Hemodynamic and energetic comparison of bucindolol and metoprolol for the treatment of congestive heart failure

Exploring Sex Differences of Beta-Blockers in the Treatment of Hypertension: A Systematic Review and Meta-Analysis

AIMS

In the prevention of cardiovascular morbidity and mortality, early recognition and adequate treatment of hypertension are of leading importance. However, the efficacy of antihypertensives may be depending on sex disparities. Our objective was to evaluate and quantify the sex-diverse effects of beta-blockers (BB) on hypertension and cardiac function. We focussed on comparing hypertensive female versus male individuals.

METHODS AND RESULTS

A systematic search was performed for studies on BBs from inception to May 2020. A total of 66 studies were included that contained baseline and follow up measurements on blood pressure (BP), heart rate (HR), and cardiac function. Data also had to be stratified for sex. Mean differences were calculated using a random-effects model. In females as compared to males, BB treatment decreased systolic BP 11.1 mmHg (95% CI, -14.5; -7.8) vs. 11.1 mmHg (95% CI, -14.0; -8.2), diastolic BP 8.0 mmHg (95% CI, -10.6; -5.3) vs. 8.0 mmHg (95% CI, -10.1; -6.0), and HR 10.8 beats per minute (bpm) (95% CI, -17.4; -4.2) vs. 9.8 bpm (95% CI, -11.1; -8.4)), respectively, in both sexes' absolute and relative changes comparably. Left ventricular ejection fraction increased only in males (3.7% (95% CI, 0.6; 6.9)). Changes in left ventricular mass and cardiac output (CO) were only reported in males and changed -20.6 g (95% CI, -56.3; 15.1) and -0.1 L (95% CI, -0.5; 0.2), respectively.

CONCLUSIONS

BBs comparably lowered BP and HR in both sexes. The lack of change in CO in males suggests that the reduction in BP is primarily due to a decrease in vascular resistance. Furthermore, females were underrepresented compared to males. We recommend that future research should include more females and sex-stratified data when researching the treatment effects of antihypertensives.

Targeting Adrenergic Receptors in Metabolic Therapies for Heart Failure

The heart has a reduced capacity to generate sufficient energy when failing, resulting in an energy-starved condition with diminished functions. Studies have identified numerous changes in metabolic pathways in the failing heart that result in reduced oxidation of both glucose and fatty acid substrates, defects in mitochondrial functions and oxidative phosphorylation, and inefficient substrate utilization for the ATP that is produced. Recent early-phase clinical studies indicate that inhibitors of fatty acid oxidation and antioxidants that target the mitochondria may improve heart function during failure by increasing compensatory glucose oxidation. Adrenergic receptors (α₁ and β) are a key sympathetic nervous system regulator that controls cardiac function. β-AR blockers are an established treatment for heart failure and α_1A-AR agonists have potential therapeutic benefit. Besides regulating inotropy and chronotropy, α₁- and β-adrenergic receptors also regulate metabolic functions in the heart that underlie many cardiac benefits. This review will highlight recent studies that describe how adrenergic receptor-mediated metabolic pathways may be able to restore cardiac energetics to non-failing levels that may offer promising therapeutic strategies.

Sex-dependent changes in physical, mental, and quality of life outcomes in metoprolol-treated Chinese chronic heart failure patients

This study assessed sex differences in cardiac and motor functions, quality of life (QoL), and mental status in Chinese chronic heart failure (CHF) patients after metoprolol treatment.This single-center prospective study, conducted from February 2013 to April 2016, included CHF patients (men and women) with resting heart rate (HR) >80 beats/min using metoprolol continuous release tablets. Metoprolol-induced changes in cardiac and motor functions, QoL, and mental status at 1, 3, 6, 9, and 12 months from baseline, within and between the sexes, were analyzed. Descriptive data were represented as counts, percentages, and mean ± standard deviation. Differences at various follow-up periods were compared using repeated measures one-way analysis of variance, followed by post hoc Dunnett's multiple comparison test. Statistical significance was considered at P < .05.Compared with men, women reported significantly higher systolic blood pressure (SBP) (122.28 ± 6.76 vs 125.47 ± 6.67 mm Hg, P < .05) and Veterans Specific Activity Questionnaire score (8.16 ± 0.98 vs 8.47 ± 0.89, P = .05) at 12 months. Men reported higher Hospital Anxiety and Depression Scale scores for depression than women at 1 month (10.27 vs 8.83, P < .05) and for anxiety at 12 months (8.4 vs 7.72, P < .05). Metoprolol significantly decreased HR and Minnesota Living with Heart Failure Questionnaire score in men (64.5 ± 3.13 and 53.7 ± 8.00) and women (65.38 ± 3.32 and 53.85 ± 8.42, respectively). Ejection fraction (%, men: 50.00 ± 4.45, women: 50.72 ± 4.09), cardiac index (L/min/m, men: 2.70 ± 0.25, women: 2.78 ± 0.23), 6-minute walk test distance (m, men: 414.41 ± 20.84, women: 420.34 ± 20.35), and short form-8 questionnaire scores (men: 52.05 ± 1.94, women: 52.19 ± 2.58) increased significantly in both the sexes (P < .001 for all) at 12 months. Copenhagen Burnout Inventory score significantly increased in men (mean score 62.43, P < .05).Metoprolol treatment improves cardiac and motor functions, QoL, and anxiety scores but causes greater depression and burnout in men and women. Sex was seen to affect mental status of CHF patients the most.

Bucindolol: a pharmacogenomic perspective on its use in chronic heart failure

Bucindolol is a non-selective β-adrenergic receptor blocker with α-1 blocker properties and mild intrinsic sympatholytic activity. The Beta-Blocker Evaluation of Survival Trial (BEST), which is the largest clinical trial of bucindolol in patients with heart failure, was terminated prematurely and failed to show an overall mortality benefit. However, benefits on cardiac mortality and re-hospitalization rates were observed in the BEST trial. Bucindolol has not shown benefits in African Americans, those with significantly low ejection fraction and those in NYHA class IV heart failure. These observations could be due to the exaggerated sympatholytic response to bucindolol in these sub-groups that may be mediated by genetic polymorphisms or changes in gene regulation due to advanced heart failure. This paper provides a timely clinical update on the use of bucindolol in chronic heart failure.

Comparison of Metoprolol With Low, Middle and High Doses of Carvedilol in Prevention of Postinfarction Left Ventricular Remodeling in Rats

The dose-related beneficial effects of carvedilol on survival in heart failure have been verified, however, the effects on left ventricular remodeling (LVRM) after acute myocardial infarction (AMI) have not been defined. This experiment was designed to compare the effects of low, middle, and high doses of carvedilol (LD-car, MD-car, and HD-car) with metoprolol (Meto) in preventing postinfarction LVRM in rats. After the left coronary artery was ligated, 177 surviving female SD rats were randomized to: (1) AMI (n = 35), (2) LD-car (0.1 mg x kg(-1) x d(-1), n = 35), (3) MD-car (1 mg x kg(-1) x d(-1), n = 35), (4) HD-car (10 mg x kg(-1) x d(-1), n = 37) and (5) Meto (2 mg x kg(-1) x d(-1), n = 35) groups. A sham-operated group (n = 16) was also randomly selected. Gastric gavage therapy lasted for 4 weeks. After hemodynamic studies, the rat hearts were fixed and pathologically analyzed. After exclusion of rats which died or had an infarct size < 35% or > 55%, complete data were obtained in 69 rats, comprising AMI (n = 11), LD-car (n = 11), MD-car (n = 12), HD-car (n = 12), Meto (n = 11) and sham (n = 12) groups. There were no significant differences in MI size among the five AMI groups (44.5-46.3%, all P > 0.05). Compared with the sham group, left ventricular (LV) end-diastolic pressure (LVEDP), volume (LVV), weight (LVW) and septal thickness (STh) were all significantly increased, while +/- dp/dt was significantly decreased in the AMI group (all P < 0.001). Compared with the AMI group, heart rate was significantly decreased in all except the LD-car treatment groups (P < 0.05-0.01); LVEDP, LVV, LVW, and STh in the four treatment groups were also significantly decreased (P < 0.05-0.001) except LVW and STh in the Meto group (both P > 0.05)(LVEDP: 14.5 +/- 4.6, 12.1 +/- 2.4, 7.7 +/- 1.9 and 13.0 +/- 6.7 mmHg vs 24.1 +/- 5.2 mmHg; LVV: 0.82 +/- 0.1, 0.79 +/- 0.1, 0.72 +/- 0.1 and 0.72 +/- 0.1 mL vs 0.92 +/- 0.1 mL; LVW: 666 +/- 57, 622 +/- 70, 589 +/- 57 and 699 +/- 78 mg vs 730 +/- 79 mg; STh: 1.14 +/- 0.12, 1.18 +/- 0.21, 1.19 +/- 0.15 and 1.35 +/- 0.20 mm vs 1.33 +/- 0.29 mm; P < 0.05-0.001); while +/- dp/dt was significantly increased in each therapy group (P < 0.05-0.001). There were dose-effect relations in LVEDP and LVV in the carvedilol groups. The results indicate that low, middle and high dose carvedilol has dose-related effects in the prevention of postinfarction LVRM with respect to volume expansion and segmental hypertrophy in rats, while metoprolol prevents only LV dilatation but not hypertrophy.

Bucindolol displays intrinsic sympathomimetic activity in human myocardium

BACKGROUND

Most clinical studies have shown that beta-adrenergic receptor antagonists improve long-term survival in heart failure patients. Bucindolol, a nonselective beta-receptor blocker, however, failed to reduce heart failure mortality in a recent large clinical trial. The reasons for this failure are not known. Bucindolol has partial agonist properties in rat myocardium, but whether it has agonist activity in human heart is controversial. To address this, we measured the ability of bucindolol to increase cAMP accumulation in human myocardium.

METHODS AND RESULTS

Myocardial strips ( approximately 1 mm(3)) obtained from rat and nonfailing human hearts were confirmed to be viable for > or = 48 hours in normoxic tissue culture by MTT assay and histology. Freshly isolated strips were exposed to beta-adrenergic antagonists and agonists and assayed for cAMP. In both rat and human strips, the full beta-adrenergic agonist isoproterenol raised cAMP levels by >2.5-fold at 15 minutes. Carvedilol and propranolol had no effect on basal cAMP levels, whereas metoprolol reduced basal cAMP by approximately 25%. In contrast, bucindolol and xamoterol increased cAMP levels in a concentration-dependent manner in both rat and human myocardium (maximum 1.64+/-0.25-fold and 2.00+/-0.27-fold over control, respectively, P<0.01 for human tissue).

CONCLUSIONS

Bucindolol exhibits approximately 60% of the beta-adrenergic agonist activity of xamoterol in normal human myocardial tissue.

A new aspect of view in synthesizing new type beta-adrenoceptor blockers with ancillary antioxidant activities

A series of vanilloid-type beta-adrenoceptor blockers derived from antioxidant traditional Chinese herbal medicines were synthesized and tested for their antioxidant and adrenoceptor antagonistic activities. They all possessed significant beta-adrenoceptor blocking activities under in vitro experiments and radioligand binding assays. In addition, some compounds were further examined in in vivo tests and produced antagonist effects matching that of propranolol and labetalol by measurements of antagonism toward (-)isoproterenol-induced tachycardia and (-)phenylephrine-induced pressor responses in anesthetized rats. Furthermore, all of the compounds had antioxidant effects inherited from their original structures. In conclusion, compound 11 had the most potent beta-adrenoceptors blocking activity, 12 and 13 possessed high cardioselectivity, whereas 14, 15 and 16 possessed additional alpha-adrenoceptor blocking activity and 15 is the most effective antioxidant of all. The antioxidant activity may be due to their alpha and beta unsaturated side chain at position 1 and ortho-substituted methoxy moiety on 4-phenoxyethylamine.

Myocardial Free Fatty Acid and Glucose Use After Carvedilol Treatment in Patients With Congestive Heart Failure

Background —Use of β-adrenoreceptor blockade in the treatment of heart failure has been associated with a reduction in myocardial oxygen consumption and an improvement in myocardial energy efficiency. One potential mechanism for this beneficial effect is a shift in myocardial substrate use from increased free fatty acid (FFA) oxidation to increased glucose oxidation.

Methods and Results —We studied the effect of carvedilol therapy on myocardial FFA and glucose use in 9 patients with stable New York Heart Association functional class III ischemic cardiomyopathy (left ventricular ejection fraction ≤35%) using myocardial positron emission tomography studies and resting echocardiograms before and 3 months after carvedilol treatment. Myocardial uptake of the novel long chain fatty acid metabolic tracer 14(R, S)-[ 18 F]fluoro-6-thia-heptadecanoic acid ([ 18 F]-FTHA) was used to determine myocardial FFA use, and [ 18 F]fluoro-2-deoxy-glucose ([ 18 F]-FDG) was used to determine myocardial glucose use. After carvedilol treatment, the mean myocardial uptake rate for [ 18 F]-FTHA decreased (from 20.4±8.6 to 9.7±2.3 mL · 100 g –1 · min –1 ; P <0.005), mean fatty acid use decreased (from 19.3±7.0 to 8.2±1.8 μmoL · 100 g –1 · min –1 ; P <0.005), the mean myocardial uptake rate for [ 18 F]-FDG was unchanged (from 1.4±0.4 to 2.4±0.8 mL · 100 g –1 · min –1 ; P =0.14), and mean glucose use was unchanged (from 11.1±3.1 to 18.7±6.0 μmoL · 100 g –1 · min –1 ; P =0.12). Serum FFA and glucose concentrations were unchanged, and mean left ventricular ejection fraction improved (from 26±2% to 37±4%; P <0.05).

Conclusions —Carvedilol treatment in patients with heart failure results in a 57% decrease in myocardial FFA use without a significant change in glucose use. These metabolic changes could contribute to the observed improvements in energy efficiency seen in patients with heart failure.

Beta-blockade therapy in chronic heart failure: diastolic function and mitral regurgitation improvement by carvedilol

BACKGROUND

In patients with chronic heart failure, the use of carvedilol therapy induces clinical and hemodynamic improvement. However, although the benefits of this beta-blocker have been established in patients with chronic heart failure, the mechanisms underlying them and the changes in left ventricular systolic function, diastolic function, and mitral regurgitation during long-term therapy remain unclear.

OBJECTIVE

To identify the clinical and functional effects of carvedilol, focusing on diastolic function and mitral regurgitation variations.

METHODS

Forty-five consecutive patients with chronic heart failure (ejection fraction 24% +/- 7%), 17 with dilated ischemic and 28 with nonischemic cardiomyopathy, were treated with carvedilol (mean dose 44 +/- 30 mg) and matched for clinical (New York Heart Association functional class and heart failure duration) and hemodynamic (cardiac index and pulmonary wedge pressure) characteristics to a control group. Clinical and echocardiographic variables were measured in the 2 groups at baseline and after 6 months and the results compared.

RESULTS

After 6 months of treatment with carvedilol, left ventricular ejection fraction had increased from 24% +/- 7% to 29% +/- 9% (P <.0001); this change was caused by a reduction in end-systolic volume index (106 +/- 41 vs 93 +/- 37 mL/m(2); P <. 0001). Deceleration time of early diastolic filling increased (134 +/- 74 vs 196 +/- 63 ms; P <.0001). Seventeen of the 27 patients with demonstrated improvement of left ventricular diastolic filling moved from having a restrictive filling pattern to having a normal or pseudonormal left ventricular filling pattern. In the control group, no significant changes in deceleration time of early diastolic filling were found (139 +/- 74 vs 132 +/- 45 ms; P = not significant). The effective regurgitant orifice area decreased significantly in the carvedilol group but not in the control group. These changes were associated with a significant reduction of the mitral regurgitant stroke volume in the carvedilol group (50 +/- 25 vs 16 +/- 13 mL; P <.0001) but not in the control group (57 +/- 29 vs 47 +/- 24 mL; P = not significant). These changes of mitral regurgitation were closely associated with significant improvement of forward aortic stroke volume (r = -.57, P <.0001). These findings were not observed in patients in the control group.

CONCLUSIONS

The results of this study show that long-term carvedilol therapy in patients with chronic heart failure was able to prevent or partially reverse progressive left ventricular dilatation. The effects on left ventricular remodeling were associated with a concomitant recovery of diastolic reserve and a decrease of mitral regurgitation, which have been demonstrated to be powerful prognostic predictors in such patients. Overall these findings provide important insights into the pathophysiologic mechanisms by which carvedilol improves the clinical course of patients with chronic heart failure.

Effect of selective versus nonselective beta blockade on QT dispersion in patients with nonischemic dilated cardiomyopathy

We retrospectively examined the electrocardiograms in all of our patients with nonischemic dilated cardiomyopathy and normal sinus rhythm before and after at least 3 months of metoprolol (n = 12), bucindolol (n = 8), carvedilol (n = 6), or no beta blocker (n = 9). Both beta1-selective and nonselective beta-adrenergic blockade reduced QTc dispersion equally in patients with dilated cardiomyopathy.

Eugenodilol: a third-generation beta-adrenoceptor blocker, derived from eugenol, with alpha-adrenoceptor blocking and beta2-adrenoceptor agonist-associated vasorelaxant activities

Eugenodilol, derived from natural eugenol, was first investigated with in vivo and in vitro models. In our in vivo study, eugenodilol (0.5, 1.0, and 1.5 mg/kg, i.v.) produced dose-dependent hypotensive and bradycardic responses in pentobarbital-anesthetized Wistar rats. Eugenodilol also inhibited the tachycardia and arterial pressor effects induced by (-)isoproterenol and phenylephrine, respectively. In our in vitro study, eugenodilol competitively antagonized (-)isoproterenol-induced positive inotropic and chronotropic effects and tracheal-relaxation responses on isolated guinea pig tissues in a concentration-dependent manner. The apparent pA2 values were 7.88+/-0.12 for right atria, 7.52+/-0.05 for left atria, and 7.33+/-0.15 for trachea, indicating that eugenodilol was a nonselective beta-adrenoceptor blocker. In thoracic aorta experiments, the apparent pA2 values of alpha-adrenoceptor blockade were 7.05+/-0.25 and 6.87+/-0.08 for eugenodilol and labetalol, respectively. In addition, eugenodilol produced cumulative relaxation responses on isolated guinea pig tracheal strips. The effects were competitively antagonized by ICI 118,551 (10(-8)-10(-6) M), a relatively selective beta2-adrenoceptor antagonist. In the radioligand-binding assay, the Ki values of [3H]CGP-12177 binding to rat ventricle and lung membranes were 9.72 and 48.29 nM, respectively, and the value of [3H]prazosin binding to rat brain membrane was 38.72 nM. These results further confirmed the alpha/beta-adrenoceptors-blocking activities of eugenodilol reported in the functional studies. We conclude that eugenodilol is a novel third-generation beta-adrenoceptor blocker with ancillary blocking activity at alpha-adrenoceptors and weak sympathomimetic activity at beta2-adrenoceptors.

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.

Ejection fraction improvement by beta-blocker treatment in patients with heart failure: an analysis of studies published in the literature

Because ejection fraction (EF) is one of the most important predictors of survival in patients with left ventricular (LV) dysfunction and because Packer showed a large reduction in mortality figures with carvedilol, in contrast to former studies with bisoprolol and metoprolol, we investigated if this difference in survival may be related to a difference in improvement of LV function by different beta-blockers. We searched the MEDLINE database and all reference lists of articles obtained through the search for the relation between beta-blocker treatment and improvement in EF. Forty-one studies met the criteria and we added two of our own studies. Four hundred and fifty-eight patients were treated with metoprolol with a mean follow-up of 9.5 months and a mean increase in EF of 7.4 EF units. One thousand thirty patients were treated with carvedilol with a mean follow up of 7 months and a mean increase in EF of 5.7 EF units. One hundred ninety-nine patients were treated with bucindolol with a mean follow-up of 4 months and a mean increase in EF of 4.6 EF units. Several small studies with nebivolol, atenolol, and propranolol were also studied and, when combined, the mean increase in EF was 8.6 EF units. When patients with idiopathic and ischemic cardiomyopathies were compared, the average increase in EF units was 8.5 vs. 6.0, respectively. The use of beta-blocker treatment in heart failure patients, irrespective of the etiology, improved LV function in almost all studies and it appears that the differences among beta-blockers and among etiologies is small and probably insignificant. However, there is a difference in survival rate when the various beta-blockers are compared, suggesting that mechanisms other than improvement of LV function by beta-blockers are responsible for the difference in survival.

Beta-receptor blockade decreases carnitine palmitoyl transferase I activity in dogs with heart failure

BACKGROUND

Pharmacological inhibition of carnitine palmitoyl transferase I (CPT-I), the enzyme controlling the rate of fatty acid transport into the mitochondria, prevents the contractile dysfunction, myosin isozyme shift and deterioration in sarcoplasmic reticulum Ca2+ handling that occurs in rat models of left ventricular hypertrophy. In this study we examine whether the improved cardiac function with beta blockade therapy in heart failure is associated with an alteration in CPT-I activity.

METHODS AND RESULTS

We examined dogs with coronary microembolism-induced heart failure treated for 12 weeks with metoprolol (25 mg twice daily). Myocardial activities of CPT-I, medium-chain acyl co-enzyme A dehydrogenase (MCAD, a beta-oxidation enzyme), citrate synthase, and triglyceride content were measured. The progressive decrease in cardiac function was prevented by treatment with metoprolol, as reflected by an improved ejection fraction over 12 weeks in the metoprolol group (from 35% to 40%) compared to the untreated heart failure dogs (decrease from 36% to 26%). Dogs treated with metoprolol had a marked decrease in CPT-I activity (0.46 +/- 0.03 vs. 0.64 +/- 0.02 micromol min(-1) g(-1) wet weight; P < .02) along with an increase in triglyceride concentration compared to untreated heart failure dogs (3.9 +/- 0.3 v 4.9 +/- 0.2 micromol/g wet weight, respectively; P < .003). By contrast, MCAD and citrate synthase activities did not change.

CONCLUSION

Metoprolol induced a decrease in CPT-I activity and an increase in triglyceride content. These results suggest that the improved function observed with beta blockers in heart failure could be due, in part, to a decrease in CPT-I activity and less fatty acid oxidation by the heart.

A review of why and how we may use beta-blockers in congestive heart failure

The history of the use of beta-blockers for congestive heart failure, beginning with the innovative seminal study by the Swedish group in 1975 to studies in 1995, is reviewed and shows that almost all trials favored the use of beta-blockers. They tended to demonstrate an increase in ejection fraction, a decrease in left ventricular mass, and in some studies, even a decrease in mortality. Even after the introduction of angiotensin-converting enzyme inhibitors, additional improvement in function and mortality was observed. Patients with nonischemic dilated cardiomyopathy derived more benefit from beta-blockers than did patients with ischemic cardiomyopathy. Least likely to benefit were patients treated for <2 months, patients with alcoholic cardiomyopathy, and those with marked intercellular fibrosis. Although the starting dose of metoprolol, the most common beta-blocker used, may have to be as low as 2.5 mg/d, mortality analysis failed to show a decrease in sudden death unless the dose was raised to about 300 mg/d, a dose at which beta-selectivity is generally not expected to be present. The non-beta-specific bucindolol or carvedilol may ultimately be preferred to metoprolol because they are better tolerated initially due to a slight vasodilatation effect. Initial studies with carvedilol showed remarkable promise in reducing mortality. However, these agents cannot yet be said to have been studied adequately.

Comparative hemodynamic, left ventricular functional, and antiadrenergic effects of chronic treatment with metoprolol versus carvedilol in the failing heart

BACKGROUND

The basic pharmacology of the third-generation beta-blocking agent carvedilol differs considerably from second-generation compounds such as metoprolol. Moreover, carvedilol may produce different, ie, more favorable, clinical effects in chronic heart failure. For these reasons, we compared the effects of carvedilol and metoprolol on adrenergic activity, receptor expression, degree of clinical beta-blockade, hemodynamics, and left ventricular function in patients with mild or moderate chronic heart failure.

METHODS AND RESULTS

The effects of carvedilol versus metoprolol were compared in two concurrent placebo-controlled trials with carvedilol or metoprolol that had common substudies focused on adrenergic, hemodynamic, and left ventricular functional measurements. All subjects in the substudies had chronic heart failure resulting from idiopathic dilated cardiomyopathy. Carvedilol at 50 to 100 mg/d produced reductions in exercise heart rate that were similar to metoprolol at 125 to 150 mg/d, indicating comparable degrees of beta-blockade. Compared with metoprolol, carvedilol was associated with greater improvement in New York Heart Association functional class. Although there were no significant differences in hemodynamic effects between the carvedilol and metoprolol active-treatment groups, carvedilol tended to produce relatively greater improvements in left ventricular ejection fraction, stroke volume, and stroke work compared with changes in the respective placebo groups. Carvedilol selectively lowered coronary sinus norepinephrine levels, an index of cardiac adrenergic activity, whereas metoprolol did not lower coronary sinus norepinephrine and actually increased central venous norepinephrine levels. Finally, metoprolol was associated with an increase in cardiac beta-receptor density, whereas carvedilol did not change cardiac beta-receptor expression.

CONCLUSIONS

The third-generation beta-blocking agent carvedilol has substantially different effects on left ventricular function, hemodynamics, adrenergic activity, and beta-receptor expression than dose the second-generation compound metoprolol. Some or all of these differences may explain the apparent differences in clinical results between the two compounds.