Effect of amiodarone on electric induction, morphology, and rate of ventricular tachycardia and its relation to clinical efficacy

Antiarrhythmic Drug Therapy to Avoid Implantable Cardioverter Defibrillator Shocks

Implantable cardioverter defibrillators (ICDs) are effective in the prevention of arrhythmic sudden cardiac death. Many patients receiving an ICD are affected by heart failure and are at risk of ventricular arrhythmias, which may lead to appropriate shocks. On the other hand, in this population the incidence of atrial fibrillation, giving rise to inappropriate ICD shocks, is high. Accordingly, ICD discharges occur frequently and many patients with an ICD will need concomitant antiarrhythmic drug therapy to avoid or reduce the frequency of shocks. Therapeutic agents such as β-blockers, class I or class III antiarrhythmic drugs effectively suppress arrhythmias, but may have side-effects. Some drugs could eventually influence the function of ICDs by altering defibrillation or pacing threshold. Few prospective randomised trials are available, but current data suggest that amiodarone is most effective for prevention of appropriate or inappropriate ICD shocks. This review article summarises current knowledge regarding the antiarrhythmic management of patients with ICDs.

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.

Invasive and noninvasive methods to predict the long-term efficacy of amiodarone: a compilation of clinical observations using meta-analysis

BACKGROUND

The method of choice to predict the long-term efficacy of amiodarone in the treatment of complex ventricular arrhythmias is unknown. Whether electrophysiological testing or Holter monitoring better predicts long-term outcome is controversial.

METHODS AND RESULTS

We performed a meta-analysis of trials using electrophysiological testing or electrocardiographic monitoring to predict the efficacy of amiodarone in patients with sustained ventricular tachycardia. Arrhythmia recurrence data were combined after homogeneity testing across trials. Bayesian estimates and 95% credibility intervals were constructed to compare the arrhythmia-free probability among groups. Nine studies using electrophysiological testing (351 patients) and three using Holter monitoring (167 patients) met criteria for inclusion determined a priori. The combined arrhythmia-free probability estimate and credibility intervals were 0.86 (0.78-0.92) for patients rendered noninducible and 0.81 (0.73-0.87) for patients with abolition of ventricular tachycardia during Holter monitoring on amiodarone. With this primary analysis, there was no significant difference between the predictive value of noninducibility during electrophysiological testing and abolition of ventricular tachycardia with Holter. However, if only those electrophysiological studies using at least triple extrastimuli were included, arrhythmia-free probability for patients rendered noninducible increased to 0.96 (0.88-0.99), significantly better than noninvasive testing.

CONCLUSIONS

Noninducible ventricular tachycardia during electrophysiological testing and abolition of ventricular tachycardia during electrocardiographic monitoring on amiodarone appear equally predictive of long-term amiodarone success, but this conclusion seems dependent on the stimulation protocol used. Although the yield is lower (compared to Holter monitoring), ventricular tachycardia rendered noninducible with a stimulation protocol using triple extrastimuli is the most highly predictive test of long-term amiodarone efficacy.

Pharmacology and pharmacokinetics of amiodarone

Amiodarone is a unique antiarrhythmic agent originally developed as a vasodilator. Classified electrophysiologically as a Type III antiarrhythmic, it also has both nonspecific antisympathetic and direct, fast channel-membrane effects. Hemodynamic effects of orally administered amiodarone (a negative inotropic agent) are usually negligible, and are usually compensated for by induced vasodilation. Effects on thyroid and hepatic function may help to explain some of the unique pharmacologic as well as toxicologic effects of the drug. Amiodarone is poorly bioavailable (20-80%) and undergoes extensive enterohepatic circulation before entry into a central compartment. The principal metabolite, mono-n-desethyl amiodarone is also an antiarrhythmic. From this central compartment, it undergoes extensive tissue distribution (exceptionally high tissue/plasma partition coefficients). The distribution half-life of amiodarone out of the central compartment to peripheral and deep tissue compartments (t1/2 alpha) may be as short as 4 hours. The terminal half-life (t1/2 beta) is both long and variable (9-77 days) secondary to the slow mobilization of the lipophilic medication out of (primarily) adipocytes. A pharmacokinetically based loading scheme is described, and data suggesting a role for routine amiodarone plasma levels are presented.

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.

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.

Predictors of efficacy of amiodarone and characteristics of recurrence of arrhythmia in patients with sustained ventricular tachycardia and coronary artery disease

The value of serial electropharmacologic testing during long-term oral amiodarone therapy for prediction of long-term drug efficacy as well as characteristics of arrhythmia recurrence is controversial. One-hundred four consecutive patients with coronary artery disease and sustained ventricular tachyarrhythmias (VT) underwent initial electrophysiologic (EP) evaluation in the drug-free state and again after an amiodarone loading period of 25 +/- 14 days (mean +/- SD). Twenty-six patients (25%) had no inducible ventricular tachyarrhythmia during therapy with amiodarone (VT control group), whereas arrhythmia inducibility persisted in the remaining 78 patients (VT noncontrol group). During 17.4 +/- 13.7 months of follow-up, two patients in the VT control group either had VT recurrence or died suddenly compared with 21 VT recurrences and eight sudden cardiac deaths in the VT noncontrol group (actuarial event rates at 36 months of 0.11 and 0.56, respectively, p = .0065). The cycle lengths of recurrent VT in these 21 patients in the VT noncontrol group were compared with those observed at final EP testing. A significant linear correlation was demonstrated (r = .76, p = .0001). Subgroup analysis of patients in the VT noncontrol group showed no EP predictors of outcome, including cycle length of induced VT. However, patients dying suddenly during the follow-up period had a higher prevalence of new or worsening congestive heart failure (75%) compared with patients with VT recurrence (19%) or those with no arrhythmic event (29%) (p less than .02).2off

Effects of chronic amiodarone therapy on ventricular tachycardia induced by programmed ventricular stimulation

Several studies have reported upon the inducibility of ventricular tachycardia (VT) with programmed ventricular stimulation (PVS) during chronic amiodarone therapy; however, few studies have systematically described and compared the morphology, duration, and cycle length of VT induced by PVS before and after amiodarone. In this study, 26 patients with symptomatic VT or ventricular fibrillation were evaluated by PVS by means of one to three extrastimuli (ES) before treatment and after 2 months of amiodarone therapy. Before amiodarone, sustained unimorphic VT was induced in 21 patients (group A) and symptomatic, nonsustained VT was induced in five patients (group B). After 65 +/- 8 days of amiodarone (total dose 64.5 +/- 8.9 gm, mean +/- S.D.), 15 of 21 patients (71%) in group A had sustained VT, five patients (24%) had nonsustained VT, and one patient had no VT induced. Four of five patients (80%) in group B had sustained VT and one patient had no VT induced. VT was induced by the same or by fewer number of ES in 79% of cases. When the morphologies of the VT induced before and after amiodarone were compared, the morphology of VT induced after amiodarone was the same in only 8 of 24 patients (33%), unimorphic but different in 14 patients (58%), and polymorphic in the remaining two patients. No correlation was found between the serum concentrations of amiodarone, desethylamiodarone, tetraiodothyronine, triiodothyronine, or reverse triiodothyronine, and similarities or differences in VT morphology, VT cycle length, or the relative number of ES required to induce VT after treatment with amiodarone.(ABSTRACT TRUNCATED AT 250 WORDS)

Amiodarone: value of programmed electrical stimulation and Holter monitoring

The value of programmed electrical stimulation (PES) and Holter monitoring in the assessment of amiodarone efficacy was reviewed. Many physicians have been disturbed by the persistent inducibility of arrhythmias in patients treated with amiodarone, who nevertheless do very well during the follow-up period. Noninducibility was associated with a favorable prognosis among 366 VT patients. Eighty-eight (24%) were noninducible on amiodarone, and 10% of these had recurrences, vs 39% in patients who remained inducible. Further, increased difficulty of induction with PES or induction of a slower or better tolerated VT may indicate a favorable outlook, and add to the value of PES. Few papers rigorously employed Holter monitoring in the assessment of amiodarone. In general, suppression of previously frequent arrhythmias implies excellent protection for patients with benign arrhythmias and moderate protection with malignant arrhythmias. By Holter assessment in 186 VT patients, arrhythmias were suppressed in 114 (61%), and 18% of these had recurrences vs 50% in patients whose arrhythmias were not suppressed. Studies attempting to correlate the results of PES and Holter monitoring in the same patients are lacking and may prove useful.