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.