Conduction system pacing versus biventricular pacing for cardiac resynchronization: the CSP-SYNC randomized single centre study

Conduction system pacing with left bundle branch area pacing (LBBAP) for cardiac resynchronization therapy (CRT) is an emerging alternative to standard biventricular (BiV) pacing. However, prospective randomized studies comparing both strategies are limited.

The study compared left ventricular (LV) reverse remodelling and clinical endpoints between LBBAP and BiV pacing in patients with Class I indication for CRT.

The CSP-SYNC study was a prospective, single-centre study, which included 62 patients with Class I indication for CRT and left bundle branch block fulfilling Strauss criteria. Patients were randomly assigned 1:1 to LBBAP or BiV and followed for at least 6 months. Crossovers were allowed if the primary allocation strategy was unsuccessful. The primary endpoint was the difference in improvement of left ventricular ejection fraction (LVEF). Secondary echocardiographic endpoints included reduction of end systolic volume (ESV) and CRT response defined as ESV reduction ≥ 15 %. Non-echocardiographic endpoints were post-procedural QRS duration, reduction of NT-proBNP, improvement of 6-minute walk test (6-MWT) and incidence of heart failure (HF) hospitalizations. Analysis was performed using intention-to-treat principle.

Thirty-one patients were randomized to each group. Most patients were males (71%), 32 % had ischemic cardiomyopathy and all were receiving optimal medical treatment. There was one crossover (1.6%) from LBBAP to BiV pacing. At six months, there was a greater improvement of LVEF in the LBBAP group (14.0 ± 10.4%, P < 0.01) than in the BiV group (8.5 ± 7.5 %, P < 0.01) (P = 0.02). Similarly, ESV reduction was more significant in the LBBAP group (-62.5 ± 45.1 ml, P < 0.01) than in the BiV group (-39.6 ± 40.1 ml, P < 0.01) (P = 0.04). (Figure). While the number of patients with ESV reduction ≥15% did not differ between both groups (P = 0.09), significantly more patients in the LBBAP group achieved LVEF ≥50% (P < 0.01). Reduction of QRS duration, level of NT-proBNP, and improvement in 6-MWT distance were significant and comparable in both groups. During a mean follow-up of 22.1 ± 7.5 months, there were 2 HF hospitalizations in the LBBAP group (6.5%) and 7 (22.6%) in the BiV group, however, using time to event analysis statistical significance was not reached (p=0.09).

In patients with Class I indication for CRT, LBBAP demonstrated a greater degree of LV reverse remodelling and similar clinical outcomes compared to BiV pacing. Further adequately powered studies to address cardiovascular outcomes are warranted to establish LBBAP as a first-line therapeutic option in CRT patients.

Echo at baseline and 6 months follow-up.