Painful left bundle branch block

ECG 1: In the first portion of the tracing, rhythm is sinus with a normal PR interval and a narrow QRS; upon a slight increase in heart rate, appearance of a left bundle branch block (QRS width > 120 ms, absence of q wave and wide and notched R wave in leads I, aVL, V5 and V6 with delayed intrinsicoid deflection > 60 ms, QS and rS pattern in V1 and V2, ST segment depression and negative T wave in leads I, aVL, V5 and V6);

ECG 2: Other tracing; upon a slight slowing of the heart rate, disappearance of the left bundle branch block pattern and return of narrow QRS complexes;

Comments: This young patient presented typical chest pain in the absence of prior history or risk factors. These pain episodes appeared during relatively modest exertion. The electrocardiogram performed at rest showed narrow QRS complexes of normal morphology and duration, as well as repolarization without abnormality. An exercise ECG was recorded with evidence of a limited increase in heart rate, a typical left bundle branch block pattern concomitant with the occurrence of pain. Upon stopping the exercise, the normalization of the tracing was accompanied by the cessation of pain. Cardiac ultrasound was normal. Coronary angiography revealed healthy coronary arteries without any evidence of spasm.

The final diagnosis was hence that of a painful exercise-induced left bundle branch block given the association of chest pain concomitant with the appearance of a left block and disappearing with the normalization of the ECG along with absence of abnormality in the coronary arteries. The mechanisms involved in the genesis of pain are still poorly understood. Different hypotheses have been proposed: ventricular asynchrony, septal ischemia linked to septal hypoperfusion or a relative lateral hyperperfusion. Evolution is variable depending on the patients. The branch block can become permanent with disappearance of pain. In the absence of coronary artery disease, it would appear that the prognosis of these patients remains preserved.

Take-home message: The appearance of a left bundle branch block on exertion can cause chest pain without abnormal coronary circulation.