N-acetylprocainamide's antiarrhythmic action in patients with ventricular tachycardia

Antiarrhythmic properties of N-acetylprocainamide, an active metabolite of procainamide, were studied in 15 patients who presented with a cardiac arrest or documented sustained ventricular tachycardia. Programmed electrical stimulation studies were performed. All patients tested had inducible ventricular tachycardia by programmed electrical stimulation techniques while off all antiarrhythmic therapy. Patients were then tested on procainamide 1000 mg administered intravenously, and ventricular tachycardia could be provoked in 8 of 10 patients. Twenty-four to 36 hours later, N-acetylprocainamide was administered, intravenously, and programmed stimulation was performed after 20 minutes. N-acetylprocainamide did not significantly change heart rate, mean arterial blood pressure, electrocardiographic intervals, A-H or H-V conduction times. N-acetylprocainamide prevented ventricular tachycardia induction in 6 of 15 patients. The mean serum N-acetylprocainamide levels in the group protected was 15.7 +/- 4 micrograms/ml and 16.2 +/- 4 micrograms/ml in the group not protected. These 6 patients were discharged on N-acetylprocainamide 1.5 grams orally every 8 hours. Three patients have been maintained on chronic N-acetylprocainamide every 8 hours. Three patients have been maintained on chronic N-acetylprocainamide therapy (6 +/- 2 months), two patients had breakthrough ventricular tachycardia on follow-up Holter monitoring and alternative therapy was given. N-acetylprocainamide has antiarrhythmic efficacy in preventing induction of ventricular tachycardia by programmed electrical stimulation in a high risk group of patients. On chronic oral therapy, N-acetylprocainamide appears to be well tolerated with antiarrhythmic efficacy that may be enhanced with further upward dose titration.

Antiarrhythmic drug efficacy at electrophysiology testing: predictive effectiveness of procainamide and flecainide

In an effort to assess the ability of procainamide to predict effectiveness of antiarrhythmic agents at programmed electrical stimulation (PES) testing, we compared the result of procainamide at PES testing with that of all of the other agents studied. One hundred fifty-three patients underwent PES studies because of either sustained or nonsustained ventricular tachycardia (VT). Procainamide prevented VT induction in 79 of 153 patients. Seventy-four of the remaining 153 were inducible for VT on procainamide, with 55 of these being protected by another antiarrhythmic agent (p less than 0.001). If procainamide failed to prevent VT induction, other conventional and experimental agents were equally as likely to be effective in preventing VT induction. Analysis of flecainide acetate as a predictor of efficacy was also evaluated. Fifty-five patients received flecainide and 29 of these were protected at PES testing; 26 of these patients were also protected with another agent. When VT was inducible in patients who received flecainide, 15 of these 26 patients were protected by another agent, either conventional or experimental (p less than 0.01). Thus, if procainamide or flecainide prevented VT induction they accurately predicted effectiveness of other drugs; however, when they did not prevent VT induction, they served as a poor predictor of the possible effectiveness of other drugs. Serial drug testing at PES studies with multiple conventional and experimental drugs increases the likelihood of finding an effective antiarrhythmic agent.

Digitalis: its place in therapy

Since the initial introduction of digitalis 200 years ago by Withering, its low therapeutic ratio has limited the use of this agent. The utility of digitalis in patients with congestive heart failure and a recent myocardial infarction has been questioned recently. Findings of rigorously controlled clinical studies suggest a small but definite hemodynamic and clinical improvement in patients administered digitalis. Congestive heart failure can be effectively treated without cardiac glycosides. However, when used judiciously, digitalis provides an additional agent in our therapeutic armamentarium. The inotropic, dormotropic, and vagomimetic properties are uniquely suited for the patient with supraventricular arrhythmias and compromised left ventricular function.

The clinical significance of polymorphic ventricular tachycardia provoked at electrophysiologic testing

Ventricular tachycardia (VT) induced at electrophysiologic studies is felt to be clinically significant if the morphology of the induced arrhythmia and the spontaneous arrhythmia are similar. Yet many times in referral patients, an adequate 12-lead ECG does not exist to permit determination of the VT morphology. Since the significance of differences in induced and spontaneous arrhythmias has not been clearly established, we reviewed the records of 153 patients and correlated induced VT morphology with the incidence of sudden death. Polymorphic VT was induced in 88 patients (57%) and monomorphic VT was induced in 65 patients (43%). The total mortality and sudden death rates were similar in the two groups in spite of antiarrhythmic therapy, 12% and 7% (polymorphic) versus 10% and 5% (monomorphic). All the sudden deaths occurred in patients who presented with cardiac arrest and hemodynamically symptomatic VT and none in the asymptomatic VT group, regardless of VT morphology (p less than 0.005). The induced VT morphology cannot be used to predict the potential efficacy of antiarrhythmic drugs, since patients with either morphology are as likely to respond to conventional or experimental agents. Thus, induced polymorphic VT can be a useful index of electrical instability in high-risk patients (cardiac arrest and hemodynamically symptomatic VT) and may be of utility in guiding antiarrhythmic therapy.

Prolonged repolarization: a historical perspective

This symposium will more fully discuss QT prolongation--an area of controversy--prolonged QT syndromes, and new groups of agents that prolong repolarization and the QT interval (calcium blockers and antiarrhythmic agents). This is an important evolving field with old biases confronting a new and more thorough understanding of the phenomenon of prolonged repolarization.

Long-term lorcainide therapy in patients with ventricular tachycardia

One hundred patients inducible at electrophysiologic studies underwent serial drug testing with procainamide, lidocaine, and lorcainide to determine comparative efficacy. Acute intravenous administration was followed by repeat programmed electrical stimulation (PES) studies on separate days for each antiarrhythmic drug. Lorcainide prevented ventricular tachycardia (VT) induction in 69% of the 100 patients studied, procainamide was effective in 50% of the 75 patients studied, and lidocaine prevented VT induction in 30% of 53 patients. Following PES and serial drug testing, 46 patients were started on lorcainide, nine patients on procainamide, and 45 patients were started on other antiarrhythmic drug regimens. Seventy percent of the patients have remained on lorcainide therapy, while 47% have continued on other drug therapies started over a 20.5 +/- 3.2-month mean follow-up period. Despite sleep-wake disturbances and a need for sedation at night, lorcainide therapy was tolerated well in this population and remained an effective antiarrhythmic with prolonged administration.

Antiarrhythmic drug therapy. Recent advances and current status

A number of conventional and newer antiarrhythmic agents are available for the treatment and prophylaxis of ventricular tachycardia and sudden death. Using a multifaceted approach of programmed electrical stimulation studies, drug level determinations, exercise tolerance testing, and 24-hour ambulatory electrocardiographic monitoring, the physician can identify those patients who require therapy and then predict the likelihood of efficacy with each antiarrhythmic agent. This approach affords evaluation of both aspects of the sudden death equation-ectopy frequency (triggering mechanism) and vulnerability to development of sustained ventricular tachycardia (substrate). After institution of therapy, careful follow-up is necessary to document sustained drug efficacy and detect side effects. Serious adverse reactions necessitate a change in antiarrhythmic therapy, as opposed to lowering drug dosage to an ineffective level. The unacceptably high incidence of sudden death due to electrical instability can be reversed only by a rigorous and dedicated long-term approach to the management of serious ventricular arrhythmias.

Prolongation of QT interval and antiarrhythmic action of bepridil

Studies were undertaken with bepridil, a new calcium blocker that prolongs the QT interval, to determine the antiarrhythmic and possible arrhythmogenic properties of this agent. The technique of programmed electrical stimulation was employed to evaluate bepridil in 15 patients with symptomatic ventricular tachycardia (VT). Bepridil prevented VT induction in 7 of 15 patients. Bepridil prolonged the QT and refractoriness and a linear correlation could be demonstrated between the percent change in QTc and refractory period prolongation for the bepridil-protected group. Bepridil in one patient reduced by one the number of stimuli required to induce VT, but no spontaneous arrhythmias were noted. Bepridil thus possesses antiarrhythmic properties with a minimal proarrhythmic effect.

Intravenous quinidine by intermittent bolus for electrophysiologic studies in patients with ventricular tachycardia

The safety and efficacy of intravenous quinidine gluconate, using intermittent boluses of 80 mg/cc every 5 minutes to a total dose of 800 mg, was evaluated in 61 patients referred for electrophysiologic studies (EPS). Patients were referred because of out-of-hospital cardiac arrest (12), symptomatic ventricular tachycardia (VT) (24), asymptomatic VT (18), syncope of unknown origin (6), and supraventricular arrhythmias (1). Clinical heart failure was present in 74% of patients, with a mean ejection fraction of 45 +/- 3 for all patients. Quinidine prevented VT induction in 78% of patients at a mean dose of 9.6 mg/kg and facilitated VT induction in 7% of patients. Quinidine failed to decrease mean arterial pressure in 14 patients, and in the remaining 47 patients arterial pressure decreased by 16%. Six patients had hemodynamically significant hypotension. Two patients had hypotension severe enough to require saline administration, while four had hypotension not needing fluid replacement. Sixteen percent of patients experienced other side effects. Quinidine can be administered safely by intermittent infusion and is effective in preventing programmed stimulation induction of VT. Carefully monitored, intravenous intermittent bolus administration of quinidine should be utilized more frequently in EPS, since significant adverse side effects are infrequent.

The efficacy of cibenzoline in preventing PES induction of ventricular tachycardia in the dog

The electrophysiologic effects of cibenzoline were studied using programmed electrical stimulation (PES) techniques and were compared to those of quinidine. Cibenzoline, like the conventional class 1 agent quinidine, was effective in preventing arrhythmia induction. Twelve dogs were given 0.02 mg/kg digoxin intravenously for seven days to achieve a steady-state digoxin level. On the eighth day, cibenzoline was administered in incremental doses (0.5 to 10.5 mg/kg) and PES was performed at 30-minute intervals. A mean dose of 2.6 +/- 0.8 mg/kg cibenzoline prevented ventricular tachycardia induction. At this dose, cibenzoline had no significant effect on mean arterial blood pressure, but PR interval increased by 17 +/- 9 per cent, QRS duration by 27 +/- 14 per cent, and the ventricular refractory period (ERP) for the first extra stimulus increased by 35 +/- 9 per cent. A gradual decrease in heart rate and an increase in PR interval and QRS duration was caused by incremental doses of cibenzoline. In six additional animals, quinidine was administered in incremental doses (1 to 30 mg/kg) and PES performed at 30-minute intervals. A mean of 15 +/- 5 mg/kg prevented induction of ventricular tachycardia in five animals. No significant change in heart rate, PR, QRS, and ERP was found at the effective dose.

The influence of heart rate on ouabain cardiotoxicity in cats with spinal cord transection

The dose, serum level and ventricular content of ouabain needed to produce cardiotoxicity were examined in control cats, cats with transected spinal cords and cats with transected spinal cords whose heart rates were restored to control values by artificial pacing. The lethal dose of ouabain was higher in cats with transected spinal cords and not paced than it was in the control group. However, the lethal dose of ouabain in spinal-sectioned cats with ventricular pacing was no different from that in controls. However, in both groups of spinal-sectioned cats, death was associated with higher ventricular and serum levels of ouabain than in controls. The ventricular ouabain content of paced animals with transected spinal cords was higher than that of controls and lower than that of unpaced spinal cats. Thus, restoration of heart rate to control levels in spinal animals appeared to accelerate myocardial ouabain uptake. The lower myocardial ouabain content in the spinal-sectioned animals which were paced suggests that pacing sensitizes the heart to cardiotoxicity. Spinal section itself appears to decrease the sensitivity to ouabain partly through a decrease in cardiac rate and partly through a loss of neurogenic influence.

The effect of diphenidol on ouabain cardiotoxicity in the cat

The capacity of diphenidol to influence ouabain-induced cardiotoxicity was studied in anaesthetized cats with and without spinal cord transection. 2 Diphenidol pretreatment increased the lethal dose of ouabain in both intact cats and cats in which the spinal cords had been transected. Diphenidol pretreatment increased the myocardial content of ouabain associated with death in the intact animals, but failed to influence the lethal ventricular concentration in cats with transected spinal cords. 3 The failure of diphenidol to influence tissue thresholds for toxicity in the spinal cat and the equivalence of tissue ouabain requirements for death in spinal cats and diphenidol-treated intact animals, suggest a neural mechanism for the protective effect in intact animals. 4 Ouabain administration prolonged atrio-ventricular conduction time in all animals and diphenidol attenuated this effect. Thus, the influence of both drugs on antrioventricular conduction may not be entirely mediated by central neurones.

Blockade of tissue uptake of the antineoplastic agent, doxorubicin

Myocardial uptake of doxorubicin (Adriamycin) and its inhibition by digoxin and propranolol were studied in paced, isolated perfused cat hearts using tritiated doxorubicin. Contractility was studied using a Walton-Brody strain gauge arch and its first derivative. Coronary blood flow was measured by collecting the effluent from the heart. The myocardial content of doxorubicin was 0.069 +/- 0.101 nmol/mg after 30 minutes. Combined administration of doxorubicin and digoxin reduced the myocardial content of doxorubicin to 0.025 +/- 0.010 nmol/mg (P less than .02). The combination increased contractility compared with doxorubicin alone and increased coronary blood flow compared with digoxin alone. The reduction in the myocardial content of digoxin by doxorubicin was not significant. Propranolol also reduced the myocardial uptake of doxorubicin (P less than .05) without changing coronary blood flow and without further reducing contractility. Thus, both propranolol and digoxin merit evaluation in preventing doxorubicin cardiotoxicity.

Effects of actodigin on the heart

Actodigin is a new semisynthetic cardiac glycoside reported to have a rapid onset and brief duration of action in dogs. Five patients with congestive heart failure in normal sinus rhythm were given incremental doses of actodigin. Overall, there was no significant change in heart rate, aortic or pulmonary artery pressure, systemic vascular resistance, cardiac index, and stroke volume. This lack of response to actodigin is consistent with previous reports of acute administration of other cardiac glycosides. Four patients with atrial fibrillation and a rapid ventricular rate were given similar doses of actodigin. The ventricular rate was readily controlled. After drug administration was stopped, the ventricular rate quickly returned toward predrug levels. Thus, the rapid onset and brief duration of action of actodigin may be useful in the initial management of atrial fibrillation.

A comparison of actodigin and ouabain in cats

The effects of actodigin and ouabain at infusion rates which produce death in equivalent times were compared in anesthetized cats. Actodigin-induced ventricular tachycardia occurred sooner than that induced by ouabain. However, in animals in which the infusion of drug was stopped one minute after the onset of ventricular tachycardia, the arrhythmia terminated sooner in cats given actodigin than in those given ouabain. Actodigin produced a slower heart rate and greater prolongation of the PR interval than did ouabain suggesting a greater increase in vagal tone in the actodigin treated cats. Left ventricular pressure was not changed by either drug while peak dp/dt was increased after 30 min of the ouabain infusion but not significantly more than changes produced by actodigin. Thus, the use of actodigin may be limited by the early appearance of ventricular arrhythmias.

The influence of metiamide on ouabain cardiotoxicity

The effect of metiamide on the cardiotoxicity produced by ouabain was studied in pentobarbital-anesthetized cats. The onset of ouabain-induced ventricular tachycardia and fibrillation was significantly delayed in cats treated with metiamide as compared with cats that did not receive metiamide. Although the mechanism by which metiamide inhibits ouabain toxicity is speculative, the data suggest that histamine H2-receptor blocking agents may be useful as anti-arrhythmic drugs in digitalis cardiotoxicity.