LAUSR

With the emergence of cardiac resynchronization therapy (CRT) as a powerful tool to reverse left ventricular dysfunction in patients with left bundle branch block (LBBB), there is increasing awareness that LBBB-induced dyssynchrony may be a primary cause of heart failure with reduced ejection fraction (HFrEF). Current guidelines for implanting CRT require at least 3 months of guideline-directed medical therapy (GDMT) before device implantation in the hopes that medications will reverse cardiomyopathy and obviate the need for device therapy. However, no randomized controlled trial demonstrating efficacy of medications ever stratified outcomes by patients with conduction abnormalities. Consequently, CRT, not GDMT, may be a more effective first-line therapy for patients with LBBB and HFrEF. This review evaluates the evidence for LBBB-induced cardiomyopathy, examines the rationale for GDMT in this population, and presents the evidence for direct implantation of CRT. It is likely that many patients would benefit from earlier intervention with CRT, though about 25% of patients with LBBB and HFrEF may respond to GDMT.