This is a prospective, multicenter, randomized controlled trial designed to determine whether direct capture of the left ventricular conduction system must be achieved as the procedural endpoint of left bundle branch area pacing (LBBAP), or whether left ventricular septal capture alone is sufficient to obtain comparable clinical outcomes.
A total of 300 patients aged 19 years or older who have a guideline-based indication for permanent pacemaker implantation for bradyarrhythmia, an expected ventricular pacing burden of 40% or more, and a planned LBBAP procedure will be enrolled at 5 or more centers in the Republic of Korea. Participants will be randomly assigned in a 1:1 ratio, stratified by baseline left ventricular ejection fraction (LVEF \<50% versus \>=50%), to one of two procedural strategies:
1. LBBP mandatory group - the implanting operator continues the procedure, repositioning the lead as required, until left bundle branch pacing (LBBP) or left fascicular pacing (LFP) is confirmed by at least one predefined conduction system capture criterion. 2. LVSP enough group - the operator may complete the procedure at his or her discretion once left ventricular septal pacing (LVSP) is confirmed, irrespective of whether direct conduction system capture is achieved.
The same commercially approved lead and pulse generator platform is used in both groups, so the randomized variable is the procedural endpoint strategy rather than the device.
The primary outcome measure is the absolute change in LVEF from baseline to 12 months, adjudicated by a blinded central echocardiography core laboratory. Secondary outcome measures include echocardiographic response, pacing-induced cardiomyopathy, procedure-related major complications, procedure and fluoroscopy time, paced QRS duration, acute procedural success, achievement and long-term maintenance of conduction system capture, all-cause death, cardiovascular death, heart failure hospitalization, upgrade to cardiac resynchronization therapy, and new-onset atrial fibrillation.
All participants are followed for 12 months after implantation, with study visits at 2 weeks to 1 month, 6 months, and 12 months. The primary analysis follows the intention-to-treat principle, with a prespecified per-protocol analysis according to whether conduction system capture was actually achieved.
Patients with a guideline-based indication for permanent pacemaker implantation for bradyarrhythmia and an expected ventricular pacing burden (VP) of 40% or more.
Patients in whom a left bundle branch area pacing (LBBAP) procedure is planned in accordance with the above indication.
Age 19 years or older.
Provision of written informed consent to participate in the study.
Inability to understand the study or unwillingness to consent to participation.
History of mechanical tricuspid valve replacement.
History of myocardial infarction involving the interventricular septum.
Life expectancy of 12 months or less.
Parallel
LBBAP with mandatory left ventricular conduction system capture (LBBP or LFP)
Procedure/SurgeryLeft bundle branch area pacing is performed with an Ingevity Plus active-fixation helical pacing lead (Boston Scientific) and a commercially approved Boston Scientific pulse generator. The lead is advanced into the interventricular septum until direct capture of the left conduction system is confirmed by at least one of the following: a diagnostic QRS morphology transition during threshold testing or programmed stimulation (non-selective to selective LBBP, or LBBP to LVSP); S-V6RWPT \<75 ms with narrow QRS or simple right bundle branch block, or \<80 ms with advanced ventricular conduction disturbance; an LBB potential-to-V6RWPT interval equal to the stimulus-to-V6RWPT interval within 10 ms; or a V6-V1 interpeak interval \>44 ms. The lead is repositioned and the attempt repeated if capture is not obtained; more than three attempts are generally not recommended.
LBBAP with left ventricular septal capture as the accepted procedural endpoint (LVSP)
Procedure/SurgeryLeft bundle branch area pacing is performed with the same Ingevity Plus active-fixation helical pacing lead (Boston Scientific) and commercially approved Boston Scientific pulse generator used in the comparator group. The procedure may be completed once left ventricular septal pacing is confirmed, defined as stable lead fixation in the deep interventricular septum reaching the left ventricular subendocardial region with a terminal R-wave present in lead V1, and without fulfilment of conduction system capture criteria. Deep septal position may be verified by the fluoroscopic fulcrum sign, contrast injection, echocardiography, or post-procedural computed tomography. Additional lead advancement to attempt conduction system capture is permitted at the operator's discretion but is not required by protocol.
Change from baseline in left ventricular ejection fraction (LVEF) at 12 months
Absolute change in LVEF (percentage points) from baseline to 12 months, compared between the LBBP mandatory group and the LVSP enough group. LVEF is measured by the Simpson biplane method on transthoracic echocardiography and is determined by a central echocardiography core laboratory whose readers are blinded to treatment allocation, participating site, and acquisition time point. Baseline and 12-month studies are read as pairs by the same reader with the time point order randomly presented, in order to minimise measurement error in the change score. Only core laboratory values are used in the analysis; values reported by the enrolling site are collected for reference only. The primary analysis is an analysis of covariance with 12-month LVEF as the dependent variable and treatment group, baseline LVEF, and the stratification factor as covariates.
Echocardiographic response rate at 12 months (proportion achieving LVESV reduction >=15%)
Proportion of participants with a \>=15% reduction in left ventricular end-systolic volume (LVESV) from baseline to 12 months, by central core laboratory reading.
Incidence of pacing-induced cardiomyopathy (PICM), composite definition
PICM is defined as either (a) LVEF \<50% together with an absolute LVEF decrease \>=10%, or (b) an increase in LVESV \>=15%, on echocardiography performed after implantation.
Incidence of procedure-related major complications
Procedure-related major complications comprise any death related to LBBAP; permanent loss of LBBAP lead function; need for lead reposition, replacement, explant, or revision; prolongation of hospitalization by \>=48 hours beyond the anticipated stay; hemothorax or pneumothorax confirmed by chest radiography or computed tomography; and interventricular septal perforation confirmed echocardiographically or fluoroscopically, whether intraprocedural or post-procedural, with concomitant pericardial effusion or tamponade recorded separately.
Procedure time (min)
Total procedure time and total fluoroscopy time recorded in minutes from the procedure log.
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