Study Title

Efficacy and Safety of Coronary Sinus-Based Left Atrial Mapping for Guiding Atrial Lead Implantation Targeting Bachmann Bundle Capture in Cardiac Resynchronization Therapy Research Objectives

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

Study Endpoints

Primary Endpoint

• Technical success rate Key Secondary Endpoints
• Procedure time② Radiation dose③ Number of attempts for atrial lead screw-in during the operation: cumulative number of atrial lead implantation attempts during the operation④ Lead repositioning/reoperation rate⑤ 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-up⑥ Comparison of the effects of BBAP and right atrial appendage pacing (RAAP) on acute intraoperative hemodynamics⑦ Comparison of the differences in atrial high-rate (AHR) response in pacemaker programming data between BBAP and RAAP during 1-month, 3-month, 6-month, 9-month, and 12-month follow-up Safety Endpoints
• Major safety endpoint: Composite of severe complications② Minor safety endpoint: Incidence of specific adverse events Exploratory Endpoints

Health economics, electrophysiological indicators Secondary Efficacy Endpoints

To be further clarified according to the study design and clinical data collection.

Revisions Summary

Full expansion of all abbreviations on first occurrence CS = coronary sinus BB = Bachmann bundle BBAP = Bachmann bundle atrial pacing CTA = computed tomographic angiography RAAP = right atrial appendage pacing AHR = atrial high-rate Minor wording & clarity improvements Specified "pacing threshold, lead impedance, intracardiac sensing" for clearer electrical parameter description Spelling/typo check No spelling errors, typos, or grammatical issues identified in the original text Consistent terminology maintained throughout

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 expected survival < 12 months Pregnancy or lactation: Positive pregnancy test in women of childbearing age or planned pregnancy Cognitive impairment: Inability to provide informed consent or follow the study protocol Mental illness: Severe mental disorders affecting treatment compliance Geographical restrictions: Inability to maintain contact or return to the medical center regularly during follow-up Venous access disorders: Inability to implant CRT via venous route (e.g., bilateral subclavian vein occlusion) Contralateral device: Implanted contralateral CIED leading to risk of lead crossing or interference Participation in other interventional clinical trials, or other conditions deemed unsuitable for enrollment by the investigator 4.3 Mid-term Withdrawal Criteria

   Active withdrawal by the subject and withdrawal of informed consent: The subject or their legal representative has the right to withdraw informed consent at any time without providing a reason.

   Refusal to continue follow-up: The subject explicitly refuses subsequent study treatment or key follow-up assessments.

   Lost to follow-up: Failure to contact via telephone, email, or other means for 3 consecutive times (or a total of 6 months).

   Severe adverse events: Life-threatening arrhythmias (sustained ventricular tachycardia/ventricular fibrillation); acute coronary syndrome requiring emergency revascularization; stroke/TIA causing severe neurological deficits; acute pulmonary edema/cardiogenic shock requiring mechanical circulatory support.

   Deterioration of clinical status: NYHA cardiac function deteriorates to class IV (non-ambulatory) requiring continuous intravenous inotropic drug therapy; progressive decrease in LVEF > 10% accompanied by significant clinical symptom deterioration; acute renal function deterioration (eGFR decrease > 50%) requiring dialysis.

   Contraindications to study treatment: Newly diagnosed malignant tumor requiring chemotherapy/radiotherapy; active infection/sepsis requiring long-term antibiotic treatment; extremely high bleeding risk precluding continued anticoagulant/antiplatelet therapy.

   Pregnancy or planned pregnancy: Confirmation of pregnancy or clear plan for pregnancy in female subjects of childbearing age.

   CRT implantation failure: Coronary sinus intubation failure (anatomical abnormalities or venous occlusion); inability to obtain stable capture threshold (pacing threshold > 3.0 V @ 0.5 ms); phrenic nerve stimulation that cannot be resolved by parameter adjustment.

   Device complications: Lead dislodgement/perforation requiring surgical intervention; pocket infection/hematoma requiring device removal; lead failure/insulation rupture leading to device dysfunction.

   Severe non-compliance: Medication compliance < 80% or consecutive missed ≥ 2 key follow-ups.

   Death: Occurrence of all-cause death, automatic withdrawal from the study (recorded as an endpoint event).

   Investigator judgment: The investigator believes that continued participation in the study is not in the subject's best interest.

   Handling After Withdrawal

   Data retention: Collected data may be retained for statistical analysis after ethical approval.

   Device handling: Implanted CRT devices will be managed according to clinical routine and will not be removed due to withdrawal.

   Follow-up conversion: Converted to routine clinical follow-up; study-specific procedures will no longer be performed.

   Safety monitoring: Severe adverse events must still be reported within 30 days after withdrawal.

   4.4 Exclusion Criteria (Protocol Violation)

   I. Violation of Inclusion/Exclusion Criteria (Protocol Violation)

   Forgery or misjudgment of key inclusion criteria:

   Post-enrollment verification reveals LVEF > 35% (Group A) or > 40% (Group B); QRS duration < 130 ms or misjudged as non-LBBB morphology (re-reviewed by the core electrocardiogram laboratory); Misjudged NYHA classification: Actually class I or bedridden IV (non-ambulatory IV).

   Missed screening for exclusion criteria:

   Post-enrollment discovery of prior CIED implantation (Groups A/B) or non-compliance with replacement indications (Group C); Acute myocardial infarction or stroke within 3 months before enrollment, but not reported in a timely manner; Complicated with specific cardiomyopathies such as hypertrophic cardiomyopathy and ARVC (misdiagnosed as ischemic or dilated cardiomyopathy at enrollment); In the active infection window at enrollment (white blood cell count > 15,000/μL or C-reactive protein > 50 mg/L).

   Insufficient drug washout period:

   Claimed to have received ≥ 3 months of GDMT, but drug prescription records or patient logs show actual medication duration < 8 weeks.

   II. Informed Consent and Ethical Issues

   Invalid informed consent:

   Lack of civil capacity when signing the informed consent form (failed Mini-Mental State Examination (MMSE) with score < 24); No independent witness during the informed consent process or failure to document in accordance with Good Clinical Practice (GCP) requirements; Discovery of major omitted information after signing (e.g., not informed of surgical risks or alternative treatment options).

   Duplicate enrollment:

   The same subject has participated in this study or other CRT-related interventional studies (concealed during screening).

   III. Pregnancy and Lactation

   Pregnancy at enrollment:

   Positive pregnancy test (serum human chorionic gonadotropin > 5 mIU/mL) found after signing informed consent but before randomization.

   Pregnancy during the study:

   Confirmation of pregnancy after randomization, having received X-ray fluoroscopy or surgical procedures, even if subsequently withdrawn.

   Lactating women:

   Lactating at enrollment and planning to continue breastfeeding (violating radiation protection principles).

5. Endpoint Indicators

   (All endpoint indicators should be fully defined, including endpoint name, observation time points or periods, measurement methods and tools, calculation methods, evaluation methods, etc. If necessary, an independent third-party endpoint event adjudication committee may be established, with implementation methods described such as standard operating procedures (SOP).) 5.1 Primary Study Endpoint

   Endpoint name: Success rate of BBAP lead implantationDefinition: The proportion of subjects in the study group (guided by 10-pole mapping LAAT) or control group (Lustgarten standard group) whose electrode lead tip reaches the Bachmann bundle region confirmed by postoperative CTA.

   Technical success rate = (Number of subjects in the group with lead tip confirmed by CTA to reach the Bachmann bundle region / Number of subjects randomized to the corresponding group) × 100% 5.2 Secondary Study Endpoints

   Total procedure time Definition: Time from skin puncture to completion of final incision suture Measurement tool: Operating room automatic timing system + manual review Observation point: Real-time recording during surgery Statistical method: Continuous variable, comparison of mean/median X-ray radiation dose Definition: Total fluoroscopy time (minutes) and dose-area product (DAP) (unit: cGy·cm²) Measurement tool: Digital subtraction angiography (DSA) machine built-in dose recording system Observation point: Automatic collection during surgery Statistical method: Comparison of median and radiation excess rate (DAP > 5000 cGy·cm²) Number of attempts for atrial lead screw-in during surgery: Cumulative number of atrial lead implantation attempts during surgery.

   Lead repositioning/reoperation rate Definition: Proportion requiring re-intervention within 30 days after surgery due to increased capture threshold, lead dislodgement, or phrenic nerve stimulation Observation time points: 24 hours, 7 days, 30 days after surgery (outpatient follow-up) Judgment method: Chest X-ray + pacemaker programming + clinical evaluation Changes in electrical parameters (threshold, impedance, 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 RAAP on acute intraoperative hemodynamics.

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

   5.3 Safety Endpoints

   Major Safety Endpoint (Composite Severe Complications)

   Incidence of composite severe surgical complications (within 30 days after surgery)Definition: Proportion of subjects who experience at least one of the following severe events from the start of surgery to 30 days postoperatively:

   Death (all-cause, Common Terminology Criteria for Adverse Events (CTCAE) grade 5) Cardiac tamponade or myocardial perforation requiring pericardiocentesis or surgical intervention (CTCAE grade 4) Coronary sinus dissection or rupture requiring emergency treatment or surgery termination (CTCAE grade 4) Ischemic stroke or TIA (CTCAE grade 3) Acute myocardial infarction (CTCAE grade 3) Lead-related thrombosis leading to symptomatic pulmonary embolism (CTCAE grade 3) Pocket hematoma requiring surgical drainage or blood transfusion (CTCAE grade 3) Systemic infection or infective endocarditis (CTCAE grade 3) Minor Safety Endpoints (Incidence of Specific Adverse Events)

   Incidence of phrenic nerve stimulation (PNS) Definition: Diaphragmatic capture caused by left ventricular pacing during surgery or follow-up, resulting in abdominal pulsation or hiccups

   Grading:

   Grade 1: Detected only during intraoperative testing, resolved after parameter adjustment Grade 2: Occurred postoperatively but resolvable by reducing output voltage or changing pacing vector Grade 3: Persistent PNS requiring lead repositioning Occurrence time: Intraoperative, 24 hours, 7 days, 30 days, 6 months after surgery (assessed at each programming session) Frequency calculation: First PNS incidence (time-event analysis) + total PNS episodes (Poisson regression for repeated events) Lead dislodgement rate Definition: Chest X-ray or programming shows lead tip displacement > 5 mm, leading to increased capture threshold > 1.0 V or sensing abnormalities

   Grading:

   Micro-dislodgement (CTCAE grade 2): Mild threshold increase without intervention Macro-dislodgement (CTCAE grade 3): Reoperation required for lead adjustment Occurrence time: 24 hours, 7 days, 30 days after surgery Verification tool: Transthoracic X-ray (comparison of immediate postoperative and follow-up films) + pacemaker programming report Dynamic changes in pacing threshold Definition: Temporal trend of left ventricular lead pacing threshold Measurement method: Measured intraoperatively with pacing system analyzer (PSA), automatically measured during pacemaker programming follow-up Assessment time points: Baseline (intraoperative), before discharge, 30 days, 6 months, 12 months Abnormal threshold definition: Acute phase > 3.0 V @ 0.5 ms; chronic phase (after 30 days) > 2.5 V @ 0.5 ms Statistical method: Repeated measures mixed-effects model Bleeding events

   Definition: Classified using the Bleeding Academic Research Consortium (BARC) system:

   BARC Type 1: Minor bleeding, no intervention required BARC Type 2: Requiring medical intervention or hospitalization BARC Type 3: Requiring transfusion, surgery, or fatal bleeding Coding mapping: BARC Type 2 corresponds to CTCAE grade 2; BARC Type 3 corresponds to CTCAE grades 3-4 Collection method: Hemoglobin reduction, transfusion records, imaging evidence

6. Study Process

6.1 Study Steps and Related Examinations

Overall study cycle: Screening period (Day -28 to Day -1) → Baseline/enrollment day (Day 0) → Surgery day (Day 0 or Day +1) → Hospitalization period (up to Day 7 postoperatively) → Outpatient follow-up period (1 month, 3 months, 6 months, 9 months, 12 months) Phase 1: Screening Period (Visit 1, Day -28 to Day -1)

Study content:

Informed consent: Investigators explain the study in detail; subjects sign the informed consent form (ICF) (in duplicate).

Medical history collection: Heart failure etiology and duration, prior treatment, allergy history, surgical history.

Physical examination: Vital signs (blood pressure, heart rate, respiration, temperature), NYHA class, weight, height, body mass index (BMI).

Laboratory examinations:

Complete blood count: 2 mL venous blood for hemoglobin, white blood cells, platelets Comprehensive biochemistry: 5 mL venous blood including liver function (ALT, AST, bilirubin), renal function (creatinine, eGFR), electrolytes (K⁺, Na⁺, Cl-), glucose, lipids NT-proBNP/BNP: 3 mL venous blood to assess heart failure severity Coagulation function: 2.5 mL venous blood including INR, APTT (for anticoagulated patients) Thyroid function: 3 mL venous blood (if indicated, e.g., atrial fibrillation patients) Serum pregnancy test: 2 mL venous blood for women of childbearing age (hCG testing)

Auxiliary examinations:

12-lead electrocardiogram: Standard ECG for heart rate, rhythm, QRS morphology and duration (LBBB confirmed by core ECG laboratory) Echocardiography: Transthoracic echocardiography (TTE); LVEF, left ventricular end-diastolic diameter (LVEDD), left atrial volume index (LAVI) measured by Simpson's biplane method, analyzed blindly by the Echo Core Lab 24-hour ambulatory electrocardiogram (Holter): To assess arrhythmia burden, atrial fibrillation burden, and expected ventricular pacing percentage

Imaging examinations:

Chest X-ray (AP and lateral): To assess heart size, pulmonary congestion, and planned lead pathway Inclusion confirmation: Investigators complete the Post-Screening Eligibility Assessment Form, signed and confirmed by the principal investigator (PI) before randomization.

Phase 2: Baseline/Enrollment Day (Visit 2, Day 0)

Study content:

Final confirmation: Recheck all inclusion/exclusion criteria to confirm ≥ 3 months of optimized GDMT.

Randomization: Obtain group assignment (10-pole guided vs. conventional) via the interactive web response system (IWRS).

Preoperative preparation: Sign surgical consent, skin preparation. Preoperative medication: Continue GDMT per protocol, prophylactic antibiotics. Vital signs: Baseline recording before surgery. Surface electrocardiogram: Reconfirm QRS morphology and duration. Phase 3: Surgery Day (Day 0 or Day +1)

Operational procedure for the 10-pole guided group:

Anesthesia: Local anesthesia (± sedation) or general anesthesia. Vascular puncture: Preferred left subclavian vein (or axillary vein) puncture for vascular sheath placement.

10-pole mapping: Insert a 10-pole electrophysiological mapping catheter (e.g., Boston Scientific Polaris or equivalent) through the sheath.

Coronary sinus intubation: Advance a guiding catheter into the coronary sinus ostium.

Target vein mapping: Insert the 10-pole catheter into the preselected target vein branch and record local electrograms (EGM).

Pacing test: Use PSA to pace through different electrode pairs to assess capture threshold and phrenic nerve stimulation.

Optimal atrial lead target selection: In the 10-pole guided group, the electrode pair with the lowest threshold + shortest LAAT is selected as the implantation target; in the control group, the site meeting the Lustgarten standard is used.

Right atrial/right ventricular lead implantation: Standard implantation of left ventricular/CS and right ventricular leads.

Connect pulse generator: Implant CRT-P/CRT-D and test all lead parameters. Incision suture: Layered closure and pressure dressing of the device pocket.

Intraoperative data collection:

Procedure time: From skin incision to suture completion (minutes) Fluoroscopy time: Automatically recorded by DSA (minutes) Radiation dose: DAP (cGy·cm²) and air kerma (mGy) 10-pole catheter data: Number of mapped veins, optimal target threshold, EGM signal quality (A/V wave amplitude) PSA parameters: Threshold, impedance, sensing for each lead Complications: Real-time adverse event recording

Intraoperative monitoring:

Continuous ECG monitoring: Heart rate, blood pressure, oxygen saturation. Phase 4: Postoperative Hospitalization Period (Day 0 to Day 7)

Within 24 hours after surgery (Day 0-1):

Continuous ECG monitoring: Arrhythmia and threshold change surveillance Bedside chest X-ray: Confirm lead position, rule out pneumothorax and pericardial effusion Incision observation: Daily assessment for pocket hematoma and infection Pacemaker programming: Initial comprehensive programming to optimize CRT parameters (AV/VV intervals) 12-lead ECG: Confirm P-wave duration

Before discharge (Day 5-7):

Wound care: Assess healing, suture removal (or outpatient removal at 7-10 days) Pacemaker programming: Final parameter setup and activation of home monitoring/remote monitoring Chest X-ray: Confirm lead stability Coronary CTA: Assess lead position relative to the Bachmann bundle Discharge medications: Optimized GDMT and follow-up plan Phase 5: Outpatient Follow-up Period

Visit 3: 30 days after surgery (±5 days) Pacemaker programming: Threshold, impedance, sensing, pacing percentage, AHR 12-lead ECG Chest X-ray (AP/lateral): Lead position assessment TTE: LVEF, LVEDD, mitral regurgitation severity (Echo Core Lab analysis) Adverse event collection: Adverse event (AE) / serious adverse event (SAE) recording Visit 4: 3 months after surgery (±10 days) Pacemaker programming: AHR assessment Visit 5: 6 months after surgery (±14 days) - Key efficacy assessment Comprehensive pacemaker programming Adverse event collection Visit 6: 12 months after surgery (±21 days) - Study completion Final pacemaker programming: All parameter documentation Device status: Lead parameters, battery longevity Study completion confirmation: Signed study completion form 6.5 Study End

Definition of study end:The study ends when the last enrolled subject completes the 12-month follow-up, all data are confirmed by source data verification (SDV), and the database is locked.

Specific milestones:

Clinical end: Last subject completes 12-month ±21-day follow-up Data entry completion: All case report form (CRF) data entered into the electronic data capture (EDC) system Data cleaning completion: All queries resolved; data quality meets FDA/National Medical Products Administration (NMPA) inspection standards Database lock: Blinded database lock with no further modifications permitted Statistical analysis completion: Finalization of the statistical analysis report (SAR) Study end confirmation: Jointly signed Study End Statement by sponsor, PI, and statistician

Subject follow-up after study end:

Converted to standard clinical follow-up; CRT management continues per guidelines May be transitioned to a long-term registry if clinically indicated (separate informed consent required) 6.6 Early Termination or Suspension of the Study

Early Termination Conditions

I. Safety Reasons

Excessive severe adverse events: Quarterly Data Safety Monitoring Board (DSMB) review shows major safety endpoint (30-day severe complication) rate > 15% in the 10-pole group, with relative risk (RR) > 3.0 vs. conventional group (P < 0.01), warranting immediate termination.

Device defects: Batch quality issues with the 10-pole mapping catheter (e.g., insulation rupture causing shock) leading to Class I recall by NMPA or manufacturer.

Unfavorable risk-benefit ratio: Interim analysis shows significantly higher all-cause mortality in the 10-pole group (hazard ratio (HR) > 2.0, P < 0.05).

II. Efficacy Reasons

Futility termination: Conditional power analysis at 50% enrollment (n = 20 total in this design) shows < 10% difference in primary endpoint (10-pole group success rate < 60% vs. prespecified 90%), with < 20% probability of achieving a positive result; DSMB recommends termination.

Inclusion Criteria:

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

Exclusion Criteria:

• Prior implantation of CRT/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 (PCI or 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)
• Types of cardiomyopathy: Hypertrophic cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy (ARVC), and other specific etiologies not suitable for CRT
• Severe renal insufficiency: Estimated glomerular filtration rate (eGFR) < 30 mL/min/1.73m² or uncontrolled renal failure
• Severe liver dysfunction: Child-Pugh class C
• Active infection: Including sepsis, infective endocarditis, etc.
• Malignant tumor: Advanced malignant tumor with expected survival < 12 months
• Pregnancy or lactation: Positive pregnancy test in women of childbearing age or planned pregnancy
• Cognitive impairment: Inability to provide informed consent or follow the study protocol
• Mental illness: Severe mental disorders affecting treatment compliance
• Geographical restrictions: Inability to maintain contact or return to the medical center regularly during follow-up
• Venous access disorders: Inability to implant CRT via venous route (e.g., bilateral subclavian vein occlusion)
• Contralateral device: Implanted contralateral CIED leading to risk of lead crossing or interference
• Participation in other interventional clinical trials, or other conditions deemed unsuitable for enrollment by the investigator