Clinical and electrophysiologic assessment of oral flecainide acetate for recurrent ventricular tachycardia: evidence for exacerbation of electrical instability

Proarrhythmia

The concept that antiarrhythmic drugs can exacerbate the cardiac rhythm disturbance being treated, or generate entirely new clinical arrhythmia syndromes, is not new. Abnormal cardiac rhythms due to digitalis or quinidine have been recognized for decades. This phenomenon, termed "proarrhythmia," was generally viewed as a clinical curiosity, since it was thought to be rare and unpredictable. However, the past 20 years have seen the recognition that proarrhythmia is more common than previously appreciated in certain populations, and can in fact lead to substantially increased mortality during long-term antiarrhythmic therapy. These findings, in turn, have moved proarrhythmia from a clinical curiosity to the centerpiece of antiarrhythmic drug pharmacology in at least two important respects. First, clinicians now select antiarrhythmic drug therapy in a particular patient not simply to maximize efficacy, but very frequently to minimize the likelihood of proarrhythmia. Second, avoiding proarrhythmia has become a key element of contemporary new antiarrhythmic drug development. Further, recognition of the magnitude of the problem has led to important advances in understanding basic mechanisms. While the phenomenon of proarrhythmia remains unpredictable in an individual patient, it can no longer be viewed as "idiosyncratic." Rather, gradations of risk can be assigned based on the current understanding of mechanisms, and these will doubtless improve with ongoing research at the genetic, molecular, cellular, whole heart, and clinical levels.

Antiarrhythmic agents and proarrhythmia

The Vaughn Williams classification divides antiarrhythmic agents into four groups according to their effects on various ion channels. Class I agents block sodium channels and are subdivided into three groups. The use of class Ia agents is gradually on the decline, secondary to lack of a favorable risk/benefit ratio. Class Ib agents include lidocaine, which is extensively used for the acute treatment of ventricular tachyarrhythmias. Class Ic drugs are not advisable for patients with structural cardiac abnormalities secondary to a high risk of proarrhythmia. They are mainly used for supraventricular tachyarrhythmias. beta blockers form class II. Class III agents, such as amiodarone and sotalol, prolong action potential duration and repolarization and are among the most widely used antiarrhythmics. They are the subject of active research, and newer agents are being developed. Calcium-channel blockers are grouped under class IV. Digoxin and adenosine have unique antiarrhythmic properties, which can be useful in the management of selected patients. All antiarrhythmic drugs have the potential to provoke arrhythmias and, therefore, should be used with caution. The risk of proarrhythmia is increased in patients with abnormal cardiac substrate, with electrolyte abnormalities, and during drug initiation. Correction of electrolyte imbalance and prevention of bradycardia while the drug is metabolized and/or excreted are the cornerstones of proarrhythmia management.

Mechanisms and management of proarrhythmia

It is now well recognized that therapy with antiarrhythmic drugs can not only suppress cardiac arrhythmias, but also may increase their frequency or provoke new ones. Specific proarrhythmia syndromes, each with a distinct underlying mechanism and approach to therapy, have been described. The best-recognized examples are digitalis intoxication, proarrhythmia associated with sodium-channel block, and torsade de pointes occurring during QT-prolonging therapies. In the case of sodium-channel blockers, 2 forms of proarrhythmia are commonly recognized: slow atrial flutter with 1:1 atrioventricular conduction, and frequent ventricular tachycardia ([VT], most often found in patients with pre-existing VT reentrant circuits). In all cases, the best approach to therapy is to identify patients at risk (and thereby avoid therapy entirely), to recognize proarrhythmia when it occurs, to withdraw offending agent(s), and to use specific corrective therapies when available. Although most recognized episodes of proarrhythmia are thought to occur early in drug therapy, the increased mortality during chronic antiarrhythmic therapy demonstrated in large randomized trials suggests this phenomenon can also develop during long-term drug treatment. The recognition of proarrhythmia and the delineation of its underlying mechanisms should not only improve therapy with available drugs, but may also direct development of newer agents devoid of this potential.

Conduction velocity depression and drug-induced ventricular tachyarrhythmias. Effects of lidocaine in the intact canine heart

Depression of myocardial conduction velocity can be an important mechanism of action of antiarrhythmic drugs but it can also facilitate arrhythmogenesis. We used lidocaine in an anesthetized canine preparation to address the hypothesis that drug-induced rate-dependent conduction velocity depression causes ventricular tachyarrhythmias. A closely spaced square array of 64 electrodes was used to determine conduction velocity longitudinal and transverse to epicardial ventricular fiber direction. Lidocaine caused rate-dependent decreases in conduction velocity that were proportionately greater in the longitudinal direction at the shortest pacing cycle lengths. Conduction velocity depression developed rapidly in the presence of lidocaine with a new steady state present by the second beat of the rapid train. Recovery from rate-dependent depression of conduction velocity was exponential with a time constant of 122 +/- 20 msec (mean +/- SD) in the longitudinal direction and 114 +/- 30 msec in the transverse direction; this difference was not significant. The relation between conduction velocity depression and ventricular arrhythmias was assessed by pacing for 3 minutes at cycle lengths of 1,000, 500, 300, and 250 msec, and for 1 minute at a cycle length of 200 msec. Arrhythmias did not occur in the baseline period in the dogs that received lidocaine, nor in 12 control dogs that were subjected to the same stimulation protocol except that saline was administered in place of lidocaine. Sustained polymorphic ventricular tachycardia (VT) occurred in six of 16 dogs given lidocaine. VT occurred in the presence of relatively high plasma lidocaine concentrations (8.4 +/- 2.3 micrograms/ml) and only at pacing cycle lengths of 300 msec or shorter. The dogs that developed VT demonstrated greater rate-dependent depression of conduction velocity than the other dogs, and activation patterns obtained just before the onset of VT showed marked conduction disturbances. Furthermore, QRS prolongation, loss of one-to-one capture, and increasingly distorted activation patterns preceded the onset of VT during fixed-rate pacing, suggesting progressive sodium channel block. In summary, rate-dependent conduction velocity depression and nonuniform activation were associated with VT in this model and can be responsible for some arrhythmias induced by antiarrhythmic drugs.

Facilitation of ventricular tachycardia initiation by procainamide during programmed ventricular stimulation in patients with heart failure

Antiarrhythmic drugs occasionally facilitate, rather than prevent, ventricular tachycardia. The purpose of this study was to assess the incidence of procainamide facilitation of ventricular tachycardia initiation during programmed electrical stimulation in patients with no history of spontaneous sustained ventricular tachycardia but who are at high risk. Twenty patients with advanced heart failure (mean left ventricular ejection fraction 0.19 +/- 0.09) and nonsustained ventricular tachycardia and in whom sustained ventricular tachycardia was not inducible by programmed electrical stimulation in the basal state were studied. Six patients had coronary artery disease, 13 had idiopathic dilated cardiomyopathy, and 1 had valvular heart disease. All patients received programmed stimulation from the right ventricular apex with one to three extra-stimuli before and after the intravenous infusion of 10 mg/kg of procainamide (serum level 6.6 +/- 2.4 mcg/l). In two patients (10%) sustained monomorphic ventricular tachycardia was initiated only after the administration of procainamide. One of these patients later died in ventricular tachycardia during hyperkalemia. Of the noninducible patients, during a follow-up period of 6 +/- 5 months, two died suddenly and one developed symptomatic ventricular tachycardia. Thus, procainamide can unmask potential reentry circuits in some patients who have not had spontaneous sustained ventricular tachycardia. In patients with heart failure, this risk, as assessed by programmed stimulation after a single dose of procainamide, appears to be low.

Antiarrhythmic efficacy, clinical electrophysiology, and pharmacokinetics of 3-methoxy-O-desmethyl encainide (MODE) in patients with inducible ventricular tachycardia or fibrillation

In most patients, the clinical effects of therapy with encainide are mediated by the generation of the active metabolites O-desmethyl encainide and 3-methoxy-O-desmethyl encainide (MODE). Data from in vitro and animal studies have indicated that MODE has electrophysiologic and pharmacokinetic features that make its further evaluation desirable; in earlier studies, we found that MODE suppressed chronic high-frequency nonsustained ventricular arrhythmias at plasma concentrations of 50-160 ng/ml. We now report the clinical electrophysiology, antiarrhythmic activity, and pharmacokinetics of MODE in 17 patients with inducible ventricular tachyarrhythmias (VTs) in whom programmed electrical stimulation was performed before drug administration and after one or two sequences of loading and maintenance infusions of MODE. Because the relation between plasma concentration and effect had been incompletely defined, a dose-titration approach was adopted: available pharmacokinetic data were used to construct loading and maintenance infusion regimens that were predicted to attain low plasma concentrations in initial patients while higher infusion rates were evaluated in subsequent patients. MODE prevented VT induction in three of 17 patients and VT cycle length was increased by greater than or equal to 100 msec in a further seven of 17; most responses to MODE occurred at plasma concentrations greater than 556 ng/ml (greater than 1 SD above mean plasma MODE during encainide therapy). Response to MODE did not predict subsequent response to oral therapy with encainide. MODE increased intracardiac conduction times, QT intervals during atrial and ventricular pacing, and right ventricular effective refractory periods (RVERP); changes in RVERP were most prominent at rapid pacing rates, while changes in intracardiac conduction were rate-independent at cycle lengths between 400 and 600 msec. Plasma MODE concentrations measured during electrophysiology study correlated well with those predicted by the pharmacokinetic simulations (r = 0.91, p less than 0.001). Serial plasma sampling after programmed electrical stimulation indicated a minimum MODE elimination half-life of 8.2 +/- 5.4 hours. Side effects were confined to three instances of asymptomatic conduction system depression in subjects with latent conduction system disturbances. We conclude that MODE slows intracardiac conduction, delays repolarization, and can suppress or substantially modify inducible VT. Moreover, it was only with the adoption of the dose-titration strategy that we were able to safely demonstrate that plasma MODE concentrations higher than those routinely observed during encainide therapy were required to substantially alter cardiac electrophysiology.

Electrophysiologic and clinical effects of flecainide for recurrent paroxysmal supraventricular tachycardia

The antiarrhythmic effects of flecainide acetate were evaluated in 9 patients with paroxysmal atrioventricular (AV) nodal tachycardia and 17 patients with AV tachycardia. An electrophysiologic study was performed before and after intravenous flecainide acetate, 2 mg/kg body weight, was infused over 15 minutes and was followed by a maintenance infusion of 1.6 mg/kg given over 1 hour to 26 patients and during oral treatment to 15. Treatment with oral flecainide acetate was continued for 14 +/- 5 months. Intravenous flecainide acetate terminated AV nodal tachycardia by blocking the retrograde fast pathway conduction in 7 of 7 patients and AV tachycardia by blocking retrograde conduction in the extranodal pathway in 10 of 10 patients. AV nodal tachycardia and AV tachycardia were noninducible in 8 of 9 patients (90%, p less than 0.001) and 11 of 17 patients (65%, p less than 0.001), respectively. Long-term treatment with oral flecainide acetate suppressed AV nodal tachycardia and AV tachycardia in 8 of 9 patients (90%, p less than 0.001) and 11 of 17 patients (65%, p less than 0.001), respectively. A favorable outcome was associated with block in the accessory pathway after intravenous flecainide acetate and noninducibility during oral treatment. Recurrences preferentially occurred in the younger patients. Flecainide acetate is effective in the acute and long-term management of paroxysmal supraventricular reentry tachycardia by suppressing conduction through the retrograde fast limb of the tachycardia circuit. The clinical effect can be predicted by electrophysiologic testing.

Clinical electrophysiologic effects of flecainide acetate

Flecainide acetate depresses the rate of depolarization of action potential (Vmax), the so-called "membrane stabilizing action." In the intact heart it has a unique profile of substantial effect on conduction with modest effect on refractoriness. After intravenous administration, clinical electrophysiologic studies show that conduction through atrial myocardium, atrioventricular (AV) node, His-Purkinje system, and ventricular myocardium is depressed, the most prominent effect being on the His-Purkinje system. Refractorines of the normal atrial and AV nodal myocardium is not prolonged while that of the ventricular muscle is slightly increased. Atrial fibrillation (60% to 70%), atrial tachycardia (90% to 100%), and nodal and AV tachycardia (80% to 90%) are generally terminated, while flutter is usually slowed, but in a small proportion of patients (10% to 20%) might be terminated by the intravenous use of flecainide acetate. This drug has also been shown to be effective in terminating stable ventricular tachycardia (70%). However, it appears to be slightly less effective in suppressing inducibility of ventricular arrhythmias. Administered orally, flecainide is very effective in decreasing ventricular ectopic activity (80% to 95%) and nonsustained ventricular tachycardia. Thus, flecainide has a wide range of antiarrhythmic properties, making it a useful agent in the management of a variety of supraventricular and ventricular arrhythmias. In a small proportion of patients, however, its use can lead to apparent arrhythmogenic effects, the most dangerous being exacerbation of ventricular tachycardia.

Clinical and electrophysiologic effects of flecainide in patients with refractory ventricular tachycardia

The electrophysiologic effects and antiarrhythmic efficacy of flecainide were evaluated by electrophysiologic study (EPS) in 20 patients with ventricular tachycardia (VT) refractory to an average 2.9 drugs. In 19 patients EPSs were performed with patients not receiving antiarrhythmic medications and receiving oral flecainide therapy at steady state (mean dose, 235 +/- 67 mg/day). Flecainide significantly increased the QRS complex duration (27%, P less than .001), PR interval (17%, P less than .001), and right ventricular effective refractory periods 8.5% and 21.1% (P less than .01) for the first and second extrastimuli, respectively. During baseline EPS, 17 patients were induced into VT and two were noninducible. Flecainide prevented EPS-induced VT in five patients and the induced VT became slow and hemodynamically stable in three. Two patients who failed flecainide monotherapy were induced into slow hemodynamically stable VT with flecainide in combination with amiodarone. The two noninducible patients, during baseline EPS, had suppression of spontaneous VT with flecainide. Overall, 13 of 20 patients received flecainide either alone or in combination with amiodarone for chronic therapy. Side effects encountered during the study consisted of blurred vision, dizziness, weakness, lethargy, nausea, worsened heart failure and bradyarrhythmias. After a mean 9-month follow-up (3 to 16 months) nine patients remain on flecainide therapy. There were three recurrences of slow, hemodynamically stable VT and no episodes of sudden death. Low-dose flecainide, either alone or in combination with other agents, is effective therapy for certain patients with refractory VT but heart failure remains a significant concern in patients with depressed left ventricular function.

New antiarrhythmic drugs: tocainide, mexiletine, flecainide, encainide, and amiodarone

Tocainide, mexiletine, flecainide, encainide, and amiodarone are antiarrhythmic agents that have recently been approved by the Food and Drug Administration for general use in the treatment of ventricular arrhythmias. All five agents are effective in the treatment of patients with ventricular arrhythmias, whereas encainide, flecainide, and amiodarone are also useful in patients with supraventricular arrhythmias and the Wolff-Parkinson-White syndrome (although not yet approved for these indications). Tocainide and mexiletine are similar to lidocaine and are as effective as quinidine in patients with ventricular arrhythmias. Encainide and flecainide are superior to quinidine for the control of ventricular ectopic beats and as effective as quinidine for patients with ventricular tachycardia. Amiodarone is the most effective agent available for treating patients with ventricular tachycardia, but it is also the most toxic antiarrhythmic agent and should be used only when other antiarrhythmic drugs have not been effective or tolerated.

Arrhythmogenesis--a European perspective

Arrhythmogenesis as an effect of antiarrhythmic therapy is a relatively recent concern. Satisfactory definitions are lacking, but 2 categories, clinical and technical, can be recognized. Although arrhythmogenesis is an international problem and multifactorial, its expression depends on variables that differ according to geographic location. In Europe, use of antiarrhythmic therapy is more conservative than it is in the U.S. In the U.S., many antiarrhythmic drugs commonly used in Europe are either recently released, are on limited release or are available only in investigational protocols. Mexiletine, class IC agents and sotalol are agents in routine use in Europe. All have arrhythmogenic potential, although this appears lowest with mexiletine.

Pharmacologic causes of arrhythmogenic actions of antiarrhythmic drugs

All currently known antiarrhythmic agents can induce or worsen arrhythmias. Inappropriate dosage selection, mistakenly based on pharmacokinetic data from "normal" subjects, may result in adverse reactions when an antiarrhythmic drug is given to patients. Unexpected variations in drug clearance can increase plasma concentration of antiarrhythmic agents and aggravate arrhythmias. Changes in the rate of drug metabolism by the liver, e.g., due to cessation of alcohol or drugs that induce hepatic metabolism, can reduce drug clearance, making a previously well-tolerated dose toxic. Another possible explanation for adverse drug reactions is nonlinear protein binding. Recently, genetic determinants of drug metabolism have been identified as explanations of interindividual variations in drug responsiveness. Finally, the interactions of antiarrhythmic agents may also lead to aggravation of arrhythmias. A better understanding of the pharmacology of antiarrhythmic agents can reduce, if not prevent, the occurrence of potentially lethal proarrhythmic events.

Effects of congestive heart failure on the pharmacokinetics and pharmacodynamics of antiarrhythmic agents

Changes in the pharmacokinetics of antiarrhythmic agents should be expected in patients with congestive heart failure (CHF). The direction of the changes, however, is not always predictable. The volume of distribution is often decreased by as much as 40%, and loading doses should, therefore, be appropriately reduced. Drug clearance may also be diminished due to decreased blood flow to the liver and kidneys, as well as decreased hepatic drug-metabolizing activity. Infusion rates should similarly be lowered to avoid toxicity. However, decreases in both volume of distribution and clearance may result in little, if any, change in elimination half-life, despite higher plasma concentrations. On the other hand, the elimination half-life of antiarrhythmic agents that have a large volume of distribution and are highly cleared by the liver may be twice as long in patients with CHF compared with normal subjects. Thus, the total daily dose of drug should also be lower in these patients. In addition, the time necessary to reach steady state is longer, so that premature dose escalation may lead to excessive drug accumulation. In terms of their pharmacodynamic effects, all antiarrhythmic agents have the potential to manifest a degree of negative inotropy, which must be anticipated as a possible side effect in patients with CHF. Some of the newer agents, such as tocainide and encainide, appear to cause only minimal myocardial depression. Other potential complications of all antiarrhythmic therapy include proarrhythmia and possible drug interactions with digitalis and diuretics.

Short- and long-term experience with flecainide acetate in the management of refractory life-threatening ventricular arrhythmias

Thirty-eight patients with organic heart disease and history of sudden cardiac arrest or recurrent sustained ventricular tachycardia were treated with flecainide. Coronary artery disease was present in 33 patients. Previous antiarrhythmic therapy consisted of two to eight drugs (mean four). Fourteen patients were resuscitated from sudden cardiac death and 24 patients had chronic recurrent sustained ventricular tachycardia. Twenty-eight patients had electrophysiologic testing before and during flecainide treatment. Sustained ventricular tachycardia became noninducible in 5 patients, nonsustained in 5 patients and slowed in 13 patients (cycle length increased from 278 +/- 64 to 395 +/- 91 ms; p = 0.002). Three of the 14 patients with sudden cardiac death and 15 of the 24 patients with recurrent sustained ventricular tachycardia remained on long-term flecainide treatment. The mean left ventricular ejection fraction in 16 of these 18 patients was 37%. Nonlimiting side effects occurred in seven patients (18%). Proarrhythmic effects were seen in four patients (10%). At a mean follow-up time of 11 +/- 3 months, 15 patients (39%) had had no recurrence, including 5 who had inducible sustained ventricular tachycardia and 5 who did not on retesting during treatment. In the 18 patients who received long-term therapy, 3 late deaths occurred, 1 of which was of arrhythmic origin. These data suggest that flecainide is effective in about 40% of patients with severe refractory ventricular arrhythmias. Its value as a single drug in the treatment of sudden cardiac death remains to be defined.

Flecainide: a new class Ic antidysrhythmic

Flecainide acetate is a new orally active antidysrhythmic agent classified in the Ic category. Flecainide is effective in suppressing 88 to 100 percent of abnormal cardiac rhythms in the form of complex ventricular dysrhythmias, including couplets, ventricular tachycardia, reentrant junctional tachycardia, and Wolff-Parkinson-White syndrome. Flecainide appears to have a greater effect on conduction than on repolarization and only minimal effects on hemodynamic parameters. Flecainide is rapidly and completely absorbed after oral administration and has a 13-hour elimination half-life, allowing for twice-daily dosing regimens. Flecainide is generally well tolerated, with dizziness, blurred vision, nausea, and headache the most common side effects. Flecainide has been shown to be superior to quinidine and disopyramide in suppressing ventricular ectopic activity and may be considered a first-line oral agent for this indication. It is believe that flecainide has enough therapeutic advantages to be added to drug formularies.

Flecainide: electrophysiologic and antiarrhythmic properties in refractory ventricular tachycardia

Twenty-two patients with coronary artery disease and spontaneous ventricular tachycardia (VT) or ventricular fibrillation (VF) underwent intracardiac electrophysiologic evaluation and, when possible, ambulatory monitoring before and after therapy with flecainide (mean dose 418 +/- 87 mg [mean +/- standard deviation]). An average of 4 antiarrhythmic agents were used and were unsuccessful before therapy with flecainide was begun. During 64 +/- 16 hours of control Holter monitoring in 16 patients, all had 1 or more salvos of VT, as well as ventricular premature complexes (VPCs). Programmed stimulation during the control period induced VT in 17 of 22 patients. After flecainide therapy, Holter monitoring showed elimination of all forms of VT in all but 1 patient, as well as significant reduction of paired VPCs by 95% (p less than 0.03) and single VPCs by 70% (p less than 0.005). Electrophysiologic study during flecainide therapy showed significant increases in AH, HV, PR, QRS and QTc intervals, and the ventricular effective refractory period. Programmed stimulation in 17 patients taking flecainide, with a mean plasma level of 1,075 +/- 521 ng/ml, showed ablation of inducible VT in only 2 patients, a worsening in 5 and continued VT inducibility in 10. Adverse effects that required drug withdrawal were infrequent and encountered in patients who received higher drug levels: 1 patient with congestive heart failure and 1 with severe sinus bradycardia. Thus, although flecainide suppresses complex ventricular arrhythmias on Holter recordings, it rarely alters the response to programmed stimulation. Caution is recommended in its use for recurrent sustained VT or VF and in the interpretation of electrophysiologic studies until the predictive value of programmed stimulation with flecainide therapy is established.

Flecainide. A preliminary review of its pharmacodynamic properties and therapeutic efficacy

Flecainide is a Class I antiarrhythmic drug of the local anaesthetic type. It can be given either intravenously or orally and its pharmacokinetic properties allow relatively long (12 hours) dosing intervals with oral administration. In several open and a few controlled therapeutic trials, orally administered flecainide has brought about a greater than 90% suppression of ventricular ectopic beats in about 80% of patients. A similar percentage of patients (83%) experienced at least an 80% suppression of their ventricular tachycardia in these trials. A slightly greater response rate was reported with intravenous infusion of flecainide. Initial results in arrhythmias complicating the Wolff-Parkinson-White syndrome have been favourable. Comparative trials are few in number but flecainide has proved to be more effective than quinidine, and possibly more effective than disopyramide, mexiletine, tocainide and propafenone, in suppressing ventricular ectopic activity. The most commonly reported extracardiac adverse effects have been dizziness and visual disturbances. Proarrhythmic effects have been reported in 7 to 8% of patients, with a higher incidence in patients with serious ventricular tachycardia and reduced myocardial function. The moderate negative inotropic effects of flecainide can become clinically significant in patients with impaired ventricular function. Thus flecainide, with its convenient dose schedule and apparently low incidence of serious side effects, would appear to be a useful addition to the antiarrhythmic agents available. Further studies are needed though, to confirm its long term tolerability when used prophylactically.

Exacerbation of ventricular tachycardia by tocainide

Exacerbation of ventricular arrhythmias by antiarrhythmic drugs the lignocaine-type has not been reported previously. In this paper we describe three patients with a variety of ventricular arrhythmias who were treated with tocainide and developed worsening of the ventricular arrhythmias. In one patient, frequent ventricular ectopic beats were converted to sustained ventricular tachycardia (VT) in another, nonsustained VT was converted to sustained VT, and in a third, monomorphic VT was converted to multimorphic VT. These patients illustrate the need for careful supervision of antiarrhythmic therapy for VT, even when lignocaine-like drugs are being used.

Therapy with investigational antiarrhythmic drugs

The investigational antiarrhythmic agents available for use in this country are predominantly class I drugs with local anesthetic membrane effects. These drugs are often used successfully to control arrhythmias refractory to treatment with the standard antiarrhythmic drugs. Side effects often limit their use, and particular attention needs to be paid to their cardiac side effects, such as exacerbation of arrhythmia or enhanced conduction defects.