Development of rapid preexcited ventricular response to atrial fibrillation in a patient with intermittent preexcitation.

Intermittent preexcitation during sinus rhythm is indicative of an accessory pathway at a very low risk for sudden death. We present the case of a 49-year-old man with intermittent preexcitation who subsequently developed rapid atrial fibrillation with a shortest preexcited R-R interval of 230 milliseconds. Electrophysiology study showed intermittent preexcitation at baseline and 1:1 anterograde accessory pathway conduction to 220 milliseconds in the presence of 1 mcg/min isoproterenol infusion. The pathway was successfully ablated at the lateral mitral annulus. Accessory pathways highly sensitive to catecholamines may show intermittent preexcitation at baseline with potential for rapid conduction during atrial fibrillation and sudden death.