Electrophysiologic Effects of Carvedilol: Is Carvedilol an Antiarrhythmic Agent?

Effect of Carvedilol vs Metoprolol on Atrial and Ventricular Arrhythmias Among Implantable Cardioverter-Defibrillator Recipients

BACKGROUND

Both selective and nonselective beta-blockers are used to treat patients with heart failure (HF). However, the data on the association of beta-blocker type with risk of atrial arrhythmia and ventricular arrhythmia (VA) in HF patients with a primary prevention implantable cardioverter-defibrillator (ICD) are limited.

OBJECTIVES

This study sought to evaluate the effect of metoprolol vs carvedilol on the risk of atrial tachyarrhythmia (ATA) and VA in HF patients with an ICD.

METHODS

This study pooled primary prevention ICD recipients from 5 landmark ICD trials (MADIT-II, MADIT-CRT, MADIT-RIT, MADIT-RISK, and RAID). Fine and Gray multivariate regression models, stratified by study, were used to evaluate the risk of ATA, inappropriate ICD shocks, and fast VA (defined as ventricular tachycardia ≥200 beats/min or ventricular fibrillation) by beta-blocker type.

RESULTS

Among 4,194 patients, 2,920 (70%) were prescribed carvedilol and 1,274 (30%) metoprolol. The cumulative incidence of ATA at 3.5 years was 11% in patients treated with carvedilol vs 15% in patients taking metoprolol (P = 0.003). Multivariate analysis showed that carvedilol treatment was associated with a 35% reduction in the risk of ATA (HR: 0.65; 95% CI: 0.53-0.81; P < 0.001) when compared to metoprolol, and with a corresponding 35% reduction in the risk of inappropriate ICD shocks (HR: 0.65; 95% CI: 0.47-0.89; P = 0.008). Carvedilol vs metoprolol was also associated with a 16% reduction in the risk of fast VA. However, these findings did not reach statistical significance (HR: 0.84; 95% CI: 0.70-1.02; P = 0.085).

CONCLUSIONS

These findings suggests that HF patients with ICDs on carvedilol treatment experience a significantly lower risk of ATA and inappropriate ICD shocks when compared to treatment with metoprolol.

Differential Effects of the Betablockers Carvedilol, Metoprolol and Bisoprolol on Cardiac Kv4.3 (Ito) Channel Isoforms

Cardiac Kv4.3 channels contribute to the transient outward K+ current, Ito, during early repolarization of the cardiac action potential. Two different isoforms of Kv4.3 are present in the human ventricle and exhibit differential remodeling in heart failure (HF). Cardioselective betablockers are a cornerstone of HF with reduced ejection fraction therapy as well as ventricular arrhythmia treatment. In this study we examined pharmacological effects of betablockers on both Kv4.3 isoforms to explore their potential for isoform-specific therapy. Kv4.3 isoforms were expressed in Xenopus laevis oocytes and incubated with the respective betablockers. Dose-dependency and biophysical characteristics were examined. HEK 293T-cells were transfected with the two Kv4.3 isoforms and analyzed with Western blots. Carvedilol (100 µM) blocked Kv4.3 L by 77 ± 2% and Kv4.3 S by 67 ± 6%, respectively. Metoprolol (100 µM) was less effective with inhibition of 37 ± 3% (Kv4.3 L) and 35 ± 4% (Kv4.3 S). Bisoprolol showed no inhibitory effect. Current reduction was not caused by changes in Kv4.3 protein expression. Carvedilol inhibited Kv4.3 channels at physiologically relevant concentrations, affecting both isoforms. Metoprolol showed a weaker blocking effect and bisoprolol did not exert an effect on Kv4.3. Blockade of repolarizing Kv4.3 channels by carvedilol and metoprolol extend their pharmacological mechanism of action, potentially contributing beneficial antiarrhythmic effects in normal and failing hearts.

Comparison of new-onset post-operative atrial fibrillation between patients receiving carvedilol and metoprolol after off-pump coronary artery bypass graft surgery

OBJECTIVE

Post-operative atrial fibrillation (POAF) is a common complication of coronary artery bypass graft (CABG) surgery. Previous studies suggest carvedilol is more effective than metoprolol in preventing POAF in on-pump CABG. This study investigated if the same benefit would be seen in off-pump CABG.

METHODS

This single-center, retrospective review compared rates of new-onset POAF between adult patients who received carvedilol and metoprolol after off-pump CABG surgery. Safety endpoints included hypotension, bradycardia, dyspnea, and the composite. Multivariate logistic regression was conducted to identify associations between demographics, potential confounders, and beta-blocker dose and POAF. Kaplan-Meier plots and Cox proportional-hazards models examined differences in time-to-event for POAF.

RESULTS

134 patients were included (34 carvedilol and 100 metoprolol). The mean age was 63 years, 70.9% were male, 85% had history of hypertension, 3.7% had history of heart failure with reduced ejection fraction, and 38.8% were taking beta blockers prior to admission. POAF developed in 2 patients (5.8%) in the carvedilol group and 24 patients (24.0%) in the metoprolol group (odds ratio 0.17 [95% CI 0.03-0.83], p = 0.023). Safety endpoints occurred in 10 carvedilol (29.4%) and 44 metoprolol (44.0%) patients (p = 0.134). Hypotension and dyspnea rates were similar between groups; bradycardia occurred more commonly among metoprolol-treated patients (p = 0.040). Time-to-event analyses revealed a hazard ratio = 0.22 (95% CI 0.05-0.93, p = 0.040) for carvedilol use.

CONCLUSIONS

In this single-center, retrospective study of off-pump CABG patients, carvedilol was associated with reduced POAF risk and enhanced safety compared to metoprolol.

Oxidative status, inflammation, and postoperative atrial fibrillation with metoprolol vs carvedilol or carvedilol plus N-acetyl cysteine treatment

BACKGROUND

Atrial fibrillation is associated with inflammation and oxidative stress.

HYPOTHESIS

Carvedilol and N-acetyl cysteine (NAC) combination decreases inflammation, oxidative stress, and postoperative atrial fibrillation (POAF) rates more than metoprolol or carvedilol.

METHODS

Preoperative and postoperative total oxidative stress (TOS), total antioxidant capacity (TAC), and white blood cells (WBC) were measured in metoprolol, carvedilol, or carvedilol plus NAC groups, and association with POAF was evaluated.

RESULTS

Preoperative TAC, TOS, and WBC levels were similar among the groups. Postoperative TAC levels were lower in the metoprolol group compared with the carvedilol group (1.0 vs 1.4) or the carvedilol plus NAC group (1.0 vs 1.9) and were also lower in the carvedilol group compared with the carvedilol plus NAC group (all P < 0.0001). Postoperative TOS levels were higher in the metoprolol group as compared with the carvedilol (29.6 vs 24.2; P < 0.0001) or the carvedilol plus NAC groups (P < 0.0001), and were also higher in the carvedilol group as compared with the carvedilol plus NAC group (24.2 vs 19.3; P < 0.0001). Postoperative WBC counts were lower in the carvedilol plus NAC group compared with the metoprolol group (12.9 vs 14.8; P = 0.004), were similar between the carvedilol and the metoprolol groups (13 vs 14.8) and between the carvedilol plus NAC group and the carvedilol group (both P > 0.05). Postoperative TAC, TOS, and WBC were associated with POAF.

CONCLUSIONS

Carvedilol plus NAC reduced oxidative stress and inflammation compared with metoprolol and decreased oxidative stress compared with carvedilol. Postoperative TAC, TOS, and WBC were associated with POAF.

Prevention of post-coronary artery bypass grafting (CABG) atrial fibrillation: efficacy of prophylactic beta-blockers in the modern era: a meta-analysis of latest randomized controlled trials

BACKGROUND

Atrial fibrillation/flutter (AF) is a common complication of open heart surgery and ACC/AHA guidelines strongly recommend the use of prophylactic beta-blockers (BB) for its prevention. Several recent studies, however, have failed to show the desired protective effects of BB against post-coronary artery bypass grafting (CABG) AF. As the protocols of CABG, medical management of CAD (coronary artery disease) and demographic features of the patients undergoing open heart surgery have evolved significantly over the last two decades, we decided to perform a review of evidence from latest randomized controlled trials (RCTs) to confirm the efficacy of prophylactic BB.

METHODS

We searched for RCTs comparing the efficacy of prophylactic BB versus placebo/control against post-CABG AF. We limited our search to 1995 till present to reflect ongoing advancements in the protocols of CABG and the medical management of CAD. Initially, 34 trials were selected; however after certain exclusions only 10 RCTs were included in the final analysis.

RESULTS

Prophylactic BB decreased the incidence of post-CABG AF from 32.8% in the control group to 20% in the prophylactic group with risk ratio (RR) of 0.50 with 95% CI of 0.36-0.69, P value < 0.001. In a subgroup analysis, carvedilol appears to be superior to metoprolol for the prevention of postoperative AF.

CONCLUSIONS

Despite several limitations, this analysis confirms the efficacy of prophylactic BB against post-CABG AF in this era. We recommend continuing perioperative BB in the open heart surgery patients in the absence of contraindications.

Carvedilol analogue inhibits triggered activities evoked by both early and delayed afterdepolarizations

BACKGROUND

Carvedilol and its analogues suppress delayed afterdepolarizations (DADs) and catecholaminergic polymorphic ventricular tachycardias by direct action on the cardiac ryanodine receptor type 2 (RyR2).

OBJECTIVE

To test a hypothesis that carvedilol analogue may also prevent triggered activities (TAs) through the suppression of early afterdepolarizations (EADs).

METHODS

Intracellular Ca(2+) and membrane voltage were simultaneously recorded by using optical mapping technique in Langendorff-perfused mouse and rabbit hearts to study the effect of carvedilol analogue VK-II-36, which does not have significant beta-blocking effects.

RESULTS

Spontaneous intracellular Ca(2+) elevations (SCaEs) during diastole were induced by rapid ventricular pacing and isoproterenol infusion in intact rabbit ventricles. Systolic and diastolic SCaEs were simultaneously noted in Langendorff-perfused RyR2 R4496(+/-) mouse hearts after creating atrioventricular block. VK-II-36 effectively suppressed SCaEs and eliminated TAs observed in both mouse and rabbit ventricles. We tested the effect of VK-II-36 on EADs by using a rabbit model of acquired long QT syndrome, in which phase 2 and phase 3 EADs were observed in association with systolic SCaEs. VK-II-36 abolished the systolic SCaEs and phase 2 EADs, and greatly decreased the dispersion of repolarization and the amplitude of phase 3 EADs. VK-II-36 completely prevented EAD-mediated TAs in all ventricles studied.

CONCLUSIONS

A carvedilol analogue, VK-II-36, inhibits ventricular tachyarrhythmias in intact mouse and rabbit ventricles by the suppression of SCaEs, independent of beta-blocking activity. The RyR2 may be a potential target for treating focal ventricular arrhythmias triggered by either EADs or DADs.

Carvedilol blocks the cloned cardiac Kv1.5 channels in a β-adrenergic receptor-independent manner

Carvedilol, a non-selective β-adrenergic blocker, is widely used for the treatment of angina pectoris and hypertension. We examined the action of carvedilol on cloned Kv1.5 expressed in CHO cells, using the whole-cell patch clamp technique. Carvedilol reduced the peak amplitude of Kv1.5 and accelerated the inactivation rate in a concentration-dependent manner with an IC50 of 2.56 μM. Using a first-order kinetics analysis, we calculated k(+1) = 19.68 μM(-1)s(-1) for the association rate constant, and k(-1) = 44.89 s(-1) for the dissociation rate constant. The apparent K(D) (k(-1)/k(+1)) was 2.28 μM, which is similar to the IC50 value. Other β-adrenergic blockers (alprenolol, oxprenolol and carteolol) had little or no effect on Kv1.5 currents. Carvedilol slowed the deactivation time course, resulting in a tail crossover phenomenon. Carvedilol-induced block was voltage-dependent in the voltage range for channel activation, but voltage-independent in the voltage range for full activation. The voltage dependences for both steady-state activation and inactivation were unchanged by carvedilol. Carvedilol affected Kv1.5 in a use-dependent manner. When stimulation frequencies were increased to quantify a use-dependent block, however, the block by carvedilol was slightly increased with IC50 values of 2.56 μM at 0.1 Hz, 2.38 μM at 1 Hz and 2.03 μM at 2 Hz. Carvedilol also slowed the time course of recovery from inactivation of Kv1.5. These results indicate that carvedilol blocks Kv1.5 in a reversible, concentration-, voltage-, time-, and use-dependent manner, but only at concentrations slightly higher than therapeutic plasma concentrations in humans. These effects are probably relevant to an understanding of the ionic mechanism underlying the antiarrhythmic property of carvedilol.

Sudden Cardiac Death Thirty Years Ago and at Present. The Role of Autonomic Disturbances in Acute Myocardial Infarction Revisited

The most common cause of sudden cardiac death is ventricular fibrillation (VF). In addition to the status, size and location of the ventricular focus, a major pathogenic mechanism triggering VF is autonomic dysbalance (disturbance). This term refers to a wide range of reflex changes in the ratio of sympathetic to vagal ventricular activation over time, occurring immediately after coronary artery occlusion at the onset of acute myocardial infarction (AMI). Another trigger of VF is autonomic disturbance due to emotional stress. Experimental and clinical research into autonomic disturbances associated with coronary artery occlusion and emotional stress was given considerable attention as early as some 30 years ago when researchers were already searching for ways of inhibiting autonomic disturbances using predominant sympathetic and vagal activation by beta-blockers (BB) and atropine, respectively. The aim of our paper is to compare results obtained 30 years ago with current status of experimental and clinical research into SCD prevention. Another aim is to identify questions that have remained unanswered to date; answers to these outstanding questions could help further reduce the risk of SCD.

Carvedilol targets human K2P 3.1 (TASK1) K+ leak channels

BACKGROUND AND PURPOSE

Human K(2P) 3.1 (TASK1) channels represent potential targets for pharmacological management of atrial fibrillation. K(2P) channels control excitability by stabilizing membrane potential and by expediting repolarization. In the heart, inhibition of K(2P) currents by class III antiarrhythmic drugs results in action potential prolongation and suppression of electrical automaticity. Carvedilol exerts antiarrhythmic activity and suppresses atrial fibrillation following cardiac surgery or cardioversion. The objective of this study was to investigate acute effects of carvedilol on human K(2P) 3.1 (hK(2P) 3.1) channels.

EXPERIMENTAL APPROACH

Two-electrode voltage clamp and whole-cell patch clamp electrophysiology was used to record hK(2P) 3.1 currents from Xenopus oocytes, Chinese hamster ovary (CHO) cells and human pulmonary artery smooth muscle cells (hPASMC).

KEY RESULTS

Carvedilol concentration-dependently inhibited hK(2P) 3.1 currents in Xenopus oocytes (IC(50) = 3.8 µM) and in mammalian CHO cells (IC(50) = 0.83 µM). In addition, carvedilol sensitivity of native I(K2P3.1) was demonstrated in hPASMC. Channels were blocked in open and closed states in frequency-dependent fashion, resulting in resting membrane potential depolarization by 7.7 mV. Carvedilol shifted the current-voltage (I-V) relationship by -6.9 mV towards hyperpolarized potentials. Open rectification, characteristic of K(2P) currents, was not affected.

CONCLUSIONS AND IMPLICATIONS

The antiarrhythmic drug carvedilol targets hK(2P) 3.1 background channels. We propose that cardiac hK(2P) 3.1 current blockade may suppress electrical automaticity, prolong atrial refractoriness and contribute to the class III antiarrhythmic action in patients treated with the drug.

Role of drug therapy for sustained ventricular tachyarrhythmias

Antiarrhythmic drug therapy, broadly defined, is the mainstay of treatment and prevention of ventricular tachycardia (VT)/ventricular fibrillation (VF), which can lead to sudden death. This article evaluates the evidence for and appropriate use of class I antiarrhythmic drugs, class III antiarrhythmic drugs, beta-blockers, nondihydropyridine calcium-channel blockers, statins, angiotensin enzyme inhibitors, angiotensin receptor blockers, aldosterone blockers, and digoxin for antiarrhythmic benefits in patients who have a propensity for VT/VF and therefore are at risk of sudden death.

Comparison of the efficacy of metoprolol and carvedilol for preventing atrial fibrillation after coronary bypass surgery

BACKGROUND

Atrial fibrillation (AF) occurs frequently after coronary artery bypass grafting (CABG) and often results in prolonged postsurgical hospital stays and increased mortality and morbidity. Beta blockers are known to prevent postoperative AF. In this prospective study, we investigated the efficacy of carvedilol compared with metoprolol succinate in preventing postoperative AF.

METHODS

Subjects included 110 patients (31 women, 79 men; mean age, 60+/-10 years, range, 39-82 years) who had undergone CABG. Patients were randomized to receive either metoprolol or carvedilol, and all patients received the drugs 3 days prior to surgery. Metoprolol was started at 50 mg twice daily and carvedilol was started at 12.5 mg twice daily. The doses were titrated according to the patients' hemodynamic responses. All patients were monitored for 3 days after the surgery.

RESULTS

Of the 110 patients, 55 (50%) were treated with metoprolol succinate, and 55 (50%) were treated with carvedilol. Baseline characteristics and operative data of the patients did not differ between groups. During follow-up, 20 patients (36%) in the metoprolol group and 9 patients (16%) in the carvedilol group developed AF (P=0.029). Multiple stepwise logistic regression analysis showed that metoprolol use, older age, and impaired left ventricular ejection fraction were independent risk factors for developing AF, and carvedilol use was found to be independently related to sinus rhythm maintenance after CABG (P=0.02).

CONCLUSIONS

These results show that carvedilol is superior to metoprolol in decreasing development of early postoperative AF.

Beta blockers for the prevention of atrial fibrillation after coronary artery bypass surgery: carvedilol versus metoprolol

Although all beta blockers appear to be effective in the prevention of postoperative atrial fibrillation (AF) following coronary artery bypass surgery (CABG), carvedilol was found to be much more effective than metoprolol in this respect as the current study clearly delineated. We believe that the ongoing COMPACT trial will answer the question of whether or not carvedilol is more superior than metoprolol to prevent postoperative AF in patients undergoing CABG.

Predictors of Therapeutic Response to Beta-blockers in Patients with Heart Failure in Taiwan

BACKGROUND/PURPOSE

Chinese are more sensitive to beta-blockers than Caucasians. However, data regarding beta-blocker therapy in heart failure (HF) patients in Taiwan are lacking. We aimed to evaluate the improvement of left ventricular function and the potential predictors of response to beta-blocker therapy in Taiwanese HF patients.

METHODS

We enrolled 34 HF patients with baseline left ventricular ejection fraction (LVEF) </= 40%. Beta-blockers were titrated up to the maximum tolerable dose. LVEF prior to beta-blocker usage and at the stable dose were obtained. We also sequenced the entire gene encoding beta1-adrenoceptor to assess the relationships between LVEF improvement and gene polymorphisms.

RESULTS

Beta-blocker therapy (25 +/- 22 months) with a mean stable dose of 12 +/- 8 mg carvedilol/day significantly improved LVEF (from 28 +/- 8% to 40 +/- 15%, p < 0.001). Stepwise multiple linear regression analysis identified dilated cardiomyopathy (beta = 18.32, p = 0.0004), baseline LVEF (beta = -0.85, p = 0.0020), use of amiodarone (beta = -22.58, p = 0.0034) and square of digoxin dose (beta = -314.25, p = 0.0059) at stable beta-blocker dose as independent predictors of LVEF improvement, where beta is the estimated regression coefficient. We did not find any novel variant of beta1-adrenoceptor gene other than those previously reported at codons 49 and 389, with the allele distributions similar to those found in Caucasians, and these polymorphisms did not imply therapeutic response to beta-blocker.

CONCLUSION

We demonstrated the therapeutic effects of beta-blockers in Taiwanese HF patients with a dose lower than what has been reported in Western people. Moreover, patients with the etiology of dilated cardiomyopathy or lower baseline LVEF predicted a greater LVEF improvement. The beta1-adrenoceptor gene polymorphisms were not responsible for the difference in sensitivity to beta-blockers in this Taiwanese population.

Regression of paroxysmal atrial fibrillation associated with thiazolidinedione therapy

Thiazolidinediones (TZDs) represent insulin-sensitizing agents that have several pleiotropic properties, possibly related to their favorable effects on cardiovascular remodeling. We briefly describe 2 diabetic patients who experienced a remarkable improvement in their paroxysmal atrial fibrillation (AF) after treatment with rosiglitazone. Current evidence suggests that atrial remodeling represents a prominent mechanism of AF development and perpetuation while inflammation and oxidative stress are possibly implicated in this process. It could therefore be speculated that the pleiotropic effects of TZDs favorably affect atrial remodeling reducing the arrhythmia burden. Further studies are needed in order to elucidate the merit of this pharmacological approach in AF.

The role of oxidative stress in the pathogenesis and perpetuation of atrial fibrillation

Atrial fibrillation (AF) is the most common arrhythmia encountered in clinical practice representing a major health hazard. Owing to relative inefficacy and side effects of classic antiarrhythmic drugs, current interest has shifted to treatments that target AF substrate. Accumulating evidence suggests that there is a link between oxidative processes and AF. In atrial myocardium during AF, there is substantial oxidative damage that may contribute to atrial remodeling. Several pathophysiological changes that possibly associated with increased oxidative stress in AF have been proposed. These include changes in gene transcriptional profiles and mitochondrial DNA, increased activity of enzymes such as NAD(P)H oxidase and xanthine oxidase, inflammatory processes, activation of the renin-angiotensin system and others. Moreover, oxidative stress is involved in the pathophysiology of several predisposing factors and cardiovascular disorders that correspondingly associated with AF. Preliminary studies using dietary antioxidants such as vitamin C have shown promising results. More evidence has been obtained from studies examining agents with pleiotropic effects, including antioxidant, such as inhibitors of the renin-angiotensin system, statins, corticosteroids and carvedilol. Further investigations are needed in order to elucidate the impact of oxidative stress on atrial remodeling. The clarification of these processes in the setting of AF may lead to the development of novel therapeutic strategies.