Transformation of left bundle branch block into masquerading bundle branch block after ablation of the right bundle in a patient with branch to branch reentrant ventricular tachycardia.

Masquerading bundle branch block associates left bundle branch block in the standard lead and right bundle branch block in the precordial leads. Mr 8., 67 year old, was referred for investigation of syncope. He had a history of idiopathic dilated cardiomyopathy (normal coronary arteries; EF : 14 %, CI : 2.2 I/min/m(2) at later investigations). The ECG showed LBBB with left axis deviation, a PR interval at the upper limits of normal and ventricular premature beats. During observation, he had another syncopal episode and the ECG showed wide complex tachycardia (160 bpm) reduced by external cardioversion. Electrophysiological investigations showed inducible VT due to bundle branch reentry. The HV interval in sinus rhythm was 80 ms. Radiofrequency ablation of the right bundle led to first degree AVE with masquerading bundle branch block with an increased HV interval of 120 ms. The usual facility of ablation of the right bundle branch block is an argument in favour of the hypothesis whereby masquerading bundle branch block is a variety of RBBB with severe conduction defects of the two branches.