Incidence of drug-induced torsades de pointes with intravenous amiodarone

Abstract

Aim: To define the incidence, presentation, and outcomes of drug-induced Torsades de Pointes (TdP) with intravenous (IV) amiodarone.

Methods: From January 2014 to August 2016 a total of 268 patients received IV amiodarone, 142 for ventricular tachycardia, 104 for atrial flutter/fibrillation, and 22 for incessant atrial tachycardia. A uniform dosing of amiodarone to yield 1gm/day was used in all patients.

Results: Four of the 268 patients (M:F 1:3) with mean age of 51.25+9.17years developed pause dependent TdP degenerating to VF, after a mean dose of 690+176.63mg, infused over 12+5.88h. The QTc that was 505+9.02ms at the time of TdP normalized to 433.75+6.13ms 48-72h after stopping amiodarone. There was no immediate or late mortality, and patients are well at 5-10 months of follow-up. None of the patients tested positive for LQTS genes.

Conclusion: The incidence of drug-induced TdP with IV amiodarone is about 1.5%. Risk factors include female sex, left ventricular dysfunction, electrolyte abnormalities, baseline prolonged QTc, concomitant beta-blocker, and digoxin therapy. Amiodarone induced TdP has favorable prognosis if recognized and treated promptly, and these patients should not receive amiodarone by any route in future.

Keywords: Acquired LQT; Amiodarone; Proarrhythmia; Torsades de pointes.

Fig. 1

(a) ECG of case 1 showing atrial flutter with a ventricular rate of 150 beats per minute. (b) ECG of case 1 after defibrillation of TdP six hours after IV amiodarone infusion. The sinus rhythm ECG shows marked sinus bradycardia with prolonged QT interval with QTc interval of 500 ms and R on T ectopic’s.

Fig. 2

ECG of case 3 showing rapid monomorphic ventricular tachycardia/flutter with LBBB morphology and a ventricular rate of 300 bpm following IV isoprenaline infusion to prevent pause dependent TdP.

Fig. 3

(a) ECG of case 4 showing sinus bradycardia with QTc of 506 ms after 12 h of IV amiodarone therapy and conversion of atrial fibrillation to sinus rhythm. (b) Continuous monitoring strip of the ECG of case 4 showing pause dependent Torsades de pointes immediately after conversion to sinus rhythm preceded by long-short sequence. The TdP degenerated to ventricular fibrillation requiring DC cardioversion.