The present study is a prospective, multicenter, non-inferiority, randomized controlled trail. It aims to investigate whether the efficacy of conduction system pacing (CSP) is non-inferior to biventricular pacing (BiVP) in patients with heart failure and right ventricular pacing (RVP) requiring upgrading to cardiac resynchronization therapy (CRT).

RVP is a standardized treatment strategy for severe bradyarrhythmia. However, RVP can result in electrical and mechanical dyssynchrony of the heart, which will adversely affect cardiac function. Until now, many studies have shown that RVP can promote the progression of heart failure, especially in patients with high ventricular pacing percentage. For these heart failure patients, upgrading to CRT is a feasible and effective therapy.

BiVP is a traditional method to achieve CRT, which can improve cardiac synchrony and provide great clinical outcomes for heart failure patients upgraded from RVP. CSP contains left bundle branch pacing (LBBP) and His bundle pacing (HBP), which is able to activate native His-Purkinje conduction system and solve the problems caused by RVP. Although HBP has high technical requirements, lower sense value and higher threshold, it is the pacing modality closest to physiological conditions so far. Since first reported by Huang et al. in 2017, LBBP has been carried out boomingly all over the world. LBBP has been reported to offer higher success rate with higher sense value and lower pacing thresholds compared with HBP, which can also achieve similar electrical and mechanical resynchronization as well as HBP.

However, no randomized controlled studies have been reported to compare the efficacy of CSP and BiVP in patients with heart failure and RVP requiring upgrading to CRT. CSP-UPGRADE is a non-inferiority study, and the purpose of which is to investigate whether the efficacy of CSP is not inferior to BiVP in such patients. Eligible patients will be 1:1 randomized to two groups. The primary outcome is change in LVEF between baseline and six months after device implantation assessed by echocardiography. According to BUDAPEST-CRT Upgrade trial, half of lower limit of the 95% confidence interval for difference in mean ΔLVEF between the CRTD and ICD group is about 3.8%, which is used as non-inferiority margin in the present study. Based on previous studies and cases, it is assumed that the mean ΔLVEF values in patients upgraded to CSP and BiVP are equal and the standard deviations are both 5%. With power as 80%, alpha as 0.025, rate of lost-of-follow-up as 10%, the final sample size was estimated as 66 by using PASS Version 21.0.3 (33 patients for each group). If the non-inferiority test reaches positive results, then we will further verify whether CSP is superior to BiVP in such patients.

Inclusion Criteria:

1. Patients with symptomatic heart failure (LVEF <50%) after right ventricular pacing for at least 3 months;
2. NYHA class II-IV;
3. NT-proBNP >125pg/mL in patients with sinus rhythm, NT-proBNP >250pg/mL in patients with atrial fibrillation;
4. Right ventricular pacing percentage >40%;
5. Adult patients aged 18-80;
6. With informed consent signed.

Exclusion Criteria:

1. History of acute myocardial infarction within 3 months before enrollment;
2. Frequent premature ventricular contraction (>15%) or malignant ventricular arrhythmia which is difficult to control;
3. History of valvular heart disease intervention within 3 months before enrollment;
4. After mechanical tricuspid valve replacement;
5. Ventricular septal hypertrophy (≥15mm during diastole);
6. Complex congenital heart disease;
7. History of heart transplantation;
8. Enrollment in any other study;
9. Pregnant or with child-bearing plan;
10. A life expectancy of less than 12 months.