Objectives Normal QRS Escape Rhythm Occurred after Transit Artificial Complete Heart Block in a Patient with Dilated Cardiomyopathy and Complete Left Bundle Branch Block

Methods A male with 65 years old was admitted because of chronic shortness of breath, fatigue and palpitation. Cardiac ultrasound examination showed LVED 76 mm, EF 25% and moderate mitral insufficiency. Complete left bundle branch block (LBBB) was found in his surface electrophysiology. Cardiac resynchronization therapy (CRT) was decided because he was refractory to the standard treatment of heart failure. During coronary sinus canalization, a transit complete atrioventricular conduction block was provoked and followed by a narrow QRS escape rhythm (Fig A). CRT device was implanted without complications.

Results Theoretically, the escape rhythm after LBBB will display wide QRS morphology due to infra-His escape pulse. But in this patient, a normal QRS escape rhythm occurred after an artificial transit complete heart block. The possible mechanism could be as followings: (1) His LBBB may be caused by slow conduction between left bundle branches and myocardium and priority conduction between right bundle branch and myocardium. (2) The escape focus is exactly located at the left posterior septum close to the left posterior branch bundle. (3) The escape pulse conducted to the right bundle branch normally and to the left bundle branch slowly. If above explanation is confirmed, we postulate: (1) LBBB in dilated myocardium is due to functional block between left bundle branche and myocardium. (2) Active pacing in critical sites close to left bundle branch could normalise the QRS morphology in patient with dilated cardiomyopathy and LBBB (Fig B).

Conclusions Normal QRS escape rhythm occurred during transit complete heart block in patient with dilated cardiomyopathy and LBBB may suggest critical escape focus very close to the left bundle branch.