Antiarrhythmic treatment: an overview

Diuretics and risk of arrhythmic death in patients with left ventricular dysfunction

Background-Treatment with diuretics has been reported to increase the risk of arrhythmic death in patients with hypertension. The effect of diuretic therapy on arrhythmic death in patients with left ventricular dysfunction is unknown. Methods and Results-We conducted a retrospective analysis of 6797 patients with an ejection fraction <0.36 enrolled in the Studies Of Left Ventricular Dysfunction (SOLVD) to assess the relation between diuretic use at baseline and the subsequent risk of arrhythmic death. Participants receiving a diuretic at baseline were more likely to have an arrhythmic death than those not receiving a diuretic (3.1 vs 1.7 arrhythmic deaths per 100 person-years, P=0.001). On univariate analysis, diuretic use was associated with an increased risk of arrhythmic death (relative risk [RR] 1.85, P=0.0001). After controlling for important covariates, diuretic use remained significantly associated with an increased risk of arrhythmic death (RR 1.37, P=0.009). Only non-potassium-sparing diuretic use was independently associated with arrhythmic death (RR 1.33, P=0.02). Use of a potassium-sparing diuretic, alone or in combination with a non-potassium-sparing diuretic, was not independently associated with an increased risk of arrhythmic death (RR 0.90, P=0.6). Conclusions-In SOLVD, baseline use of a non-potassium-sparing diuretic was associated with an increased risk of arrhythmic death, whereas baseline use of a potassium-sparing diuretic was not. These data suggest that diuretic-induced electrolyte disturbances may result in fatal arrhythmias in patients with systolic left ventricular dysfunction.

Frequency of sudden cardiac death and profiles of risk

The epidemiology of ventricular tachycardia/fibrillation (VT/VF) and sudden cardiac death (SCD) must be explored from multiple aspects, each of which contributes insights into the problem and no one of which exerts exclusive dominance for preventive or therapeutic strategies. These include: (1) population dynamics, using conventional epidemiologic approaches; (2) risk as a function of time from an index event; (3) conditioning risk factors, based on the presence of underlying disease states; (4) transient risk factors that are dynamic and trigger a potentially fatal event at a specific point in time; and (5) "response risk," which refers to individual susceptibility (possibly determined genetically) to the adverse effects of longitudinal and/or dynamic risk factors. Major inroads into profiling individual or population risk of SCD will require better understanding of each of these epidemiologic-clinical-physiologic interactions. The disciplines range from epidemiology, through clinical medicine, to membrane channel physiology, genetic determinants, and molecular biology.

Signal-averaged ECG in prediction of the short-term suppression of ventricular premature beats by Mexiletine

We analyzed whether baseline parameters of time-domain and spectrotemporal analysis of a signal-averaged ECG or their changes during Mexiletine therapy can predict the antiarrhythmic efficacy of the drug. On 60 post-MI patients with > 100 ventricular premature beats per hour, signal-averaged ECGs were recorded before and after a constant infusion of Mexiletine (7 mg/kg) for 1 h and again after 4 days of oral Mexiletine therapy (Mexiletine SR, 360 mg twice daily). Spectrotemporal analysis was performed on a fixed analyzed signal duration of QRS-complex and ST-segment of X-, Y-, Z-leads using the temporal window of the rectangular type, measuring signals between 10-20 Hz. Intravenous and oral Mexiletine did not produce significant changes in mean values of any time-domain parameters. However, using informative variables of spectra of the signal-averaged ECG, we managed retrospectively to predict antiarrhythmic efficacy in 92% of the patients. Only certain frequency bands (from the range of the spectra at baseline, 10-120 Hz) were predictive for intravenous Mexiletine efficacy: 40-55 Hz in lead Y (P = 0.0116); 55-70 Hz in leads X and Z (P = 0.0063 and P = 0.0269, respectively); 70-85 Hz in lead Z, (P = 0.0227). When the treatment with intravenous Mexiletine was effective, the baseline power spectrum density was lower than when the drug was ineffective, and vice versa. Moreover, the efficacy of oral Mexiletine can be predicted by power density spectrum at baseline (10-25 Hz in lead Z, P = 0.0210; 70-85 Hz in lead Y, P = 0.0254) and by one of the possible (increased, decreased, unchanged) effects of intravenous Mexiletine on the spectra at frequency bands (70-85 Hz in lead X, P = 0.0432 and 40-120 Hz in lead Z, P = 0.0156). These results show the value of spectrotemporal signal-averaged ECG in selecting a subgroup of post-myocardial infarction patients that may benefit from Mexiletine therapy.

Future evaluation of antiarrhythmic therapy

The expansion of antiarrhythmic therapy beyond pharmacologic agents to include surgery, devices, and ablation procedures, plus the reaffirmation by the Cardiac Arrhythmia Suppression Trial (CAST) of the need for concurrent placebo-controlled trials to establish a mortality benefit, have resulted in the need to consider the requirements for evaluating therapy. Pharmacologic therapy may be used in three ways: (1) primary; (2) alternative; and (3) adjunctive. To accurately identify a mortality benefit from primary therapy, a placebo-controlled study is necessary. In contrast, control of symptoms may be identified without the same rigorous demands. Current data are limited by the absence of true negative controls for most interventions that claim a possible mortality benefit. Alternative therapy provides a choice between equally effective therapies, neither of which has necessarily been documented to have a mortality benefit. Adjunctive therapy is that which is used for control of symptoms, whereas another therapy is used to provide a presumed or proved mortality benefit. For any of these approaches, therapy must be further evaluated in terms of four modifying variables: (1) impact of therapy on the basis of both its efficacy and efficiency; (2) interpretation of outcome data based on analysis of competing risks; (3) measurement of efficacy in terms of extension of life; and (4) analysis of outcome as the equilibrium between antiarrhythmic benefit and proarrhythmic risk. With these approaches a rational analysis of the effect of therapy and its cost-based benefit can be achieved.

Circadian variation in ventricular arrhythmias in hypertensive men

Circadian patterns have been observed for various cardiovascular functions and events including sudden cardiac death. This study examined whether ventricular arrhythmias could be a pathophysiologic explanation for the increase in prevalence of sudden cardiac death observed between 6 A.M. and noon. Hypertensive men 35 to 70 years of age and without a history of symptomatic cardiac disease were withdrawn from diuretic treatment and received 1 month of oral electrolyte repletion with both 40 mmol of potassium chloride and 400 mg of magnesium oxide daily. Then continuous 24-hour Holter monitoring was performed and ventricular arrhythmias were classified by 6-hour time intervals. The interval from 6 A.M. to noon revealed a higher prevalence of complex or frequent ventricular arrhythmias than the interval from midnight to 6 A.M., as well as a higher mean number of ventricular premature complexes per hour. The differences were statistically significant (p less than 0.01) and amounted to increases of about one third. Ventricular arrhythmias during the other two 6-hour periods were intermediary in frequency. It is concluded that the increase in sudden cardiac death noted in the morning might be related, at least in part, to an increase in frequency of ventricular arrhythmias; the implications of this observation for preventive cardiology deserve further investigation.

Influence of lorcainide on microsomal Na+, K(+)-ATPase in guinea-pig isolated heart preparations

1. The effects of lorcainide on the myocardial Mg2(+)-dependent, Na+ and K(+)-activated adenosine triphosphatase (Na+, K(+)-ATPase) were compared in guinea-pig heart preparations with those of ouabain, a specific inhibitor of the enzyme activity. 2. Both ouabain and lorcainide inhibited the microsomal Na+, K(+)-ATPase activity in a concentration-dependent fashion. Their inhibitory effective ranges were 0.05-100 microM and 0.15-125 microM, respectively, and the concentrations for half maximal inhibition (IC50 values) were 2.1 +/- 0.3 and 33.5 +/- 7.3 microM, respectively. 3. In a second series of experiments, the combined effects of the two drugs on the enzyme activity were studied. In these experiments, lorcainide produced a concentration-dependent potentiation of the inhibitory effects of ouabain on Na+, K(+)-ATPase activity. 4. The present study demonstrates that lorcainide is a potent inhibitor of myocardial Na+, K(+)-ATPase.

Lack of effect of hypertonic sodium bicarbonate on QRS duration in patients taking therapeutic doses of class IC antiarrhythmic drugs

Hypertonic sodium bicarbonate (HSB) has been reported to reduce the toxicity of Class IC antiarrhythmic agents in rats and, anecdotally, in patients. A pilot study was conducted of the safety and efficacy of HSB for reversing the electrocardiographic effects of therapeutic doses of encainide or flecainide in ten patients taking these drugs for chronic ventricular arrhythmias. Patients had a mean drug-induced QRS prolongation before treatment of 27.6 +/- 8.8%. Each patient received a single dose of HSB 100 mEq or normal saline IV over 5 minutes on two separate occasions. The administration of treatments was blinded and balanced. There were no important side effects of HSB. Venous blood pH, CO2 content and sodium concentration were all significantly increased by HSB in comparison to saline. No differences were found during the 2-hour observation period in the primary endpoint, QRS duration, the PR or QT intervals, or the frequency of premature ventricular beats. It was concluded that HSB 100 mEq does not reduce QRS duration in patients taking therapeutic doses of flecainide or encainide. Because HSB was well tolerated, investigation of its use in higher doses or in patients with overt toxicity due to Class IC drugs is feasible.

Antiarrhythmic drug therapy for suppression of ventricular arrhythmia: experience with 122 patients treated for two years

Although there are many reports of the short-term effectiveness of antiarrhythmic drugs for suppression of ventricular ectopic depolarizations, there are less data available on the long-term use of these drugs. We treated 122 patients for up to 2 years with antiarrhythmic drugs for suppression of frequent ventricular ectopic depolarizations. The percent suppression of ventricular ectopic depolarizations and nonsustained ventricular tachycardia for each drug was determined at 1, 3, 6, 12, 18, and 24 months of therapy. Among 33 patients treated with flecainide, the mean suppression of ventricular ectopic depolarizations (average of all data during 24 months) was 93 +/- 17% and of nonsustained ventricular tachycardia was 97 +/- 7%. In 27 patients treated with encainide, the mean suppression of ventricular ectopic depolarizations was 88 +/- 18% and of ventricular tachycardia was 95 +/- 16%. Among 26 patients treated with propafenone, the mean suppression of ventricular ectopic depolarizations was 77 +/- 32% and of ventricular tachycardia was 93 +/- 15%. For the 20 patients treated with moricizine, the mean suppression of ventricular ectopic depolarizations was 62 +/- 35% and of ventricular tachycardia was 90 +/- 14%. Among 16 patients treated with amiodarone, the mean suppression of ventricular ectopic depolarizations was 92 +/- 14% and of nonsustained ventricular tachycardia was 99 +/- 3%. In 54 of the 122 patients (44%), the study drug was stopped during 2 years of therapy because of death (2 sudden, 2 unwitnessed and 6 noncardiac), side effects (21 patients), lack or of loss of efficacy (13 patients), and noncompliance (10 patients).(ABSTRACT TRUNCATED AT 250 WORDS)

Classification of deaths after myocardial infarction as arrhythmic or nonarrhythmic (the Cardiac Arrhythmia Pilot Study)

The Cardiac Arrhythmia Pilot Study (CAPS) was a randomized, double-blind trial of antiarrhythmic drugs (encainide, flecainide, moricizine, imipramine and placebo) in 502 patients with at least 10 ventricular premature complexes/hour, 6 to 60 days after acute myocardial infarction. CAPS tested the feasibility of performing a larger study to determine if suppression of ventricular ectopic activity after acute myocardial infarction could improve survival. Patients in CAPS were followed for 1 year. All death or cardiac arrest events were evaluated by at least 2 investigators using a classification scheme that characterized the underlying mechanism as cardiac arrhythmic, cardiac nonarrhythmic or noncardiac. Forty-five patients (9%) died or had cardiac arrest during the 1-year follow-up, 29 (64%) within 1 hour from the onset of symptoms and 16 greater than 1 hour from the onset of symptoms. Twenty-three deaths (51%) were classified as arrhythmic, 19 (42%) as nonarrhythmic and 3 (7%) as noncardiac. Acute myocardial ischemia or infarction was associated with the death/cardiac arrest event in 16 patients (36%), 8 in the arrhythmic death group. Discrepancies in classification among reviewers were particularly common in patients with long-standing symptoms of congestive heart failure, in whom it was frequently difficult to identify the precise moment of the onset of symptoms in the death/cardiac arrest event. Using only the temporal relation of symptoms to categorize deaths or cardiac arrests, the mechanism of 12 (27%) of the 45 patients was in disagreement with the classification based on the Events Committee review. Classification of death as sudden or nonsudden is not equivalent to the classification of death as arrhythmic or nonarrhythmic.

Frequency- and voltage-dependent depression of maximum upstroke velocity of action potentials by pirmenol in guinea pig ventricular muscles

The frequency-dependency and voltage-dependency of the suppressing effect of pirmenol, a novel antiarrhythmic agent, on the maximum upstroke velocity (Vmax) of action potentials were examined and compared with those of disopyramide in guinea pig papillary muscles. Pirmenol in concentrations higher than 3 microM decreased Vmax with a slight increase in action potential duration. The reduction of Vmax by pirmenol was enhanced in a frequency-dependent manner over the range of 0.1-2.0 Hz. Pirmenol (30 microM) produced a small resting block (5.5%), whereas disopyramide (100 microM) produced a greater one (25.8%). The onset of frequency-dependent Vmax reduction at 2.0 Hz followed a monoexponential function with a slow rate constant (0.308 +/- 0.055 AP-1). The time constant for the recovery from the frequency-dependent block by pirmenol was also slow (33.5 +/- 5.4 sec), but faster than that of disopyramide (82.5 +/- 12.3 sec). At 1.0 Hz, pirmenol caused a shift (9.5 mV) of the curve relating the resting membrane potential and Vmax along the voltage axis in the hyperpolarizing direction. Thus, pirmenol is a Class Ia drug that has frequency- and voltage-dependent inhibitory actions on Vmax, and its onset and offset kinetics are relatively slow.

Treatment of life-threatening ventricular tachycardia with encainide hydrochloride in patients with left ventricular dysfunction. The Encainide-Ventricular Tachycardia Study Group

Encainide, a newly released class IC antiarrhythmic agent, was studied in 193 patients with ventricular tachycardia (VT) and depressed left ventricular ejection fraction or important arrhythmia-related symptoms. Therapy was evaluated by 24-hour continuous Holter monitoring if patients had nonsustained VT or by electrophysiologic testing if they had sustained VT. Holter monitoring was used in 99 patients and electrophysiologic testing in 94 patients. At baseline the mean age, percent men, percent with coronary artery disease and mean ejection fraction in the 2 groups was 62 versus 58 years, 76 versus 72%, 62 versus 89%, and 27 versus 30%, respectively. In the Holter monitoring group, 71 of 99 (72%) responded with a significant reduction in VT (35% received 25 mg 3 times day, 47% received 35 mg 3 times a day, 14% received 50 mg 3 times a day and 4% received 50 mg 4 times a day). Adverse cardiac effects in these patients included a 7% incidence of serious proarrhythmic events that were probably related to encainide and a 2% incidence of sick sinus syndrome. In this group no patient developed congestive heart failure that was clearly attributed to encainide. Using electrophysiologic testing, 14 of 94 (15%) had sustained VT rendered noninducible, whereas 18 of 94 (19%) additional patients had partial electrophysiologic response defined as a more tolerable, slower VT. Overall, 32 of 94 (34%) were believed to be effectively treated in this group and were treated with encainide long-term. In the population evaluated by electrophysiologic testing, serious proarrhythmic events occurred in 15 of 94 (16%) and 3% had sinus pauses.(ABSTRACT TRUNCATED AT 250 WORDS)

Signal-averaged electrocardiography: a new noninvasive test to identify patients at risk for ventricular arrhythmias

Signal-averaged electrocardiography (ECG) is a new noninvasive test for identifying patients at risk for ventricular arrhythmias. This computerized method of analyzing standard ECGs identifies particular microvolt-level signals called late potentials. Late potentials have been correlated with clinical ventricular tachycardia, are predictive of ventricular tachycardia inducibility at the time of electrophysiologic testing, and are predictive of arrhythmic events after myocardial infarction. In this review, we describe late potentials, the method of obtaining and processing the signal-averaged ECG, and clinical studies in various patient groups that have assessed the predictive value of the signal-averaged ECG for identification of patients at risk for subsequent ventricular arrhythmias.

Cumulative effects of amiodarone on inducibility of ventricular tachycardia: implications for electrophysiological testing

To determine whether the slow onset of action of amiodarone might result in a delayed effect on the inducibility of sustained ventricular arrhythmias, 45 patients with ischemic heart disease and inducible sustained monomorphic ventricular tachycardia were prospectively studied. Each patient had at least one initial repeat study on amiodarone and those with persistently inducible arrhythmias were rescheduled for further studies over the following 24 weeks. After 2-3 weeks of amiodarone therapy, nine patients no longer had inducible tachycardias, and tachycardia in another eight patients (18%) later became noninducible. Using life-table methods, analysis based on the results of the first re-study showed 18-month recurrence rates of 43% in the inducible vs 17% in the noninducible groups (p = 0.056). When the results of additional testing were then used to reclassify patients, the recurrence rates for these two groups were 50% and 17%, respectively (p = 0.004). Observation of blood pressure and level of consciousness during induced arrhythmias was also predictive of clinical tolerance in patients having recurrences; 16 of 19 patients experienced symptoms of similar severity to those produced during testing. We conclude: (1) early testing of amiodarone may result in misclassification of some patients as remaining inducible; (2) re-testing at a later time more accurately predicts tachycardia recurrence; (3) observation of hemodynamic response also provides important prognostic information.

Overview of the clinical pharmacology of antiarrhythmic drugs

Antiarrhythmic drugs have been recognized to possess 1 or more classes of antiarrhythmic action. This classification scheme is useful, but has major limitations because the available drugs and their metabolites have multiple actions. This report presents an overview of the distinguishing features of the most frequently used agents having class I or III actions. Agents with class I actions are local anesthetic agents that depress the fast inward depolarizing sodium current and thereby slow the rate of the rise of the action potential (phase 0). This category is further divided into classes IA, IB, and IC according to the degree of potency as sodium channel inhibitors, and the individual effects of the drug on action potential, conduction velocity and repolarization. Included in the spectrum of agents with class I action are quinidine, procainamide, disopyramide, lidocaine, tocainide, mexiletine, flecainide, amiodarone, encainide and lorcainide. The antiarrhythmic drugs that exert class III action lengthen repolarization and refractoriness; included in this category are amiodarone, quinidine, bretylium and sotalol. Because of the broad range of effects that antiarrhythmic agents may exert, safe and effective therapy requires a thorough familiarity with the pharmacologic profile of each drug administered and a careful evaluation of the presenting condition and the patient history. In some cases, a multiple drug regimen may be most appropriate. Various combinations such as class IA and IB agents, have been shown to slow conduction synergistically and increase refractoriness while keeping adverse effects to a minimum.

A multicenter dose-response study of pirmenol hydrochloride in patients with ventricular premature contractions

The efficacy of pirmenol in suppressing ventricular premature complexes (VPCs) was assessed in 196 patients in a placebo-controlled, double-blind, multicenter study. At a daily dosage of 200 to 400 mg, pirmenol was effective in suppressing VPCs. In the double-blind phase of the trial, 60% of patients had at least a 70% reduction in VPC frequency and at least 70% of those patients who entered the open-label phase of the study continued to show at least a 70% reduction in VPC rate. Pirmenol was well tolerated by most patients; 66% of the patients treated with pirmenol in the double-blind phase had no adverse experiences. Of those who did have an adverse experience, the most common complaint was unusual taste. Serious adverse reactions were rare and only 2% of the patients had what may have been a proarrhythmic response. The same pattern of tolerance was seen in the open-label phase of the study when 151 patients were treated for an extended length of time with pirmenol. Pirmenol shows considerable promise for patients in whom the reduction of VPC frequency is desirable. Currently available antiarrhythmic drugs may have limited efficacy, cause serious or intolerable side effects or require frequent administration. Pirmenol has a convenient twice-daily dosing regimen, dependable antiarrhythmic action and a good safety record. This study demonstrated the effectiveness and safety of pirmenol in the control of VPCs.

Effects of flecainide on the cellular electrophysiology of neonatal and adult cardiac fibers

The acute cellular electrophysiologic actions of flecainide acetate on isolated neonatal and adult canine ventricular myocardium and Purkinje fibers were evaluated with standard microelectrode techniques. Flecainide, 0.1 to 10.0 micrograms/ml, produced concentration-dependent decreases in action potential amplitude, overshoot, and phase O Vmax of adult ventricular myocardium and Purkinje fibers. The greatest effects were on Vmax. Neonatal action potential characteristics were affected to a lesser degree by flecainide. Flecainide had disparate effects on myocardial and Purkinje fiber repolarization and refractoriness. In adult ventricular myocardium, action potential duration (APD) and effective refractory period (ERP) increased progressively with drug concentration. APD and ERP were increased to a lesser degree in neonatal myocardium. In adult Purkinje fibers, APD decreased progressively with increasing flecainide concentrations. ERP decreased at 0.1 and 1.0 microgram/ml, but returned to control values at 10.0 micrograms/ml. APD and ERP of neonatal Purkinje fibers responded to a lesser degree. At faster stimulation frequencies (2 to 4 Hz), flecainide produced significant frequency-dependent decreases in Vmax in adult Purkinje fibers. Such use-dependency was not evident in neonatal fibers. These data indicate a significantly lower sensitivity of immature cardiac tissues to the electrophysiologic effects of flecainide.

Cardiac arrhythmias. An update on identification and therapy

Cardiac arrhythmias result from conduction block, abnormal impulse formation, or a combination of both. The decision to treat arrhythmias depends on symptoms, hemodynamic problems, the presence or absence of organic heart disease, and the presence of malignant arrhythmias. Holter monitoring, treadmill exercise testing, and electrophysiologic stimulation can facilitate identification. Control involves correction of precipitating or contributing factors and selection of an appropriate antiarrhythmic drug or surgical technique.

Long-term continuous electrocardiographic recordings and electrophysiologic testing to select patients with ventricular arrhythmias for drug trials and to determine antiarrhythmic drug efficacy

Long-term continuous electrocardiographic recordings (Holter recordings) and electrophysiologic testing are useful for selecting patients for antiarrhythmic drug trials and for evaluating efficacy and adverse effects during therapy. These 2 methods are used to establish patient eligibility and to stratify patients during randomization. Both noninvasive testing and electrophysiologic studies help to classify arrhythmias as benign, potentially malignant or malignant. Holter monitoring and electrophysiologic studies each have unique advantages and disadvantages for baseline evaluation before starting antiarrhythmic drug treatment and for evaluation of efficacy or adverse effects during follow-up. Both methods have been shown to predict outcome of treatment in patients with malignant ventricular arrhythmias (i.e., can be used as surrogates for sudden death). Several ongoing studies are attempting to extend our knowledge of these 2 techniques. A multicenter study in the United States is comparing the 2 methods for applicability, predictive accuracy and cost. Investigators in the Netherlands are testing the validity of electrophysiologic studies by continuing antiarrhythmic drug treatment whether or not programmed ventricular stimulation predicts success or failure. Finally, new proposals have been made for conducting randomized, controlled studies in selected patients with malignant ventricular arrhythmias using time to drug failure as the endpoint.

Recainam, a potent new antiarrhythmic agent: effects on complex ventricular arrhythmias

The antiarrhythmic efficacy and safety of intravenous recainam, a newly synthesized compound displaying potent class I antiarrhythmic activity, were tested in 10 hospitalized patients with frequent (greater than 30/h) complex ventricular ectopic beats. There were seven men and three women of average age 57 years (range 21 to 74); five had ischemic heart disease, three had cardiomyopathy and two had valvular heart disease. Recainam was given as a 3.0 mg/kg per 40 min loading infusion followed by a 0.9 mg/kg per h maintenance infusion over a 24 hour observation period. Arrhythmia response was assessed both in the short term (comparing 2 hours before and 1 hour after drug loading) and in the long term (comparing 48 hours before drug loading and 23 hours of maintenance infusion). The median frequency of total premature ventricular complexes decreased in the short term by 99.6% (from 392.5 to 1.5/h, p less than 0.005) and in the long term by 99.7% (from 435 to 1.3/h, p less than 0.01). Repetitive beats were suppressed by a median of 100% both in the short term (p less than 0.006) and during 24 hour infusion (from 80.9 to 0/h, p less than 0.003). More than 90% suppression of repetitive beats occurred in all 10 patients (100%) and more than 90% suppression of total arrhythmias occurred in 9 patients (90%) during the maintenance period. Electrocardiographic PR and QRS intervals increased by 19% (p less than 0.001) and 24% (p less than 0.003), respectively, during therapy, but the JTc interval decreased (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms underlying the antiarrhythmic and arrhythmogenic actions of quinidine in a Purkinje fiber-ischemic gap preparation of reflected reentry

The effects of therapeutic levels of quinidine were studied in an ischemic gap preparation of reflected reentry. The preparation consisted of a Purkinje fiber mounted in a three-compartment chamber. A narrow central compartment was perfused with a solution prepared to mimic the extracellular milieu at a site of ischemia. Quinidine in concentrations that exert little effect on normal Purkinje tissue, 1 to 2 micrograms/ml, greatly impaired conduction and markedly prolonged refractoriness across the ischemic gap. The drug effected these changes by (1) extending the inexcitable zone within the depressed region, (2) decreasing the amplitude of the input signal entering this zone, and (3) decreasing the excitability of the tissue beyond the depressed zone (evaluated by current clamp techniques). These actions of the drug produced both antiarrhythmic and proarrhythmic effects. When the initial level of conduction impairment was high, quinidine totally suppressed reflected reentry at all frequencies by precipitating complete anterograde conduction block. At intermediate levels of block, the drug generally caused a prominent shift of the frequency dependence of reentrant activity to lower stimulation rates. Finally, when conduction was relatively less impaired, quinidine created the conditions for reflected reentry to occur. Our results suggest that the heart rate dependence of reentrant arrhythmias might be of prognostic value in the administration of antiarrhythmic drugs.

Relation between left ventricular dysfunction and ventricular arrhythmias after myocardial infarction

Ventricular arrhythmias occurring in the coronary care unit are not good predictors of ventricular arrhythmias or death during follow-up. However, arrhythmias detected by 24-hour electrocardiographic recordings at the time of hospital discharge are predictive of mortality over the subsequent 2 years. At discharge, only about 20% of patients have significant ventricular arrhythmias, defined as frequent or repetitive ventricular premature depolarizations. Using programmed ventricular stimulation, which can detect significant ventricular arrhythmias in patients with very little ectopy in 24-hour electrocardiographic recordings, 20% of patients have ventricular tachycardia 2 to 6 weeks after acute myocardial infarction (AMI). Both diastolic left ventricular (LV) dysfunction in the coronary care unit (i.e., rales or pulmonary congestion) and systolic LV dysfunction (i.e., LV ejection fraction) during hospitalization for AMI are potent predictors of mortality. Two large prospective studies examining the relations between LV dysfunction, ventricular arrhythmias and mortality concluded that mechanical dysfunction and ventricular arrhythmias are independently related to mortality. This finding provides a rationale for treating patients with frequent or repetitive ventricular arrhythmias detected near the time of hospital discharge after AMI. However, no study has yet examined whether reducing ventricular arrhythmias with antiarrhythmic drugs after AMI also reduces mortality. Lacking an answer to this question and given the frequency of adverse effects with antiarrhythmic drugs, most physicians are conservative in the treatment of patients with ventricular arrhythmias after AMI.

Initial and long-term outpatient experience with pirmenol for control of ventricular arrhythmias

Pirmenol, a new class IA antiarrhythmic agent, has shown promise in short-term trials, but long-term efficacy has not been documented. We thus evaluated 11 patients with frequent (greater than or equal to 60/h) premature ventricular complexes (PVC) given oral pirmenol for 25-727 days. Ten of 11 patients entering the long-term open trial had shown greater than or equal to 70% (mean 83%) PVC suppression during in-hospital pirmenol dose ranging. Long-term pirmenol was given in divided doses of 100-600 mg/day. Mean PVC frequency during baseline was 13,078/24 h (range, 3,218-32,718); couplets averaged 481/24 h (1-2,829) and runs 45/24 h (0-334). Ambulatory monitoring was performed at 1, 3, 6, and 12 months, then semiannually. Mean absolute PVC suppression at 1 month averaged 75% (p less than or equal to 0.02). Median individual percentage PVC suppression was 94%. During the first 3 months, 8 patients (73%) continued to show a favorable response (greater than or equal to 70% suppression), and 3 had arrhythmia recurrence and were dropped. One responder was withdrawn after the onset of paroxysmal atrial fibrillation, and another early responder was withdrawn after 3 months because of arrhythmia relapse. Six patients have been treated for over 1 year, with 99% mean PVC suppression. Mean couplet and run frequencies at 1 month decreased by means of 76% (p less than or equal to 0.05) and 92% (p = 0.001) respectively. At 1 year, couplets were suppressed 99.8% and runs by 99.7% in the 6 patients remaining on pirmenol.(ABSTRACT TRUNCATED AT 250 WORDS)

Flecainide: a new prototype antiarrhythmic agent

Flecainide acetate is the first class IC antiarrhythmic agent marketed in the United States. In vitro, animal and human studies have shown that the drug markedly prolongs conduction and has minimal effect on repolarization. Efficacy trials have shown flecainide to be effective in a wide range of ventricular and selected atrial arrhythmias. The drug is generally well tolerated, although minor adverse effects are common. These generally are related to the central nervous system and respond to a reduction in dosage. Like other antiarrhythmic agents, flecainide may demonstrate proarrhythmic effects. It is excreted in the urine as the parent compound and inactive metabolites. The elimination half-life ranges from 12-27 hours in patients with normal renal function, allowing convenient dosing regimens of 100-200 mg twice daily in most patients. Flecainide has the potential for widespread use.

Patients with malignant or potentially malignant ventricular arrhythmias: opportunities and limitations of drug therapy in prevention of sudden death

Almost 90% of patients resuscitated from out of hospital cardiac arrest have coronary heart disease and can be categorized in one of three groups: acute myocardial infarction, ischemic event or primary arrhythmic event. The patients who have acute myocardial infarction have the best prognosis, and those with primary arrhythmic events have the worst. Recent studies show that ventricular arrhythmias after myocardial infarction are associated with mortality independent of any association with left ventricular dysfunction. Ventricular arrhythmias that have caused cardiac arrest or hemodynamic collapse, that is, malignant arrhythmias, should be treated aggressively and evaluated carefully with one of two methods that have high predictive accuracy for outcome: 1) the Holter recording/exercise test approach, or 2) the electrophysiologic approach. It is not yet known whether treating potentially malignant ventricular arrhythmias after myocardial infarction with class I or III antiarrhythmic drugs will reduce mortality, but two clinical trials are under way in the United States to address this question. Beta-adrenergic blocking drugs do reduce mortality, probably as a result of both antiischemic and antiarrhythmic effects. Calcium channel blocking agents, various antiplatelet drugs and alpha-adrenergic blocking drugs are under investigation to determine their value in secondary prevention of ventricular fibrillation.

Identification of patients at high risk for sudden cardiac death

Ventricular arrhythmias play an important role in the pathophysiologic aspects of sudden cardiac death. To increase the precision in predicting sudden cardiac death, ventricular arrhythmias can be classified into 3 groups: benign, potentially malignant and malignant. Benign ventricular arrhythmias pose negligible risk of sudden cardiac death; they usually present as palpitations and are not associated with heart disease. The frequency of ventricular premature depolarizations is usually moderate and repetitive forms are usually moderate and repetitive forms are usually absent in benign ventricular arrhythmias. Potentially malignant ventricular arrhythmias pose a moderate risk of sudden cardiac death; they present as palpitations or are discovered on routine screening and are associated with significant heart disease. The frequency of ventricular premature depolarizations usually is moderate, and repetitive forms are present. It is not known whether treatment with antiarrhythmic drugs will decrease the mortality associated with potentially malignant ventricular arrhythmias. Malignant ventricular arrhythmias pose a high risk of sudden cardiac death; they may present as palpitations, syncope or cardiac arrest and have a strong association with heart disease. The frequency of ventricular premature depolarizations is moderate to high, repetitive forms are present and intermittent sustained ventricular arrhythmias occur. Patients who have malignant ventricular arrhythmias and respond to antiarrhythmic drug treatment are proven to have a much lower mortality than those who do not.

Double-blind placebo-controlled evaluation of propafenone in suppressing ventricular ectopic activity

The effectiveness of oral propafenone in treating ventricular premature complexes (VPCs) was assessed with a single-blind dose-ranging trial followed by a double-blind, randomized, crossover comparison of propafenone and placebo. Patients subsequently were treated with propafenone for up to 24 months. During dose ranging, the average of individual percent suppressions was 83% at the largest dose (300 mg/8 hours). During the double-blind trial, the effectiveness of propafenone was confirmed, with 7 of 12 patients achieving greater than or equal to 80% reduction in VPCs (p less than 0.05 versus double-blind placebo study). Propafenone was also effective in controlling couplets and nonsustained ventricular tachycardia. Seven patients were treated with propafenone for 24 months, during which effectiveness continued, with mean suppression ranging from 67 to 79% (p less than 0.05 versus initial single-blind placebo). Propafenone prolonged PR and QRS intervals by 16 and 18%, respectively; these prolongations continued during long-term therapy. Propafenone increased serum digoxin levels in 5 of 5 patients (mean increase 83%). Cardiovascular side effects included congestive heart failure (1 patient) and conduction abnormalities (3 patients). Thus, propafenone was effective in the treatment of total and repetitive VPCs. Side effects were few, but congestive heart failure, conduction disturbances and increases in serum digoxin were observed.

Flecainide versus quinidine: results of a multicenter trial

In this multicenter trial, the efficacy and safety of flecainide, a new antiarrhythmic agent, were compared with those of quinidine, a standard antiarrhythmic agent in the United States. A randomized, parallel, placebo-controlled design was used. Flecainide was more effective than quinidine (p less than 0.0001) in reducing ventricular premature complexes, couplets and ventricular tachycardia. Flecainide continued to be effective in reducing ventricular arrhythmias during a 12-month follow-up period. The incidence of side effects was similar for the 2 drugs in both short- and long-term studies. Therefore, flecainide should be an excellent drug to use in treating patients with ventricular arrhythmias classified as either benign or potentially malignant.