Expanding Benefits from Cardiac Resynchronization Therapy to Exercise-Induced Left Bundle Branch Block in the Setting of Advanced Heart Failure: A Case Report

Abstract

Introduction Exercise-induced left bundle branch block (LBBB) is rarely observed in exercise testing, and usually implies a worse prognosis. Cardiac resynchronization therapy (CRT) is well validated in patients with heart failure with reduced ejection fraction (HFrEF) and LBBB. Although the indications of CRT do not include exercise-induced LBBB, the functional impairment secondary to dynamic electromechanical dyssynchrony could potentially be improved with CRT. Case Report A 57-year-old woman with long-standing idiopathic dilated cardiomyopathy (ejection fraction of 23%) presented with clinical deterioration to NYHA functional class 4 and recurrent hospitalizations despite optimal medical treatment. During evaluation for cardiac transplant, new-onset of intermittent LBBB was observed on the cardiopulmonary exercise test (her resting QRS duration was 100ms). A stress echocardiography showed exertion-induced intraventricular and interventricular dyssynchrony. Cardiac resynchronization therapy was then indicated, and 97% resynchronization rate was obtained. There was clinical improvement to NYHA class 2 and no hospitalizations since the CRT initiation. Functional reassessment at 6 and 12 months post-implant demonstrated significant improvement in prognostic exercise parameters (Figure). She currently remains off the transplant list. Summary In HFrEF patients with no LBBB at rest, exercise test and stress echocardiography may uncover dynamic electromechanical dyssynchrony that may benefit from CRT. This is the first report of CRT for treatment of an advanced heart failure patient with worsening symptoms attributed to exercise-induced LBBB.