Encainide

Cardiovascular

In the wake of the preliminary and final reports of the Cardiac Arrhythmia Suppression Trial (CAST) [ , ], which showed that there was an increased risk of death among patients who took encainide and flecainide after myocardial infarction, there have been many publications in which the implications of these findings have been thoroughly discussed [ ]. The relative risk of death or cardiac arrest due to dysrhythmias in the treated patients was 2.6 and the relative risk due to all causes was 2.38. The risk of non-fatal cardiac adverse effects was no different in treated patients from that in those taking placebo and there was no difference between the groups in the use of other drugs.

Although there is a consensus that encainide and flecainide were associated with an increase in the rate of mortality in CAST, there are still some open questions. First, all the patients recruited to CAST had asymptomatic ventricular dysrhythmias after myocardial infarction, and it is not clear whether the results can be extrapolated to other patients. Secondly, the reasons for the increased mortality in the treated patients are not clear: ventricular dysrhythmias and worsening of left ventricular function are both possible. Thirdly, it is not clear whether the results of CAST in patients with asymptomatic ventricular dysrhythmias after myocardial infarction can also be applied to other Class I antidysrhythmic drugs.

Separate studies have confirmed the prodysrhythmic actions of encainide [ ]. The incidence of prodysrhythmias is much higher in patients being treated for ventricular dysrhythmias than in those being treated for supraventricular dysrhythmias [ ].

Encainide has been reported to cause sinus node arrest in association with prolonged sinus node recovery time [ ]. It also raises the pacing threshold in patients with chronic implanted pacemakers [ ], although this has not been reported to increase the failure rate of pacemakers.

Encainide has a negative inotropic effect on the heart and can cause hypotension [ ] or worsen heart failure [ ].

Nervous system

The most common non-cardiac effects of encainide are on the central nervous system, and include abnormal or blurred vision (11%), dizziness (7.3%), headaches (6.0%), nausea (4.3%), vertigo (2.3%), insomnia, and fatigue. The figures in parentheses are taken from a review of 349 patients with supraventricular dysrhythmias treated with encainide (14). These effects are common during long-term therapy, but may also occur transiently during intravenous administration and appear to be dose-related [ , ].

Encephalopathy has been attributed to encainide [ ].