An Unpredictable Atrioventricular Accessory Pathway: Low-Risk or High-Risk?

A 66-year-old man with known asymptomatic preexcitation was admitted to our department for symptomatic complete infranodal atrioventricular block and scarce intermittent anterograde conduction through the atrioventricular accessory pathway. The accessory pathway was not further stratified due to evidence of intermittent conduction with a sinus node heart rate of 60 bpm, and a bicameral pacemaker was implanted. Surprisingly, after 4 months, the patient developed preexcited, rapidly conducted atrial fibrillation and ultimately underwent successful accessory pathway catheter ablation. Even when intermittent ventricular preexcitation is documented at low heart rates, it does not exclude the presence of an accessory pathway with high-risk conduction properties during follow-up.