This study is a prospective, single-arm, target value clinical trial. We plan to prospectively enroll and follow 24 patients across three centers nationwide who have a low baseline heart rate (HR ≤ 60 bpm), meet the indication for permanent pacemaker implantation, and have right-sided heart failure with severe or greater tricuspid regurgitation. All patients will undergo pacemaker implantation using left bundle branch pacing (LBBP), and the pacing rate will be uniformly increased to 90 bpm (reduced to 80-85 bpm in case of intolerance). Patients will be followed for 6 months to evaluate the effects of heart-rate increase on hemodynamics, heart failure symptoms, and physical function in patients with right-sided heart failure.

After eligibility screening and written informed consent are obtained, all participants will undergo baseline assessments including vital signs, biochemical tests, New York Heart Association (NYHA) functional class, diuretic index, edema grade, echocardiographic parameters, 6-minute walk distance (6MWD), and the Kansas City Cardiomyopathy Questionnaire (KCCQ). All patients will then receive pacemaker implantation with the lead positioned for left bundle branch pacing to achieve conduction system pacing. The pacing rate will initially be set at 60 bpm, followed by right heart catheterization. Hemodynamic parameters will be recorded during both diastole and systole, including pressures in the superior vena cava, inferior vena cava, right atrium, right ventricle, and pulmonary artery. Mean pressure values will then be calculated, and mean pulmonary capillary wedge pressure and pulmonary vascular resistance will be measured. Cardiac output (CO) will be assessed invasively using a cardiac output monitoring system integrated with the right heart catheterization setup, based on the Fick principle. The pacing rate will then be increased to 90 bpm; after 5 minutes of stabilization, right heart catheterization will be repeated.

On the day after pacemaker implantation, transthoracic echocardiography (TTE) will be performed, and relevant parameters will be measured at pacing rates of 60 and 90 bpm. Before discharge, the pacing rate will be set to 90 bpm. Diuretics will be prescribed as clinically indicated, and escalation of diuretic dosage will not be permitted during the follow-up period.

Follow-up visits will be scheduled at 1 month, 3 months, and 6 months after discharge. Assessments at each visit will include vital signs, biochemical tests, NYHA functional class, diuretic index, edema grade, KCCQ score, 6MWD, and echocardiographic parameters.

Inclusion Criteria:

1. Mean resting heart rate ≤ 65 beats/min (based on a resting electrocardiogram).

2. Clinically confirmed right-sided heart failure, requiring ≥2 diuretic units to fully control edema, or having persistent grade ≥1 edema despite diuretic therapy.

   Diuretic unit definition: expressed as the number of daily doses at the standard oral dose. For example, the standard units for furosemide, torasemide, and spironolactone are 20 mg/day, 10 mg/day, and 20 mg/day, respectively. If a patient takes furosemide 20 mg twice daily and spironolactone 20 mg once daily, the total diuretic units equal 3.

3. Echocardiography shows severe or greater tricuspid regurgitation.

4. With/without an indication for permanent pacemaker implantation.

5. Is able to understand the purpose of the trial, voluntarily participates and signs written informed consent, and is willing to complete follow-up visits as required by the protocol.

Exclusion Criteria:

1. Mean pulmonary artery pressure (mPAP) > 35 mmHg measured by right heart catheterization at a pacing rate of 60 bpm.
2. Left ventricular ejection fraction (LVEF) < 50% or left ventricular end-diastolic diameter (LVEDD) > 56 mm as measured by echocardiography.
3. Prior implantation of a cardiac pacemaker.
4. Moderate or greater left-sided valvular regurgitation or stenosis.
5. Current use of heart rate-lowering medications, such as beta-blockers, digoxin, ivabradine, etc.
6. Untreated hypothyroidism.
7. Participation in another drug or medical device clinical trial that has not yet been completed.
8. Deemed unsuitable for participation in this clinical trial by the investigator.