Hemodynamics, ECG Mapping Point to His-Bundle CRT Superiority vs Biventricular Pacing

December 14, 2018

A within-patient comparison of His-bundle pacing (HBP) and biventricular (BiV) pacing for cardiac resynchronization therapy (CRT) showed electromechanical and hemodynamic differences between them that seems to explain HBP's greater CRT effectiveness, researchers say.

Pacing the His bundle led to more shortening of left ventricular activation time (LVAT) followed by greater acute hemodynamic improvement compared with conventional BiV pacing in a single-center study with 17 patients. They had standard CRT indications, including heart failure, left-bundle-branch block (LBBB), and long QRS durations.

"What we've done is show, significantly, the theoretical advantage of more effective ventricular resynchronization with His-bundle pacing does appear to translate into improvements in acute function," Zachary I. Whinnett, BM, BS, PhD, Imperial College London, told theheart.org | Medscape Cardiology.

The study, which involved only patients who had shown LVAT shortening on HBP, used noninvasive electrocardiographic imaging (ECGi) in conjunction with high-precision hemodynamic measurements to compare mechanistic effects of the two pacing strategies.

"The other interesting thing that we've shown for the first time is the relationship between the electrical and hemodynamic response, that the incremental improvement in ventricular activation time of His-bundle pacing compared with biventricular pacing correlates with the hemodynamic response," said Whinnett.

He is senior author on the study published in the December 18 issue of in the Journal of the American College of Cardiology, with lead author Ahran D. Arnold, MBBS, Imperial College London.

As their report cautions, shorter activation time and the hemodynamic boost on His-bundle CRT do not necessarily translate to similar gains over the long term. However, "previous experience with BiV pacing supports the concept that short-term resynchronization-induced improvements translate into longer-term benefits."

An accompanying editorial states that "these findings, in conjunction with a growing body of published reports on the subject, indicate that it is time to redefine CRT as an end with multiple means, one of which — His bundle pacing — is physiological, in that activation emanates from the His-Purkinje system."

That, writes Daniel L. Lustgarten, MD, PhD, University of Vermont, Burlington, "raises the possibility that non-LBBB patients may benefit from His-bundle CRT, with recently published data providing support for that expectation."

Whinnett, a coauthor on that referenced report, agreed that HBP might allow the extension of CRT to patients with heart failure without current guideline-recommended ECG prerequisites, such as prolonged QRS durations and LBBB.

Indeed, he is principal investigator for the ongoing His-Optimised Pacing Evaluated for Heart Failure Trial (HOPE-HF) double-blind crossover evaluation of HBP in a planned 160 patients with narrow QRS intervals (≤140 ms) or prolonged QRS with typical right bundle-branch (RBBB) morphology.

The current study looked at 17 patients for whom complete ECGi and hemodynamic data were available during both HBP and BiV pacing CRT sessions, plus one patient with complete hemodynamic data.

On average, the QRS durations were significantly shortened during both forms of pacing, but by 18.6 ms more on HBP (P = .007).

LVAT across 95% of activations (LVAT-95) followed a similar pattern, dropping significantly compared with intrinsic activation with both forms of pacing but more so, by 26.4 ms (P = .02), on HBP.

In line with QRS durations and LVAT-95, the left-ventricular dyssynchrony index (LVDI) fell significantly regardless of pacing method, but 11.3 ms more with HBP.

Similarly, acute systolic blood pressure rose significantly with both HBP and BiV pacing compared with standard AAI-mode pacing, but 4.6 mm Hg further on HBP (P = .04).

Shortening of LVAT-95 by HBP compared with BiV pacing was significantly correlated with the improved blood pressure response on HBP compared with BiV pacing (P = .04). But corresponding reductions in QRS duration were not significantly correlated with the blood pressure response, the group reports.

"The correlation between activation time shortening and acute hemodynamic response suggests that the improved hemodynamic response with HBP is driven by more effective ventricular resynchronization," they write.

Arnold had no relevant disclosures. Whinnett reports receiving speaker fees from Medtronic and Boston Scientific. Disclosures for the other authors are in the report. Lustgarten discloses consulting for Medtronic and Abbott Medical, serving as an advisor to Medtronic, and receiving research support from Medtronic and Abbott Medical.

J Am Coll Cardiol. 2018;72:3112-3122 and 3123-3125. Full text, Editorial

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