The efficacy of amiodarone in the treatment of ventricular tachycardia or ventricular fibrillation

Catheter ablation of well tolerated ventricular tachycardia in patients with structural heart disease and without automatic defibrillator implantation: long term follow-up

BACKGROUND

The occurrence of a sustained monomorphic ventricular tachycardias (SMVT) in patients with underlying structural heart disease (SHD) is considered related to poor prognosis. The purpose of our work was to evaluate if these patients could benefit from radiofrequency (RF) ablation, and the defibrillator (ICD) implantation could be deferred during follow-up.

METHODS

We reviewed consecutive patients with well-tolerated SMVT, SHD and left ventricular ejection fraction over 30%. These patients were treated by RF ablation and were discharged without ICD. The primary outcome was a composite of all-cause death and recurrence of SMVT; the secondary outcome was death from all causes.

RESULTS

62 patients were selected. After a median follow-up of 38.8 months, the primary outcome occurred in 24 (38.7%) and the secondary in 11 (17.7%) patients. The annual mortality rate was 4.3% and no patient died from sudden death.

CONCLUSIONS

RF ablation as a first-choice therapy seems to represent an effective and beneficial therapeutic approach.

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.

Population pharmacokinetics of intravenous amiodarone and comparison with two-stage pharmacokinetic analysis

The disposition of amiodarone, an antiarrhythmic agent was evaluated after a single intravenous infusion (5 mg/kg over 15 minutes) in patients of various ages and with various degrees of renal function and left ventricular function. The plasma concentration-time data were obtained from three clinical studies with similar protocols. The data were analyzed by nonlinear mixed-effects modeling (NONMEM) to estimate the population pharmacokinetic parameters of amiodarone and to determine the significant demographic covariates affecting these parameters. The pharmacokinetic parameters of amiodarone (weight-corrected) also were calculated using two-stage analysis and were compared with the results obtained from the mixed-effects analysis. The population plasma concentration-time profile of amiodarone was best described by a four-compartment model. Demographic covariates (i.e., creatinine clearance and ejection fraction) did not improve the final pharmacostatistical model significantly. The results from the two-stage analysis showed no significant relationship between amiodarone pharmacokinetic parameters and age, gender, renal function, or ejection fraction. The results from one study, however, demonstrated that advanced age (> or = 65 years) resulted in reduced amiodarone clearance coupled with a prolonged elimination half-life. No such correlation was detected with NONMEM analysis, which may be partly attributable to the small number of elderly patients. Overall, the results from NONMEM analysis validated the results obtained from the two-stage analysis.

Efficacy, safety, and determinants of conversion of atrial fibrillation and flutter with oral amiodarone

Amiodarone is effective for long-term maintenance of sinus rhythm after electrical cardioversion of refractory atrial fibrillation or flutter. To examine its efficacy and safety for pharmacologic conversion of these arrhythmias, we studied 129 patients with refractory atrial fibrillation or flutter who had failed previous intensive conventional antiarrhythmic treatment. In anticipation of electrical cardioversion, patients were loaded with amiodarone, 600 mg/day during a 4-week period. The main outcome measure was pharmacologic conversion during this period. During the loading period, 23 patients (18%) converted to sinus rhythm. When analyzed in a multivariate model, conversion was related to desethylamiodarone plasma level (p = 0.0006), arrhythmia duration (p = 0.04), left atrial area (p = 0.02), and concomitant treatment with verapamil (p = 0.01). During ongoing atrial fibrillation after loading, the ventricular rate decreased from 100 +/- 25 to 87 +/- 27 beats/ min (p <0.001). Amiodarone appeared to be safe and did not have to be discontinued because of intolerable side effects. Thus, amiodarone loading is safe and is still able to convert refractory atrial fibrillation or flutter. Conversion is related to increased desethylamiodarone plasma levels and concomitant treatment with verapamil. Because prolonged loading may increase desethylamiodarone plasma concentrations, this may enhance efficacy and obviate the need for electrical cardioversion.

Pharmacokinetics of intravenous amiodarone in patients with impaired left ventricular function

To evaluate the potential need for modification of dose regimens of intravenous amiodarone in patients with left ventricular dysfunction, the pharmacokinetics of amiodarone and its active metabolite, desethylamiodarone (DEA), were examined after a single 15-minute intravenous infusion of amiodarone 5 mg/kg. Three parallel groups of otherwise healthy volunteers with normal (n = 12), moderately impaired (ejection fraction > 30 but < or = 45%; n = 6), or severely impaired (ejection fraction < or = 30%; n = 6) left ventricular function were enrolled in the study. Serial blood samples were obtained over a 76-day period for estimation of pharmacokinetic parameters. With the exception of the half-life (t1/2) of DEA, statistical comparisons revealed no significant between-group differences in pharmacokinetic parameters or correlations between pharmacokinetic parameters and ejection fractions. The t1/2 of DEA was increased by approximately 60% in patients with severe left ventricular dysfunction compared with that in patients with moderately impaired and normal left ventricular function. The rate of DEA formation is slow, however, and its concentration relative to amiodarone is low. Therefore, it is unlikely that concentrations of DEA in serum would reach levels that contribute significantly to the pharmacologic activity of amiodarone during short-term (up to 2 weeks) intravenous amiodarone therapy. Single doses of amiodarone were well tolerated. The results of this study suggest that intravenous amiodarone can be used with appropriate observation to control arrhythmias, regardless of the degree of left ventricular dysfunction.

Proarrhythmia with class III antiarrhythmic drugs: definition, electrophysiologic mechanisms, incidence, predisposing factors, and clinical implications

Antiarrhythmic drugs can and do induce unexpected and sometimes fatal reactions by either producing new symptomatic arrhythmias or by aggravating existing arrhythmias. The definition of proarrhythmia has changed since controlled clinical studies showed a dichotomy between arrhythmia suppression and mortality. The nature of proarrhythmic reactions is linked to the electrophysiologic effects of various antiarrhythmic drugs. Whereas Class I agents without accompanying effects on repolarization generally produce ventricular tachycardia (often incessant) or fibrillation, Class III agents typically produce torsades de pointes that may deteriorate into ventricular fibrillation. The precise mechanism of torsades de pointes is not fully elucidated, although early after-depolarization and increases in spatial or temporal dispersion of repolarization are likely possibilities. Proarrhythmic risk is lowest for amiodarone and is probably related to the drug's complex electrophysiologic profile. The incidence of torsades with sotalol increases with dose and the baseline values of the QT interval; the incidence with d-sotalol and other pure Class III agents remains unclear. Prospective, randomized, placebo-controlled studies to evaluate this are under way. The fact that d-sotalol increases mortality in postinfarction patients suggests that it may possibly be a common property of most, if not all, pure Class III compounds. The ongoing clinical trials with various Class III agents are likely to provide the critical information on this important therapeutic issue.

Effects of amiodarone on refractory ventricular fibrillation in acute myocardial infarction: experimental study

OBJECTIVES

The aim of this study was to evaluate the efficacy of a single dose of intravenous amiodarone in facilitating defibrillation of ventricular fibrillation refractory to lidocaine and epinephrine plus direct current countershocks in experimental acute myocardial infarction.

BACKGROUND

Amiodarone has been hailed as the most effective single antiarrhythmic drug for the treatment of ventricular arrhythmias. However, intravenous amiodarone has only sporadically been used in the defibrillation of ventricular fibrillation in acute myocardial infarction.

METHODS

Acute myocardial infarction was induced in 60 dogs by ligation of the proximal left anterior descending coronary artery for 2 h. Animals that developed spontaneous ventricular fibrillation were treated with lidocaine and epinephrine plus five direct-current countershocks. Dogs with ventricular fibrillation refractory to this regimen were randomized to further treatment with additional intravenous administration of epinephrine and bolus lidocaine plus < or = 15 direct-current countershocks (group I) or administration of amiodarone, 10 mg/kg body weight intravenously, followed by defibrillation with direct-current counter-shock (group II).

RESULTS

Sixteen (27%) of the 60 dogs in which the protocol was attempted developed spontaneous ventricular fibrillation 21 min after ligation and were included in the study. Lidocaine and epinephrine plus five direct-current countershocks succeeded in converting ventricular fibrillation in one dog (6%). The other 15 dogs were randomized to group I (8 dogs) or group II (7 dogs). Defibrillation was achieved in one of the eight dogs in group I and in six of the seven dogs in group II (p < 0.005).

CONCLUSIONS

In an experimental model of acute ischemia, intravenous amiodarone (10 mg/kg) influences positively the response to defibrillation of ventricular fibrillation refractory to lidocaine and epinephrine plus direct current countershocks.

Amiodarone and post-MI patients

Amiodarone is a viable drug for preventing sudden cardiac death, particularly during the first year after MI. If larger trials confirm the aforementioned prospective trials of Ceremuzynski et al, Cairns et al, and the BASIS trial, the efficacy of amiodarone would outweigh the risk of its side effects during the first year after MI. Based on the long-term observation from the BASIS trial, the duration of amiodarone therapy need not be more than 1 year--which, as we have learned, is when these post-MI patients would benefit most from the drug. It is also likely that the effects of amiodarone would complement those of aspirin and angiotensin converting enzyme inhibitors. The SAVE, CONSENSUS II, and SOLVD trials demonstrated that captopril and enalapril did not reduce the mortality rate during the first year after MI, nor did they reduce the sudden cardiac death rate. Their beneficial effects became evident only during the second year and thereafter. Unlike other antiarrhythmic agents of various classes, amiodarone possesses antiarrhythmic properties but does not exert deleterious effects on ventricular function. More studies are needed to determine if the benefit of amiodarone could be enhanced by combination therapy (eg, angiotensin converting enzyme inhibitors, aspirin, or beta-blockers). Whether amiodarone will provide the same protection for patients who have poor left ventricular function or congestive heart failure is not known. The European and VA cooperative studies should help answer this question. If it turns out that amiodarone is beneficial, one must then determine whether higher doses of the drug will offer more protection, and, if so, if that greater protection would be offset by increased toxicity. How much amiodarone should be given to offer the most protection with the least risk? Another intriguing research question is this: If we treat patients with amiodarone for more than 1 year, would the drug continue to improve the mortality rate in subsequent years? Other studies are needed in patients at very high risk of sudden cardiac death (ie, those who have a low ejection fraction and high-density VPDs). A study comparing amiodarone and sotalol in high-risk patients for sudden cardiac death is also needed. These clinical studies should be carried out with basic science research investigating the actions of amiodarone at the molecular and cellular level in order to give us a better understanding of how the drug works.

The use of antiarrhythmics in advanced cardiac life support

Antiarrhythmic agents have been used to treat malignant ventricular arrhythmias in the setting of acute myocardial ischemia with proven efficacy for many years. Thus, it has been presumed that these agents would be efficacious for the treatment of cardiac arrest. Unfortunately, hard data supporting this contention are unavailable to date. Furthermore, some of the experimental data in this area are conflicting, especially regarding the relative effects of lidocaine and bretylium. Thus, little definitive can be said based on experimental information. In two randomized patient studies, lidocaine and bretylium performed comparably. Because of the frequent use of lidocaine and thus the familiarity of most health care professionals with its use, it makes educational sense to utilize lidocaine as the antiarrhythmic drug of first choice during the cardiac arrest sequence. Recent data suggesting that amiodarone may be efficacious in patients with recurrent arrhythmias require additional confirmation. Although antiarrhythmic agents have been shown to be effective in the treatment of malignant arrhythmias in patients with acute myocardial infarction, their use prophylactically for patients with suspected infarction (advocated in the past) has recently undergone reevaluation. It is now clear that despite a reduction in ventricular fibrillation, overall mortality may be increased. This may be because the prophylactic treatment of patients with suspected infarction includes a large number of patients not at risk for ventricular fibrillation who still may be at risk for drug toxicity. Thus, prophylactic administration of lidocaine to all patients with suspected acute myocardial infarction can no longer be recommended. There are inadequate data upon which to base a recommendation concerning the use of lidocaine in patients receiving thrombolytic therapy. The group most likely to benefit from lidocaine are patients with ST segment elevation who present early after the onset of acute myocardial infarction. The use of lidocaine in this group requires additional study. At present, despite enthusiasm for the prophylactic use of magnesium for the treatment of arrhythmias, data are inadequate to support its routine administration. However, given the importance of magnesium and potassium levels in the genesis of malignant arrhythmias, their levels in plasma should be assessed, and abnormalities should be promptly corrected. The potential uses of antiarrhythmic agents during advanced cardiac life support span a remarkably diverse number of applications. For the purpose of this review, only the use of these agents during CPR and during the early hours of acute or suspected acute myocardial infarction will be considered.

A prospective study of the efficacy and safety of adjuvant metoprolol and xamoterol in combination with amiodarone for resistant ventricular tachycardia associated with impaired left ventricular function

Combination antiarrhythmic drug therapy may be more effective than treatment with a single agent for control of refractory cases of sustained ventricular tachycardia (VT). In a prospective randomized crossover study of 20 patients with impaired left ventricular function (ejection fraction of 28% +/- 8%) and recurrent VT in spite of treatment with amiodarone, we compared the efficacy and safety of adjuvant therapy with metoprolol, 50 mg two times daily and xamoterol, 200 mg two times daily. Metoprolol caused hemodynamic deterioration in five patients, and only one also experienced intolerance to xamoterol. Sustained VT was inducible in all 20 patients who were receiving amiodarone alone but was suppressed or rendered nonsustained in 8 of 20 patients during treatment with amiodarone plus xamoterol and in 6 of 17 patients during treatment with amiodarone plus metoprolol. Addition of xamoterol restored sinus rhythm in four patients who presented with incessant VT, and metoprolol was effective for three of them. Neither beta-blocker significantly altered tachycardia cycle length or any electrophysiologic parameter other than the slowing of the sinus rate. Both beta-blockers suppressed exercise-induced VT in 3 of 4 patients, and addition of xamoterol significantly increased treadmill exercise duration (7.1 +/- 1.8 min) compared with administration of amiodarone alone (3.8 +/- 1.5 min; p < 0.01). Fourteen patients were discharged with prescriptions for amiodarone-beta-blocker combinations. During a mean follow-up period of 13 months (range, 2 to 24 months), there were three cases of recurrent VT (in all patients VT remained inducible) and no sudden deaths.(ABSTRACT TRUNCATED AT 250 WORDS)

Amiodarone. An overview of its pharmacological properties, and review of its therapeutic use in cardiac arrhythmias

Amiodarone, originally developed over 20 years ago, is a potent antiarrhythmic drug with the actions of all antiarrhythmic drug classes. It has been successfully used in the treatment of symptomatic and life-threatening ventricular arrhythmias and symptomatic supraventricular arrhythmias. In patients with left ventricular dysfunction amiodarone does not usually produce any clinically significant cardiodepression and the drug has relatively high antiarrhythmic efficacy. Preliminary studies indicate that amiodarone may have a beneficial effect on mortality and survival in certain groups of patients with ventricular arrhythmias, an action probably related to both its antiarrhythmic and antifibrillatory effects. The adverse effect profile of amiodarone is diverse, involving the cardiac, thyroid, pulmonary, hepatic, gastrointestinal, ocular, neurological and dermatological systems. Interstitial pneumonitis and hepatitis are potentially fatal, but the vast majority of adverse events are less serious, and some may be dose dependent. Pretreatment monitoring, regular assessments and the use of minimum effective doses are, therefore, necessary. Thus, with appropriate monitoring to control its well recognised adverse effects amiodarone has an important place as an effective 'broad spectrum' antiarrhythmic drug which has, so far, been used when other treatments have proved ineffective. More recent preliminary data also suggest that it may also have a beneficial effect in the prevention of sudden death in some patients.

Post-myocardial infarction mortality in patients with ventricular premature depolarizations. Canadian Amiodarone Myocardial Infarction Arrhythmia Trial Pilot Study

BACKGROUND

Among survivors of acute myocardial infarction, frequent and repetitive ventricular premature depolarizations (VPDs) detected on ambulatory monitoring contribute independently to the risk of all-cause mortality and sudden death. Apart from the beta-blockers, no antiarrhythmic drug has been reliably demonstrated to reduce mortality among patients with VPDs. A pilot study was undertaken to gather data to aid in the design of a multicenter trial of amiodarone for the reduction of mortality from cardiac arrhythmias in such patients.

METHODS AND RESULTS

Seventy-seven patients with acute myocardial infarction within the previous 6-30 days and 10 or more VPDs/hr or one or more runs of ventricular tachycardia on 24-hour electrocardiographic recording were randomized in a double-blind fashion in a 2:1 amiodarone-to-placebo ratio. The loading dose was 10 mg/kg/day for 3 weeks. The maintenance dose was 300-400 mg/day with reductions at 4-month intervals in response to VPD suppression, excessive plasma levels, or toxicity. VPD suppression at 1 week and 2 weeks was 63% and 85%, respectively, on amiodarone and 17% and 27%, respectively, on placebo. Apart from thyroid-stimulating hormone elevation and skin reactions, no side effects occurred more frequently with amiodarone. The study drug was stopped for side effects or noncompliance in 35% of amiodarone patients and 34% of placebo patients. Patients were followed for a maximum of 2 years (mean, 20 months). Arrhythmic death or resuscitated ventricular fibrillation occurred in two of 48 amiodarone patients (6%) and four of 29 placebo patients (14%), whereas the rates of all-cause mortality were five of 48 (10%) and six of 29 (21%), respectively.

CONCLUSIONS

Amiodarone, in moderate loading and maintenance dosages with adjustments in response to plasma levels, VPD suppression, and side effects, results in effective VPD suppression and acceptable levels of toxicity.

Electrocardiographic and antiarrhythmic effects of intravenous amiodarone: results of a prospective, placebo-controlled study

The antiarrhythmic efficacy of intravenously administered amiodarone was examined in a prospective, randomized, placebo-controlled study that involved 77 patients after coronary artery bypass surgery. Amiodarone was given after surgery in a loading bolus of 300 mg for 2 hours followed by 1200 mg every 24 hours for 2 days and 900 mg every 24 hours for the next 2 days. Amiodarone suppressed both supraventricular and ventricular arrhythmias within 12 hours after the start of therapy. Particularly, the incidence of atrial fibrillation (5% vs 21% in the control group; p less than 0.05) and of nonsustained ventricular tachycardia (3% vs 16%; p less than 0.05) was reduced by amiodarone. Heart rate was slowed (p less than 0.001) and repolarization--as judged by JTc interval--was prolonged compared with the control group (p less than 0.01). In two patients, amiodarone infusion was stopped because of excessive QTc prolongation. No detrimental hemodynamic effects of the drug were observed. Thus the intravenous administration of amiodarone appears to be suitable for patients in whom rapid suppression of symptomatic supraventricular and ventricular arrhythmias is warranted in the presence of left ventricular dysfunction.

Long-term follow-up of postmyocardial infarction patients with ventricular tachycardia or ventricular fibrillation treated with amiodarone

Amiodarone in a low dose (200 mg/day) was administered alone or in combination with other type I antiarrhythmic drugs as a first-line agent in 33 patients with ventricular tachycardia (VT) (n = 24) or ventricular fibrillation (VF) (n = 9) secondary to coronary artery disease with healed myocardial infarction. There were 30 men and 3 women (mean age 69 +/- 9 years). Left ventricular ejection fraction ranged from 16 to 45% (mean 29 +/- 8). Therapy was guided by the results of electrophysiologic studies without the use of a control study (without drugs). Predischarge electrophysiologic studies revealed inducible sustained VT in 8 patients (24%), nonsustained VT in 7 and noninducible VT in 18 patients. Mean follow-up time was 27 +/- 7 months. Eleven patients (33%) died, 5 suddenly (15%) and 6 from nonarrhythmic causes. Five patients (15%) had nonfatal recurrences of VT. Life-table analysis showed that arrhythmic recurrences or fatalities (VT or sudden death) were related to the results of the predischarge electrophysiologic studies and not to the baseline arrhythmia (VT or VF). Toxicity from amiodarone was uncommon and no patient discontinued taking the drug.