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Left bundle branch (LBB)-area pacing led to better outcomes compared with right ventricular (RV) pacing in patients with bradycardia, an observational study found.

LBB pacing was associated with a relative 54% lower likelihood of death, heart failure hospitalization, or upgrade to biventricular pacing during follow-up of at least 6 months (10% vs 23.3%, P<0.001).

The differences were significant for both all-cause mortality (7.8% with LBB pacing vs 15% with RV pacing; HR 0.585, P=0.028) and heart failure hospitalization (3.7% vs 10.5%, respectively; HR 0.383, P=0.004).

The differences were most substantial among those with higher ventricular pacing burdens, reported Parik Sharma, MD, MPH, of Rush University Medical Center in Chicago, at the hybrid Heart Rhythm Society meeting, held online and in Boston.

Among the patients with 20% or greater ventricular pacing burden who underwent LBB pacing, relative reductions were 68% for the primary endpoint, 65% for all-cause mortality, and 61% for heart failure hospitalizations.

Although Sharma cautioned that the study was not randomized and likely involved some selection bias, it does provide a step forward.

"There are limitations currently with this technique, as we realized with His bundle pacing," he said, citing reports of lead perforation and issues with durability and lead extraction. "These are all questions that will need more time to answer. To us, the study was more signal to suggest that, yes, this technique does also have same degree of benefit as we consider His bundle pacing has with conduction system pacing."

"We've been hungry for this data, especially as guidelines for conduction system pacing are being worked on," said discussant Mina Chung, MD, of the Cleveland Clinic, at the late-breaking clinical trial session.

The two-health system study included 321 patients who underwent LBB-area pacing and 382 who underwent RV pacing. The LBB group had a number of significant differences compared with the RV pacing group:

• More atrial fibrillation (46.1% vs 38.0%)
• More beta-blocker use (73.8% vs 64.2%)
• More single-chamber permanent pacemaker implantation (5.3% vs 0.5%)
• Shorter-paced QRS intervals (121 vs 155 ms)
• Longer procedures (98 vs 72 minutes)
• Longer fluoroscopy times (13 vs 6 minutes)
• More ventricular pacing burdens over 20% and over 40% (73% vs 57% and 71% vs 51%)

Despite these factors, the findings looked good for LBB pacing, noted Chung, who pointed particularly to the similar pacing thresholds compared with RV pacing, "which has been a limiting factor for His bundle pacing."

"I love this study," said discussant Paul Friedman, MD, of the Mayo Clinic in Rochester, Minnesota.

As a clinician investigator-initiated study in an area in which industry hasn't come up with much funding, he suggested that these were the data needed to push ahead with further studies.

"That same enthusiasm so many had for His bundle pacing has been dampened, of course, by the limitations that emerged over time," Friedman said at the late-breaking session. "While this study shows [LBB-area pacing's] initial promise, we need to see over time if the same limitations or different limitations emerge."

Uncertainties also include the long-term risk of lead complications, as well as implant success, which wasn't reported in the study, although previous studies have suggested that some 20% of attempts at LBB pacing haven't captured the target, he noted.

Importantly, leadless pacing is a strong competitor, Friedman added. He suggested that the next study should test whether the benefits conferred by leadless pacing, including not having a lead across the tricuspid valve and not having an extravascular structure connected to an intravascular lead, outweigh the benefits of LBB-area septal pacing.

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