The use of beta-adrenergic receptor blocking drugs in dysrhythmias

Effects of intravenous propranolol on cardiovascular hemodynamics during supraventricular tachycardia

Hemodynamic variables were evaluated in 10 patients during supraventricular tachycardia before and after administration of intravenous propranolol. The drug markedly worsened the already compromised hemodynamic pattern of supraventricular tachycardia.

Holter-guided identification of premature ventricular contractions susceptible to suppression by beta-blockers

To evaluate whether the identification of the different types of relations between premature ventricular contractions (PVCs) and the preceding sinus cycle length is capable of predicting the effect of beta-blockers on the PVCs themselves, 55 patients (43 men, 12 women, mean age 52.6 +/- 15.6 years) with different cardiac diseases, and >30 PVCs/hr characterized by stability and the same relation at two Holter monitoring periods were studied. The relation was tachycardia enhanced (the shorter the preceding cycle length, the higher the incidence of PVCs) in 23 patients (group 1); indifferent (no correlation between the preceding cycle length and PVC incidence) in 21 (group 2); and bradycardia enhanced (the longer the preceding cycle length, the higher the incidence of PVCs) in 11 (group 3). A third Holter monitoring was performed 6 days after nadolol administration (80 mg/day) to evaluate its effect on the three types of PVCs. Incidence in all patients (-88;p<0.001). In group 2, it caused a reduction in the majority of patients (-60%;p<0.05) but an increase in five. In group 3, it caused a reduction in only half of the patients (-45%) and a 91% increase in the remainder. The difference in the effect of nadolol in the three groups was highly significant (X2=27.5;p<0.0001). The relation between the incidence of PVCs and the preceding cycle length is a useful means of identifying subsets of patients with PVCs who will benefit from beta-blockers.

Sustained atrial tachycardia in adult patients. Electrophysiological characteristics, pharmacological response, possible mechanisms, and effects of radiofrequency ablation

BACKGROUND

Mechanisms and electropharmacological characteristics in adult patients with atrial tachycardia (AT) are not well described. We proposed that a combination of electropharmacological characteristics, recording of monophasic action potential, and effects of radiofrequency ablation could further determine the mechanisms and achieve a new classification in adults with various types of AT because they were important in regard to the correlation between mechanisms and pathophysiology, clinical syndrome, and responses to specific pharmacological or nonpharmacological therapies.

METHODS AND RESULTS

Thirty-six patients (11 female, 25 male; mean age, 57 +/- 13 years) with AT were referred for electropharmacological studies and radiofrequency ablation. Resetting response pattern, entrainment phenomenon, recording of monophasic action potential, serial drug test, response to Valsalva maneuver, endocardial mapping technique, and radiofrequency ablation were performed. Seven patients had automatic AT provocable with isoproterenol; neither initiation nor termination was related to programmed electrical stimulation. The other 29 patients had AT initiated or terminated by electrical stimulation and mechanisms related to triggered activity or reentry; nine of them needed isoproterenol to facilitate initiation of AT, associated with delayed afterdepolarization in monophasic action potential. All responded to adenosine (15 to 60 micrograms/kg) and Valsalva maneuver. Dipyridamole terminated AT and decreased the slope of afterdepolarization. Afterdepolarization was not found in the patients with automatic or reentrant AT. In 40 of 41 (98%), AT was ablated successfully, with late recurrence in 2 of 40 (5%) (follow-up, 18 +/- 4 months).

CONCLUSIONS

This study demonstrates the diverse mechanisms and electropharmacological characteristics of AT in adults. Furthermore, radiofrequency ablation of various types of AT could achieve high success and low recurrence rates.

Effects of antiarrhythmic drugs (verapamil, propranolol and lignocaine) on the electrocardiogram and haematology in adrenaline-induced arrhythmias in dogs anaesthetized with halothane

Twenty adult (1-3 year old) mongrel dogs of either sex were used to study the effects of antiarrhythmic drugs in adrenaline-induced arrhythmias. The dogs were divided randomly into four groups of five dogs each (n = 5), anaesthetized with halothane and pretreated intravenously (i.v.) with verapamil 0.1 mg kg-1, propranolol 0.06 mg kg-1, or lignocaine 4 mg kg-1 while the controls received sterile physiological saline. Adrenaline (4 micrograms kg-1) was administered i.v. 10 min after drug pretreatments. Lead II of the ECG was recorded and blood collected for haematology. Ventricular fibrillations preceded by ventricular tachycardia occurred in the control dogs and three died within one minute of adrenaline administration. The predominant arrhythmias were ventricular premature beats, ventricular tachycardia, and second degree heart block. A significant increase (P < 0.05) in T wave amplitude was observed in the control group from 0.16 +/- 0.05 mV to 0.43 +/- 0.09 mV while only minimal increases were noted in the drug pretreated groups and there were no deaths. Data obtained from this study suggest that verapamil when administered early compares well with propranolol in the control of adrenaline-induced ventricular arrhythmias in the dog. Lignocaine when administered early prior to the induction of the arrhythmias protected against death but not arrhythmias. Drug pretreatments did not have any clinically significant effects on electrocardiographic parameters.

Digitalis toxicity. Using immunotherapy when supportive care isn't enough

Significant digitalis toxicity, although uncommon, is a medical emergency. Recognition of the problem and good supportive care (eg, administration of activated charcoal and binding resins, correction of potassium levels, restoration of heart rhythm) are the cornerstones of treatment. If indicated, immunotherapy with digoxin immune Fab (Digibind) is a valuable and effective tool.

Treatment of digitalis intoxication with emphasis on the clinical use of digoxin immune Fab

Many studies and cases of digitalis intoxication have been reported since the time of William Withering's first publication in 1785. Recognition and management of digitalis toxicity is challenging. Before digoxin immune Fab was commercially available, treatment consisted of managing the signs and symptoms of toxicity until the digitalis was eliminated. Digoxin immune Fab offers a safe, effective, and specific method of quickly reversing digitalis toxicity. Factors that must be considered with the clinical use of this agent include the dosage calculation, administration technique, postdose monitoring, pharmacokinetics, mechanism of action, interference with commercially available digoxin assays, partial neutralizing dosing, rebound of free digoxin, and indications for use. For severe, life-threatening toxicity, digoxin immune Fab is the treatment of choice.

Measurement and cardiovascular relevance of partial agonist activity (PAA) involving beta 1- and beta 2-adrenoceptors

In the normal heart the ratio of beta 1/beta 2-receptors in both atria and ventricles is about 75:25; in the failing heart the ratio is about 60:40. Stimulation of either beta 1- or beta 2-receptors results in a positive chronotropic and inotropic response. In the periphery, with the exception of lipolysis, renin release, control of intraocular pressure and intestinal relaxation, beta 2-related activity predominates. The nature of the beta 2-receptor is being unravelled and it has now been cloned. The beta-receptor antagonist is 'anchored' via disulfide bonding. Subsequent events involve the regulatory protein guanine nucleotide which couples the receptor to adenylate cyclase. beta-receptor density may by up- or down-regulated. beta-stimulation down-regulates (uncouples and internalizes or sequestrates) and beta-antagonism up-regulates beta-receptor numbers, but the functional implications of such changes are not always clear. A partial agonist occupies a receptor site and competitively inhibits the full agonist (e.g. noradrenaline). A partial agonist differs from a full agonist in that maximal response of a tissue is less. When background sympathetic activity is absent or very low a partial agonist will act as an agonist, e.g. increase heart rate, but when background tone is high the partial agonist will behave functionally as an antagonist, e.g. decrease heart rate. In animals partial agonist activity (PAA) can be assessed in many ways. In the catecholamine-depleted (reserpine or syrosingopine), vagotomized or pithed, intact animal beta-activity can be assessed via changes in heart rate, cardiac contractility and atrioventricular conduction. Isolated organs can also be used such as atria, papillary muscle, tracheal, mesenteric artery and uterine preparations. The choice of animal is important as marked species differences in response can occur. In man assessing PAA is difficult due to the presence of an intact sympathetic system: the problem can be overcome by autonomic blockade of constrictor and vagal reflexes with prazosin, clonidine and atropine but leaving the beta-receptor mediated responses unimpaired. beta 1- and beta 2-selective PAA can also be gauged via an increased sleeping heart rate (basal sympathetic tone) in the presence and absence of a beta 1- and beta 2-selective antagonist. beta 1-selective PAA can also cause an increase in resting systolic blood pressure, beta 2-selective PAA may be further assessed by a fall in DBP, increased blood flow, fall in peripheral resistance or increased finger tremor.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Effects of beta-adrenergic blockade on verapamil-responsive and verapamil-irresponsive sustained ventricular tachycardias

To assess effects of beta-adrenergic blockade on ventricular tachycardia (VT) of various mechanisms, electrophysiology studies were performed before and after intravenous infusion of propranolol (0.2 mg/kg) in 33 patients with chronic recurrent VT, who had previously been tested with intravenous verapamil (0.15 mg/kg followed by 0.005 mg/kg/min infusion). In the verapamil-irresponsive group, 10 patients (group IA) had VT that could be initiated by programmed ventricular extrastimulation and terminated by overdrive ventricular pacing, and 11 patients (group IB) had VT that could be provoked by isoproterenol infusion (3-8 micrograms/min) but not by programmed electrical stimulation, and that could not be converted to a sustained sinus rhythm by overdrive ventricular pacing. Notably, in the group IA patients, all 10 patients had structural heart disease (coronary arteriosclerosis or idiopathic cardiomyopathy); beta-adrenergic blockade accelerated the VT rate in one patient but exerted no effects on the VT rate in the remaining 9 patients, and VT remained inducible in all 10 patients. By contrast, in the group IB patients, 7 of the 11 patients had no apparent structural heart disease; beta-adrenergic blockade completely suppressed the VT inducibility during isoproterenol infusion in all 11 patients. There were 12 patients with verapamil-responsive VT (group II). 11 of the 12 patients had no apparent structural heart disease. In these patients, the initiation of VT was related to attaining a critical range of cycle lengths during sinus, atrial-paced or ventricular-paced rhythm; beta-adrenergic blockade could only slow the VT rate without suppressing its inducibility. Of note, 14 of the total 33 patients had exercise provocable VT: two in group IA, five in group IB, and seven in group II. Thus, mechanisms of VT vary among patients, and so do their pharmacologic responses. Although reentry, catecholamine-sensitive automaticity, and triggered activity related to delayed afterdepolarizations are merely speculative, results of this study indicate that beta-adrenergic blockade is only specifically effective in a subset group (group IB) of patients with VT suggestive of catecholamine-sensitive automaticity.

Efficacy and safety of oral nadolol for exercise-induced ventricular arrhythmias

Sixty-four patients with reproducible exercise-induced ventricular arrhythmias were enrolled in an open-label, multicenter study to assess the efficacy and safety of oral nadolol therapy. There were 53 men and 11 women ranging in age from 19 to 75 years (mean 53.9). The severity of arrhythmias varied from frequent ventricular premature beats to nonsustained and sustained ventricular tachycardias. Using serial treadmill exercise tests, patients underwent dose titration for 1 month and were followed up for 3 to 6 months. Depending on drug tolerance and response to treadmill exercise testing, the single daily required dose of oral nadolol ranged from 20 to 240 mg (average 66). Twenty-three (36%) of the patients experienced a total of 30 adverse effects of nadolol therapy; however, only 9 (14%) patients had to be withdrawn from the study. The adverse effects observed were those commonly associated with beta-adrenergic blocking agents, and all were dose-dependent and reversible. At the last patient visit, the severity of exercise-induced ventricular arrhythmias was significantly decreased compared with pretreatment in 36 (75%) of 48 evaluable patients. Eighteen (38%) of the patients demonstrated total suppression of arrhythmias. This was accompanied by significant increases from pretreatment in both the mean duration of symptom-limited exercise (+1.02 +/- 0.41 minutes, p less than 0.05) and the mean time of exercise required for arrhythmia induction (+1.80 +/- 0.66 minutes, p less than 0.01), a significant decrease from pretreatment in the mean peak exercise double-product (-4,775, p less than 0.001) and a decrease in the incidence of exercise-induced ST-segment depression (-33%).(ABSTRACT TRUNCATED AT 250 WORDS)

Beta blockers in combination with class I antiarrhythmic agents

The hemodynamic and antiarrhythmic interactions between nadolol and a commonly used class I antiarrhythmic agent, quinidine or procainamide, were evaluated in 18 patients with ventricular arrhythmias in a double-blind, parallel study. Patients qualified for entry into the study if their ventricular arrhythmias remained poorly controlled (greater than or equal to 10 ventricular premature complexes/hr) with the class I agent alone and they had a left ventricular ejection fraction greater than 30%. Patients received their usual therapeutic doses of quinidine or procainamide throughout the study, which consisted of 3 treatment periods; a 2-week placebo treatment period, a 2-week open-label oral nadolol dose titration period, during which the dosages of nadolol were gradually increased from 40 mg daily to a maximum tolerated dose up to 120 mg daily, and a 4-week randomized, parallel comparison period during which patients were treated with either a class I agent alone or a combination of a class I agent and nadolol. Left ventricular ejection fractions by radionuclide ventriculography and 24-hour ambulatory electrocardiographic (Holter) recordings were obtained at the end of each treatment period. A positive treatment response was defined as greater than or equal to 75% reduction in ventricular premature complex frequency. During the dose titration phase, combination therapy with nadolol (mean dose 94 mg daily) and class I agents produced a mean decrease in ventricular premature complexes of 79% (p less than 0.01), and a mean decrease in ventricular couplets of 95% (p less than 0.01). A positive response was observed in 57% of patients treated with nadolol plus a class I agent.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiology of beta blockers in supraventricular arrhythmias

beta-adrenergic blocking agents are efficacious in the treatment of patients with a variety of supraventricular tachycardias, based directly on their capacity to counter the effects of beta-adrenergic stimulation on sinus and atrioventricular nodal tissue. Specifically, beta blockers depress sinus node automaticity and inhibit atrioventricular nodal function by prolonging refractoriness and slowing conduction. Supraventricular arrhythmias that depend on these structures either for perpetuation or for conduction to the ventricles are predictably sensitive to beta blockade. These arrhythmias include sinus tachycardia, sinoatrial reentrant, atrioventricular nodal reentrant (dual pathway) and atrioventricular reciprocating (concealed bypass tract) tachycardias, as well as atrial flutter and fibrillation. beta blockers may also be used, in selected patients, to inhibit catecholamine-facilitated accessory pathway function by prolonging refractoriness. beta blockers offer particular clinical advantages, including an acceptable side-effect profile, titratable effect, varied pharmacology and reasonable concordance between efficacy of parenteral and oral dosage forms. The key element in the most effective use of these drugs appears to be an accurate arrhythmia diagnosis that allows for the most appropriate application of a reliable treatment form.

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)

Esmolol: a novel cardioselective, titratable, intravenous beta-blocker with ultrashort half-life

Esmolol is an ultrashort-acting, cardioselective, intravenous beta-blocker with an elimination half-life of about nine minutes. After administration of a loading dose, its full therapeutic effect is evident within five minutes. Its efficacy in treating supraventricular arrhythmias is equal to that of propranolol, but unlike propranolol, the action of esmolol is titratable and is largely reversed within 10 to 30 minutes after stopping its administration. Esmolol is also effective in attenuating life-threatening perioperative tachycardia and hypertension caused by adrenergic stimulation in high-risk patients.

Antiarrhythmic efficacy of propranolol: comparison of low and high serum concentrations

Propranolol has been effective in suppressing ventricular arrhythmias in up to 70% of patients in some series; however, a wide range of concentrations was required to produce this degree of efficacy. In one series, 40% of responders required high serum concentrations (greater than 500 ng/ml) in excess of those required for physiologic beta-receptor blockade (25 to 150 ng/ml). To assess the relative contribution of high concentration electrophysiologic effects to antiarrhythmic efficacy the results of programmed electrical stimulation were compared at high and low (beta-blocking) concentrations in 28 patients with inducible sustained ventricular tachycardia. Propranolol was given as a series of loading and maintenance infusions producing first a mean concentration of 130 +/- 72 ng/ml (beta-blocking) and then a mean concentration of 743 +/- 523 ng/ml (high). Beta-blockade was assessed by the percent reduction in exercise-induced tachycardia. Near maximal beta-blockade was achieved by a concentration of 150 ng/ml. At a low concentration, 6 of 28 patients had a response to propranolol (complete in 5 and partial in 1). At a high concentration, one additional patient had a complete response while three had a partial antiarrhythmic response. At high concentrations of propranolol there was a significant shortening of the QTc interval relative to that seen during the low dose infusion. No other significant electrophysiologic changes occurred at high versus low concentration. In summary, an antiarrhythmic response to propranolol occurs most frequently at a beta-blocking concentration. High concentration electrophysiologic effects occur and these appear to contribute to antiarrhythmic efficacy in some patients.

Combination antiarrhythmic drug therapy for ventricular tachyarrhythmias

New antiarrhythmic drug regimens are constantly being sought because of the relatively low efficacy rates of standard antiarrhythmic agents in preventing induction of ventricular tachyarrhythmias; the application of these agents is also limited due to serious or debilitating side-effects. The combination of two antiarrhythmic agents with complimentary electrophysiologic activities and differing toxicities might offer significant advantages in overcoming the drawbacks of standard antiarrhythmic drug therapy. A knowledge of the pharmacodynamics of the major classes of antiarrhythmic agents will allow informed choices of drugs for use in combination therapy. Judging antiarrhythmic drug efficacy is a complex problem, requiring an understanding of the influence of the arrhythmia monitoring technique, arrhythmia morphology and the response to previous drugs on drug efficacy rates, so that accurate comparisons of drug effectiveness can be made among different agents or combinations. A number of combination therapies have been tested for suppression of complex ventricular ectopy, nonsustained ventricular tachycardia and sustained ventricular tachycardia and ventricular fibrillation. The most successful combinations have been those using class IA and IB agents and class IA and II agents. In general, these combinations tend to show higher efficacy rates in suppressing all forms of ventricular ectopy and ventricular tachyarrhythmias, and usually have a lower incidence of toxic side-effects compared with individual agents alone. On the basis of these initial results, it seems warranted to perform further studies to explore these combinations in larger populations and to test new combinations developed on the basis of pharmacodynamic principles.

Effects of atenolol in patients with reciprocating supraventricular tachycardia

We studied 12 patients with crisis of paroxysmal reciprocating supraventricular tachycardia before and after intravenous injection of 5 mg of atenolol. The patients were then followed for periods ranging from 6 to 50 months (median 34 months). During this time, they received oral atenolol therapy, at 200 mg for the first two weeks, and 100 mg daily thereafter. Tachycardia was due to reciprocation within the atrioventricular node in 9 patients, and to pre-excitation in 3 patients. Atenolol slowed the sinus rate, prolonged the atrioventricular conduction time, and increased the atrial cycle length at which atrioventricular nodal Wenckebach phenomenon occurred. During the tachycardia, atenolol increased the tachycardia During the tachycardia, atenolol increased the tachycardia cycle length, due to prolongation of the intranodal atrioventricular conduction time. Of the 11 patients who were observed for the full period, 7 had no further episodes of arrhythmia. One patient (with left-sided pre-excitation) failed to respond to any antiarrhythmic medication, one patient remained free of symptoms for two years, but received an atrial pacemaker for control of the tachycardia at the end of this period. Two patients (one with dual atrioventricular nodal pathways, and one with concealed left-sided pre-excitation) await other treatment for their tachycardia, after remaining free of symptoms for one and two years, respectively. These findings suggest that atenolol is an effective beta blocker for use in controlling arrhythmias in patients with reciprocating supraventricular tachycardia, for use in once daily dosage, and is a medication largely free of side effects.

Comparison of acebutolol and propranolol therapy for ventricular arrhythmias

The effects of acebutolol, a new investigational cardioselective beta blocker, and propranolol on ventricular arrhythmias were compared in 14 patients with more than 30 premature ventricular contractions (PVCs) per hour. Each patient served as their own control, receiving both drugs and placebo in random sequence and in double-blind fashion, with an intervening one-week, drug-free period. Each drug was given for a two-month period, the maximum acebutolol dosage reaching 600 mg tid and the maximum propranolol dosage 80 mg tid. Seventy-two-hour ambulatory electrocardiographic monitoring assessed arrhythmia frequency for each study period. Mean PVC counts did not significantly differ during the two control periods. Acebutolol decreased mean PVC count by 65% (P less than .02), with eight patients exhibiting a 70% or greater decrease. Only three patients exhibited a similar decline with propranolol. The incidence of PVCs was not significantly decreased by propranolol. Acebutolol reduced the number of couplets by 70% (P less than .04), whereas propranolol did not significantly affect couplets. At the dosage of 600 mg tid, acebutolol was well tolerated, effectively suppressed total PVCs and couplets, and appeared to be more effective than propranolol administered at 80 mg tid.

Beta-adrenergic blockade by nadolol in control of ventricular tachyarrhythmias

The antiarrhythmic effect of nadolol, a long-acting, nonselective beta antagonist without intrinsic sympathomimetic or membrane-stabilizing properties, was evaluated in 36 patients with ventricular dysrhythmias as determined by three baseline 24-hour Holter recordings at a time when subjects were receiving placebo. Nadolol was administered once daily at a dose of 40 to 80 mg and increased at weekly intervals to a maximum daily dose of 640 mg. Thereafter the drug was stopped gradually and placebo was given again for a period of 2 weeks. Nadolol was effective in reducing premature ventricular contractions (PVCs) in 17 of 36 patients (48%), in reducing ventricular couplets in 24 of 27 patients (89%), and in reducing nonsustained runs of ventricular tachycardia in all 13 subjects. Serum nadolol levels obtained at dosages resulting in a 75% reduction in PVCs varied from 58 to 853 ng/ml. In the majority of the subjects studied, a nadolol dosage of 160 mg/day or less was effective for arrhythmia suppression.

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.

Beta-adrenoceptor blockade: electrophysiology and antiarrhythmic mechanisms

Beta-adrenoceptor-blocking agents reduce beta-adrenergic activity and depress sinoatrial and atrioventricular nodal conduction. These agents are thus useful for controlling supraventricular tachyarrhythmias. For the treatment of ventricular arrhythmias, beta-adrenoceptor-blocking agents possess antifibrillatory properties, depress diastolic depolarization of ectopic pacemaker activity, reduce electrical instability associated with prolongation of the QT interval, and are specifically effective in suppressing ventricular arrhythmias that are rate (tachycardia) dependent and/or caused by catecholamine-sensitive automaticity. Furthermore, beneficial hemodynamic effects of beta-adrenoceptor blockade on ischemic myocardium may also contribute to the antiarrhythmic potency of these agents.

Electrophysiologic actions of high plasma concentrations of propranolol in human subjects

The authors have previously shown that 40% of patients whose ventricular arrhythmias respond to propranolol require plasma concentrations in excess of those producing substantial beta-receptor blockade (greater than 150 ng/ml). However, the electrophysiologic actions of propranolol have only been examined in human beings after small intravenous doses achieving concentrations of less than 100 ng/ml. In this study, the electrophysiologic effects of a wider concentration range of propranolol was examined in nine patients. Using a series of loading and maintenance infusions, measurements were made at baseline, at low mean plasma propranolol concentrations (104 +/- 17 ng/ml) and at high concentrations (472 +/- 68 ng/ml). Significant (p less than 0.05) increases in AH interval and sinus cycle length were seen at low concentrations of propranolol, with no further prolongation at the high concentrations; these effects are typical of those produced by beta-blockade. However, progressive shortening of the endocardial monophasic action potential duration and QTc interval were seen over the entire concentration range tested (p less than 0.05). At high concentrations, there was significant (p less than 0.05) further shortening of both the QTc and monophasic action potential duration beyond that seen at low propranolol concentrations, along with a progressive increase in the ratio of the ventricular effective refractory period to monophasic action potential duration. No significant changes were seen in HV interval, QRS duration or ventricular effective refractory period. In summary, the concentration-response relations for atrioventricular conductivity and sinus node automaticity were flat above concentrations of 150 ng/ml.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Atrioventricular node reentry: intravenous verapamil as a method of defining multiple electrophysiologic types

Fourteen patients with recurrent supraventricular tachycardia (SVT) underwent electrophysiological evaluation. Each patient was shown to have reentry confined to the region of the atrioventricular (AV) node. Verapamil, 0.075 to 0.15 mg/kg was administered intravenously to each patient during a stable episode of SVT, resulting in termination in each instance. There was more than one mechanism for termination of SVT. Nine patients showed termination by anterograde AV node block preceded by an increase in conduction time in the anterograde limb of the tachycardia circuit (Ae-H intervals) with no change in the conduction time in the retrograde limb (H-Ae intervals). Three patients showed termination by block in the retrograde limb of the circuit preceded by increases in both Ae-H and H-Ae intervals. An additional example of termination by spontaneous ventricular premature complexes and usurpation by sinus rhythm were also seen. Common features were that verapamil had significant effects on anterograde and retrograde conduction and refractoriness in the AV node. It prolonged the refractory periods of both fast and slow pathways in patients with dual anterograde AV node pathways, and observable effects on retrograde conduction and refractoriness were seen even in patients with constant ventriculoatrial conduction times during incremental ventricular pacing in a control study. However, three distinct groups of patients were identified on the basis of their response to ventricular pacing in a control study and upon verapamil effects recorded during their SVT. An explanation for these latter findings may be that there is a normal variation in the retrograde response of parts of the AV node to ventricular pacing, and a variability in some of the patients' responses to verapamil.

Inhalation challenge with carbachol and isoproterenol to predict bronchospastic response to propranolol in COPD

Disabling propranolol-induced bronchospasm occasionally prevents use of this drug in patients with chronic obstructive pulmonary disease (COPD). A means was developed to identify patients who have high risk for this adverse effect using bronchial challenge by inhaling the parasympathomimetic drug, carbachol, and isoproterenol. After baseline pulmonary function tests, 12 patients with varying degrees of COPD and 13 control patients underwent maximal beta-blockade using intravenously administered propranolol during cardiac catheterization followed by repeat pulmonary function testing. Seven of the patients with COPD and ten of the control subjects were restudied while taking propranolol orally for at least three weeks. The results indicated that the bronchodilator response to inhaled isoproterenol does not reliably identify patients who develop bronchoconstriction with propranolol, but bronchoconstriction after inhaling carbachol is indicative of the high risk of developing bronchoconstriction from propranolol.

Beneficial effect of intravenous diltiazem in the acute management of paroxysmal supraventricular tachyarrhythmias

We tested the effectiveness and safety of i.v. diltiazem in the management of paroxysmal supraventricular tachyarrhythmias in 39 patients, 21 with organic heart disease and seven in heart failure. Fifteen patients presented with supraventricular tachycardia, 12 with atrial fibrillation and 12 with atrial flutter. End points were conversion to sinus rhythm or slowing of the ventricular rate to 100 beats/min or less. Diltiazem was given as an i.v. bolus of either 150 or 300 micrograms/kg over 2 minutes. A second injection was administered to patients who received the lower dose and failed to reach either end point within 30 minutes. The overall success rate was 82% (32 of 39 patients). Time to end point was 5 minutes or less in 20 patients. Conversion to sinus rhythm occurred in 13 of 15 patients (87%) with supraventricular tachycardia and in two of 12 patients with atrial fibrillation. Treatment side effects included a slow ventricular rate in one patient who had a sick sinus syndrome and hypotension in two patients that rapidly responded to fluid administration. We conclude that i.v. diltiazem is effective and well tolerated and advocate its use in the management of paroxysmal supraventricular tachyarrhythmias.

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.

A long-term prevention study with oxprenolol in coronary heart disease

We carried out a randomized double-blind controlled secondary-prevention trial of oxprenolol over seven years. Forty milligrams of oxprenolol or placebo was given twice daily to 1103 men 35 to 65 years old who had an acute myocardial infarction between 1 and 90 months previously. Overall, there was no difference in mortality or cardiac events between the placebo and oxprenolol groups. The major influence on prognosis was the time at which treatment was started after infarction. In 417 patients in whom treatment was started within four months of infarction oxprenolol increased the six-year cumulative survival rate from 77 to 95 per cent (P less than 0.001). In 274 patients with treatment starting between 5 and 12 months of infarction the survival rate was similar in the two groups, but in 412 patients entered between 1 and 7 1/2 years after their first infarction oxprenolol reduced the six-year survival rate from 92 to 79 per cent (P = 0.002). The increased mortality in this latter group mainly occurred late after withdrawal from active treatment. The value of low-dose oxprenolol in secondary prevention appears to be confined to patients treated relatively soon after myocardial infarction.

Ventricular antiarrhythmic effects of beta-adrenergic blocking drugs: a review of mechanism and clinical studies

Beta-adrenergic blocking drugs are now commonly used in patients with ventricular arrhythmias. This review examines the possible mechanisms of their ventricular antiarrhythmic effect. Actions on the myocardial cell, as well as actions on the central and autonomic nervous system, are reviewed. Many clinical studies have attempted to show the efficacy of beta blockers in controlling ventricular arrhythmia and decreasing the incidence of sudden death after acute myocardial infarction. Although some of these clinical trials tended to show an impact on sudden death, the size of these trials or their design problems do not allow firm conclusions to be made. The Beta Blocker Heart Attack Trial (BHAT) is a placebo-controlled, double-blind, randomized trial of propranolol currently under way in the United States. Important additions to the previous trials include the addition of drug levels to ensure beta-blocking dosage, long-term electrocardiographic monitoring, and a study population of 4200 patients followed for an average of three years. These important design features will be of value in addressing some of the unanswered questions presented in this review.

Verapamil (Isoptin, Knoll; Calan, Searle)

Verapamil is a calcium antagonist that is pharmacologically different from other currently marketed antiarrhythmics. It is used for the acute treatment of PSVT and atrial fibrillation and flutter. It appears to be more effective than beta-adrenergic blocking agents in the treatment of PSVT. Approximately 80 percent of patients with PSVT will convert to normal sinus rhythm after verapamil 0.075-0.15 mg/kg. Atrial fibrillation and flutter seldom convert to sinus rhythm with verapamil, but it successfully reduces the ventricular rate in 90 percent of these patients. Verapamil is useful for the rapid conversion of PSVT to normal sinus rhythm and for the rapid control of ventricular rate in atrial fibrillation and flutter before other antiarrhythmics have taken effect. Because of its short plasma half-life, other agents or cardioversion can be used if verapamil is unsuccessful. The use of verapamil in the treatment of classical and variant angina, hypertrophic cardiomyopathy, and hypertension is being evaluated. Mild reduction in blood pressure and heart rate may occur with verapamil therapy. Caution must be exercised when verapamil is administered to patients with sinus node disease, advanced AV block, concomitant beta-adrenergic blocking agents, and digitalis intoxication.

Clinical use of oral verapamil in chronic and paroxysmal atrial fibrillation

We evaluated the effectiveness of oral verapamil therapy for control of ventricular rate in digitalized patients with atrial fibrillation (AF) with three clinical problems: chronic AF with rapid rate at rest (four patients), chronic AF with accelerated rate during modest exercise (five patients), and rapid rates during paroxysmal AF (four patients). Patients in the first two categories were evaluated both by open-label dosage titration and by a randomized, double-blind, cross-over protocol. In chronic AF with rapid rate of rest, there was a significant reduction in resting heart rate (from 125 +/- 7 to 87 +/- 14, P less than 0.01) and in peak exercise heart rate (from 162 +/- 33 to 126 +/- 25, P less than 0.01). In chronic AF with rapid rate during exercise, there was also a significant decrease in resting heart rate (from 90 +/- 7 to 66 +/- 4, P less than 0.01) and in peak exercise heart rate (from 126 +/- 19 to 101 +/- 15, P less than 0.01). These effects continued during longterm follow-up of one to 12 months (mean seven months). In patients with paroxysmal AF, verapamil slowed the ventricular response from 16- +/- 24 to 72 +/- 4 P less than 0.01) with only some amelioration of symptoms. Therapy was well tolerated despite a high prevalence (seven of 13 patients) of radiographic cardiomegaly (cardiothoracic ratio greater than 0.55). We conclude that verapamil is a safe and useful drug for control of ventricular rate in digitalized patients with chronic and paroxysmal AF.

Verapamil in the treatment of PSVT

Verapamil is considered by many investigators to be the drug of choice for the acute management of uncomplicated PSVT. Several clinical investigators have demonstrated termination of PSVT in more than 90% of their patients within minutes following IV drug administration. The incidence of reported severe adverse reactions has been less than 1%. PSVT may be complicated by underlying heart disease, or by antegrade accessory pathway conduction in individuals with pre-excitation syndrome. Such conditions, or the prior use of beta-blocking agents, may contraindicate the use of verapamil. However, the history of recent myocardial ischemia or the prior use of digitalis does not appear to contraindicate verapamil therapy. Guidelines for the emergency management of the patient in PSVT are presented.

Hemodynamic effects of intravenous prenalterol in severe heart failure

Nine patients with chronic severe low output heart failure (radionuclide left ventricular ejection fraction 17 +/- 5 percent [mean +/- standard deviation], left ventricular filling pressure 26 +/- 6 mm Hg, cardiac index 1.9 +/- 0.4 liters/min per m2, left ventricular stroke work index 18 +/- 6 g-m/m2) from various causes were treated with intravenous prenalterol (a new catecholamine-like inotropic agent) in doses of 1,4 and 8 mg. Significant hemodynamic improvement occurred as measured by increased left ventricular ejection fraction (to 26 +/- 4 percent), decreased left ventricular filling pressure (to 21 +/- 8 mm Hg) and increased cardiac index (to 2.4 +/- 0.6 liters/min per m2) and left ventricular stroke work index (to 25 +/- 8 g-m/m2). Significant increases in heart rate (from 87 +/- 18 to 91 +/- 18 beats/min) and mean systemic arterial pressure (from 87 +/- 8 to 92 +/- 7 mm Hg) also occurred. Peak hemodynamic response occurred at various doses. Significant adverse effects associated with prenalterol consisted of increased ventricular ectopic beats in two patients and asymptomatic ventricular tachycardia in two patients. Thus, intravenous prenalterol produces hemodynamic improvement in patients with a chronic severe low output state but may be associated with increased ventricular ectopic activity.

Antiarrhythmic effects of acute betablockade with atenolol on supraventricular tachycardias at rest and during exercise

In a total of 18 patients, 7 females and 11 male patients with ages ranging from 23 to 70 years (mean: 45.5 +/- 14.5) diagnostic His bundle studies incorporating programmed atrial and ventricular pacing for the induction of tachycardias was performed before and after betablockade with the cardioselective betablocking agent atenolol, in a dose of 5 mg given iv. over 3 to 5 minutes. In 7 patients the pacing procedure could be repeated following ergometric exercise in order to evaluate the influence of a raised sympathetic tone on the conditions initiating paroxysmal tachycardias. At rest, atenolol prevented the pacing induced tachycardias (20 dysrhythmias in 18 patients) in 3/5 individuals with Wolff-Parkinson-White (WPW)-syndrome, in 4/6 cases with atrial tachycardias, in 4/6 patients presenting atrial flutter, in 2/2 cases developing AV-nodal tachycardias and in 1/1 individual with ventricular tachycardia. Thus, in 13 out of 19 (68%) supraventricular dysrhythmias patients benefitted from atenolol by preventing or controlling the tachycardia. Ergometric exercise changed the tachycardia or echo zone in 5/8 arrhythmias after betablockade when compared to the controls before administration of atenolol (3/5 improvement by narrowing of the tach- or echo zone, 1/5 prevention of tachycardia, 1/5 impairment due to widening of the tachycardia zone). Considering only the prevention of tachycardias, the antiarrhythmic potency of atenolol was improved in one patient with pacing induced flutter and impaired in one individual with a WPW syndrome, by ergometric exercise. These results suggest that atenolol seems to provide a good antiarrhythmic action, especially in supraventricular tachycardias, and that an increased sympathetic tone during exercise may modify the antidysrhythmic strength of betablockade.

Classification of cardioactive drugs in vivo by using programmed electrical stimulation in combination with monophasic action potential recordings at different pacing rates

The effect of antiarrhythmic drugs on myocardial refractoriness may be due to changes either in Vmax of phase 0 or the phase of repolarization of the AP or both. By using programmed electrical stimulation in combination with MAP recordings at different pacing rates in the intact dog heart, it was possible to classify and to a certain extent to elucidate the mode of action of various cardioactive drugs in vivo.