Effects of carvedilol on ventricular arrhythmias

Modulation of K2P 2.1 and K2P 10.1 K(+) channel sensitivity to carvedilol by alternative mRNA translation initiation

BACKGROUND AND PURPOSE

The β-receptor antagonist carvedilol blocks a range of ion channels. K2P 2.1 (TREK1) and K2P 10.1 (TREK2) channels are expressed in the heart and regulated by alternative translation initiation (ATI) of their mRNA, producing functionally distinct channel variants. The first objective was to investigate acute effects of carvedilol on human K2P 2.1 and K2P 10.1 channels. Second, we sought to study ATI-dependent modulation of K2P K(+) current sensitivity to carvedilol.

EXPERIMENTAL APPROACH

Using standard electrophysiological techniques, we recorded currents from wild-type and mutant K2P 2.1 and K2P 10.1 channels in Xenopus oocytes and HEK 293 cells.

KEY RESULTS

Carvedilol concentration-dependently inhibited K2P 2.1 channels (IC50 ,oocytes = 20.3 μM; IC50 , HEK = 1.6 μM) and this inhibition was frequency-independent. When K2P 2.1 isoforms generated by ATI were studied separately in oocytes, the IC50 value for carvedilol inhibition of full-length channels (16.5 μM) was almost 5-fold less than that for the truncated channel variant (IC50 = 79.0 μM). Similarly, the related K2P 10.1 channels were blocked by carvedilol (IC50 ,oocytes = 24.0 μM; IC50 , HEK = 7.6 μM) and subject to ATI-dependent modulation of drug sensitivity.

CONCLUSIONS AND IMPLICATIONS

Carvedilol targets K2P 2.1 and K2P 10.1 K(+) channels. This previously unrecognized mechanism supports a general role of cardiac K2P channels as antiarrhythmic drug targets. Furthermore, the work reveals that the sensitivity of the cardiac ion channels K2P 2.1 and K2P 10.1 to block was modulated by alternative mRNA translation initiation.

A critical review of the use of carvedilol in ischemic heart disease

β-Adrenergic receptor antagonists (β-blockers) have been recognized for their cardioprotective properties, prompting use of these pharmacologic agents to become more mainstream in acute myocardial infarction (AMI) and congestive heart failure (CHF). Despite their popularity as a class, the ability to protect the myocardium varies significantly between different agents. Carvedilol is a non-selective β-blocker with α₁-adrenergic receptor antagonism properties. It is unique among β-blockers because in addition to improving exercise tolerance and its anti-ischemic properties secondary to a reduction in heart rate and myocardial contractility, carvedilol exerts other beneficial effects including: antioxidant effects; reduction in neutrophil infiltration; apoptosis inhibition; reduction of vascular smooth muscle migration; and improvement of myocardial remodeling post-AMI. These properties, documented in animal models and subsequent clinical trials, are consistent with established evidence demonstrating decreased morbidity and mortality in patients with CHF and post-AMI. This article reviews the role of carvedilol compared with other β-blockers in the treatment of CHF and post-AMI management.

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.

Electrophysiological effects of carvedilol administration in patients with dilated cardiomyopathy

PURPOSE

Several studies suggest the clinical efficacy of carvedilol in reducing atrial and ventricular arrhythmias in patients with left ventricular dysfunction (LVD) due to congestive heart failure (CHF) or following myocardial infarction. However, the mechanisms supporting its antiarrhythmic efficacy have been derived from experimental studies. In this prospective, placebo-controlled trial we examined the electrophysiological effects of a high oral dose of carvedilol in patients with CHF and LVD due to non-ischemic dilated cardiomyopathy.

METHODS

Thirty-one patients with stable CHF underwent electrophysiological study and were randomly assigned to treatment with carvedilol or placebo. After 2 months of treatment the study was repeated.

RESULTS

Carvedilol prolonged almost all conduction times. In the same group atrial and ventricular effective refractory periods were significantly prolonged, while the parameters of repolarization remained virtually unchanged. The prolongation of refractoriness was most pronounced in the atrium. The change in ventricular refractoriness was correlated with ejection fraction (r = 0.94, p < 0.01) suggesting that patients with more preserved left ventricular function responded to treatment with greater prolongation.

CONCLUSION

Even after a short period of administration carvedilol has marked and diffused electrophysiological effects that would be beneficial for patients with CHF and may contribute to the positive outcome of clinical trials.

Electrophysiologic Effects of Carvedilol: Is Carvedilol an Antiarrhythmic Agent?

The cardiovascular drug carvedilol is characterized by multiple pharmacological actions, which translate into a wide-spectrum therapeutic potential. Its major molecular targets are membrane adrenoceptors, ion channels, and reactive oxygen species. Carvedilol's favorable hemodynamic effects are due to the fact that the drug competitively blocks beta(1)-, beta(2)-, and alpha(1)- adrenoceptors. Several additional properties have been documented and may be clinically important, including antioxidant, antiproliferative/antiatherogenic, anti-ischemic, and antihypertrophic effects. The antiarrhythmic action of carvedilol may be related to a combination of its beta-blocking effects with its modulating effects on a variety of ion channels and currents. Several studies suggest that the drug may be useful in reducing cardiac death in high-risk patients with prior myocardial infarction and/or heart failure, as well as for primary and secondary prevention of atrial fibrillation. This article will review experimental data available on the electrophysiologic properties of carvedilol, with a focus on their clinical relevance.

Carvedilol's antiarrhythmic properties: therapeutic implications in patients with left ventricular dysfunction

Carvedilol is a beta- and alpha-adrenergic-blocking drug with clinically important antiarrhythmic properties. It possesses anti-ischemic and antioxidant activity and inhibits a number of cationic channels in the cardiomyocyte, including the HERG-associated potassium channel, the L-type calcium channel, and the rapid-depolarizing sodium channel. The electrophysiologic properties of carvedilol include moderate prolongation of action potential duration and effective refractory period; slowing of atrioventricular conduction; and reducing the dispersion of refractoriness. Experimentally, carvedilol reduces complex and repetitive ventricular ectopy induced by ischemia and reperfusion. In patients, carvedilol is effective in controlling the ventricular rate response in atrial fibrillation (AF), with and without digitalis, and is useful in maintaining sinus rhythm after cardioversion, with and without amiodarone. In patients with AF and heart failure (HF), carvedilol reduces mortality risk and improves left ventricular (LV) function. Large-scale clinical trials have demonstrated that combined carvedilol and angiotensin-converting enzyme inhibitor therapy significantly reduces sudden cardiac death, mortality, and ventricular arrhythmia in patients with LV dysfunction (LVD) due to chronic HF or following myocardial infarction (MI). Despite intensive neurohormonal blockade, mortality rates remain relatively high in patients with post-MI and nonischemic LVD. Recent trials of implantable cardioverter-defibrillators added to pharmacologic therapy, especially beta blockers, have shown a further reduction in arrhythmic deaths in these patients.

Carvedilol: molecular and cellular basis for its multifaceted therapeutic potential

Carvedilol is a unique cardiovascular drug of multifaceted therapeutic potential. Its major molecular targets recognized to date are membrane adrenoceptors (beta 1, beta 2, and alpha 1), reactive oxygen species, and ion channels (K+ and Ca2+). Carvedilol provides prominent hemodynamic benefits mainly through a balanced adrenoceptor blockade, which causes a reduction in cardiac work in association with peripheral vasodilation. This drug assures remarkable cardiovascular protection through its antiproliferative/atherogenic, antiischemic, antihypertrophic, and antiarrhythmic actions. These actions are a consequence of its potent antioxidant effects, amelioration of glucose/lipid metabolism, modulation of neurohumoral factors, and modulation of cardiac electrophysiologic properties. The usefulness of carvedilol in the treatment of hypertension, ischemic heart disease, and congestive heart failure is based on a combination of hemodynamic benefits and cardiovascular protection.

Carvedilol as therapy in pediatric heart failure: an initial multicenter experience

OBJECTIVE

The objective was to determine the dosing, efficacy, and side effects of the nonselective beta-blocker carvedilol for the management of heart failure in children.

STUDY DESIGN

Carvedilol use in addition to standard medical therapy for pediatric heart failure was reviewed at 6 centers.

RESULTS

Children with dilated cardiomyopathy (80%) and congenital heart disease (20%), age 3 months to 19 years (n = 46), were treated with carvedilol. The average initial dose was 0.08 mg/kg, uptitrated over a mean of 11.3 weeks to an average maintenance dose of 0.46 mg/kg. After 3 months on carvedilol, there were improvements in modified New York Heart Association class in 67% of patients (P =.0005, chi2 analysis) and improvement in mean shortening fraction from 16.2% to 19.0% (P =.005, paired t test). Side effects, mainly dizziness, hypotension, and headache, occurred in 54% of patients but were well tolerated. Adverse outcomes (death, cardiac transplantation, and ventricular-assist device placement) occurred in 30% of patients.

CONCLUSIONS

Carvedilol as an adjunct to standard therapy for pediatric heart failure improves symptoms and left ventricular function. Side effects are common but well tolerated. Further prospective study is required to determine the effect of carvedilol on survival and to clearly define its role in pediatric heart failure therapy.

Clinical Pharmacology of Carvedilol

BACKGROUND: There is now a wealth of data supporting the use of beta-blockers in heart failure and the additional pharmacological properties of carvedilol are thought to play an important role in the therapeutic efficacy of carvedilol in this disease. METHODS AND RESULTS: Carvedilol is licensed for the treatment of essential hypertension, chronic stable angina, and mild to moderate chronic heart failure. This article provides an up-to-date review of the clinical pharmacology of carvedilol, with particular emphasis on its clinical effects in heart failure. CONCLUSION: Carvedilol is a multiple-action neurohormonal antagonist that offers nonselective beta-blockade, alpha-1 blockade, antioxidant, anti-ischemic mortality, and anti-proliferative properties. In addition to reductions in hospitalization and mortality rates, benefits of carvedilol in heart failure include dramatic improvements in left ventricular function and other parameters of cardiac remodeling.

Carvedilol blocks the repolarizing K+ currents and the L-type Ca2+ current in rabbit ventricular myocytes

Carvedilol ((+/-)-1-(carbazol-4-yloxy)-3-[[2-(o-methoxyphenoxy)ethyl]am ino]-2-propanol), a beta-adrenoceptor-blocking agent with vasodilator properties, has been reported to produce dose-related improvements in left ventricular function and reduction in mortality in patients with chronic heart failure. However, its electrophysiological effects have not been elucidated. We studied ion channel and action potential modulation by carvedilol in rabbit ventricular preparations using whole-cell voltage-clamp and standard microelectrode techniques. In ventricular myocytes, carvedilol blocked the rapidly activating component of the delayed rectifier K+ current (I(Kr)) in a concentration-dependent manner (IC50 = 0.35 microM). This block was voltage- and time-independent; a prolongation of the depolarizing pulses from a holding potential of -50 mV to +10 mV within the range of 100-3000 ms did not affect the extent of I(Kr) block. Carvedilol also inhibited the L-type Ca2+ current (I(Ca)), the transient outward K+ current (I(to)) and the slowly activating component of the delayed rectifier K+ current (I(Ks)) with IC50 of 3.59, 3.34, and 12.54 microM, respectively. Carvedilol (0.3-30 microM) had no significant effects on the inward rectifier K+ current. In papillary muscles from rabbits pretreated with reserpine, action potential duration was prolonged by 7-12% with 1 microM and by 12-24% with 3 microM carvedilol at stimulation frequencies of 0.1-3.0 Hz. No further action potential duration prolongation was observed at concentrations higher than 3 microM. These results suggest that concomitant block of K+ and Ca2+ currents by carvedilol resulted in a moderate prolongation of action potential duration with minimal reverse frequency-dependence. Such electrophysiological effects of carvedilol would be beneficial in the treatment of ventricular tachyarrhythmias.

The role of neurohormonal antagonists in hibernating myocardium

Hibernating myocardium is characterized by chronic reduction of myocardial blood flow due to obstructive coronary artery disease, causing reversible left ventricular dysfunction and flow-metabolism mismatch. The condition is unstable and increasing demand may lead to further left ventricular dysfunction or necrosis causing death or worsening heart failure. Recognition of the condition is difficult and requires complex cardiac imaging protocols. Treatment protocols are also poorly defined. This review addresses both the diagnostic and therapeutic aspects of hibernating myocardium.

Carvedilol. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic efficacy

Carvedilol is a beta-adrenoceptor antagonist which also causes peripheral vasodilation primarily via alpha 1-adrenergic blockade. Carvedilol produces its antihypertensive effect partly by reducing total peripheral resistance by blocking alpha 1-adrenoceptors and by preventing beta-adrenoceptor-mediated compensatory mechanisms. This combined action avoids many of the unwanted effects associated with traditional beta-blocker or vasodilator therapy. In clinical trials published to date, most of which enrolled small numbers of patients, the antihypertensive efficacy of carvedilol administered once daily was similar to that of atenolol, labetalol, pindolol, propranolol, metoprolol, nitrendipine (in elderly patients), slow release nifedipine or captopril in patients with mild-to-moderate essential hypertension. Combined therapy with carvedilol 25 mg and hydrochlorothiazide 25 mg, nicardipine 60 mg or slow release nifedipine 20 mg has an additive antihypertensive effect. Carvedilol and atenolol at similar doses were equally effective at reducing blood pressure in patients who had previously not responded adequately to hydrochlorothiazide monotherapy. As a result of its multiple mechanisms of action, carvedilol is suited for the management of specific groups of hypertensive patients, such as those with renal impairment. In patients with non-insulin-dependent or insulin-dependent diabetes mellitus carvedilol does not appear to affect glucose tolerance or carbohydrate metabolism. Initial studies have demonstrated that carvedilol and slow release nifedipine have similar efficacy in patients with stable angina pectoris and there is evidence that carvedilol has a beneficial haemodynamic effect in patients with congestive heart failure (NYHA class II or III) secondary to ischaemic heart disease. A postmarketing surveillance study has shown that carvedilol is generally well tolerated with only 7% (164/2226) of patients (83% of the total number received 25mg daily for 12 weeks) withdrawing from treatment because of adverse events. Vertigo, headache, bronchospasm, fatigue and skin reactions were the most common events causing withdrawal. Thus, clinical experience to date suggests that carvedilol is likely to be a valuable addition to the options currently available for treating patients with mild-to-moderate essential hypertension, and may offer particular benefit in specific populations of hypertensive patients.