size. In summary, cardiac-directed overexpression of the human beta(1)-AR in transgenic mice leads to a significant histopathological phenotype with no apparent functional consequence in younger mice and a variable degree of cardiac dysfunction in older animals. This model system may ultimately prove useful for investigating the biological basis of adrenergically-mediated myocardial damage in humans.

Myosin heavy chain isoform expression in the failing and nonfailing human heart

In the heart, the relative proportions of the 2 forms of the motor protein myosin heavy chain (MyHC) have been shown to be affected by a wide variety of pathological and physiological stimuli. Hearts that express the faster MyHC motor protein, alpha, produce more power than those expressing the slower MyHC motor protein, beta, leading to the hypothesis that MyHC isoforms play a major role in the determination of cardiac contractility. We showed previously that a significant amount of alphaMyHC mRNA is expressed in nonfailing human ventricular myocardium and that alphaMyHC mRNA expression is decreased 15-fold in end-stage failing left ventricles. In the present study, we determined the MyHC protein isoform content of human heart samples of known MyHC mRNA composition. We demonstrate that alphaMyHC protein was easily detectable in 12 nonfailing hearts. alphaMyHC protein represented 7.2+/-3.2% of total MyHC protein (compared with approximately 35% of the MyHC mRNA), suggesting that translational regulation may be operative; in contrast, there was effectively no detectable alphaMyHC protein in the left ventricles of 10 end-stage failing human hearts.

Inotropes in the beta-blocker era

Beta-adrenergic blocking agents are now standard treatment for mild to moderate chronic heart failure (CHF). However, although many subjects improve on beta blockade, others do not, and some may even deteriorate. Even when subjects improve on beta blockade, they may subsequently decompensate and need acute treatment with a positive inotropic agent. In the presence of full beta blockade, a beta agonist such as dobutamine may have to be administered at very high (> 10 micrograms/kg/min) doses to increase cardiac output, and these doses may increase afterload. In contrast, phosphodiesterase inhibitors (PDEIs) such as milrinone or enoximone retain their full hemodynamic effects in the face of beta blockade. This is because the site of PDEI action is beyond the beta-adrenergic receptor, and because beta blockade reverses receptor pathway desensitization changes, which are detrimental to PDEI response. Moreover, when the combination of a PDEI and a beta-blocking agent is administered long term in CHF, their respective efficacies are additive and their adverse effects subtractive. The PDEI is administered first to increase the tolerability of beta-blocker initiation by counteracting the myocardial depressant effect of adrenergic withdrawal. With this combination, the signature effects of beta blockade (a substantial decrease in heart rate and an increase in left ventricular ejection fraction) are observed, the hemodynamic support conferred by the PDEI appears to be sustained, and clinical results are promising. However, large-scale placebo-controlled studies with PDEIs and beta blockers are needed to confirm these results.

Mechanisms of development of heart failure in the hypertensive patient

Hypertension is a major risk factor for the development of heart failure. Mechanisms which maintain normal function in the short term in the pressure overloaded heart have longer term deleterious effects. These include left ventricular (LV) hypertrophy and chronic activation of the adrenergic and renin-angiotensin systems. beta-Blocking agents are capable of blocking the adrenergic system and, to some extent, the renin-angiotensin system. They are therefore attractive in treating hypertension, both for preventing the development of abnormalities and for reversing established LV dysfunction and hypertrophy. Trials in heart failure have shown that these agents prevent progressive myocardial dysfunction, prevent and reverse remodelling and improve intrinsic systolic function. Non-selective beta-blocking agents appear to offer greater anti-adrenergic effects than selective ones. However, more research is needed, including direct comparisons of different agents.

Hypotension with dobutamine: beta-adrenergic antagonist selectivity at low doses of carvedilol

OBJECTIVE

To report a case of marked hypotension resulting from the concomitant use of low-dose carvedilol and intravenous dobutamine.

CASE SUMMARY

A 54-year-old white man with severe heart failure was placed on carvedilol 3.125 mg orally twice a day; three days later the dosage was increased to 6.25 mg orally twice a day. His symptoms of heart failure worsened with increasing fluid retention, orthopnea, paroxysmal nocturnal dyspnea, and elevated blood urea nitrogen and creatinine. He was admitted for treatment of decompensated heart failure with intravenous dobutamine. With each increase in intravenous dobutamine, systolic blood pressure fell. Dobutamine was discontinued when systolic blood pressure reached 56 mm Hg. In a subsequent admission for decompensated heart failure, when the patient was not taking carvedilol, he was treated with intravenous dobutamine and systolic blood pressure increased.

DISCUSSION

Although carvedilol is a nonselective beta-adrenergic antagonist, at low doses it is a selective beta1-adrenergic antagonist. Dobutamine is a beta1-, beta2-, and alpha1-adrenergic agonist. Typically, patients with heart failure treated with intravenous dobutamine have a small increase in systolic blood pressure. We propose that the drop in blood pressure with dobutamine in this patient was caused by a fall in systemic vascular resistance due to vascular beta2-adrenergic receptor activation. The normal increase in cardiac output was partially blocked by selective beta1-adrenergic blockade at low doses of carvedilol.

CONCLUSIONS

Beta-adrenergic blockade with carvedilol is now common therapy for patients with congestive heart failure. Intravenous dobutamine is often used when these patients have worsening heart failure. Recognition that treatment with dobutamine in patients taking low doses of carvedilol may result in hypotension is important for appropriate monitoring and therapy.

Cellular and molecular remodeling in a heart failure model treated with the beta-blocker carteolol

Broad-breasted white turkey poults fed furazolidone developed dilated cardiomyopathy (DCM) characterized by ventricular dilatation, decreased ejection fraction, beta1-receptor density, sarcoplasmic reticulum (SR) Ca2+-ATPase, myofibrillar ATPase activity, and reduced metabolism markers. We investigated the effects of carteolol, a beta-adrenergic blocking agent, by administrating two different dosages (0.01 and 10.0 mg/kg) twice a day for 4 wk to control and DCM turkey poults. At completion of the study there was 59% mortality in the nontreated DCM group, 55% mortality in the group treated with the low dose of carteolol, and 22% mortality in the group treated with the high dose of carteolol. Both treated groups showed a significant decrease in left ventricle size and significant restoration of ejection fraction and left ventricular peak systolic pressure. Carteolol treatment increased beta-adrenergic receptor density, and the high carteolol dose restored SR Ca2+-ATPase and myofibrillar ATPase activities, along with creatine kinase, lactate dehydrogenase, aspartate transaminase, and ATP synthase activities, to normal. These results show that beta-blockade with carteolol improves survival, reverses contractile abnormalities, and induces cellular remodeling in this model of heart failure.

Effects of carvedilol on left ventricular mass, chamber geometry, and mitral regurgitation in chronic heart failure

We and others have previously shown that carvedilol improves left ventricular (LV) function and symptoms in chronic heart failure. This improvement in LV function has also been shown to be associated with an improvement in survival. This study evaluates the effect of carvedilol on LV mass, geometry, and degree of mitral regurgitation (MR). In 59 patients with symptomatic heart failure and LV ejection fraction <0.35, previously randomized to either treatment with carvedilol or placebo, we evaluated LV mass, geometry, and degree of MR over the time period of carvedilol treatment. LV mass decreased as early as 4 months into the treatment protocol and continued to decrease over a period of 1 year. LV geometry, defined by the length/diameter ratio, and severity of MR also improved with 4 months of therapy. Thus, compared with placebo treatment, carvedilol decreases LV mass while improving cardiac geometry and decreasing MR in patients with chronic heart failure. These changes occur in association with an improvement in LV systolic function. This process begins by 4 months of treatment and continues for 12 months.

Right ventricular phenotypic characteristics in subjects with primary pulmonary hypertension or idiopathic dilated cardiomyopathy

BACKGROUND

Studies of animal models and human subjects with cardiomyopathies suggest that cardiac myocyte and ventricular chamber remodeling show distinct phenotypic characteristics that may be dependent on specific signaling pathways.

METHODS AND RESULTS

In this study, we characterize right ventricular (RV) chamber size, end-diastolic thickness, myocardial mass, and ejection fraction (EF) in human subjects with chronic heart failure from primary pulmonary hypertension (PPH; n = 10) and idiopathic dilated cardiomyopathy (IDC; n = 10). Subjects underwent gated cardiac magnetic resonance imaging (MRI), and the RVs were phenotypically classified based on the presence or absence of hypertrophy (increased mass), systolic dysfunction (reduced EF), and degree of wall thickness (concentric v eccentric pattern of hypertrophy). Within this schema, five abnormal phenotypes could be identified. In PPH subjects, in whom the RV is subjected to the uniform insult of chronic pressure overload, four different abnormal phenotypes were identified.

CONCLUSIONS

These data indicate that distinct structural/functional ventricular chamber phenotypes may be classified by MRI, and that a uniform insult can result in multiple RV phenotypes.

Increased protein kinase C activity and expression of Ca2+-sensitive isoforms in the failing human heart

BACKGROUND

Increased expression of Ca2+-sensitive protein kinase C (PKC) isoforms may be important markers of heart failure. Our aim was to determine the relative expression of PKC-beta1, -beta2, and -alpha in failed and nonfailed myocardium.

METHODS AND RESULTS

Explanted hearts of patients in whom dilated cardiomyopathy or ischemic cardiomyopathy was diagnosed were examined for PKC isoform content by Western blot, immunohistochemistry, enzymatic activity, and in situ hybridization and compared with nonfailed left ventricle. Quantitative immunoblotting revealed significant increases of >40% in PKC-beta1 (P<0.05) and -beta2 (P<0.04) membrane expression in failed hearts compared with nonfailed; PKC-alpha expression was significantly elevated by 70% in membrane fractions (P<0.03). PKC-epsilon expression was not significantly changed. In failed left ventricle, PKC-beta1 and -beta2 immunostaining was intense throughout myocytes, compared with slight, scattered staining in nonfailed myocytes. PKC-alpha immunostaining was also more evident in cardiomyocytes from failed hearts with staining primarily localized to intercalated disks. In situ hybridization revealed increased PKC-beta1 and -beta2 mRNA expression in cardiomyocytes of failed heart tissue. PKC activity was significantly increased in membrane fractions from failed hearts compared with nonfailed (1021+/-189 versus 261+/-89 pmol. mg-1. min-1, P<0.01). LY333531, a selective PKC-beta inhibitor, significantly decreased PKC activity in membrane fractions from failed hearts by 209 pmol. min-1. mg-1 (versus 42.5 pmol. min-1. mg-1 in nonfailed, P<0.04), indicating a greater contribution of PKC-beta to total PKC activity in failed hearts.

CONCLUSIONS

In failed human heart, PKC-beta1 and -beta2 expression and contribution to total PKC activity are significantly increased. This may signal a role for Ca2+-sensitive PKC isoforms in cardiac mechanisms involved in heart failure.

New method to evaluate myocyte remodeling from formalin-fixed biopsy and autopsy material

BACKGROUND

Excessive lengthening of cardiac myocytes attributed to series addition of sarcomeres is a consistent feature of left ventricular dilation in chronic heart failure. Currently, it is not feasible to assess myocyte dimensions, particularly myocyte length, in a manner that is of potential diagnostic usefulness.

METHODS AND RESULTS

Isolated myocytes from three groups of normal rats (100, 200, and 300 g) were obtained by using two different methods: (1) digestion of formalin-fixed myocardial tissue using potassium hydroxide (KOH) and (2) retrograde aortic perfusion of fresh hearts with collagenase. There was no difference in mean cell length between the two methods. The KOH method was also used to isolate intact, rod-shaped myocytes from formalin-fixed human cadaver left ventricles (control, n = 3; heart failure, n = 3) and from human right ventricle biopsy specimens (n = 6). Confirming our previous work using collagenase-isolated myocytes from fresh human explants, left ventricular myocytes from failing hearts showed longer mean cell length compared with control hearts. Data from human right ventricle biopsy specimens confirmed our previous finding in rats that myocyte lengthening is less pronounced in this chamber in heart failure.

CONCLUSIONS

The KOH method can be used to obtain reliable measurements of myocyte length and other cellular parameters from myocardial biopsies and autopsy material. Such data may be useful in the diagnostic assessment of remodeling associated with heart failure.

Differential regulation of cardiac angiotensin converting enzyme binding sites and AT1 receptor density in the failing human heart

BACKGROUND

The regulation and interaction of ACE and the angiotensin II (Ang II) type I (AT1) receptor in the failing human heart are not understood.

METHODS AND RESULTS

Radioligand binding with 3H-ramiprilat was used to measure ACE protein in membrane preparations of hearts obtained from 36 subjects with idiopathic dilated cardiomyopathy (IDC), 8 subjects with primary pulmonary hypertension (PPH), and 32 organ donors with normal cardiac function (NF hearts). 125I-Ang II formation was measured in a subset of hearts. Saralasin (125I-(Sar1,Ile8)-Ang II) was used to measure total Ang II receptor density. AT1 and AT2 receptor binding were determined with the AT1 receptor antagonist losartan. Maximal ACE binding (Bmax) was 578+/-47 fmol/mg in IDC left ventricle (LV), 713+/-97 fmol/mg in PPH LV, and 325+/-27 fmol/mg in NF LV (P<0.001, IDC or PPH versus NF). In IDC, PPH, and NF right ventricles (RV), ACE Bmax was 737+/-78, 638+/-137, and 422+/-49 fmol/mg, respectively (P=0.02, IDC versus NF; P=0.08, PPH versus NF). 125I-Ang II formation correlated with ACE binding sites (r=0.60, P=0.00005). There was selective downregulation of the AT1 receptor subtype in failing PPH ventricles: 6.41+/-1.23 fmol/mg in PPH LV, 2.37+/-0.50 fmol/mg in PPH RV, 5.38+/-0.53 fmol/mg in NF LV, and 7.30+/-1.10 fmol/mg in NF RV (P=0.01, PPH RV versus PPH LV; P=0.0006, PPH RV versus NF RV).

CONCLUSIONS

ACE binding sites are increased in both failing IDC and nonfailing PPH ventricles. In PPH hearts, the AT1 receptor is downregulated only in the failing RV.

Combined oral positive inotropic and beta-blocker therapy for treatment of refractory class IV heart failure

OBJECTIVES

We sought to assess the effects of combined oral positive inotropic and beta-blocker therapy in patients with severe heart failure.

BACKGROUND

Patients with severe, class IV heart failure who receive standard medical therapy exhibit a 1-year mortality rate >50%. Moreover, such patients generally do not tolerate beta-blockade, a promising new therapy for chronic heart failure. Positive inotropes, including phosphodiesterase inhibitors, are associated with increased mortality when administered over the long term in these patients. The addition of a beta-blocker to positive inotropic therapy might attenuate this adverse effect, although long-term oral inotropic therapy might serve as a bridge to beta-blockade.

METHODS

Thirty patients with severe heart failure (left ventricular ejection fraction [LVEF] 17.2+/-1.2%, cardiac index 1.6+/-0.1 liter/min per m2) were treated with the combination of oral enoximone (a phosphodiesterase inhibitor) and oral metoprolol at two institutions. Enoximone was given at a dose of < or = 1 mg/kg body weight three times a day. After clinical stabilization, metoprolol was initiated at 6.25 mg twice a day and slowly titrated up to a target dose of 100 to 200 mg/day.

RESULTS

Ninety-six percent of the patients tolerated enoximone, whereas 80% tolerated the addition of metoprolol. The mean duration of combination therapy was 9.4+/-1.8 months. The mean length of follow-up was 20.9+/-3.9 months. Of the 23 patients receiving the combination therapy, 48% were weaned off enoximone over the long term. The LVEF increased significantly, from 17.7+/-1.6% to 27.6+/-3.4% (p=0.01), whereas the New York Heart Association functional class improved from 4+/-0 to 2.8+/-0.1 (p=0.0001). The number of hospital admissions tended to decrease during therapy (p=0.06). The estimated probability of survival at 1 year was 81+/-9%. Heart transplantation was performed successfully in nine patients (30%).

CONCLUSIONS

Combination therapy with a positive inotrope and a beta-blocker appears to be useful in the treatment of severe, class IV heart failure. It may be used as a palliative measure when transplantation is not an option or as a bridge to heart transplantation. Further study of this form of combined therapy is warranted.

Systemic hemodynamic, neurohormonal, and renal effects of a steady-state infusion of human brain natriuretic peptide in patients with hemodynamically decompensated heart failure

BACKGROUND

Human brain natriuretic peptide (hBNP) is a promising agent for the treatment of decompensated cardiac failure. However, the systemic hemodynamic, neurohormonal, and renal effects of hBNP have been incompletely studied in human heart failure.

METHODS AND RESULTS

The effects of a continuous 4-hour infusion of hBNP were determined in 16 decompensated heart failure patients in an invasive, randomized, double-blind, placebo-controlled study. Patients were evaluated during three 4-hour study periods: baseline, treatment (placebo [n = 4] versus hBNP 0.025 or 0.05 microgram/kg/min [n = 12]), and post-treatment. Urinary volume losses were replaced hourly to separate the vasodilatory and diuretic effects of hBNP. Two patients in the hBNP group were excluded from the analysis because of adverse events. hBNP significantly (P < .001) reduced right atrial pressure and pulmonary capillary wedge pressure by approximately 30% and 40%, respectively. hBNP also significantly lowered systemic vascular resistance from 1722 +/- 139 to 1101 +/- 83 dynes.s.cm-5 (P < .05). These unloading effects of hBNP produced a 28% increase in cardiac index (P < .05) with no change in heart rate. Compared to placebo, hBNP decreased plasma norepinephrine and aldosterone. Renal hemodynamics were unaffected by hBNP; however, most patients were resistant to its natriuretic effect.

CONCLUSIONS

1) The predominant hemodynamic effects of hBNP were a decrease in cardiac preload and systemic vascular resistance. 2) hBNP also improved cardiac output without increasing heart rate. 3) Plasma norepinephrine and aldosterone levels decreased during hBNP infusion. 4) hBNP is pharmacologically active and has potential in the therapy for decompensated heart failure.

Effects of carvedilol on right ventricular function in chronic heart failure

This study investigated the effects of carvedilol on right ventricular (RV) volume and systolic function in chronic heart failure patients. Carvedilol treatment resulted in a significant improvement of RV ejection fraction and systolic performance, which paralleled the improvement of systolic function demonstrated in the left ventricle.

Mechanism of action of beta-blocking agents in heart failure

Antiadrenergic treatment is currently an emerging and very promising approach to the treatment of chronic heart failure. Although the adrenergic nervous system can be pharmacologically inhibited at multiple levels, it is the use of receptor-blocking agents that has generated the most interest and provided the most data for the "proof of concept" of this approach. In part because antiadrenergic treatment of chronic heart failure has developed in an atmosphere in which it was initially considered to be contraindicated (i.e., before Phase III clinical trials could be initiated), a large body of hypothesis-driven basic and clinical investigation was required to define the overall rationale and demonstrate feasibility. This article will review these data and propose a single primary mechanism of action to explain most of the clinical benefits of these agents.

Changes in gene expression in the intact human heart. Downregulation of alpha-myosin heavy chain in hypertrophied, failing ventricular myocardium

Using quantitative RT-PCR in RNA from right ventricular (RV) endomyocardial biopsies from intact nonfailing hearts, and subjects with moderate RV failure from primary pulmonary hypertension (PPH) or idiopathic dilated cardiomyopathy (IDC), we measured expression of genes involved in regulation of contractility or hypertrophy. Gene expression was also assessed in LV (left ventricular) and RV free wall and RV endomyocardium of hearts from end-stage IDC subjects undergoing heart transplantation or from nonfailing donors. In intact failing hearts, downregulation of beta1-receptor mRNA and protein, upregulation of atrial natriuretic peptide mRNA expression, and increased myocyte diameter indicated similar degrees of failure and hypertrophy in the IDC and PPH phenotypes. The only molecular phenotypic difference between PPH and IDC RVs was upregulation of beta2-receptor gene expression in PPH but not IDC. The major new findings were that (a) both nonfailing intact and explanted human ventricular myocardium expressed substantial amounts of alpha-myosin heavy chain mRNA (alpha-MHC, 23-34% of total), and (b) in heart failure alpha-MHC was downregulated (by 67-84%) and beta-MHC gene expression was upregulated. We conclude that at the mRNA level nonfailing human heart expresses substantial alpha-MHC. In myocardial failure this alteration in gene expression of MHC isoforms, if translated into protein expression, would decrease myosin ATPase enzyme velocity and slow speed of contraction.

Myosin heavy chain gene expression in human heart failure

Two isoforms of myosin heavy chain (MyHC), alpha and beta, exist in the mammalian ventricular myocardium, and their relative expression is correlated with the contractile velocity of cardiac muscle. Several pathologic stimuli can cause a shift in the MyHC composition of the rodent ventricle from alpha- to beta-MyHC. Given the potential physiological consequences of cardiac MyHC isoform shifts, we determined MyHC gene expression in human heart failure where cardiac contractility is impaired significantly. In this study, we quantitated the relative amounts of alpha- and beta-MyHC mRNA in the left ventricular free walls (LVs) of 14 heart donor candidates with no history of cardiovascular disease or structural cardiovascular abnormalities. This group consisted of seven patients with nonfailing (NF) hearts and seven patients with hearts that exhibited donor heart dysfunction (DHD). These were compared with 19 patients undergoing cardiac transplantation for chronic end-stage heart failure (F). The relative amounts of alpha-MyHC mRNA to total (i.e., alpha + beta) MyHC mRNA in the NF- and DHD-LVs were surprisingly high compared with previous reports (33.3+/-18.9 and 35.4+/-16.5%, respectively), and were significantly higher than those in the F-LVs, regardless of the cause of heart failure (2.2+/-3.5%, P < 0.0001). There was no significant difference in the ratios in NF- and DHD-LVs. Our results demonstrate that a considerable amount of alpha-MyHC mRNA is expressed in the normal heart, and is decreased significantly in chronic end-stage heart failure. If protein and enzymatic activity correlate with mRNA expression, this molecular alteration may be sufficient to explain systolic dysfunction in F-LVs, and therapeutics oriented towards increasing alpha-MyHC gene expression may be feasible.

Safety and efficacy of carvedilol in severe heart failure. The U.S. Carvedilol Heart Failure Study Group

BACKGROUND

Many patients remain markedly symptomatic despite optimal current therapy for heart failure. Beta-blockers have often been viewed as contraindicated in this group because of their potential adverse short-term effects on cardiac function.

METHODS AND RESULTS

One hundred thirty-one patients with severe congestive heart failure were enrolled into a double-blind, placebo-controlled study of the vasodilating beta-blocker carvedilol. All patients had symptomatic, advanced heart failure while on standard triple therapy, as evidenced by a mean ejection fraction of 0.22, marked reduction in distance traveled in a 6-minute corridor walk test, and severe impairment in quality of life measured by the Minnesota Living With Heart Failure Questionnaire. After a 2-week, open-label test of 6.25 mg twice daily carvedilol, 105 patients were randomized (2:1) to receive either carvedilol (up to 25 mg twice daily, n = 70) or matching placebo (n = 35) for 6 months while background therapy with digoxin, diuretics, and an angiotensin-converting enzyme inhibitor remained constant. Ten patients (8%) did not complete the open-label period because of adverse events and 11.4% in both the carvedilol and placebo groups dropped out in the double-blind phase. The study was terminated early by the Data Safety and Monitoring Board and follow-up evaluation was therefore aborted before the projected number of patients and follow-up time was achieved. Quality of life, which was the primary endpoint, improved similarly in the carvedilol and placebo groups, whereas the global assessment by the physicians and the patient exhibited a better response to carvedilol (P < .05). Hospitalization and mortality rate were too low to evaluate a difference, and exercise time and New York Heart Association classification did not change significantly in response to the drug. Left ventricular ejection fraction rose significantly (+0.09) in the carvedilol group compared with the placebo group (+0.02, P = .004).

CONCLUSION

The beta-blocker carvedilol can be safely employed in patients with severe heart failure. Improved left ventricular function with a trend for some improvement in symptoms combined with the experience with the drug in the larger population of less severe patients in this multicenter trial suggests that carvedilol may have a favorable long-term effect in heart failure of diverse severity.