Role of His pacing: Better option than BiV pacing?
His bundle pacing (HBP) has been considered as an alternative to RV
pacing and in patients with bundle branch block with indication for BIV
pacing or as a rescue strategy in failed LV lead implantation. It is
frequently possible with HBP to recruit the native conducting system.
The mechanisms for the reduction in QRS duration with HBP remain to be
fully elucidated but may include recruitment of fibers distal to the
site of delay, longitudinal dissociation, capture attributable to higher
pacing outputs, and hyperpolarizing dormant His bundle
tissue56. In the His Resynchronization Versus
Biventricular Pacing in Patients With Heart Failure and Left Bundle
Branch Block trial57, Arnold et al. have conducted a
study on patients with heart failure and left bundle branch block
referred for conventional BIV pacing and using noninvasive epicardial
electrocardiographic imaging to identify patients in whom His bundle
pacing shortened left ventricular activation time. In these patients,
the authors compared the hemodynamic effects of His bundle pacing
against biventricular pacing. In 18 of 23 patients, left ventricular
activation time was significantly shortened by His bundle pacing. In the
17 patients who had a complete electromechanical dataset, His bundle
pacing was more effective than biventricular pacing at delivering
ventricular resynchronization: greater reduction in QRS duration (-18.6
ms; 95% confidence interval [CI]: -31.6 to -5.7 ms; p = 0.007),
left ventricular activation time (-26 ms; 95% CI: -41 to -21 ms; p
=0.002), and left ventricular dyssynchrony index (-11.2 ms; 95% CI:
-16.8 to -5.6 ms; p < 0.001). His bundle pacing also produced
a greater acute hemodynamic response (4.6 mm Hg; 95% CI: 0.2 to 9.1 mm
Hg; p = 0.04). The authors concluded that His resynchronization delivers
better ventricular resynchronization, and greater improvement in
hemodynamic parameters, than biventricular pacing.
Lustgarten et al58, in his crossover comparison study
between HBP and BiV pacing, HBP have shown that the effect of His pacing
is equivalent to BIV pacing.
Twenty-nine patients were enrolled and were implanted with RA pacing
lead, RV defibrillation lead, LV lead via the coronary sinus, and HBP
lead. His and LV leads were plugged into the LV port via a Y-adapter.
After successful implant, patients were randomized in single
patient-blinded fashion to either HBP or BIV pacing. There was no
difference between the two groups. After 6 months, patients were crossed
over to the other pacing modality and followed for another 6 months. 21
patients (72%) in the HIS pacing group demonstrated QRS narrowing at
implant. Clinical outcomes (quality of life, New York Heart Association
functional class, 6-minute hall walk test, LV ejection fraction) were
significantly improved for both pacing modes compared with baseline
measures. The HIS Sync trial59 is the first trial that
compared His pacing to BIV pacing in patients with heart failure and
LBBB. In this trial the average LVEF was 28%, and QRS width 168 +/-18
ms with 35 patients having left bundle branch block pattern,2 patients
with right bundle branch block and 3 patients with RV paced rhythm. 21
patients were randomized to His-CRT and 20 patients to BiV-CRT. Baseline
characteristics were pretty much similar between the two groups except
that LVEF was significantly lower among patients in the His-CRT group
(median 26.3%) compared with patients in the BiV group (30.5%) with a
p value of 0.011. 48% of patients in the His-CRT group and 26% of
patients in the BiV group crossed over. The most common reasons for
crossover were inability to correct QRS width (5 patients) in the His
pacing group and suboptimal venous anatomy (4 patients) in BiV group.
Using intention-to-treat analysis, the QRS duration was significantly
reduced with His pacing (172+/- 16 ms to 144+/- 30 ms; p = 0.002) but
not with BiV pacing (165 +- 18 ms to 152 +-30 ms; p=0.11). This
difference was not significant when comparing both groups (p= 0.42).
There was similar improvement in LVEF at a median follow up of 6.2
months (26.3% to 31.9%; p < 0.001 in the His pacing group)
and (30.5% to 34.0%; p<0.001 in the BIV pacing group). The
HIS SYNC trial did not show any difference between HIS pacing and BIV
pacing in terms of electrical and echocardiographic parameters keeping
in mind that the cross over rate was high and that could have impacted
treatment efficacy.