EFFECTS OF BETA-ADRENERGIC BLOCKADE WITH PROPRANOLOL IN PATIENTS WITH ATRIAL ARRHYTHMIAS

Acute Cardiovascular and Cardiorespiratory Effects of JWH-018 in Awake and Freely Moving Mice: Mechanism of Action and Possible Antidotal Interventions?

JWH-018 is the most known compound among synthetic cannabinoids (SCs) used for their psychoactive effects. SCs-based products are responsible for several intoxications in humans. Cardiac toxicity is among the main side effects observed in emergency departments: SCs intake induces harmful effects such as hypertension, tachycardia, chest pain, arrhythmias, myocardial infarction, breathing impairment, and dyspnea. This study aims to investigate how cardio-respiratory and vascular JWH-018 (6 mg/kg) responses can be modulated by antidotes already in clinical use. The tested antidotes are amiodarone (5 mg/kg), atropine (5 mg/kg), nifedipine (1 mg/kg), and propranolol (2 mg/kg). The detection of heart rate, breath rate, arterial oxygen saturation (SpO2), and pulse distention are provided by a non-invasive apparatus (Mouse Ox Plus) in awake and freely moving CD-1 male mice. Tachyarrhythmia events are also evaluated. Results show that while all tested antidotes reduce tachycardia and tachyarrhythmic events and improve breathing functions, only atropine completely reverts the heart rate and pulse distension. These data may suggest that cardiorespiratory mechanisms of JWH-018-induced tachyarrhythmia involve sympathetic, cholinergic, and ion channel modulation. Current findings also provide valuable impetus to identify potential antidotal intervention to support physicians in the treatment of intoxicated patients in emergency clinical settings.

Historical Aspects of the Use of Antiarrhythmic Drugs in Clinical Practice

Heart rhythm disorders are one of the most urgent problems in cardiology. The first reports on the possibility of using drugs in the treatment of cardiac arrhythmias began to appear in the scientific literature from the middle of the 18th century. This pharmacotherapeutic direction has been developed since the second half of the 20th century, when new antiarrhythmic drugs began to be used in clinical practice. The introduction of new drugs and modern methods of treating arrhythmias into clinical practice has significantly improved the prognosis and quality of life of patients. Combination antiarrhythmic therapy, including antiarrhythmic drugs and radiofrequency ablation, seems to be the most promising and successful tactic for treating patients in the future. A historical review of the literature on the clinical use of antiarrhythmic drugs both in past years and at present is presented in the article.

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.

Treatment of cardiac arrhythmias in a mouse model of Rett syndrome with Na+-channel-blocking antiepileptic drugs

One quarter of deaths associated with Rett syndrome (RTT), an X-linked neurodevelopmental disorder, are sudden and unexpected. RTT is associated with prolonged QTc interval (LQT), and LQT-associated cardiac arrhythmias are a potential cause of unexpected death. The standard of care for LQT in RTT is treatment with β-adrenergic antagonists; however, recent work indicates that acute treatment of mice with RTT with a β-antagonist, propranolol, does not prevent lethal arrhythmias. In contrast, acute treatment with the Na⁺ channel blocker phenytoin prevented arrhythmias. Chronic dosing of propranolol may be required for efficacy; therefore, we tested the efficacy of chronic treatment with either propranolol or phenytoin on RTT mice. Phenytoin completely abolished arrhythmias, whereas propranolol showed no benefit. Surprisingly, phenytoin also normalized weight and activity, but worsened breathing patterns. To explore the role of Na⁺ channel blockers on QT in people with RTT, we performed a retrospective analysis of QT status before and after Na⁺ channel blocker antiepileptic therapies. Individuals with RTT and LQT significantly improved their QT interval status after being started on Na⁺ channel blocker antiepileptic therapies. Thus, Na⁺ channel blockers should be considered for the clinical management of LQT in individuals with RTT.

Analysis of drug interactions with very low density lipoprotein by high-performance affinity chromatography

High-performance affinity chromatography (HPAC) was utilized to examine the binding of very low density lipoprotein (VLDL) with drugs, using R/S-propranolol as a model. These studies indicated that two mechanisms existed for the binding of R- and S-propranolol with VLDL. The first mechanism involved non-saturable partitioning of these drugs with VLDL, which probably occurred with the lipoprotein's non-polar core. This partitioning was described by overall affinity constants of 1.2 (±0.3) × 10(6) M(-1) for R-propranolol and 2.4 (±0.6) × 10(6) M(-1) for S-propranolol at pH 7.4 and 37 °C. The second mechanism occurred through saturable binding by these drugs at fixed sites on VLDL, such as represented by apolipoproteins on the surface of the lipoprotein. The association equilibrium constants for this saturable binding at 37 °C were 7.0 (±2.3) × 10(4) M(-1) for R-propranolol and 9.6 (±2.2) × 10(4) M(-1) for S-propranolol. Comparable results were obtained at 20 and 27 °C for the propranolol enantiomers. This work provided fundamental information on the processes involved in the binding of R- and S-propranolol to VLDL, while also illustrating how HPAC can be used to evaluate relatively complex interactions between agents such as VLDL and drugs or other solutes.

The drug treatment of atrial fibrillation

1. Atrial fibrillation is an inefficient cardiac rhythm associated with impaired exercise tolerance, exertional dyspnoea, palpitation and a substantial risk of thromboembolism. 2. The first decision in management is to consider cardioversion which can be achieved in suitable cases electrically, or pharmacologically with a class Ic antiarrhythmic drug like flecainide or propafenone. 3. Prophylaxis in paroxysmal atrial fibrillation is best achieved with a class Ic drug or a class III drug such as sotalol or amiodarone. 4. Control of ventricular rate in chronic atrial fibrillation can be achieved by pharmacological manipulation of the atrioventricular node by digoxin alone, or in combination with the calcium channel blockers verapamil or diltiazem, or beta-adrenoceptor blockers with intrinsic sympathomimetic activity like pindolol or xamoterol. 5. In view of the considerable risk of thromboembolism in patients with chronic atrial fibrillation anticoagulation or at least treatment with aspirin should be considered.

Esmolol versus verapamil in the acute treatment of atrial fibrillation or atrial flutter

The effects of esmolol, an ultrashort-acting beta blocker, and verapamil were compared in controlling ventricular response in 45 patients with atrial fibrillation or atrial flutter, in a randomized, parallel, open-label study. Patients with either new onset (less than 48 hours, n = 31) or old onset (greater than 48 hours, n = 14) of atrial fibrillation or flutter with rapid ventricular rate were stratified to receive esmolol (n = 21) or verapamil (n = 24). Drug efficacy was measured by ventricular rate reduction and conversion to sinus rhythm. The heart rate declined with esmolol from 139 to 100 beats/min (p less than 0.001) and with verapamil from 142 to 97 beats/min (p less than 0.001). Fifty percent of esmolol-treated patients with new onset of arrhythmias converted to sinus rhythm, whereas only 12% of those who received verapamil converted (p less than 0.03). Mild hypotension was observed in both treatment groups. Esmolol compares favorably with verapamil with respect to both efficacy and safety in acutely decreasing ventricular response during atrial fibrillation or flutter. Moreover, conversion to sinus rhythm is significantly more likely with esmolol.

Esmolol: safety and efficacy in postoperative cardiothoracic patients with supraventricular tachyarrhythmias

Esmolol, an intravenous, ultrashort-acting beta-blocker, was studied for its ability to safely control supraventricular arrhythmias up to 24 hours in 15 postoperative cardiothoracic surgery patients with atrial fibrillation or flutter and rapid ventricular response. Esmolol obtained an initial therapeutic response in nine (60 percent) patients. Mean heart rate for the 15 patients was reduced from 139 +/- 12 beats/min before therapy to 106 +/- 21 beats/min during esmolol infusion (p less than 0.01). The mean time to a therapeutic response after initiation of therapy, using a multistep titration regimen (500 micrograms/kg/min loading infusions over one minute, prior to incremental titration steps from 50 to 300 micrograms/kg/min over 4 to 14 minutes), was 22 +/- 9 minutes, and therapy was continued for 17 +/- 9 hours in responders. Esmolol significantly lowered blood pressure in the group studied and resulted in mild supine or orthostatic hypotension in ten (67 percent) patients. Side effects, including hypotension (10/15 patients), gastrointestinal disturbances (2/15), and weakness or somnolence (6/15), were transient and were not associated with serious clinical sequelae. We conclude that esmolol is effective for rate control in a majority of postoperative cardiothoracic surgery patients with atrial fibrillation or flutter. Side effects, although mild, occur relatively frequently, limiting prolonged infusions and warranting close surveillance of patients.

Comparative effects of nadolol-digoxin combination therapy and digoxin monotherapy for chronic atrial fibrillation

In some patients with chronic atrial fibrillation, treatment with digitalis alone may fail to produce a satisfactory decrease in heart rate at rest or during exercise or emotional stress. Findings of a few clinical studies suggest that beta blockade in combination with digitalis therapy may be of benefit in these patients. In a randomized, double-blind, placebo-controlled, parallel-group, 8-week study of 32 patients with chronic atrial fibrillation, the effects of digoxin therapy alone were compared with a combination of digoxin and nadolol. Criteria for entry into the study included ventricular rate at rest greater than or equal to 80/min or greater than or equal to 120/min with exercise, and serum digoxin levels within the therapeutic range. After digoxin dose titration to produce therapeutic levels, digoxin dosage remained constant throughout the balance of the study. After a 2-week, single-blind placebo lead-in period, patients were randomized to receive either digoxin plus placebo or a combination of digoxin and nadolol. The dose of nadolol/placebo was titrated from 20 to 120 mg daily as tolerated. Twenty-four hour ambulatory electrocardiographic (Holter) recordings, symptom-limited exercise treadmill tests and serum digoxin and nadolol levels were obtained at the end of the single and double-blind treatment periods. Comparing endpoint with baseline, results from Holter recordings showed that patients treated with a combination of digoxin and nadolol had significant (p less than 0.001) decreases in 24 hour average (78 +/- 4 to 63 +/- 3).(ABSTRACT TRUNCATED AT 250 WORDS)

Intravenous esmolol for the treatment of supraventricular tachyarrhythmia: results of a multicenter, baseline-controlled safety and efficacy study in 160 patients. The Esmolol Research Group

Efficacy and safety of esmolol in the treatment of supraventricular tachyarrhythmias (SVT) was evaluated in this open-label, baseline-controlled, multicenter study. One hundred sixty patients with SVT received an intravenous infusion of esmolol in doses ranging from 25 to 300 micrograms/kg/min for up to 24 hours. All of the 160 patients were evaluated for safety, and 147 of them were eligible for evaluation of therapeutic response. Therapeutic response was defined as greater than or equal to 15% reduction in the average baseline heart rate of conversion to normal sinus rhythm. Seventy-nine percent (116 of 147) of the patients exhibited a therapeutic response. The cumulative percentage response increased significantly with increasing esmolol doses up to 200 micrograms/kg/min. The mean (+/- SEM) dose of esmolol producing a therapeutic response was 97.2 +/- 5.5 micrograms/kg/min. Among all patients (n = 160), 39% exhibited hypotension. In 58% of these patients, hypotension resolved with or without adjustment of the esmolol dose while the infusion continued; among almost all of the remaining patients, hypotension resolved within 30 minutes after esmolol was discontinued. Most patients at risk for adverse effects during beta blockade (i.e., those with diabetes mellitus, congestive heart failure, asthma, etc.) tolerated esmolol therapy, and there were no clinically important trends among the reported changes in laboratory variables. The results of the study indicate that esmolol is effective and well tolerated for the treatment of SVT.

Esmolol: a new ultrashort-acting beta-adrenergic blocking agent for rapid control of heart rate in postoperative supraventricular tachyarrhythmias

Prompt control of heart rate is important for successful treatment of supraventricular tachyarrhythmias early after open heart surgery when sympathetic tone is high and ventricular response rates may be rapid. Esmolol, a new ultrashort-acting (9 minute half-life) beta-receptor blocking agent, was given by continuous intravenous infusion for up to 24 hours in 24 patients (21 with isolated coronary bypass surgery and 3 with valve replacement) 1 to 7 days after surgery. Atrial fibrillation was present in 9 patients, atrial flutter in 2 and sinus tachycardia in 13. Eleven patients had received intravenous digoxin (average dose 0.6 mg, average serum level 1.19 mg/100 ml) before esmolol infusion without adequate control of the supraventricular tachyarrhythmia. After a 1 minute loading infusion of esmolol (500 micrograms/kg per min), maintenance dose, titrated to heart rate and blood pressure response, varied from 25 to 300 micrograms/kg per min. After esmolol administration, at an average dose of 139 +/- 83 micrograms/kg per min, mean heart rate decreased from 130 +/- 15 to 99 +/- 15 beats/min. Within 5 to 18 minutes after initiation of therapy, all patients had achieved a 15% reduction in heart rate at a maintenance dose of 150 micrograms/kg per min or less. A 20% reduction in heart rate was attained in 19 of the 24 patients, and conversion to sinus rhythm occurred during esmolol infusion in 5 of the 11 patients with atrial flutter or fibrillation. Transient asymptomatic hypotension (less than 90/50 mm Hg) was seen in 13 patients, requiring cessation of esmolol therapy in 2.(ABSTRACT TRUNCATED AT 250 WORDS)

Beta blockers and exercise: physiologic and biochemical definitions and new concepts

Exercise training effects occur in man after chronic exposure to aerobic exercise, which should be defined quantitatively to permit a precise mechanistic understanding. Exercise adaptations result from circulatory and metabolic changes that involve altered responsiveness to neurohumoral transmitters at the receptor level. The adrenergic mechanisms are most important and are linked to new understandings of the adrenergic receptor and its coupling with biochemical processes in the cell. The adrenergic receptor is a specialized protein in the cell membrane linked to the catalytic moiety of the enzyme adenylate cyclase by a coupling protein controlled by guanine nucleotides. The sensitivity of this receptor mechanism may be altered by exposure to agonists and antagonists and by circulatory and metabolic diseases. The effects of beta- adrenergic blockers on exercise adaptation and the clinical sequelae are emphasized.

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.

The antiarrhythmic effects of controlled release disopyramide phosphate and long acting propranolol in patients with ventricular arrhythmias

The antiarrhythmic effect of slow-release disopyramide phosphate (DR) 300 mg twice daily and of long-acting propranolol (PR) 1 X 160 mg daily was compared in a randomized cross-over study in patients with premature ventricular beats (PVB). 12 patients with PVB (Lown Classes II-V) were given: placebo I for 3 days, DR or PR for 7 days, placebo II for 5 days and PR or DR for 7 days. During each study phase Holter-ECG recordings were taken over a period of 24 h. With DR 6 patients showed a positive qualitative effect, improving by at least one Lown class, whereas only 2 patients did so with PR. With DR reduction of PVB greater than 80% occurred in 7 patients, and with PR in 2 patients. In all patients with any reduction in PVB, the median decrease was 85% with DR and 59% with PR. The overall results suggest that the antiarrhythmic effect of disopyramide phosphate in the slow-release preparation is at least satisfactory and comparable to that of disopyramide phosphate in the standard capsule formulation given in the usual and more complicated regime of four divided doses. The antiarrhythmic effect of PR in the recommended dose as given was not convincing.

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.

Hemodynamic response to exercise after propranolol in patients with mitral stenosis

Hemodynamic response to exercise before and 10 minutes after propranolol (5 mg intravenously) was studied in 10 young patients with pure mitral stenosis who had normal sinus rhythm and no cardiac failure. After propranolol the mean heart rate and cardiac index at rest were lower than during the control state (respectively, 95 +/- 4 versus 82 +/- 3 beats/min, P less than 0.005; 3.4 +/- 0.2 versus 2.8 +/- 0.1 liters/min per m2, P less than 0.025). As a result, the mean pulmonary wedge pressure and mean mitral valve gradient at rest were lower (respectively, 22 +/- 2 versus 18 +/- 2 mm Hg, P less than 0.005; 24 +/- 2 versus 17 +/- 2 mm Hg, P less than 0.001). During exercise after propranolol the values of pulmonary wedge pressure and mitral valve gradient were lower than control values during exercise (respectively, 39 +/- 3 versus 30 +/- 2 mm Hg, P less than 0.005; 44 +/- 3 versus 32 +/- 3 mm Hg, P less than 0.005), again because of the lower heart rate and cardiac index (130 +/- 6 versus 104 +/- 6 beats/min, P less than 0.001; 4.6 +/- 3 versus 3.7 +/- 2 liters/min per m2, P less than 0.01). Left ventricular end-diastolic pressure and stroke index showed no significant changes. Thus, propranolol may benefit patients with pure mitral stenosis with sinus rhythm and no cardiac failure whose symptoms occur during those reversible conditions characterized by an increase in heart rate or cardiac output, or both.

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.

Management of the patient with a prosthetic heart valve

Approximately 20,000 heart valve prostheses are inserted yearly in the United States. Even after successful heart operations, the patients who receive them cannot be regarded as healthy individuals but are a special group with special problems who need close medical attention for the rest of their lives. They are susceptible to many unusual complications because of their implanted foreign body, and it is a challenge to all physicians in contact with them to be aware of their peculiar problems in order to prevent complications if possible and to treat them immediately if they occur. General therapy, surgical complications, infection, and mechanical problems are reviewed, with means for management outlined. These difficulties can be dealt with only by careful follow-up and well-coordinated teamwork between the family physician and the institution where the operation was performed.

Effect of -adrenoceptor blocking agents on poststimulatory atrial flutter in the dog, with observations on the participation of adrenergic mechanisms in this experimental arrhythmia

1. Four beta-adrenoceptor antagonists, viz. (+/-) propranolol (0.5 mg/kg), (-) alprenolol (0.25 mg/kg), practolol (5 mg/kg) and USVC 6524 (20 mug/kg), were tested for their effects on atrial flutter produced by electrical stimulation of the right atrium around the crushed inter-venae-caval bridge in anaesthetized dogs.2. All the drugs reduced atrial and ventricular rates; this was followed by the abrupt termination of flutter and restoration to normal sinus rhythm.3. Since all the drugs (including practolol, which is devoid of local anaesthetic activity) were given in doses just sufficient to block beta-adrenoceptors, it indicated that beta-adrenoceptor blockade was responsible for their antiarrhythmic property in this test procedure.4. Further evidences in support of participation of the sympathetic nervous system in poststimulatory flutter were: (i) flutter could not be produced in nine out of ten dogs whose catecholamine stores were depleted by pretreatment with reserpine; (ii) infusion of adrenaline in these animals resulted in the production of flutter; (iii) duration of flutter after termination of exposure to adrenaline was a few minutes, which is similar to the brief time previously reported to be taken for the disappearance of catecholamines from the hearts of reserpinized animals.5. The clinical significance of the above findings is discussed.

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.

The effects of propranolol on cardiac conduction

The effects of propranolol, 0.1 mg/kg given intravenously, on atrioventricular (A-V) conduction and intraventricular (IV) conduction were studied in eight patients. Atrial pacing was used to control the heart rate. His bundle electrograms were recorded, and the interval from the pacing impulse to the His bundle electrogram (P-H interval) was used as a measure of A-V conduction and the interval from the His bundle electrogram to the S wave (H-S interval) was used as a measure of intraventricular conduction. Propranolol significantly prolonged the P-H interval in every patient at all paced heart rates, and it had no effect on the H-S interval. In two patients propranolol prolonged the effective refractory period of the atrioventricular conducting tissue.

In four dogs during His bundle pacing, propranolol (4 mg/kg iv) had no effect on intraventricular conduction as measured from the His bundle pacing spike to S wave (H-S interval). In two dogs with prolonged H-S intervals secondary to toxic doses of digitalis and procainamide, propranolol had no effect on IV conduction. It is concluded that propranolol prolongs A-V conduction and has no effect on IV conduction when administered to patients in clinically effective dosages. Propranolol's effects on cardiac conduction can be explained on the basis of its capacity to produce beta-adrenergic blockade.

Effect of propranolol on exercise tolerance of patients with atrial fibrillation

Six patients with atrial fibrillation who were taking digitalis were exercised before and after 30 mg. of propranolol twice daily. Though there was a lower pulse rate at rest and on exercise in all patients, three suffered deterioration of exercise tolerance. It is concluded that propranolol does not improve the exercise tolerance of patients with atrial fibrillation whose resting ventricular rate is controlled with digitalis.

Effects of beta-adrenergic blockade (propranolol) on left ventricular hemodynamics and the electrocardiogram during exercise-induced angina pectoris

The effects of intravenous propranolol were studied in nine patients with ischemic heart disease during cardiac catheterization. Values were obtained at rest and during exercise before and after propranolol. A work load known to produce angina and significant ST depression was selected. Pressures were monitored during exercise and correlated with electrocardiographic changes and appearance of angina. At rest and exercise, propranolol caused a decrease in heart rate, cardiac output, mean systolic ejection rate, stroke volume, left ventricular systolic pressure, first derivative, and work. Left ventricular end-diastolic pressure did not significantly change. Angina, which developed in all nine patients during control exercise, did not appear in four after propranolol, while ECG abnormalities were less marked in all cases. Comparison of exercise responses following propranolol in angina-free patients (four) with those developing angina (five) disclosed a more pronounced negative inotropism in the angina-free group. It is concluded that propranolol is beneficial in angina. Improvement derives primarily from suppression of positive chronotropic and inotropic responses, which are major determinants of myocardial oxygen consumption.

Cardio-circulatory effects of beta-adrenergic blockade in organic heart disease. Comparison between propranolol and CIBA 39,089-Ba

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Beta-adrenergic blockade and cardiac arrhythmias

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Conversion of atrial fibrillation and flutter by propranolol

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