A recent study added to the growing body of evidence supporting an expansion of the indication for a promising pacing strategy among patients with a substantial ventricular pacing burden.

Prior research has shown conduction system pacing (CSP) offers an alternative to right ventricular (RV) pacing that carries a lower risk for pacing-induced cardiomyopathy (PICM) and hospitalization for heart failure. However, those studies were smaller and observational in nature. The new study, which appeared recently in the Journal of the American College of Cardiology, provides the most robust evidence, yet the intervention is better than standard pacemakers.

“I think the scientific community has suspected that CSP has the potential to yield better clinical outcomes than conventional RV pacemakers, but what was missing was confirmation from a randomized controlled trial and the magnitude of superiority of CSP when compared with RV pacemakers,” said lead researcher Chee Loong (Dominic) Chow, MBBS, a cardiologist in the faculty of medicine, dentistry, and health sciences at The University of Melbourne in Melbourne, Australia.

Creating CSPACE

The investigator-initiated, single-blinded CSPACE trial was conducted at two Melbourne hospitals from 2020 to 2024. Participants with a pacing indication for atrioventricular (AV) block but without an indication for cardiac resynchronization therapy were recruited, matched, and randomized 1:1 to receive either CSP (implanter’s choice of His-bundle, left bundle branch, or left ventricular septal pacing) or right ventricular septal pacing (RVsP).

All electrophysiologists had performed at least 20 successful implantations prior to the study. The primary endpoint was a composite of PICM, hospitalization for heart failure, all-cause mortality, and the need for an upgrade to biventricular cardiac resynchronization therapy (CRT).

A total of 202 patients were enrolled (mean age, 77 years; 33% women), with 101 participants in each group; baseline characteristics were similar between groups. The most common pacing indication was complete heart block (40%), followed by symptomatic second-degree AV block (36%), and slow atrial fibrillation (10%). Baseline electrocardiography showed right bundle branch morphology and normal QRS in about 43% and 39% of patients, respectively. Mean QRS duration was 124 ms, and the average left ventricular ejection fraction was 61% for all participants at baseline.

CSP vs RVsP

Procedural success was documented in 100% of the RVsP cases and in 88% of the CSP cases, according to the researchers. Procedure and fluoroscopy times were longer with CSP, and the total radiation dose was higher. The authors noted that the additional time may have been due to the proportion of patients with complete heart block (40%) or second-degree AV block (36.1%) as the implanters were encouraged to position a backup lead prior to CSP implantation in case of asystole. Participants who underwent CSP earlier in the study tended to have longer procedure times.

After a mean follow-up period of 25 months, fewer occurrences of the primary composite endpoint were documented in the CSP vs RVsP groups (7.2 vs 20.7; hazard ratio [HR], 0.35 [95% CI, 0.19-0.64). This result was primarily due to fewer episodes of PICM in the CSP vs RVsP groups (4.6 vs 14.7 events per 100 person-years; HR, 0.31 [95% CI, 0.15-0.67]) and a lower need for biventricular CRT upgrade (0 vs 1.9 events per 100 person-years). No significant differences were observed between groups in hospitalizations for heart failure or for all-cause mortality.

Lead revision was significantly more likely in those who underwent CSP than RVsP (7.9% vs 1.0%; P = .017).

“This study confirms that CSP is superior to RV pacemakers and demonstrates the magnitude of clinical benefit,” Chow told Medscape Medical News.

The authors of an editorial accompanying the study noted the findings support the use of CSP as reasonable, but not required, in all patients with a substantial ventricular pacing burden. However, they added that while the outcomes support the use of physiological pacing in individuals with AV block, more data are needed on the longevity of the leads within the septum and CSP’s effect on heart failure and mortality.

“Nevertheless, the CSPACE study is a well-executed clinical trial that adds to the growing evidence that RV septal or apical pacing may not be the optimal pacing modality when anticipated ventricular pacing exceeds 20%,” they wrote.

Chow reported no relevant financial conflicts of interest.

Paul Basilio is a freelance writer and editor based in Glenside, Pennsylvania.