Transient complete heart block during radiofrequency ablation of a left lateral bypass tract

RF catheter ablation of accessory bypass tracts associated with the Wolff-Parkinson-White syndrome has become an accepted and widespread therapy. When bypass tracts are located in the free wall of the left ventricle, a single catheter technique may be utilized. A single catheter is placed via the femoral artery, across the aortic valve into the left ventricle. Mapping is performed during sinus rhythm, and ablation performed at the site of recording of Kent bundle activation. We describe a case of a patient with Wolff-Parkinson-White syndrome presenting with rapid atrial fibrillation requiring cardioversion. This patient subsequently underwent catheter ablation of a left free-wall bypass tract using the single catheter technique. At baseline, preexcitation and right bundle branch block (RBBB) were present on the EGG. During catheter ablation of She accessory pathway, transient complete AV block was seen. This was felt likely to be due to trauma to the His bundle, or more likely to the left bundle branch, as the ablation catheter crossed the aortic valve. The bypass tract was successfully ablated after placement of a temporary right ventricular pacemaker. AV conduction resumed with a pattern of RBBB. A temporary right ventricular pacing catheter should be placed prior to RF ablation of left-sided bypass tracts when the ECG is also suggestive of RBBB.