Cardiac dysrhythmias in severe verapamil overdose: characterization with a canine model

Verapamil overdose, because of its frequency and severity, represents a significant problem for the emergency physician. With recent search recommending specific therapies for verapamil toxicity, aids to rapid diagnosis hold promise for decreasing morbidity and mortality from overdose of all calcium channel blockers. At this time, diagnosis of verapamil toxicity depends primarily on patient history and identification of cardiac dysrhythmias. This study attempts to improve the diagnostic armamentarium available for verapamil poisoning by analysing cardiac conduction problems seen in a canine model of verapamil toxicity, with the goal of identifying clinically useful dysrhythmia patterns. In 43 verapamil-toxic animals, junctional rhythm without organized atrial activity was the most frequently identified rhythm (55.6%). The next most commonly seen rhythms were tertiary atrioventricular (AV) block (16.3%) and idioventricular rhythm (11.6%); other animals manifested low grade AV block. Of interest, prominent U waves were noted in 25.6% of animals. While these results are subject to the limitations inherent in the use of an animal model, the data generated provide potentially useful patterns of dysrhythmia which may be encountered in humans with verapamil toxicity.