4. Discussion
The clinical importance of cardiac resynchronization in patients with HF has already been demonstrated.1-3 Indications for CRT in patients with HFrEF with an LVEF <35% are well established, whereas those for patients with HFmrEF and an LVEF of 35–50% are less certain.4,5,33 In the PROSPECT prospective multicenter study, all echocardiograms were analyzed by a core laboratory; among patients with a NYHA functional Class III–IV status, and QRS>130 ms, those with a core laboratory-measured LVEF >35% who underwent CRT demonstrated significant clinical benefit. Additionally, they exhibited both clinical and structural benefit from CRT.34,35Meanwhile, among patients with HF and an LVEF <50% who required pacing due to atrioventricular block, the BLOCK-HF trial showed that CRT was superior to right ventricular pacing regarding mortality and HF hospitalization.11 Based on these study results, guidelines state that HBP or biventricular pacing can be considered when the ventricular pacing burden exceeds 40% in HFmrEF; still, the resynchronization strategy for HFrEF has not been clearly established.36 As the prevalence of HFmrEF increases, its clinical importance is emerging.37 Although researches have been reported to demonstrate the feasibility, efficacy, and safety of LBBAP adaptation to cardiac resynchronization (LOT-CRT, LBBAP-CRT),17,18 it is necessary to shed light on its role in the treatment of HFmrEF.