1. Introduction
The advantageous effect of cardiac resynchronization therapy (CRT) are
well known in heart failure (HF) patients with reduced left ventricular
ejection fraction (LVEF) and prolonged QRS
duration.1-3 Current global guidelines suggest CRT for
class I or IIA indications in patients with LVEF ≤35%, and symptomatic
HF despite receiving optimal drug therapy.4-6 However,
an LVEF cut-off of ≤35% was determined by the patient enrollment
criteria in major CRT trials, and of note, was adopted from cut-off
values in prior major implantable cardiac defibrillator trials, rather
than from a prospective risk-benefit analyses of CRT for all LVEF
ranges.
Although resynchronization therapy for HF patients with LVEF ≥35% is
controversial and has not been clearly established, HF with LVEF
>35% shows disease features similar to LVEF
<35%, and treatment patterns are
similar.7,8 Additionally, there are reports that
long-term clinical outcomes were poor when HF with mildly reduced
ejection fraction (HFmrEF) was accompanied by left bundle branch block
(LBBB) versus without LBBB.9 Moreover, in a
retrospective analysis of the PROSPECT trial database, CRT demonstrated
significant clinical benefit among patients with an LVEF
>35%.10 The BLOCK-HF trial proved that
CRT provided clinical benefit over right ventricular pacing in patients
with LVEF ≤50% and atrioventricular block who require ventricular
pacing, and almost 70% (483/691) of the study population had an LVEF of
36–50%.11
Conduction system pacing that directly activates the specialized
conduction system was developed, and left bundle branch area pacing
(LBBAP)—which overcomes the limitations of the previously used His
bundle pacing (HBP)—is emerging and widely
used.12-16
Furthermore, the effectiveness and safety of LBBAP in patients with HF
has also been reported.17-19 To date, LBBAP has been
used as an alternative to CRT in indicated patients, as well as a first
option for patients indicated for CRT or pacemaker
implantation.17-19 LBBAP is more simple, convenient,
and cheaper than biventricular CRT; therefore, there is increasing
clinical interest in adopting wider LVEF ranges for LBBAP-CRT among
patients with HF and a long QRS duration, especially in patients with an
LVEF of 36–50%. Therefore, this study aimed to conduct a systematic
review of the literature and meta‐analysis on the impact of the LBBAP
strategy in patients with HFmrEF with an LVEF between 35% and 50%.