People with heart block, a type of heart rhythm disorder, experienced significantly fewer serious cardiac events when treated with left bundle branch pacing rather than the standard right ventricular pacing, according to late-breaking science presented at the American Heart Association's Scientific Sessions 2026 in Chicago.
The international, multicenter OptimPacing trial tracked nearly 700 adults with atrioventricular block, also known as heart block, over a five-year period. Heart block is a condition in which electrical signals between the heart's upper and lower chambers are delayed or interrupted, potentially causing a very slow heart rate, fatigue, dizziness, fainting, chest pain, and in severe cases, cardiac arrest. The standard treatment has been a pacemaker that sends electrical signals to the heart's right ventricle, a technique called right ventricular pacing.
However, pacing only the right side can cause the heart's lower chambers to beat out of sync, which over time may enlarge or weaken the heart muscle, a condition known as pacing-induced cardiomyopathy, and contribute to heart failure. Left bundle branch pacing, a newer technique, sends the pacemaker signal into part of the heart's own electrical pathway, mimicking the heart's natural activation sequence and helping the lower chambers squeeze in a more coordinated pattern.
The trial's findings were striking. Left bundle branch pacing was associated with a 59% lower risk of death, heart failure hospitalization, or cardiomyopathy compared with right ventricular pacing. At four years, an estimated 8.5% of participants in the left bundle branch pacing group had died, been hospitalized for heart failure, or developed pacing-induced cardiomyopathy, compared with 19.2% in the right ventricular pacing group. No participants in the left bundle branch pacing group developed pacing-induced cardiomyopathy, versus 11.7% in the right ventricular pacing group. Heart failure hospitalization occurred in 1.5% of the left bundle branch pacing group compared with 2.9% of the right ventricular pacing group.
During a planned interim analysis after a median three-year follow-up, an independent data monitoring committee found that left bundle branch pacing met the study's pre-established criteria for superiority, leading the committee and the study's steering committee to recommend ending the trial early. The results were simultaneously published as a full manuscript in the New England Journal of Medicine.
"We expected that the group with left bundle branch pacing would do better than the group with right ventricular pacing. However, the difference between the two groups was greater than we expected. This study shows that left bundle branch pacing should be the first choice for patients with heart block who need a pacemaker," said study author Jiangang Zou, M.D., Ph.D., a professor of cardiology at First Affiliated Hospital, Nanjing Medical University in Nanjing, China.
The trial was conducted at 17 centers in mainland China, Hong Kong, the United Kingdom, Poland, and the United States from June 2021 to January 2025. It included 685 adults with an average age of 68.4 years; 57.5% were men. Participants had second-degree or complete atrioventricular block, or ongoing atrial fibrillation with an average heart rate below 50 beats per minute and related symptoms. Most had normal left ventricular ejection fraction at the start of the study.
The study had limitations, including its early termination, which could overestimate the benefits of left bundle branch pacing and reduce the precision of estimates. Most participants started with normal heart pumping strength, so the findings may not apply to people with already reduced heart function. Also, all left bundle branch pacing procedures used the same type of lead, so it is unknown whether results apply to other pacing tools.
"Future research is needed to refine which pacing technique is most appropriate for which patients, compare different pacing approaches that follow the heart's natural electrical system, and examine long-term safety and cost-effectiveness to help inform updates to clinical guidelines," Zou said.
The findings could have significant implications for clinical practice, as left bundle branch pacing may offer a safer and more effective alternative to the standard right ventricular pacing for the many people who require pacemakers due to heart block. The study was funded by the Project on New Technology of Jiangsu Province, Clinical Competence Improvement Project of Jiangsu Province Hospital, National Natural Science Foundation of China, and 135 Project for Disciplines of Excellence-Clinical Research Incubation Project of West China Hospital.
