BBAP With CS Mapping Guidance

This is a single-blind, randomized, controlled, multi-center clinical trial designed to evaluate the efficacy and safety of coronary sinus (CS)-based left atrial mapping for guiding atrial lead implantation targeting Bachmann bundle (BB) capture in patients undergoing cardiac resynchronization therapy (CRT). The core objective is to validate whether using a 10-pole CS catheter to map left atrial activation time (LAAT) can improve the accuracy of BB region identification and subsequent Bachmann bundle atrial pacing (BBAP) lead implantation, compared with the conventional Lustgarten standard approach.

Study Design and Randomization

The study adopts a fixed block randomization method, with random numbers generated by independent statisticians using a computerized random number generation program to ensure allocation concealment. Single-blinding is implemented, where patients are unaware of the atrial lead implantation method they receive; investigators responsible for intraoperative operations and postoperative follow-up assessments (excluding those involved in randomization) are also kept blinded to the grouping to minimize detection bias. The study includes two parallel groups: the CS 10-pole mapping LAAT guided group and the Lustgarten standard control group, with 20 subjects in each group, totaling 40 subjects across multiple participating centers.

Preoperative Preparation and Screening

Potential subjects undergo a comprehensive screening period of 28 to 1 day before enrollment (Day -28 to Day -1). After signing the informed consent form (ICF), subjects complete detailed medical history collection, physical examination, and a series of laboratory and auxiliary examinations to confirm eligibility. Key preoperative assessments include 12-lead electrocardiogram (ECG) (with left bundle branch block (LBBB) morphology confirmed by the core ECG laboratory), transthoracic echocardiography (TTE) to measure left ventricular ejection fraction (LVEF), left ventricular end-diastolic diameter (LVEDD), and left atrial volume index (LAVI) via Simpson's biplane method, 24-hour ambulatory ECG (Holter) to assess arrhythmia burden and expected ventricular pacing proportion, and chest X-ray to evaluate heart size and planned lead pathways. All subjects must have completed at least 3 months of guideline-directed medical therapy (GDMT) optimization before enrollment, with eligibility confirmed by the principal investigator (PI) prior to randomization.

Intraoperative Technical Procedures

1. Anesthesia and Vascular Access

All subjects receive either local anesthesia (with optional sedation) or general anesthesia based on clinical assessment. Vascular access is preferentially established via left subclavian vein puncture; if the left subclavian vein is inaccessible (e.g., occlusion), axillary vein puncture is an alternative. A vascular sheath is inserted to facilitate the passage of electrophysiological catheters and pacing leads. 2. 10-Pole CS Mapping (Study Group Only)

A 10-pole electrophysiological mapping catheter (e.g., Boston Scientific Polaris or equivalent) is inserted through the vascular sheath and advanced under fluoroscopic guidance. A guiding catheter is first positioned at the CS ostium, followed by insertion of the 10-pole catheter into preselected target vein branches of the CS. Local electrograms (EGM) are recorded at multiple sites to map LAAT, with special attention to identifying the region corresponding to the BB-characterized by the shortest LAAT and lowest pacing threshold. A pacing system analyzer (PSA) is used to test pacing capture at different electrode pairs of the 10-pole catheter, assessing both capture threshold and the presence of phrenic nerve stimulation (PNS) to determine the optimal BBAP lead implantation site. 3. Conventional Lustgarten Standard Implantation (Control Group)

Subjects in the control group undergo atrial lead implantation following the Lustgarten standard, where the lead is positioned at the anterolateral wall of the right atrium, approximately 1 cm below the right atrial appendage ostium, with the goal of achieving stable pacing capture without PNS, without the aid of 10-pole CS mapping. 4. Lead Implantation and Device Connection

For both groups, after determining the optimal atrial lead implantation site, right atrial and right ventricular leads are implanted routinely, followed by CS lead placement for left ventricular pacing. The CRT pulse generator (CRT-P or CRT-D, based on clinical indication) is implanted in a subcutaneous pocket, typically in the left pectoral region. All lead parameters (pacing threshold, impedance, sensing) are tested using the PSA to ensure they meet clinical standards (acute pacing threshold ≤ 3.0 V @ 0.5 ms, impedance within 200-1500 Ω, adequate sensing amplitude). The incision is then sutured in layers and pressure-dressed to prevent hematoma formation. 5. Intraoperative Data Collection

Intraoperative data are recorded in real time, including total procedure time (from skin puncture to suture completion), fluoroscopy time (automatically recorded by the digital subtraction angiography (DSA) machine), and radiation dose (dose-area product \[DAP\] and air kerma). For the study group, additional data include the number of mapped CS vein branches, optimal target site pacing threshold, and EGM signal quality (A/V wave amplitude). Any intraoperative complications (e.g., PNS, vascular injury, lead dislodgement) are documented immediately.

Postoperative Management and Follow-Up

After surgery, subjects are monitored in the hospitalization period (up to 7 days postoperatively). Within 24 hours, continuous ECG monitoring is performed to detect arrhythmias and lead parameter changes; a bedside chest X-ray is conducted to confirm lead position and rule out pneumothorax or pericardial effusion. Pacemaker programming is performed to optimize AV/VV intervals, and incision status is assessed daily for signs of infection or hematoma. Before discharge, a coronary computed tomographic angiography (CTA) is performed to visualize the anatomical relationship between the atrial lead tip and the BB, confirming lead positioning accuracy. Subjects receive optimized GDMT at discharge and are scheduled for regular outpatient follow-up.

Outpatient follow-up occurs at 30 days (±5 days), 3 months (±10 days), 6 months (±14 days), 9 months, and 12 months (±21 days) postoperatively. At each follow-up, pacemaker programming is performed to assess lead parameters (threshold, impedance, sensing), pacing proportion, and atrial high-rate response (AHR). TTE is conducted at 30 days and 12 months to evaluate cardiac function, and chest X-ray is performed to confirm lead stability. Adverse events (AEs) and serious adverse events (SAEs) are collected throughout the follow-up period, with SAEs reported within 24 hours of detection.

Safety and Efficacy Monitoring

A Data Safety Monitoring Board (DSMB) conducts quarterly reviews of study data to assess safety and efficacy. The primary efficacy endpoint (BBAP lead implantation success rate, confirmed by postoperative CTA) and safety endpoints (composite severe complications within 30 days postoperatively, incidence of specific adverse events) are closely monitored. The study may be terminated early if the DSMB identifies excessive severe adverse events, device defects, an unfavorable risk-benefit ratio, or futility (low probability of achieving the primary endpoint).

Study End and Data Management

The study ends when the last enrolled subject completes the 12-month follow-up. All study data are entered into the electronic data capture (EDC) system, followed by data cleaning, source data verification (SDV), and database lock. A statistical analysis report (SAR) is finalized, and the study end is confirmed by the sponsor, PI, and statistician. After the study, subjects are converted to routine clinical follow-up, with CRT device management continuing in accordance with clinical guidelines.

1. Primary Research Objective

This study intends to use a 10-pole coronary sinus (CS) catheter to map left atrial activation time (LAAT), assist in identifying the Bachmann bundle region, and further guide Bachmann bundle atrial pacing (BBAP) lead implantation. The anatomical relationship between the implanted lead and the Bachmann bundle will be visualized by postoperative computed tomographic angiography (CTA), thereby verifying the efficacy and safety of this method in guiding BBAP surgical procedures. 2. Secondary Research Objectives

Procedure time, fluoroscopy time, and number of attempts for atrial lead screw-in between the two methods.

Changes in electrical parameters (pacing threshold, lead impedance, intracardiac sensing) of the atrial lead at immediate postoperative, 1-month, 3-month, 6-month, 9-month, and 12-month follow-up.

Comparison of the effects of BBAP and right atrial appendage pacing (RAAP) on acute intraoperative hemodynamics.

Comparison of the differences in atrial high-rate response (AHR) between BBAP and RAAP during 1-month, 3-month, 6-month, 9-month, and 12-month follow-up based on pacemaker programming data. 3. Study Overview

3.1 Overall Study Design and Plan

This study is a single-blind, randomized, controlled, multi-center clinical trial.

3.2 Sample Size and Grouping Method

CS 10-pole mapping LAAT standard group: 20 cases Lustgarten standard group: 20 cases 3.3 Randomization and Blinding

Fixed block randomization will be adopted, and random numbers will be generated by independent statisticians using a computer program. This study will use single blinding, meaning that patients will be unaware of the method of atrial lead implantation they receive.

3.4 Study Flow Chart

(To be supplemented with the study flow chart) 4. Study Population

4.1 Inclusion Criteria

Sinus rhythm Left ventricular ejection fraction (LVEF) ≤ 35%, QRS duration ≥ 150 ms; or 130 ms \< QRS duration \< 150 ms with left bundle branch block (LBBB) morphology LVEF ≤ 40% with expected ventricular pacing \> 20% New York Heart Association (NYHA) class II, III, or ambulatory IV symptoms After at least 3 months of guideline-directed medical therapy (GDMT) optimization Age ≥ 18 years Signed informed consent form, good compliance, and ability to complete study follow-up 4.2 Exclusion Criteria

Prior implantation of cardiac resynchronization therapy (CRT) / implantable cardioverter-defibrillator (ICD) / pacemaker: Previous implantation of any cardiac implantable electronic device (CIED), except for patients in Group C requiring device replacement/upgrade Non-compliance with GDMT requirements: Failure to receive or inability to tolerate optimized medical therapy Inappropriate QRS duration: QRS \< 130 ms (Groups A and C) Excessive improvement in LVEF: Recent (within 3 months) LVEF \> 40% with clear evidence of normalized cardiac function Severe valvular heart disease: Severe aortic stenosis/regurgitation, mitral stenosis requiring surgical or interventional treatment Recent cardiovascular events: Acute myocardial infarction, stroke/transient ischemic attack (TIA) within 3 months before enrollment; coronary revascularization (percutaneous coronary intervention (PCI) or coronary artery bypass grafting (CABG)) within 6 months before enrollment Unstable angina pectoris: Canadian Cardiovascular Society (CCS) class III-IV Severe arrhythmias: History of sustained ventricular tachycardia or ventricular fibrillation (without ICD protection) Specific cardiomyopathies: Hypertrophic cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy (ARVC), and other etiologies not suitable for CRT Severe renal insufficiency: Estimated glomerular filtration rate (eGFR) \< 30 mL/min/1.73 m² or uncontrolled renal failure Severe liver dysfunction: Child-Pugh class C Active infection: Including sepsis, infective endocarditis, etc. Malignant tumor: Advanced malignant tumor with expe

• Secondary Outcome Measure [Time frame: the day of the procedure]