Evaluation by serial electrophysiologic studies of an abbreviated oral loading regimen of amiodarone

Amiodarone therapy for sustained ventricular tachycardia after myocardial infarction: long-term follow-up, risk assessment and predictive value of programmed ventricular stimulation

We determine the value of the programmed ventricular stimulation (PVS) and of clinical, angiographic and electrophysiologic variables in assessing the long-term risk of arrhythmia recurrence in a group of coronary artery diseased patients presenting with a first episode of monomorphic sustained ventricular tachycardia (VT) treated with amiodarone. Mortality and arrhythmia recurrence rates were retrospectively assessed in 55 consecutive patients with previous myocardial infarction presenting with a first VT episode. Results of left heart catheterization, echocardiography and time-domain signal-averaging were collected. Patients underwent PVS after amiodarone oral loading and were classified according to inducibility before being all discharged on amiodarone (200 mg daily). The mean follow-up was 42+/-31 months. Total and cardiac mortality rates were 29% (16 patients) and 23% (13 patients) respectively. Sudden death (SD) occurred in nine patients (16%). VT recurred in 13 patients (23%). Sustained monomorphic VT was inducible in 40 patients (72%) after amiodarone loading. Neither total mortality (10/40 vs. 6/15) nor cardiac mortality (3/40 vs. 1/15) were significantly different between inducible and non-inducible patients. Recurrent VT rate was 27% (11/40 patients) for the inducible group and 13% (2/15 patients) for the non-inducible group (NS). SD occurred in 6/40 inducible patients (15%) and in 2/15 non-inducible patients (13%) (NS). Arrhythmic events occurred in 42% (17/40) inducible patients vs. 26% (4/15) non-inducible patients (P=0.07). Parameters correlated with outcome were ejection fraction (EF) (5 SD/11 patients with EF <0.3 vs. 4/44 with EF >0.3, P=0.003), mitral insufficiency (MI) (4 SD/10 patients with MI vs. 4/44 patients without MI, P=0.004) and age (65+/-9 years for patients with VT recurrence vs. 58+/-9, P=0.02). Although the risk stratification can be improved, reliable and safe long-term prediction of recurrence of malignant ventricular arrhythmia in individual patients cannot be made. Consequently, the systematic implantation of a cardioverter-defibrillator in case of a first episode of sustained VT occurring in coronary artery disease patients should be further debated.

Comparison of electrophysiologic effects of quinidine and amiodarone in sustained ventricular tachyarrhythmias associated with coronary artery disease

Fifteen patients with spontaneous ventricular tachyarrhythmias underwent electrophysiologic studies at baseline and during therapy with quinidine and amiodarone. In 9, ventricular tachycardia (VT) with a similar QRS morphology was induced with quinidine, amiodarone and under the control state. Both quinidine and amiodarone significantly increased QRS duration and the VT cycle length. Amiodarone increased the VT cycle length more than quinidine (85 vs 121 ms, p < 0.05). Amiodarone increased the percent QRS duration (during sinus rhythm, ventricular pacing and VT) significantly less than percent VT cycle length, whereas quinidine did so only at slow rates (at faster rates the percent increase in QRS duration is not different from the percent increase in VT cycle length). The percent increase in QRS duration produced by quinidine correlated significantly with the percent increase in VT cycle length (the best correlation was observed during pacing, r = 0.78). In contrast, no such significant correlations were obtained for amiodarone. Thus, amiodarone prolongs VT cycle length more than quinidine (at the doses used). The effects of quinidine on conduction in tissue mostly unrelated to tachycardia origin predict effects in the tachycardia cycle length. In contrast, the effects of amiodarone on the latter are more intense but not predicted by those on tissue unrelated to the tachycardia origin.

Prospective, randomized comparison of conventional and high dose loading regimens of amiodarone in the treatment of ventricular tachycardia

OBJECTIVES

The purpose of this prospective randomized study was to compare the electrophysiologic effects of conventional and high dose loading regimens of amiodarone in patients with sustained ventricular tachycardia.

BACKGROUND

Uncontrolled studies in which patients have been treated with an oral loading dose of 2 to 4 g/day of amiodarone have suggested that, compared with a conventional loading dose, this dosing regimen results in more rapid control of spontaneous ventricular tachycardia and ventricular tachycardia induced by programmed stimulation.

METHODS

Patients in whom sustained monomorphic ventricular tachycardia was inducible by programmed stimulation and who were refractory to class I antiarrhythmic medications were randomly assigned to receive either a conventional (n = 15) or a high (n = 17) loading dose of amiodarone. The conventional dose consisted of 600 mg twice a day for 10 days. The high dose regimen consisted of 50 mg/kg body weight per day on days 1 to 3, 30 mg/kg per day on days 4 and 5 and 600 mg twice a day on days 6 to 10. An electrophysiologic test was performed in the baseline state and after 3 and 10 days of therapy. An adequate response to amiodarone was defined as the inability to induce ventricular tachycardia or the ability to induce only relatively slow (cycle length > or = 350 ms) hemodynamically stable ventricular tachycardia.

RESULTS

After 3 days of therapy, 2 of 14 patients who received the conventional loading dose and 6 of 15 patients who received the high dose loading regimen had an adequate response to amiodarone (p = 0.08). After 10 days of therapy, four patients in each group had an adequate response to amiodarone (p = NS). Three patients who received the high dose and one patient who received the conventional dose of amiodarone had an adequate response after 3 days of therapy but not after 10 days of therapy. There were significant increases in the sinus cycle length, atrioventricular block cycle length, ventricular effective refractory period and ventricular tachycardia cycle length after 3 and 10 days of therapy compared with baseline values regardless of the dosing regimen. The extent of the effects of amiodarone on these variables after 3 and 10 days of therapy was similar with both dosing regimens.

CONCLUSIONS

The therapeutic and electrophysiologic effects of conventional and high dose loading regimens of amiodarone do not differ significantly after 3 or 10 days of therapy. High oral loading doses of amiodarone do not offer any significant clinical advantage over a conventional loading dose of amiodarone for controlling ventricular tachycardia induced by programmed stimulation.

Frequency-dependent electrophysiologic effects of amiodarone in humans

BACKGROUND

In general, antiarrhythmic agents that prolong the action potential duration (APD) have attenuated effects on repolarization at short cycle lengths (reverse frequency dependence), and this may limit their efficacy for controlling ventricular arrhythmias. The frequency-dependent effects of amiodarone on repolarization may differ from those of other antiarrhythmic agents and have not been determined in humans.

METHODS AND RESULTS

The frequency-dependent effects of amiodarone on repolarization and conduction were determined during electrophysiologic study in 19 patients at drug-free baseline and after 11 days of amiodarone loading (1621 +/- 162 mg/d, group A) and in 15 additional patients after > or = 1 year of chronic amiodarone therapy (380 +/- 56 mg/d, group B). The two groups were similar in all clinical characteristics. The ventricular APD at 90% repolarization (APD90), right ventricular effective refractory period (VERP), and QRS duration were determined at paced cycle lengths of 300 to 600 milliseconds. In group A, amiodarone significantly (10% to 13%, P < .001) increased the APD90 at all paced cycle lengths by approximately 30 milliseconds compared with baseline. Similarly, there were no frequency-dependent effects on the percent increase in VERP. However, there was greater amiodarone-induced prolongation of the VERP magnitude at longer paced cycle lengths than at shorter cycle lengths (P = .04), although the VERP remained significantly prolonged at the shortest paced cycle length (300 milliseconds) by 33 +/- 22 milliseconds (16.9% increase from baseline, P < .001). Amiodarone significantly (P < .01) increased the QRS duration at paced cycle lengths < or = 500 milliseconds by a maximum of 28% compared with baseline measurements. The increase in ventricular conduction time was frequency dependent (P < .01), consistent with significant sodium channel blockade. The VERP/APD90 ratio (determined at twice diastolic threshold) was significantly prolonged by amiodarone (as compared with baseline) at cycle lengths > or = 400 milliseconds, indicative of both time- and voltage-dependent effects on refractoriness. The increase in induced sustained ventricular tachycardia cycle length in group A patients after amiodarone loading was significantly correlated with the increase in VERP (r = .68, P = .044) but not with increases in QRS duration or APD90. In addition, there were no significant differences in frequency-dependent effects of amiodarone between groups A and B.

CONCLUSIONS

The frequency-dependent response of the electrophysiologic effects of amiodarone are similar after 11 days of loading or > or = 1 year of chronic therapy. Amiodarone does not exert frequency-dependent effects on ventricular repolarization; it prolongs refractoriness by both time- and voltage-dependent mechanisms and exerts frequency-dependent effects on ventricular conduction. The absence of amiodarone-induced reverse frequency-dependent effects on repolarization, together with its time-dependent effects on refractoriness may account in part for the high efficacy of the drug and its low propensity to cause torsade de pointes.

High dose oral amiodarone loading: electrophysiologic effects and clinical tolerance

Although amiodarone is an effective drug for the treatment of life-threatening ventricular arrhythmias, no standard oral loading dose protocol has been defined, and patients often undergo prolonged hospitalization for amiodarone loading. High dose (greater than 1,800 mg/day) oral loading has usually been reserved for unstable patients with incessant ventricular tachyarrhythmias. The current study was designed to 1) examine the clinical and electrophysiologic effects of a high dose oral amiodarone loading regimen in more stable patients; and 2) ascertain its safety and tolerance, possibly allowing shortened amiodarone loading periods and potentially decreased length of hospital stay. The study group included 16 patients with a history of recurrent ventricular arrhythmias and decreased left ventricular function, who were refractory to prior antiarrhythmic drug therapy. The oral loading protocol was 50 mg/kg per day of amiodarone for 3 days, then 30 mg/kg per day for 2 days, followed by maintenance therapy of 300 to 400 mg twice daily. Electrophysiologic testing was performed at baseline, on days 1 and 5 and during week 6. Amiodarone and desethylamiodarone levels were measured and symptoms monitored. Clinically, the high dose loading protocol was well tolerated in 15 of the 16 patients. Arrhythmias were rendered noninducible by day 1 in three patients and remained noninducible throughout the study period in two of the three. The remaining patients continued to have inducible ventricular tachycardia. Ventricular tachycardia cycle length and right ventricular effective refractory period both progressively increased significantly over baseline, starting on day 1. The 15 patients who remained in the study had no significant side effects during the loading period.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of the results of electrophysiologic testing after short-term and long-term treatment with amiodarone in patients with ventricular tachycardia

The results of electrophysiologic testing after short-term and long-term treatment with amiodarone were compared in 71 patients with ventricular tachycardia. Electrophysiologic testing was performed in the baseline state after 11 +/- 3 days of treatment with 1.2 to 2.4 gm/day of amiodarone, and after 13 +/- 4 weeks of therapy with a daily amiodarone dose of 400 mg. After short-term therapy, 62% of the patients had an adequate response to amiodarone. In 27 patients who were hemodynamically unstable, ventricular tachycardia was induced and became noninducible or hemodynamically stable after combination therapy with a class I agent. Among 18 patients who did not have inducible ventricular tachycardia after short-term therapy, eight (44%) had inducible, hemodynamically unstable ventricular tachycardia after long-term treatment with amiodarone. On the other hand, six of the 27 patients who had hemodynamically unstable ventricular tachycardia after short-term therapy had an adequate response after long-term treatment with amiodarone. Therefore an adequate electrophysiologic response after short-term therapy does not guarantee a similar response after long-term treatment, and an inadequate response after short-term therapy does not always predict a similar response after long-term therapy.

Programmed ventricular stimulation using up to two extrastimuli and repetition of double extrastimulation for induction of ventricular tachycardia: a new highly sensitive and specific protocol

The sensitivity and specificity of a new protocol of programmed ventricular stimulation were evaluated in 71 consecutive patients who were divided into 2 groups: group 1 included 41 patients, of whom 25 had sustained ventricular tachycardia (VT) not associated with cardiac arrest and 16 had ventricular fibrillation (VF) not precipitated by any obvious factor; group 2 included 30 patients without demonstrable heart disease and no suspected or documented sustained ventricular tachyarrhythmias. The study consisted of a standard protocol (up to 2 extrastimuli given only once for each extrastimulus prematurity, 2 right ventricular sites and 3 basic pacing cycle lengths, as well as rapid ventricular pacing) in which double extrastimulation at the shortest coupling intervals that allowed ventricular capture was repeated 10 times. A stimulus current of 3 mA was used. Sustained ventricular tachyarrhythmias were induced in 23 of 25 (92%) patients who presented with sustained VT, 14 of 16 (88%) patients who presented with VF and 2 of 30 (7%) group 2 patients. Eighteen of 25 (72%) patients with sustained VT but only 4 of 16 (25%) with VF had arrhythmias inducible at "immediate" trials of single or double extrastimulation (p less than 0.01). Repetition of double extrastimulation increased the yield of inducible sustained ventricular tachyarrhythmia to 92% in patients with sustained VT (+20%, p = 0.14) and 75% (+50%, p = 0.013) in patients with VF. Rapid right ventricular pacing added a 13% increase in the overall yield in patients with VF. This new protocol of programmed ventricular stimulation has both high sensitivity (90%) and specificity (93%) for induction of sustained VT.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of disposition values obtained by two assay methods for quinidine gluconate in patients with ventricular tachycardia

Eight patients with previously untreated ventricular tachycardia, age 48.54 +/- 28.02 years (mean +/- SD), were enrolled in a protocol evaluating the disposition of quinidine gluconate as determined by two assay methods. Patients received two infusions of 5 mg/kg over 30 minutes separated by 20-30 (24.9 +/- 4.0) minutes of electrophysiologic testing. Blood samples were obtained at 0.17 hours and just prior to the second infusion, and then at 0.17, 0.25, 0.33, 1.0, 6.0, 12.0, and 24.0 hours after the second infusion. Paired serum samples were assayed for quinidine concentrations by fluorescence polarization immunoassay and high-performance liquid chromatography. The two assays compared well, with a linear regression equation of Y = 0.927X + 0.247 with a correlation coefficient of 0.985. With the exception of the beta elimination rate constant and beta distribution volume, t test comparison of disposition values demonstrated no significant difference. Differences in the estimates of the beta elimination rate constant reflected differences in the two methods and indicated that even though both assays were comparable, subtle differences in specificity could be reflected in significant differences in this variable.

Stability of electrophysiological parameters after acute amiodarone loading: implications for patient management

The appropriate timing of electrophysiological study in patients treated with amiodarone is uncertain. Twenty patients with coronary artery disease in whom sustained ventricular tachycardia was still inducible after 9 +/- 1 days of amiodarone loading (1,200-1,400 mg/day) underwent repeat electrophysiological testing after an additional month of maintenance therapy (400 mg/day). Compared with baseline, both short- and long-term amiodarone therapy caused significant changes in QTc, right ventricular effective refractory period, and ventricular tachycardia cycle length. However, there was no significant change in electrophysiological parameters between the end of the acute amiodarone loading period and 1 month of additional therapy. Sustained ventricular tachycardia remained inducible in 19 of 20 patients after 1 month of maintenance therapy. Amiodarone and desethylamiodarone plasma concentrations remained stable after amiodarone loading, but did not correlate with the magnitude of electrophysiological changes from baseline. These data suggest that electrophysiological testing after 9 days of high dose amiodarone therapy may accurately reflect long-term electrophysiological effects.

Electropharmacology of amiodarone therapy initiation. Time courses of onset of electrophysiologic and antiarrhythmic effects

The time courses of onset of the electrophysiologic and antiarrhythmic effects of amiodarone were determined with serial electrophysiologic studies in 34 patients with inducible ventricular tachycardia. A standardized oral loading dosage was used for all patients (1,200 mg/day for 14 days; 800 mg/day for 7 days; and 400 mg/day thereafter). Eleven patients had the studies performed at baseline and after 2, 6, 10, and 20 weeks. Subsequently, 23 patients had studies at baseline and after 2 and 10 weeks. Changes in atrial, sinus, and atrioventricular nodal properties and in conduction intervals were maximal within 2 weeks (early effects). For example, atrioventricular nodal Wenckebach cycle length increased between baseline (369 +/- 80 msec) and 2 weeks (498 +/- 78 msec) (p less than 0.001) but did not change further after 10 weeks (500 +/- 89 msec). However, ventricular Class III effects required 10 weeks to become maximal (late effects). For example, the QT interval during atrial pacing increased between baseline (355 +/- 36 msec) and 2 weeks (406 +/- 37 msec) (p less than 0.001) and increased further after 10 weeks (436 +/- 45 msec) (p less than 0.001). Antiarrhythmic effects also followed different time courses of onset. Suppression of ventricular premature beats was maximal within 2 weeks. However, suppression of ventricular tachycardia inducibility and slowing of ventricular tachycardia rate was not maximal for 10 weeks. Correlations between serum desethylamiodarone concentrations and some late effects suggest that the mechanism of the time delay to maximal ventricular Class III effects may involve desethylamiodarone.(ABSTRACT TRUNCATED AT 250 WORDS)

Prognostic value of early electrophysiologic studies for ventricular tachycardia recurrence in patients with coronary artery disease treated with amiodarone

Amiodarone was used in 86 patients with ventricular tachycardia (VT) (67 patients) or ventricular fibrillation (19 patients) secondary to coronary artery disease. The mean +/- standard deviation left ventricular ejection fraction was 30 +/- 12% (range 8 to 65%). Prior trials with 4 +/- 1.2 alternate antiarrhythmic agents had been unsuccessful. Amiodarone was loaded at dosages of 1,200 to 1,800 mg/day, with maintenance dosages of 400 to 600 mg/day. Drug efficacy was evaluated by programmed stimulation at 10 to 14 days in 68 patients. In 38 patients sustained VT or ventricular fibrillation was inducible (group I), whereas 30 patients (group II) had either no inducible VT (8) or had nonsustained VT induced (22). Holter monitoring was used to assess drug efficacy in 18 patients (group III). All patients were evaluated at 3- to 6-month intervals with Holter monitors for efficacy and a standard protocol for toxicity. During a long-term follow-up of 18 +/- 16 months, sudden death occurred in 5 patients and nonfatal arrhythmia recurrences were detected in 16. The actuarial probability of freedom from fatal and nonfatal arrhythmia recurrences at 24 months was 0.52 for group I, 0.97 for group II and 0.68 for group III. The mode of induction, rate change or hemodynamic tolerance of the induced ventricular tachycardia did not predict arrhythmia recurrence. Among the clinical variables analyzed, only an ejection fraction of less than or equal to 30% was identified as a significant predictor of arrhythmia recurrence. Nonsudden cardiac death occurred in 21 patients, including 19 from heart failure and 2 from myocardial infarction. Noncardiac death occurred in 7 patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Disposition of 3-hydroxyquinidine in patients receiving initial intravenous quinidine gluconate for electrophysiology testing of ventricular tachycardia

The formation rate constant and elimination rate constant for 3-hydroxyquinidine were determined in eight patients with ventricular tachycardia. These two parameters (mean +/- SD) were found to be 0.784 +/- 0.202 and 0.042 +/- 0.058 h-1, respectively. Coefficients of determination for the computer-generated line of best fit for serum concentration-time data were 0.986 +/- 0.008. Patients received two infusions of quinidine gluconate 5 mg/kg over 30 minutes separated by a 20-30 minute electrophysiologic testing period. Unbound and total 3-hydroxyquinidine concentrations were also determined. Among the eight patients, 3-hydroxyquinidine was 61.9 percent bound. Studies in healthy volunteers had shown 50 percent binding. Linear regression of unbound and total 3-hydroxyquinidine was described by the equation Y = 0.3814X-1.448, r = 0.813. Although half-lives of 3.5-12.4 hours had been reported in healthy volunteers, prolonged half-lives were observed in all but two of our arrhythmia patients.

Rapid self-terminating ventricular tachycardia induced during electrophysiologic study: a prospective evaluation

The clinical significance of rapid self-terminating ventricular tachycardia induced during electrophysiologic study was prospectively evaluated in three patient groups with clinical ventricular arrhythmias. Group A (11 patients) had inducible rapid self-terminating ventricular tachycardia only (mean cycle length less than or equal to 250 ms and greater than or equal to 10 beats in duration). In Group B (22 patients) induction of this arrhythmia was followed by the induction of sustained ventricular tachycardia. In Group C (82 patients) sustained ventricular tachycardia was induced without preceding rapid self-terminating ventricular tachycardia. All clinical characteristics of Group B patients were similar to those of Group C patients but differed markedly from those of Group A patients. Compared with Group A patients, Group B patients had a lower left ventricular ejection fraction (32 +/- 13% versus 52 +/- 17%, p = 0.004) and a greater prevalence of coronary artery disease (82% versus 0%, p less than 0.0001), structural heart disease and a history of clinical sustained ventrical arrhythmias. Similarly, the induced self-terminating ventricular tachycardia differed in Group A and Group B patients. The arrhythmias in Group B patients were more often monomorphic, were more often induced with one or two extrastimuli and had a longer cycle length than those in Group A patients. In Group B patients, the electrophysiologic characteristics of the self-terminating and the sustained induced ventricular tachycardias were similar. Cardioversion was required in 50% of Group B patients compared with 27% of Group C patients (p = 0.038).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of individual and combined effects of procainamide and amiodarone in patients with sustained ventricular tachyarrhythmias

To compare the individual and combined electrophysiological effects of amiodarone and procainamide, 35 patients with sustained ventricular arrhythmias underwent programmed stimulation in the control state, after procainamide (mean concentration, 8.7 +/- 2.8 micrograms/ml), after 13 +/- 2 days of amiodarone (1,400 mg/day x 7 days, then 400 mg/day), and after amiodarone with procainamide (mean procainamide concentration, 7.8 +/- 2.2 micrograms/ml). Sustained ventricular tachycardia (VT) was inducible in all 35 patients during treatment with procainamide alone and with amiodarone alone. Procainamide and amiodarone similarly increased the VT cycle length (+68 vs. +61 msec), the corrected QT interval (+63 vs. +49 msec), and the ventricular effective refractory period measured at paced cycle lengths of 600-550 msec (+23 vs. +21 msec) and 400 msec (+25 vs. +23 msec). Procainamide had a more pronounced effect on QRS duration than amiodarone during sinus rhythm (+18 vs. +8 msec, p less than 0.01) and during paced cycle lengths of 600-550 msec (+32 vs. +23 msec, p less than 0.01) and 400 msec (+37 vs. +28 msec, p less than 0.1) but a similar effect on the QRS duration during VT (+32 vs. +29 msec). During combination therapy, VT initiation was prevented in only two (6%) patients. The combination therapy produced a greater increase (p less than 0.001) than individual therapy in all the electrophysiological intervals assessed, with the exception of the sinus cycle length. On each drug regimen, a cycle length-dependent increase (p less than 0.05) in paced QRS duration was noted (400 more than 600-550 msec).(ABSTRACT TRUNCATED AT 250 WORDS)

Amiodarone in the management of cardiac arrhythmias: current concepts

This article reviews current information on the clinical pharmacology, therapeutic utility, and adverse reactions of amiodarone, with emphasis on guidelines for its rational use.

Dissociation of electrophysiologic and pharmacologic stability during an abbreviated oral loading regimen of amiodarone

Thirty-three patients treated with an abbreviated oral amiodarone loading regimen for ventricular tachycardia underwent electrophysiologic testing in the control state, after 1 week of high-dose (1170 +/- 88 mg/day) inpatient therapy; and after an 8-week intermediate (669 +/- 129 mg/day) dosing phase. Serum levels of amiodarone and desethylamiodarone were measured by high-pressure liquid chromatography during follow-up electrophysiologic studies. Although the corrected sinus node recovery time, sinoatrial conduction time, and AH and HV intervals remained unchanged throughout the loading period, the sinus cycle length, Wenckebach cycle length, atrial and ventricular refractory periods, and ventricular tachycardia mean and return cycle lengths lengthened significantly by 1 week. They then remained stable for the remainder of the treatment period (control less than 1 and 8 weeks, p less than 0.05). In contrast, amiodarone and especially desethylamiodarone levels rose from 1 to 8 weeks: 1.29 +/- 0.56 to 1.97 +/- 0.90 micrograms/ml (p = 0.001) and 0.63 +/- 0.29 to 1.29 +/- 0.61 micrograms/ml (p less than 0.0001), respectively. Because this regimen produces relatively prompt electrophysiologic changes, which then stabilize, early outpatient management becomes feasible before pharmacologic steady state is attained.

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.

Idiopathic ventricular fibrillation: inducibility and beneficial effects of class I antiarrhythmic agents

Ventricular fibrillation in patients without recognizable heart disease is uncommon and electrophysiologic data on such patients is limited. Over a 7 year period, five patients (three men and two women, ranging in age from 24 to 52 years) without demonstrable heart disease underwent electrophysiologic studies with pharmacologic drug testing because of single (four patients) or multiple (one patient) documented episodes of ventricular fibrillation. The arrhythmic event was unrelated to myocardial ischemia or infarction, metabolic or electrolyte disturbances, drug toxicity, preexcitation, or prolonged QT syndromes. In all three patients receiving no antiarrhythmic drugs and in two pretreated with amiodarone, a rapid poorly tolerated ventricular tachyarrhythmia requiring cardioversion was induced by programmed ventricular stimulation with up to two extrastimuli. In all instances, addition of either oral quinidine or oral disopyramide prevented the induction of sustained ventricular arrhythmias. All five patients were placed on antiarrhythmic drug regimens found effective during electrophysiologic studies and remained asymptomatic during follow-up periods ranging from 12 to 93 (mean 52) months. We conclude that in the patients with idiopathic ventricular fibrillation in our study: programmed ventricular stimulation reliably replicated the spontaneous arrhythmia, class I antiarrhythmic agents effectively prevented induction of the arrhythmia in the laboratory, and in contrast to the severity of the presenting arrhythmia, a benign clinical course was observed during long-term therapy with class I antiarrhythmic agents.