Introduction: Left bundle area pacing is a novel conduction system technique that is rapidly expanding. When the left bundle branch (LBB) alone is captured the 12-lead ECG shows an R prime in lead V1 indicative of delayed right ventricular activation. This is usually seen in unipolar pacing. Right septal myocardial capture can be achieved by anodal stimulation. This overcomes the delay in right ventricular activation. Whether overcoming this delay in right ventricular activation has positive effects on cardiac function is unknown and has never been investigated. We sought to address whether overcoming delayed right ventricular activation is associated with any haemodynamic benefit.
Methods: Patients were recruited from our pacing clinic and before attempting left bundle branch pacing (LBBP). We reviewed the 12-lead electrocardiograms of all patients to distinguish LBB-only capture from LBB plus right septal myocardial capture. With LBB-only capture there is an R prime in lead V1, this is eliminated when right septal capture is achieved by anodal stimulation. We selected patients who demonstrated both types of capture. High precision haemodynamic protocol was used to measure systolic blood pressure change with each capture type compared to a reference baseline. We undertook a within-patient comparison of QRS duration, pacing threshold and systolic blood pressure between the two types of capture.
Results: 15 patients with permanent LBBP demonstrated both LBB-only capture and LBB plus anodal capture and were included in the study. The average age was 68 ± 11 years and 11 (73%) were male. Bradycardia was the pacing indication in 3 (20%) patients, heart failure in 11 (73%) and pre-TAVI in 1 (7%). LBB plus right septal capture was associated with significantly narrower QRS duration compared to LBB-only capture (-11.7 ms; 95% CI, -15.7 to -7.6 ms; p<0.0001). However, LBB plus right septal capture required higher pacing outputs, typically seen in bipolar pacing configuration. The mean threshold with LBB-only capture was 0.69 V ± 0.25 at 0.4 ms, and LBB plus right septal capture was 3.28 V ± 2.16 at 0.4 ms; the difference was statistically significant (2.6V; 95% CI, 1.4–3.8 V; p=0.0004). Despite the narrower QRS, there was no significant difference observed in systolic blood pressure between the two capture types (-0.96 mmHg; 95% CI, -3.3–1.4 mmHg; p>0.05) (Figure 1).
Conclusion: Left bundle pacing achieves left bundle branch capture at a low output, but this is associated with delayed right ventricular activation. Anodal stimulation can be used to achieve right septal capture, and lead to earlier activation of the right ventricle. However, this requires significantly higher outputs and does not offer any haemodynamic advantage. This has important implications for device programming.
