His-Bundle Pacing for CRT: Has It Finally Hit Critical Mass?

Patrice Wendling

April 21, 2017

CHICAGO, IL — A multicenter pilot study adds to growing evidence supporting the use of permanent His-bundle pacing (HBP), demonstrating the feasibility of implanting a His bundle lead into the LV port instead of using standard ventricular leads.

Moreover, this approach achieved narrowing of the QRS interval in 76% of patients with bundle branch block and an indication for cardiac resynchronization therapy (CRT)[1].

"It's the sort of study you want everyone to be talking about because it opens up a whole new therapy, so it's important," Dr Kenneth Ellenbogen (Virginia Commonwealth University Medical Center, Richmond), who has published several papers on HBP, told heartwire from Medscape.

He said the patient numbers are small but the data is very powerful and raise questions of whether His-bundle pacing is just as good as CRT or better than CRT and whether it can be used in some patients who aren't good candidates for CRT.

"Those are really important questions, because we know on average that 25% of patients don't respond to CRT therapy. That's a big group of patients," Ellenbogen said.

"With some of the newer multipoint pacing and multipolar leads, we're slowing inching up on the number of patients who respond to therapy, but it's still a substantial number of patients and there are certain types of conduction disease like right bundle branch block and [intraventricular conduction delay] that don't do very well with CRT."

Permanent HBP was first described in 2000 and since then several studies have shown its feasibility and safety, typically in patients who have failed CRT and using both LV and HBP leads.

The present study, published online recently in Heart Rhythm, enrolled 21 patients with bundle branch block with QRS >120 ms, NYHA class 2–4, and an ejection fraction <35% at two academic centers from 2014 to 2016. Only two of the patients had failed prior CRT.

HBP using the 4.1-Fr exposed-helix SelectSecure 3830 lead (Medtronic, Minneapolis, MN) was successfully implanted in 16 patients (mean age 62 years, 75% male), with 15 patients demonstrating nonselective His-bundle capture and one selective His capture.

The average QRS duration was reduced from 181 ms to 129 ms (P<0.001), representing a narrowing of the QRS duration by 30%.

"In three out of four patients we could actually achieve His-bundle capture that resulted in QRS correction or narrowing to what we would all consider out of the normal CRT range, meaning less than 130 ms or greater than 20% narrowing from baseline QRS," senior study author Dr Roderick Tung (University of Chicago, IL) told heartwire .

He added, "We saw mostly nonselective His-bundle capture, which appeared to be totally sufficient because the echocardiographic indices and the improvement in New York Heart Association was fairly consistent across the population. So you don't have to capture only the His bundle; nonselective recruitment appears to be good enough."

At 12-month follow-up, the mean LV ejection fraction improved from 27% to 41% (P<0.001), NYHA functional class from 3 to 2 (P<0.001), and LV internal dimension from 5.4 cm to 4.5 cm.

Eleven of the 16 patients showed clinical improvement, with three "hyper-responders" showing an LV ejection fraction >50%.

Tung said it's still unclear why permanent His-bundle pacing works in some patients but not others; the HV interval did not correlate, although it appeared that the wider the baseline QRS interval the better, which is similar to outcomes with traditional LV pacing.

Commenting to heartwire , Dr Daniel Lustgarten (University of Vermont, Burlington, VT) said that while the nonresponder rate for CRT is conservatively about 30%, the proportion of superresponders who nearly normalize their ejection fraction is actually quite small.

"It would be my anticipation that in patients in whom you are able to His-bundle pace with normalization of the QRS, the superresponse rate is going to be much, much higher," he said.

Lustgarten and other HBP researchers argue that there's a built-in limitation to biventricular pacing as a means of trying to implement CRT because it activates the right and left ventricle abnormally, whereas with HBP, ventricular activation is being normalized as it should be via the native His-Purkinje system.

Supporting this idea are other recent promising developments in CRT, all involving the His-Purkinje system, such as adaptive (or fusion) pacing and LV endocardial pacing, said Lustgarten, who was the first to demonstrate the feasibility of permanent His-bundle pacing as a potential first-line therapy.

Still, the field has never really taken off, perhaps because of the perception that HBP is more difficult. It is more electrophysiologic than the purely anatomic standard pacemaker implantation and requires a good understanding of electrophysiology, but "that's something everyone who implants a device should have," Lustgarten remarked.

Industry pressures may also be keeping HBP on the sidelines. "There is the perception that His-bundle pacing could limit CRT devices as they currently exist and maybe allow us to do something better for a lot cheaper setup," he added.

That said, all three physicians agree there's still a lot more that needs to be learned about HBP, including thresholds, pacing lead designs, if there is a potential differential benefit between selective vs nonselective His-bundle capture, and the stability and durability of results. Furthermore, current systems are not optimized for HBP, with only a single sheath available specifically for this anatomy, "and this is not a single-size problem," Lustgarten quipped.

Ellenbogen said safety and durability at 12 months look good, but it's unclear what the thresholds will look like at 2, 3, or 5 years.

"It would be nice to have some more median-term data before we start putting these in everyone," he said.

Acute thresholds for His capture were 1.9 V and remained stable at follow-up (1.4 V), the investigators, led by Dr Olujimi Ajijola (David Geffen School of Medicine at the University of California Los Angeles), reported.

One patient lost nonselective His capture 1 month after implant with a para-Hisian response due to a threshold increase to 3.5 mA, which was restored with increased programmed output of 5 V. There were no lead dislodgements.

Four deaths occurred during follow-up, three in patients treated with HBP. The causes of the deaths were progression of eosinophilic myocarditis, pulseless electrical activity after appropriate VF shock, and heart-failure progression—all within 2 months of implantation.

The first prospective randomized multicenter trial comparing standard LV lead vs HBP as primary therapy, the His SYNC study, is currently recruiting 40 to 50 patients who meet CRT criteria and will look at 6-month and 1-year echocardiographic indices, lead thresholds, NYHA, and quality of life, Tung said.

The authors report no relevant financial relationships. Ellenbogen reports research support from and consulting for Medtronic. Lustgarten reports serving as an advisor to and research support from Medtronic.

Follow Patrice Wendling on Twitter: @pwendl. For more from theheart.org, follow us on Twitter and Facebook.

Editor's note: The article originally gave the incorrect measure for acute thresholds for His capture as mV. It has been corrected. heartwire regrets the error.

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