Unmasking accessory pathway conduction due to AV block following tricuspid valve replacement.

Atrioventricular block during radiofrequency (RF) ablation of an accessory pathway may be due to inadvertent RF damage or catheter pressure to the conduction system, or a pre-existent conduction defect. Conversely, block in the normal conduction system may unmask pre-excitation. We describe a case where total infra-Hisian block complicated tricuspid valve surgery, unmasking a hitherto undiagnosed left lateral accessory pathway.