His-Bundle Pacing Excels as Primary CRT Alternative in Large Series

October 23, 2017

CHICAGO, IL — Permanent His-bundle pacing turned out to be a successful alternative to standard biventricular (BiV) pacing in at least two categories of patients with heart failure and indications for cardiac resynchronization therapy (CRT) in a newly reported multicenter experience, perhaps the largest so far[1].

About a third of the 106 patients had "rescue" His-bundle pacing after unsuccessful conventional CRT, and the rest had it as first-line pacing therapy because CRT with BiV pacing was considered unlikely to perform well.

Both types of patients on His-bundle pacing showed significant gains in the salient electrocardiographic, echocardiographic, and functional outcomes that BiV pacing for CRT is known to achieve in heart failure. The improvements included shortened QRS intervals, higher LVEF, and better NYHA functional class over a mean follow-up of 14 months.

Most published His-bundle-pacing experiences have included small numbers of patients, but "what we have shown is that it is feasible in a large population," senior author Dr Pugazhendhi Vijayaraman (Geisinger Heart Institute, Wilkes-Barre, PA) told theheart.org | Medscape Cardiology.

Operators for the current series, he cautioned, were mostly very experienced in His-bundle pacing. Many of them, "if they have a hard time placing a left ventricular lead, will go straight away to His-bundle pacing during the same procedure."

Vijayaraman said that approach, which doesn't use a left ventricular lead, has the potential to supplant BiV pacing in all patients. "That is the goal," at least, especially in "patients who need resynchronization because they have AV-nodal block and need a lot of right ventricular pacing" and ultimately any patient who requires ventricular pacing.

Ultimately, His-bundle pacing "is going to change how we do pacemakers in the next 5 to 10 years." But much needs to be learned from long-term studies and randomized trials before that can happen, he said.

For example, if His-bundle pacing "corrects" left bundle-branch block (LBBB), could it lose efficacy over the long term, or will pacing thresholds increase, thereby aggravating battery drain? Also, "Can we improve lead technology so that everybody can implant them with a high success rate?" he said.

"Biventricular pacing, when all is said and done in the population with LBBB, has set a very high bar. It has worked well, with a significant mortality benefit and improved LV function. All those things we can demonstrate [with His-bundle pacing], but we need comparative data to show if it's as good or better."

In the current five-center series, published October 13, 2017 in Heart Rhythm with lead author Dr Parikshit S Sharma (Rush University Medical Center, Chicago, IL), His-bundle pacing was engaged successfully in 95 of 106 patients in whom it was attempted

It was deemed "feasible and safe" in 30 patients who received it as rescue after failed LV-lead placement or nonresponse to BiV pacing, and in the 65 patients who received it as the primary CRT option due to AV block, bundle-branch block, or an anticipated >40% need for right ventricular pacing.

The patient series is made up of selected patients but, especially the larger latter subgroup who received primary His-bundle pacing, "is representative of our CRT practice," according to Dr Niraj Varma (Cleveland Clinic, OH), who isn't connected with the current study

"And their results are pretty good, for that 1-year follow-up," Varma said in an interview. In the series, their QRS durations "narrowed to a point that is seldom achieved with BiV pacing."

In practice, "I don't think His-bundle pacing is going to normalize all left bundles, because some [LBBB] in heart-failure patients is a combination of a His-based lesion and conduction defects as well," Varma said. But, "I think it's going to be part of the practice we will be using in the future."

Gains in QRS Duration, LVEF, and NYHA Class

At baseline in the current series, 24% of patients had an LVEF of 35% to 50%, and it was 35% or lower in 76%. Three-fourths of the cohort were in NYHA class 3–4. Underlying bundle-branch block was present in 45%, and 16% had AV block or had undergone AV-nodal ablation.

Over follow-up, mean QRS duration shortened from 157 ms to 117 ms (P=0.0001) with the difference significant in both subgroups.

Mean Change in QRS duration, LVEF, and NYHA Class in CRT-Indicated Patients With Successful Institution of His-bundle Pacing[1]

End points Group 1, n=30 (P) Group 2, n=65 (P) Combined, n=95 (P)
QRS, overall, ms –47 (0.0001) –37 (0.0001) –39 (0.0001)
QRS in BBB –46 (0.0001) –48 (0.0001) –47 (0.0001)
QRS in non-BBB +10 (0.0002) +8 (0.02) +5 (0.04)
QRS in paced –60 (0.0001) –51 (0.0001) –52 (0.0001)
LVEF, overall, % +14 (0.0001) +13 (0.0001) +14 (0.0001)
LVEF ≤35% +15 (0.0001) +14 (0.0001) +15 (0.0001)
LVEF >35–50% +5 (0.72) +12 (0.0001) +11 (0.0001)
NYHA class –0.9 (0.0001) –1.0 (0.0001) –1.0 (0.0001)
Group 1=His-bundle pacing as rescue after LV-lead failure or nonresponse
Group 2=His-bundle pacing as primary strategy in patients with AV block, BBB, or high ventricular pacing burden
BBB=bundle-branch block

Mean LVEF rose from 30% to 43% (P=0.0001) overall, from 26% to 41% (P=0.0001) in patients with LBBB, and from 32% to 49% (P=0.003) in non-LBBB patients with bundle-branch block.

Among the 72 patients initially with LVEF ≤35%, mean LVEF improved from 25% to 40% (P=0.0001).

Mean NYHA class overall improved from 2.8 to 1.8 (P=0.0001) with His-bundle pacing.

No significant changes in left-ventricular end-diastolic dimensions were seen in any patient group.

An Ongoing Process

Seven patients showed marked increases in His-bundle capture thresholds after 6 months, which prompted increases in pacing outputs in four cases and His-bundle lead retraction with replacement by a left-ventricular lead in three cases.

"That tells us probably that what is affecting the His bundle is an ongoing process; it's not a discrete lesion that just stays in the confines of the His bundle," Varma said. That highlights how little is known about the natural history of the disease.

"It may be that some of these patients will begin with His-bundle pacing, but ultimately they might require conventional CRT with biventricular pacing," he said. "That remains to be seen."

On the other hand, as Vijayaraman pointed out, His-bundle pacing has the potential to greatly diminish the incidence of LV dysfunction and heart failure that might otherwise result from a high burden of right-ventricular pacing. "That is going to be a big deal."

Vijayaraman said his group will be participating in the now-ongoing His Bundle Pacing Versus Coronary Sinus Pacing for Cardiac Resynchronization Therapy (His-SYNC) trial, with an estimated enrollment of 40 patients with conventional CRT indications comparing standard BiV pacing with His-bundle pacing. Its primary end points include changes in LVEF and QRS duration and also cardiovascular hospitalization or death.

Vijayaraman discloses receiving honoraria, consulting, or conducting research in association with Medtronic and serving on an advisory board for Boston Scientific. Disclosures for the coauthors are listed in the paper. Varma reports that he is involved in research and/or consults for Medtronic, Biotronik, and Abbott.

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