Introduction: Conduction system pacing in the form of His bundle pacing (HBP) can deliver more effective ventricular resynchronization compared to biventricular pacing, which translates to greater acute haemodynamic benefit. Left bundle branch pacing (LBBP) has potential advantages over HBP; capture thresholds are typically lower and it can correct left bundle branch block occurring as a result of more distal conduction system disease. A potential disadvantage of LBBP compared to His-CRT is that is does not typically capture the right bundle branch and therefore results in delayed right ventricular activation. It is not known whether this delayed activation produces important reductions in the improvements of cardiac function compared to HBP. We conducted a within-patient comparison of acute electrical and haemodynamic response to HBP, LBBP and biventricular pacing (BVP) in patients with a CRT indication.
Methods: Patients with severely impaired left ventricular systolic function and QRS duration >120 ms were recruited into the study. HBP and LBBP was delivered to all patients and BVP was also delivered to a subgroup of these patients. Conduction system capture was confirmed using standard criteria. We defined successful delivery of resynchronization as a reduction of at least 15 ms in left ventricular activation time. We assessed the acute electrical response by measuring the change in QRS duration (12-lead ECG) and ventricular activation times (ECGi, Medtronic). Acute haemodynamic response was assessed using a high precision haemodynamic protocol.
Results: 15 patients were recruited (12 male, 3 female), mean age 66.5 years (IQR 55–76), LVEF 32% (IQR 30–35) and QRS duration 172 ms (IQR 166–178). HBP and LBBP both achieved better ventricular resynchronization compared with biventricular pacing. Reduction in left ventricular activation times were significantly greater with both HBP and LBBP compared to BVP (22 ms; 95% CI, 9.8–34.2; p<0.01 for HBP, and 26.7 ms; 95% CI, 16.0–37.5; p<0.01 for LBP). The reduction in left ventricular activation times with HBP was 46 ms ± 8.6 (95% CI, 37.5–54.5). LBBP also resulted in a reduction in left ventricular activation time of 45 ± 8.5 (95% CI, 36.5–53.3). There was no significant difference between the two modalities (-2.1; 95% CI, -11.4–7.1; p=0.6). All three modalities improved acute systolic blood pressure (median increase; HBP 11.3 mmHg, LBBP 9.1 mmHg and BVP 6.7 mmHg) (Figure 1). When we compared HBP and LBBP there was a trend towards greater improvement with HBP compared to LBBP, but this did not reach statistical significance (1.05; 95% CI, -6.1–4.0; p=0.66).
Conclusion: Conduction system pacing with HBP and LBBP both have the potential to deliver more effective ventricular resynchronization compared to biventricular pacing. The delayed right ventricular activation with LBBP does not appear to significantly impact acute cardiac function. LBBP is therefore a very promising method for delivering cardiac resynchronization therapy.