Purpose: Drug-induced bradycardia is common during antiarrhythmic therapy; the major culprits are beta-blockers. However, whether other antiarrhythmic drugs are also a significant cause of this, alone or in combination with beta-blockers, is not well known.
Methods: We retrospectively investigated the records of all patients hospitalized at our institution for drug-related bradycardia from the years 2004 to 2012. Patients with cardiac disease and electrolytic or hormonal abnormalities that could cause bradyarrhythmias were excluded.
Results: Eight patients were identified (mean age, 79±5 years; range, 71-85 years; 6 women). Three patients were taking only beta-blockers (hereafter referred to as the BB group), while five patients were on both beta-blockers and Na channel blockers (hereafter referred to as the BB + Na group). Heart rates ranged from 20∼49 beats/minute on arrival. The initial electrocardiogram showed sinus bradycardia (n=6) or sinus arrest with escape beats (n=2). QRS duration was 80-100 ms. The clinical presentation of the BB + Na group was considerably worse than that of the BB group, and included cardiogenic shock and heart failure. Four of the BB + Na patients had been on their medications for over 300 days. The BB group recovered solely with drug discontinuation, while 4 of the 5 patients in the BB + Na group needed additional treatments, such as intravenous administration of atropine or adrenergic agonist and temporary pacing. Bradycardia did not recur during follow-up (median, 687 days).
Conclusion: Although wide QRS ventricular tachyarrhythmia is a better known proarrhythmic effect of Na channel blockers, life-threatening bradycardia may also occur in combination with beta-blockers in the elderly, even months after the start of medication, and at plasma concentrations that do not prolong QRS width.
Keywords: QRS duration; elderly; proarrhythmia.