BETA-ADRENERGIC RECEPTOR BLOCKADE IN CARDIAC ARRHYTHMIAS

Evolution of Knowledge in the Treatment of Long-Standing Atrial Fibrillation in a UK Tennis Champion

During the last several decades, there have been major advances in the evolution of drug therapies for the rate management of atrial fibrillation (AF). Initially, the drug of choice was digoxin but currently, the drug of choice is beta-adrenergic blockers. Drug therapies for stroke prevention in AF have also evolved. Initially, the drug of choice was aspirin, then became warfarin, and now in the current era, there are newer oral anticoagulants, such as apixaban, which are the preferred drugs. In this case report, we present the details of a 79-year-old athletic man who developed palpitations due to rapid AF at age 31. At the time of his initial presentation, he was treated with digoxin and aspirin and has remained on these drugs to the present. In 1973, 28 years after his initial presentation, he became the United Kingdom (UK) amateur tennis champion in the 55 and over division at age 59. 

At present, the clinical applications of advances in the management of AF should include quality of life considerations in the context of patient preferences. This patient is an active and vigorous 79-year-old man who plays competitive tennis and pickleball. He steadfastly adheres to an antediluvian regimen for the management of his AF, but this may be viewed in the context of the famous quotation by Bert Lance, Director of the Office of Management and Budget in the US under President Carter who said “sometimes, if it ain’t broke, don’t fix it.”

In addition to the evolution of drug therapies from digoxin to beta-adrenergic blockers for rate control as well as from aspirin to warfarin to apixaban for the prevention of stroke, there have been other recent remarkable advances. For example, recent promising findings from randomized trials include that early rhythm control was more effective than rate control as well as that cryoballoon ablation was superior to drug therapies. These findings require confirmation in additional randomized trials designed a priori to test these promising but unproven hypotheses.

Imidacloprid, a neonicotinoid insecticide, facilitates tyrosine hydroxylase transcription and phenylethanolamine N-methyltransferase mRNA expression to enhance catecholamine synthesis and its nicotine-evoked elevation in PC12D cells

Imidacloprid is a neonicotinoid insecticide acting as an agonist of nicotinic acetylcholine receptors (nAChRs) in the target insects. However, questions about the safety to mammals, including human have emerged. Overactivation of mammalian peripheral catecholaminergic systems leads to onset of tachycardia, hypertension, vomiting, etc., which have been observed in acutely imidacloprid-poisoned patients as well. Physiological activation of the nAChRs is known to drive catecholamine biosynthesis and secretion in mammalian adrenal chromaffin cells. Yet, the impacts of imidacloprid on the catecholaminergic function of the chromaffin cells remain to be evaluated. In this study using PC12D cells, a catecholaminergic cell line derived from the medulla chromaffin-cell tumors of rat adrenal gland, we examined whether imidacloprid itself could impact the catecholamine-synthesizing ability. Imidacloprid alone did facilitate tyrosine hydroxylase (TH) transcription via activation of α3β4 nAChR and the α7 subunit-comprising receptor. The insecticide showed the TH transcription-facilitating ability at the concentrations of 3 and 30 μM, at which acetylcholine is known to produce physiological responses, including catecholamine secretion through the nAChRs in adrenal chromaffin cells. The insecticide-facilitated TH transcription was also dependent on PKA- and RhoA-mediated signaling pathways. The insecticide coincidentally raised levels of TH and phenylethanolamine N-methyltransferase (PNMT) mRNA, and as a consequence, increased catecholamine production, although the efficacy of the neonicotinoid was lesser than that of nicotine, indicating its partial agonist-like action. Intriguingly, in cultured rat adrenal chromaffin cells, imidacloprid did increase levels of TH and PNMT protein. When the chromaffin cells were treated with nicotine in the presence of the insecticide, nicotine-elevated adrenaline production was enhanced due to facilitation of nicotine-increased TH and PNMT protein expression, and simultaneous enhancement of nicotine-elevated adrenaline secretion also took place. These findings thus suggest that imidacloprid may facilitate the physiological functions of adrenal glands in mammals.

Drug therapy of sustained ventricular tachyarrhythmias. Is there still a role?

This article provides a review of the risks faced by patients with sustained ventricular tachycardia (VT) or ventricular fibrillation (VF) in the absence of a reversible or transient cause so that the goals of therapy can be clearly defined. The therapeutic approaches that have been proposed to achieve these goals are outlined and evidence comparing these various approaches to therapy is then summarized in order to propose an algorithm for the optimal use of antiarrhythmic drug therapies as primary therapy for selected VT/VF patients. Options for the ancillary uses of antiarrhythmic drug therapies in ICD patients are considered.

Antiarrhythmic efficacy of solitary beta-adrenergic blockade for patients with sustained ventricular tachyarrhythmias

To assess the efficacy and predictability of solitary beta-adrenergic blocker (BB) therapy for ventricular tachyarrhythmia (VT), 30 patients (16 men and 14 women) with a mean age of 55 years, who initially had sustained ventricular tachycardia (70%) or ventricular fibrillation (30%), were studied. Results of baseline arrhythmia tests showed VT on ECG monitoring in 57% of the patients, during exercise in 50%, induced by programmed stimulation in 69%, increasing to 86% during isoproterenol. BB therapy prevented inducible VT during programmed stimulation in 37% of the patients, prevented VT on ECG monitoring in 54%, and prevented VT during exercise in 83%. Long-term BB therapy was given to 24 of 30 patients, whereas six other patients with hemodynamically unstable VT during BB therapy received other long-term treatment. During a mean follow-up of 824 days, 6 of 24 patients had recurrent VT. BB therapy was discontinued in two patients because of side effects. Long-term success was predicted by left ventricular ejection fraction greater than 45%, absence of coronary disease, and age less than 60 years (all p less than 0.02). Neither suppression of arrhythmia during exercise testing, nor results of programmed stimulation or ECG monitoring were predictive of outcome. Thus beta-adrenergic blockers can be effective as solitary antiarrhythmic therapy in selected patients with VT.

Effects of nadolol on the spontaneous and exercise-provoked heart rate of patients with chronic atrial fibrillation receiving stable dosages of digoxin

Nadolol, a long-acting beta-adrenergic-blocking agent, was evaluated in 20 patients with chronic atrial fibrillation by means of a randomized, double-blind, crossover study. Patients were required either to demonstrate resting heart rates in excess of 80 bpm or to show a rate of 120 bpm or an increment of greater than 50 bpm during mild treadmill exercise provocation (3 minutes, 1.75 mph, 10% grade). With placebo the group averaged a heart rate of 92 +/- 19 bpm, determined by 24 hours of ambulatory ECG recordings; this rate was significantly reduced to 73 +/- 16 bpm (p less than 0.001) with nadolol (mean dosage, 87 +/- 43 mg/day). During standardized exercise testing, heart rates increased to 153 +/- 26 bpm with placebo and to 111 +/- 24 bpm with nadolol (p less than 0.001), representing 65% and 52% increments, respectively. Digoxin blood levels averaged 0.8 +/- 0.5 ng/ml with placebo and were similar with nadolol (0.9 +/- 0.4; p = NS). Total exercise time on a modified Bruce treadmill protocol was 466 +/- 143 seconds with placebo and was significantly decreased by nadolol (380 +/- 143; p less than 0.01). During initial dose titration with nadolol, one patient was dropped from study for intolerable fatigue and one for worsened claudication. No patients were dropped from the double-blind treatment periods, although two patients receiving nadolol and one patient receiving placebo complained of moderate fatigue. We conclude that nadolol is a safe and effective agent for the control of spontaneous and exercise-provoked heart rates in patients with chronic atrial fibrillation who were already receiving digoxin treatment.

Long-acting propranolol (Inderal LA): pharmacokinetics, pharmacodynamics and therapeutic use

Long-acting propranolol (Inderal LA) is a new formulation of propranolol that allows release of the drug in a controlled manner, so that the plasma concentration at 24 hr after dosing is greater with long-acting propranolol than with conventional tablets. A single dose of 160 mg of long-acting propranolol can produce cardiac beta-adrenoceptor blockade throughout a 24 hr period without variability due to multiple peak concentrations. It has been shown that this formulation is as effective in the treatment of angina pectoris, hypertension and hyperthyroidism as the standard formulation. Studies with long-acting propranolol in cardiac dysrhythmias are lacking. This new dosage form would be a means of simplifying dosing regimens and thereby hopefully enhancing patient convenience and compliance.

Pharmacologic treatment of cardiac arrhythmias: 25 years of progress

This review of practical and theoretical advances in antiarrhythmic drug therapy consists of four parts. Part 1, on clinical applications, compares the approaches to treatment 25 years ago with those of today, examines the current status of antiarrhythmic drugs used 25 years ago, reports on drugs approved for clinical use during the past 25 years, reviews new experimental drugs and suggests an approach to classification of antiarrhythmic drugs. Part 2 summarizes the contributions of cellular electrophysiology to the understanding of drug action, with emphasis on the drug-induced block of the voltage- and time-dependent properties of the rapid sodium channel. The subsequent section contains a brief discussion of the impact made by the new knowledge and the new diagnostic technology on the contemporary practices. The main conclusions are 1) that the more rational approach to treatment has benefited proportionately more patients with supraventricular than with ventricular arrhythmias, and 2) that new advances have made it possible to design successful treatments for certain patients with problems that could not be resolved in the past.

Inefficacy of digitalis in the control of heart rate in patients with chronic atrial fibrillation: beneficial effect of an added beta adrenergic blocking agent

The role of digoxin and the new beta adrenergic blocking agent, timolol, in controlling heart rate at rest and during exercise was investigated in 28 patients with chronic atrial fibrillation. Digoxin failed to prevent excessively rapid heart rates during mild to moderate exercise. Increasing digoxin blood levels from a mean of 0.6 to 1.8 ng/ml had no effect on heart rate either at rest or during exercise. The addition of timolol, 20 to 30 mg/day, resulted in a satisfactory and significant attenuation of the rapid heart rates both at rest and during exercise. Heart rates at rest were 91 and 98 beats/min in the patients with low and high digoxin dosage and rose to 135 and 139 beats/min, respectively, during exercise. Timolol reduced the heart rate to 67 at rest and to 92 beats/min during exercise. The effect of beta adrenergic blockade at rest was less pronounced in patients whose initial heart rates were below 90 beats/min. Digoxin alone may not suffice to control excessive heart rate in patients with chronic atrial fibrillation. The additional beta adrenergic blockade actually normalizes the heart rate response in these patients.

Effective treatment of supraventricular arrhythmias with acebutolol

To evaluate the antiarrhythmic efficacy of the new beta adrenergic blocking agent acebutolol, 15 monitored patients with supraventricular arrhythmias received, in double-blind fashion, an intravenous infusion of either acebutolol or saline solution after a control period. Patients treated with saline solution demonstrated no change (P greater than 0.05) in heart rate or arterial blood pressure or conversion to sinus rhythm. After administration of acebutolol, significant (P less than 0.05) reductions in heart rate were noted at 5 minutes. Peak reduction occurred at 10 to 30 minutes and correlated with maximal acebutolol plasma concentrations, antiarrhythmic activity persisted for 24 hours. Mild reductions in systolic blood pressure were observed in the majority of patients. Two patients with atrial fibrillation and one with multifocal atrial tachycardia had conversion to sinus rhythm. Frequent premature atrial complexes noted in one patient were greatly suppressed after administration of the drug. In the nine patients with clinical evidence of chronic obstructive lung disease acebutolol was well tolerated. Adverse reactions were limited to transient dyspnea in one patient with prior heart failure and a decrease in systolic blood pressure to less than 90 mm Hg in three patients who remained asymptomatic. In the patients studied, acebutolol was an effective agent for the treatment of supraventricular arrhythmias and appeared to be of special value in those with chronic obstructive lung disease.

Comparative studies on the pharmacological actions of antiarrhythmic drugs in isolated rate papillary muscle

1. The effects of ajmaline, cocaine, phenytoin, lignocaine, procainamide, propranolol, quinidine and trimetazidine on the contractility and the refractory period of isolated rat papillary muscles were compared. 2. At the higher concentrations used, all drugs suppressed the contractile tension of the rat papillary muscles. 3. The effects of these drugs on the refractory period were compared at concentrations at which the contractile tension was suppressed by 30% of the control. At this point, lignocaine, procainamide, ajmaline and quinidine prolonged the refractory period more than two-fold while the effects of propranolol and phenytoin were slight, cocaine and trimetazidine had little or no effect.

Blood pressure responses to catecholamines during beta-adrenergic blockade with propranolol in hypertensive subjects

In 14 patients with essential hypertension, the response of the heart rate and blood pressure to infusion of norepinephrine and epinephrine separately while off (control period) or on therapy with beta-adrenergic receptor blockade was examined. By titrating dosage against the response of blood pressure and pulse rate, propranolol hydrochloride was administered orally at 160 mg/day in four divided doses. There was a significant decrease in systolic blood pressure and in pulse rate during propranolol therapy, whereas diastolic blood pressure decreased but not significantly so. Normal blood pressure (140/90 mm /g or less) was attained only in five patients. The infusion of epinephrine and then norepinephrine produced a significant increase in both systolic and diastolic blood pressure during propranolol therapy, but the magnitude of the rise was significantly greater than that attained in the control period only during epinephrine infusion. We conclude that the transient hypertensive episodes which have been observed during offive visits in some hypertensive patients treated with propranolol are due mainly to release of epinephrine.

Use of oxprenolol in cardiac arrhythmias associated with acute myocardial ischaemia

Oxprenolol, a new beta-receptor blocking drug with intrinsic sympathomimetic activity, was used to treat 63 episodes of cardiac arrhythmia occurring in 43 patients with acute myocardial infarction or myocardial ischaemia. The drug was most effective in abolishing ventricular ectopic beats and supraventricular tachycardia. The best method of administration was by continuous intravenous infusion and the most satisfactory bolus does was 6 mg. The main side effect was hypotension, which occurred in 59% of episodes of arrhythmia that had responded previously to intravenous administration. Oxprenolol was often effective in lignocaine-resistant arrhythmia. The two main advantages of oxprenolol over propranolol are the reduced likelihood of adversely affecting myocardial function and the diminished tendency to produce bronchospasm.

Effects of (plus or minus)-propranolol, (plus or minus)-,(plus)-, and (minus)-alprenolol on unanaesthetized dogs with ventricular arrhythmias resulting from coronary artery ligation

1. The effects of (+/-)-propranolol, (+/-)-, (+)- and (-)-alprenolol were studied in unanaesthetized dogs with ventricular arrhythmias produced by ligation of the left coronary artery. The responses were compared with those of similar control dogs which were given only isotonic saline.2. The ventricular arrhythmias were abolished by cumulative doses of 3.5 mg/kg of (+/-)-alprenolol, 7.5 mg/kg of (-)-alprenolol and (+/-)-propranolol and by 15.5 mg/kg of (+)-alprenolol.3. At the time of maximum antiarrhythmic activity none of the drugs produced significant alterations in mean arterial pressure or atrial rate.4. Cumulative doses of 7.5 mg/kg and 15.5 mg/kg of the four drugs resulted in some instances of lip licking, emesis and/or head tremors while 31.5 mg/kg was invariably lethal.5. Since the beta-adrenoceptor blocking activity of (-)-alprenolol is 100 times greater than that of (+)-alprenolol, suppression of these ventricular arrhythmias was apparently unrelated to antagonism of sympathetic influences.6. Alprenolol and propranolol have myocardial depressant properties apart from their effects on beta-adrenoceptors which could account for the anti-arrhythmic activity observed.

Practolol in treatment of supraventricular cardiac dysrhythmias

Practolol (I.C.I. 50172) was used to treat supraventricular dysrhythmias in 32 patients with a rapid ventricular rate and with heart disease of varied aetiology. In 26 patients the average reduction in ventricular rate was 75 per minute, while immediate reversion to sinus rhythm occurred in three patients. The slowing effect was mainly due to a direct action on the atrioventricular node. The effectiveness of practolol was unrelated to the type of dysrhythmia or its aetiology. No serious adverse clinical effects were noted.

The relevance of beta-receptor blockade to ouabain-induced cardiac arrhythmias

1. (+)-propranolol and (+/-)-propranolol are comparable in their potency as a local anaesthetic on the intact and desheathed frog sciatic nerve.2. (+/-)-propranolol is much more potent than (+)-propranolol as a beta-receptor blocking agent and also more effective than the latter in protecting guinea-pigs against ouabain-induced ventricular fibrillation.3. In isolated rabbit atria (-)-, (+)- and (+/-)-propranolol, and I.C.I. 50172, which has hardly any local anaesthetic activity, greatly reduce the rate of rise of the intracellularly recorded action potential at concentrations which have no significant effect on electrical threshold, contractions, spontaneous frequency, maximum driving frequency, repolarization time or conduction velocity.