Biventricular (BiV) pacing was a game-changer for heart failure management, and it's the only kind of cardiac resynchronization therapy (CRT) backed by randomized trials a vast number of randomized trials.

But other, more physiologic versions of CRT have been gaining traction at some centers, including His-bundle pacing (HBP), ventricular septal pacing, and in a newly reported study direct pacing of the left bundle branch (LBB).

More than 70% of the study's 325 patients with heart failure and reduced ejection fraction responded to LBB pacing for CRT clinically and echocardiographically, and about 30% of the total were considered super-responders.

The current series shows that LBB pacing can provide CRT at "remarkably low and stable pacing thresholds," suggesting that it's an "excellent alternative option" compared with conventional BiV pacing, said Pugazhendhi Vijayaraman, MD, when formally presenting the results online May8 as part of the Heart Rhythm Society 2020 Scientific Sessions virtual presentation.

His-bundle pacing has received a lot of attention recently as a BiV-pacing alternative; its pacing effect is more physiologic than with BiV pacing, and possibly also LBB pacing, researchers say. But pacing thresholds are generally higher with HBP than with LBB pacing, which can increase battery drain, and achieving HBP tends to be more technically challenging so the learning curve for operators is steeper than it is for LBB pacing, said Vijayaraman, of Geisinger Heart Institute, Wilkes-Barre, Pennsylvania.

Although LBB pacing "addresses a lot of the limitations of His bundle pacing," he told theheart.org| Medscape Cardiology, it's not seen as a replacement. Having both techniques available to operators "gives us the best chance to provide the best outcome for the patient."

Conventional BiV pacing is considered a nonphysiologic approach to achieving CRT, but "the data is solid that it consistently benefits patients with wide QRS intervals," Roderick Tung, MD, University of Chicago Medicine, said in an interview. But many patients with heart failure aren't eligible or don't respond to BiV pacing, so CRT achieved by conduction-system pacing for example, either HBP or LBB pacing may be an alternative for them, he proposed.

"This is a moment to celebrate that we have more methods to access the conduction system" for providing patients with CRT, said Tung, who is principal investigator for the His SYNC study, a small randomized comparison of HBP and coronary sinus pacing for CRT.

Tung was not associated with the study presented by Vijayaraman but had praise for it. The study, he observed, suggested that 85% of patients appear to respond to LBB pacing, "and most importantly, the thresholds were less than 1volt. That's much lower than we see with His bundle pacing."

The study, Tung said, "shows that left bundle-branch pacing is viable for CRT."

Left bundle-branch pacing for CRT was attempted in 325 patients with left-ventricular ejection fractions (LVEF) less than 50% at four centers in the United States and one center in each of Brazil, the Netherlands, India, and Spain. The study used 3830 SelectSecure pacing leads (Medtronic).

Left bundle-branch block (LBBB) was identified in 42% of patients, right bundle-branch block in 18%, and interventricular conduction delay (IVCD) in 12%.

Compared with the 48 patients in whom LBB pacing could not be engaged, the 277 patients successfully treated were significantly more likely to have LBBB, nonischemic cardiomyopathy, smaller left ventricular dimensions, and shorter baseline QRS intervals and were less likely to have IVCD.

The pacing threshold for achieving LBB capture was 0.6volts at baseline and remained stable at 0.7volts 6 months later, "which is much lower than previously reported thresholds for His bundle pacing," Vijayaraman said during his presentation.

There were seven lead dislodgements, for a rate of 2.5%, also lower than reported rates for HBP, he said.

Left bundle-branch pacing was associated with significant QRS interval narrowing and improvement in LVEF (P< .0001 for both results).

The benefits of LBB pacing were more pronounced in patients with vs without LBBB, and in those with nonischemic compared to ischemic cardiomyopathy.

Clinical response, defined as improvement in NYHA functional class without heart-failure hospitalizations, was achieved by 72% of patients.

An echocardiographic response, defined as at least a 5% improvement in LVEF, occurred in 73% of patients. And 31% of patients achieved a super-response, defined as at least 20% gain in LVEF or, for patients with baseline LVEF no higher than 35%, a greater than 50% LVEF increase.

In multivariate analysis, independent predictors of an echocardiographic response included:

LBBB at baseline (odds ratio [OR], 3.90; 95% CI, 1.64- 9.26; P< .01)

Left ventricular end-diastolic dimension (OR, 0.62; 95% CI, 0.49- 0.79; P< .01)

Not independently predictive were QRS duration, age, sex, or heart-failure etiology (ischemic vs nonischemic).

Vijayaraman said currently, conduction-system pacing can be a first-choice CRT strategy for "anybody with a narrow QRS or right bundle-branch block," a group that doesn't meet criteria for CRT by BiV pacing in the guidelines.

However, he said, "left bundle-branch block patients do well with both forms of therapy," BiV or conduction-system pacing. If such patients don't respond well to standard BiV pacing, conduction-system pacing can then be an option.

"We start with the His bundle and try to get the best thresholds," less than 1.5volts, Vijayaraman said. If the pacing threshold is higher, "we move on to left bundle-branch pacing. We don't have to settle for a high threshold like we did in the past."

Vijayaraman discloses receiving fellowship and research support from; serving as a speaker or consultant for Medtronic; and consulting for Boston Scientific, Biotronik, Abbott, and Eaglepoint. Tung has previously reported no relevant financial relationships.

Heart Rhythm Society (HRS) 2020 Scientific Sessions: Late Breaking Clinical Trials2. Presented May8, 2020.

Follow Steve Stiles on Twitter: @SteveStiles2. For more from theheart.org| Medscape Cardiology, follow us on Twitter and Facebook.

Read more:

LBB Pacing Positioned to Join Arsenal of CRT Alternatives in HF - Medscape