Amiodarone therapy: role of early and late electrophysiologic studies.

Forty-two patients with a history of symptomatic ventricular tachycardia or cardiac arrest underwent electrophysiologic testing at control and early in the course of amiodarone therapy (mean 12 +/- 7 days). Late electrophysiologic studies (mean 17 +/- 4 weeks) were repeated in 23 patients on a maintenance dose of 400 mg/day. At control study, all patients had inducible ventricular tachyarrhythmias (sustained ventricular tachycardia in 35, nonsustained ventricular tachycardia in 4, ventricular fibrillation in 3), while after amiodarone loading (1,200 mg daily) 4 (10.5%) of the 42 patients developed noninducible ventricular arrhythmias. At late study, an additional 6 (26%) of the 23 patients with inducible arrhythmias at early study developed noninducible arrhythmias. The cycle length of induced ventricular tachycardia increased from 275 +/- 61 ms at control study to 340 +/- 58 ms at early study (p = 0.001). A further increase in ventricular tachycardia cycle length was noted in patients who underwent both early and late study (341 +/- 38 versus 375 +/- 63 ms, p less than 0.05). The percent of induced tachycardias that were clinically tolerated increased as patients were treated longer with amiodarone (control = 22%, early = 34%, late = 53%, p less than 0.001). Of the 23 patients who had both early and late electrophysiologic studies and were followed up for a mean of 21.7 months (range 4 to 47), there were no recurrences among the 6 patients with noninducible arrhythmias, but there were five recurrences among the 17 patients with persistently inducible arrhythmias. None of the four patients with noninducible arrhythmias at early study had a recurrence. On the basis of these findings, it is concluded that: 1) The timing of programmed electrical stimulation will affect the results of the study in patients treated with oral amiodarone.(ABSTRACT TRUNCATED AT 250 WORDS)