Studies Support Long-term Benefits of His-Bundle Pacing for BBB

BARCELONA, Spain  — Permanent His-bundle pacing (HBP) corrected bundle-branch block (BBB) in more than three fourths of all-comers referred for pacemaker implantation and provided stable results in most, even during long-term follow-up.

"The main message is that we can overcome the classical indication and go directly to a new philosophy for how we pace," study author Francesco Zanon, MD, from Santa Maria della Misericordia General Hospital, Rovigo, Italy, said at the European Heart Rhythm Association (EHRA) 2018 congress.

An early adopter of HBP, Zanon said they initially restricted the procedure to patients with sinus node dysfunction but now use it in all patients referred for pacemaker implantation.

The first study involved 147 consecutive patients referred for pacemaker implantation with varying types of BBB (left BBB in 37%; right BBB in 36%; right BBB plus left anterior or posterior hemiblock in 24%; and sinus rhythm with intraventricular conduction delay in 3%). Atrioventricular block was present in 63%, sinus node disease in 15%, and atrial fibrillation with slow ventricular rate in 22%. A backup lead was added in 45% of patients.

Their mean age was 76 years, 58% were male, and 27% had chronic atrial fibrillation.  All patients were followed yearly from implantation in a single center.

HBP resulted in narrowing of the QRS with disappearance of BBB in 117 patients (80%), while 30 patients (20%) had selective His pacing with a wide QRS identical to the native one, Zanon said.

Baseline QRS duration improved from a mean of 153 milliseconds to 137 milliseconds and left ventricular (LV) ejection fraction from 53% to 55%.

After a mean of 5.2 years, 1 patient was lost to follow-up and hisian capture terminated in 12 patients because of infections in 3, an upgrade to cardiac resynchronization therapy (CRT) in 2, and high thresholds in 7, including 1 case of syncope. Among the remaining 134 patients, "Persistence of effective His-bundle pacing was very high at 91%," Zanon said.

The average device life was 4.3 years and a backup lead was added in 3 patients during follow-up. The pacing threshold was 2.1 V at 0.5 ms vs 1.6 V at 0.5 ms at implant.

During follow-up, 81% of patients underwent ventricular pacing (83% greater than 40% pacing); 12 patients were hospitalized with heart failure and 5 with acute coronary disease. The final QRS duration was 138 ms.

The large percentage of patients with QRS narrowing confirms reports from the United States; however, results from the single-center, noncontrolled study should be interpreted with caution, chief cardiology correspondent for theheart.org | Medscape Cardiology, John Mandrola, MD, clinical electrophysiologist, Baptist Medical Associates, Louisville, Kentucky, said in an interview.

"Clearly this group has a vast experience with HBP and the results may not be generalizable to less experienced centers," he said. "But taken together, the cumulative data on His-bundle pacing are encouraging —  both from an efficacy and safety standpoint. At a minimum, the accumulated experience with HBP provides reassurance that it is an ideal way to pace the ventricle without inducing dyssynchrony and possible left ventricular dysfunction."

These data, along with other reports on reversing BBB, make the case for a randomized controlled trial comparing HBP vs CRT in patients with heart failure with preserved ejection fraction and a left BBB, Mandrola said.  

"Finally, the other disruptive aspect of His-bundle pacing is that it requires knowledge and experience with cardiac electrophysiology. In many centers, non-EP cardiologists implant pacemakers. The question is whether they are up to the challenge of learning this innovative and decidedly EP-centric technique?" Mandrola said. 

During a session highlighting key studies presented at the meeting, discussant Haran Burri, MD, from the University Hospital of Geneva, Switzerland, said HBP "is very hot now" but that many physicians, including himself, have mistakenly thought that left and right BBB are relatively peripheral when in fact many of these patients have longitudinal dissociation within the His bundle itself.

"It seems that in 80% of patients the level of the block is actually very proximal and amenable to His-bundle pacing correction," he said, noting that the paced QRS complex was roughly identical to the native QRS complex.

However, "The thresholds were relatively high, which remains one of the challenges of His-bundle pacing, and the sensing value is also quite low," Burri said. He also highlighted the need for back-up lead placement, another critical question in HBP.

Back-up Pacing

During the formal presentation, Zanon provided additional data from a second study, in which the investigators enabled a three-chamber pacemaker to provide apical back-up sensing for patients undergoing HBP.

He noted that implanting a dual-chamber device in patients with chronic atrial fibrillation provides back-up stimulation on demand, but for those also needing an atrial lead, implanting a CRT pacemaker provides back-up stimulation at every beat. This comes at the cost of battery longevity due to higher thresholds characteristic of LV leads and may negatively affect LV function over time.

To get around this, the investigators connected the atrial lead on a three-chamber pacemaker (Hera, Medico) to the atrial port, the hisian lead to the LV port, and the apical lead to the right ventricular port. Pacing was enabled in both ventricular channels and sensing enabled only in the apical lead to detect intrinsic activity or in response to hisian pacing. A blanking period of 56 ms was set in the apical lead to prevent spike oversensing and a VV-delay programmed at 120 ms.

When HBP was effective, apical sensing occurred within the VV delay and prevented apical back-up pacing. If HBP failed, a back-up pulse was delivered at the end of the VV delay, Zanon explained.

Among 22 patients, HBP with on-demand apical sensing was achieved in 100%, he said.

The His-paced R-wave was sensed in the apical lead after a mean of 96 ms. The detection upper limit of 120 ms was exceeded in "a few cases" of nonselective HBP and corrected with higher output, narrowing the QRS and sensed within the 120-millisecond interval.

At last follow-up at 19 months, device diagnostics showed that back-up pacing was less than 1% in all but one patient and V1-V2 pacing applied in 10% of cycles.

"Avoiding the back-up pacing in each lead could prolong battery longevity and have a fantastic impact for our patients," Zanon said.

During the discussion of the results, he observed that none of the devices are designed specifically for HBP. "So our main message to the companies is please, study, study, study and design devices for our patients."

Zanon reported receiving modest speaker fees from Boston Scientific, Medtronic, Livanova, and St Jude Medical. Mandrola is chief cardiology correspondent for theheart.org | Medscape Cardiology.

European Heart Rhythm Association (EHRA) 2018. Presentations 42 and 43. Presented March 18, 2018.

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