Multisite Left Ventricular Pacing Can Turn Failed CRT Into a Win

August 04, 2021

The advent of cardiac resynchronization therapy (CRT) changed the landscape of heart failure (HF) management options, but perhaps a third of patients receiving biventricular pacemakers for CRT don't respond to it.

Strategies for boosting the CRT success rate have included, with mixed results, simultaneous left ventricular (LV) pacing from more than one lead location, the vectors spanning a larger swath of ventricle than possible with standard LV pacing.

Indeed, such resynchronization therapy with multisite LV pacing (MSP) made CRT responders out of half of patients in whom CRT had failed over the previous 6 months in a prospective trial, presented July 30 at the Heart Rhythm Society (HRS) 2021 Scientific Sessions, conducted virtually and on-site in Boston.

The observational study, called SMART-MSP, demonstrated the safety and effectiveness of its multisite LV pacing strategy and that the added pacing doesn't greatly affect pacemaker longevity, a concern in previous MSP trials, Samir Saba, MD, University of Pittsburgh Medical Center, Pennsylvania, told | Medscape Cardiology.

Multisite LV pacing as part of CRT, therefore, "should be considered by clinicians for use in their nonresponder population," Saba added.

MSP effectiveness was defined as improvement in clinical composite score (CCS), which accounted for death from any cause, HF events, and NYHA functional class, and included a patient global assessment.

The estimated effect of MSP-related pacemaker battery drain "fell between something like 3 to 4 months off the life of the device," Saba at a panel discussion following his presentation of the trial at the HRS sessions.

The study "clearly showed that multisite pacing is very safe. It's not proarrhythmic and there were no other issues that were identified," said Kimberly A. Selzman, MD, MPH, as an invited discussant, after Saba's presentation.

"Most of us consider CRT to be a fairly mature technology at this point, but it's still really important to continue to investigate ways that we can improve upon its responder rate," said Selzman, from George E. Wahlen VA Medical Center, Salt Lake City. "I think multisite pacing may be one of the ways that we can do that."

The trial enrolled 584 patients with standard CRT indications at 52 sites in the United States who had received Resonate (Boston Scientific) defibrillating CRT devices with quadripolar LV leads. They were set for standard biventricular (BiV) pacing but could also be programmed to deliver LV pacing from more than one site. None of the patients had permanent atrial fibrillation or complete heart block, and none had previously had LV pacing, Saba reported.

Of the 528 patients who completed 6 months on standard BiV pacing, CCS score improved in 74.1%, who were considered CRT responders. The remaining 137 patients, or 26%, were nonresponders with unchanged or worsened CCS scores.

The device's MSP function was activated in the 102 nonresponders who were able to continue the study and who were followed an additional 6 months. They resembled the overall cohort in demographic characteristics, NYHA class, prevalence of ischemic cardiomyopathy and left-bundle branch block, and medications.

A patient who experienced "a series of HF-related events" within a few weeks of MSP activation was judged to have had a potentially MSP-related complication, the only one documented in the study. The resulting 99% rate of complication-free MSP, the primary safety endpoint, far exceeded the prespecified 90% benchmark, Saba observed.

"The efficacy endpoint was also met with flying colors," Saba told | Medscape Cardiology, in that 40 of the 78 patients who achieved at least a 93.0% prevalence of LV pacing on MSP also showed improved CCS scores at 6 to 12 months, for an MSP responder rate of 51.3%; the prespecified goal was only 5.0%.

Multiple sensitivity analyses also saw an approximately 50% rate of conversion from CRT nonresponder to responder, Saba noted.

Of the 102 initial CRT nonresponders who went on to MSP, 21 (20.6%) had experienced HF events while on conventional BiV pacing during the first 6 months, compared with 11 (10.8%) who did so while on MSP (P = .017).

The 26% rate of nonresponse to standard CRT in the initial cohort "is well within the range of what we see in most clinical trials," observed Mark Link, MD, University of Texas Southwestern, Dallas, another invited discussant. "So it's a typical group of patients."

Link questioned, however, whether MSP necessarily accounted for all of its associated CRT response rate. Routine management that could have potentially contributed include, for example, changes to the patients' medical therapy or the atrioventricular (AV) delay on their devices, Link proposed.

The study didn't follow the patients' medication use, Saba replied, although their meds were "pretty good at the outset." And there was little device reprogramming in the study, he said, and "not much change in the AV delays."

SMART-MSP was funded by Boston Scientific. Saba discloses receiving honoraria or speaking for or receiving consulting fees from Boston Scientific and Medtronic, and receiving research grants from Boston Scientific, Medtronic, and Abbott. Selzman and Link report nothing relevant to disclose.

Heart Rhythm Society (HRS) 2021 Scientific Sessions: Late Breaking Clinical Trials Updates. Presented July 30, 2021.

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