Pacing as a device therapy for heart failure (HF) is headed for what is probably its next big advance.
After decades of biventricular (BiV) pacemaker success in resynchronizing the ventricles and improving clinical outcomes, relatively new conduction-system pacing (CSP) techniques that avoid the pitfalls of right-ventricular (RV) pacing using BiV lead systems have been supplanting traditional cardiac resynchronization therapy (CRT) in selected patients at some major centers. In fact, they are solidly ensconced in a new guideline document addressing indications for CSP and BiV pacing in HF.
But , an alternative when BiV pacing isn’t appropriate or can’t be engaged.
That’s mainly because the limited, mostly observational evidence supporting CSP in the document can’t measure up to the clinical experience and plethora of large, randomized trials behind BiV-CRT.
But that shortfall is headed for change. Several new comparative studies, including a small, randomized trial, have added significantly to evidence suggesting that CSP is at least as effective as traditional CRT for procedural, functional safety, and clinical outcomes.
The new studies “are inherently prone to bias, but their results are really good,” observed Juan C. Diaz, MD. They show improvements in left ventricular ejection fraction (LVEF) and symptoms with CSP that are “outstanding compared to what we have been doing for the last 20 years,” he said in an interview.
Dr. Diaz, Clínica Las Vegas, Medellin, Colombia, is an investigator with the observational SYNCHRONY, which is among the new CSP studies formally presented at the annual scientific sessions of the Heart Rhythm Society. He is also lead author on its same-day publication in JACC: Clinical Electrophysiology.
Dr. Diaz said that CSP, which sustains pacing via the native conduction system, makes more “physiologic sense” than BiV pacing and represents “a step forward” for HF device therapy.
SYNCHRONY compared LBB-area with BiV pacing as the initial strategy for achieving cardiac resynchronization in patients with ischemic or nonischemic cardiomyopathy.
CSP is “a long way” from replacing conventional CRT, he said. But the new studies at the HRS sessions should help extend His-bundle and LBB-area pacing to more patients, he added, given the significant long-term “drawbacks” of BiV pacing. These include inevitable RV pacing, multiple leads, and the risks associated with chronic transvenous leads.
Zachary Goldberger, MD, University of Wisconsin–Madison, went a bit further in support of CSP as invited discussant for the SYNCHRONY presentation.
Given that it improved LVEF, heart failure class, HF hospitalizations (HFH), and mortality in that study and others, Dr. Goldberger said, CSP could potentially “become the dominant mode of resynchronization going forward.”
Other experts at the meeting saw CSP’s potential more as one of several pacing techniques that could be brought to bear for patients with CRT indications.
“Conduction system pacing is going to be a huge complement to biventricular pacing,” to which about 30% of patients have a “less than optimal response,” said Pugazhendhi Vijayaraman, MD, chief of clinical electrophysiology, Geisinger Heart Institute, Danville, Pa.
“I don’t think it needs to replace biventricular pacing, because biventricular pacing is a well-established, incredibly powerful therapy,” he told this news organization. But CSP is likely to provide “a good alternative option” in patients with poor responses to BiV-CRT.
It may, however, render some current BiV-pacing alternatives “obsolete,” Dr. Vijayaraman observed. “At our center, at least for the last 5 years, no patient has needed epicardial surgical left ventricular lead placement” because CSP was a better backup option.
Dr. Vijayaraman presented two of the meeting’s CSP vs. BiV pacing comparisons. In one, the 100-patient randomized HOT-CRT trial, contractile function improved significantly on CSP, which could be either His-bundle or LBB-area pacing.
He also presented an observational study of LBB-area pacing at 15 centers in Asia, Europe, and North America and led the authors of its simultaneous publication in the Journal of the American College of Cardiology.
“I think left-bundle conduction system pacing is the future, for sure,” Jagmeet P. Singh, MD, DPhil, told this news organization. Still, it doesn’t always work and when it does, it “doesn’t work equally in all patients,” he said.
“Conduction system pacing certainly makes a lot of sense,” especially in patients with left-bundle-branch block (LBBB), and “maybe not as a primary approach but certainly as a secondary approach,” said Dr. Singh, Massachusetts General Hospital, Boston, who is not a coauthor on any of the three studies.
He acknowledged that CSP may work well as a first-line option in patients with LBBB at some experienced centers. For those without LBBB or who have an intraventricular conduction delay, who represent 45%-50% of current CRT cases, Dr. Singh observed, “there’s still more evidence” that BiV-CRT is a more appropriate initial approach.
Standard CRT may fail, however, even in some patients who otherwise meet guideline-based indications. “We don’t really understand all the mechanisms for nonresponse in conventional biventricular pacing,” observed Niraj Varma, MD, PhD, Cleveland Clinic, also not involved with any of the three studies.
In some groups, including “patients with larger ventricles,” for example, BiV-CRT doesn’t always narrow the electrocardiographic QRS complex or preexcite delayed left ventricular (LV) activation, hallmarks of successful CRT, he said in an interview.
“I think we need to understand why this occurs in both situations,” but in such cases, CSP alone or as an adjunct to direct LV pacing may be successful. “Sometimes we need both an LV lead and the conduction-system pacing lead.”
Narrower, more efficient use of CSP as a BiV-CRT alternative may also boost its chances for success, Dr. Varma added. “I think we need to refine patient selection.”