Cardiac devices with class 1C antiarrhythmics: a potentially toxic combination

Abstract

A patient taking regular flecainide for paroxysmal atrial fibrillation presented with broad complex tachycardia and circulatory compromise. With no history of pacemaker insertion and no pacing spikes visible on the ECG, this was presumed to be ventricular tachycardia and treated with electrical cardioversion, leading to p-wave asystole. An indwelling pacemaker was now recognised and ventricular capture was eventually attained by significantly increasing ventricular lead output. Invasive haemodynamic support was required due to new ventricular systolic dysfunction. Pacing thresholds and ventricular function normalised within 72 h consistent with flecainide toxicity; levels were shown to be toxic. Pacemaker interrogation revealed evidence of an undiagnosed atrial flutter, at presentation this was likely slowed by flecainide toxicity to a rate below the pacemaker mode switch, such that it was tracked in the ventricle at the upper tracking rate (120 bpm). Cardioversion terminated the arrhythmia but raised the capture threshold of the ventricle above the maximum lead output.

Flecainide Toxicity Resulting in Pacemaker Latency and Intermittent Failure to Capture

“…It has been demonstrated that flecainide can increase the ventricular capture threshold for pacemakers, and patients at therapeutic doses may require pacemaker setting adjustment when initiating flecainide [11]. However, pacemaker failure to capture in the setting of acute flecainide toxicity has seldom been reported in the literature [5]. Our case also demonstrates a prolonged pacemaker latency interval in the setting of flecainide toxicity and subsequent rapid improvement in latency interval after treatment with intravenous sodium bicarbonate, which has not been previously reported.…”

“…A mortality rate of 10–25% has been reported with class Ic antiarrhythmic agent toxicity [4]. Although flecainide toxicity is described in the literature on acute kidney injury, there is a paucity of literature on the acute presentation of flecainide toxicity in the setting of a cardiac pacemaker [5]. We describe a case of flecainide toxicity secondary to acute kidney injury in the setting of dual-chamber pacing, resulting in ventricular capture latency and intermittent failure to capture [6].…”