Normalization of left ventricular function following cardiac resynchronization therapy: left bundle branch block as a potential etiology of dilated cardiomyopathy.

Patients with chronic heart failure (HF) not infrequently present conduction disturbances, which are most commonly exhibited as a left bundle branch block (LBBB). LBBB is associated with intraventricular conduction delay, paradoxical septal motion, and hemodynamic deterioration, indicating an impairment of left ventricular (LV) function. However, there is controversy as to whether dilated cardiomyopathy leading to HF could develop just as a result of conduction disturbances without apparent pre-existing heart disease. We report here 2 cases of patients with non-ischemic dilated cardiomyopathy and LBBB who had complete reversal of their LV dysfunction and enlargement after cardiac resynchronization therapy, which corrects the LV activation sequence. These cases might support the idea that conduction disturbances themselves can be a principal etiology in the development of dilated cardiomyopathy.