Conduction System Pacing for Cardiac Resynchronization Therapy

Abstract

Cardiac resynchronization therapy (CRT) via biventricular pacing (BiVP-CRT) is considered a mainstay treatment for symptomatic heart failure patients with reduced ejection fraction and wide QRS. However, up to one-third of patients receiving BiVP-CRT are considered non-responders to the therapy. Multiple strategies have been proposed to maximize the percentage of CRT responders including two new physiological pacing modalities that have emerged in recent years: His bundle pacing (HBP) and left bundle branch area pacing (LBBAP). Both pacing techniques aim at restoring the normal electrical activation of the ventricles through the native conduction system in opposition to the cell-to-cell activation of conventional right ventricular myocardial pacing. Conduction system pacing (CSP), including both HBP and LBBAP, appears to be a promising pacing modality for delivering CRT and has proven to be safe and feasible in this particular setting. This article will review the current state of the art of CSP-based CRT, its limitations, and future directions.

Keywords: His bundle pacing; cardiac resynchronization therapy; conduction system pacing; left bundle branch pacing.

Figure 1

Conventional BiVP-CRT using a quadripolar CS lead in a patient with ischemic cardiomyopathy. Panel (A) shows the baseline QRS with LBBB; panel (B) shows the final paced QRS obtained with BiVP; panels (C,D) show the final lead position in the 30° LAO and RAO views, respectively. CS: Coronary sinus; DF: Defibrillation; LAO: Left anterior oblique view; RAO: Right anterior oblique view. ECG sweep speed 25 mm/s.

Figure 2

Different capture patterns during HBP-CRT. The left side of the figure shows a patient with baseline LBBB (panel (A)); HBP results in LBBB correction at high outputs (panel (B)), partial LBBB correction at intermediate output (panel (C)) and selective HB capture but without LBBB correction at lower output (panel (D)). The right side shows a patient with baseline RBBB (panel (E)) shows complete RBBB correction at high output (panel (F)), partial correction at intermediate outputs (panel (G)) and selective HB capture without RBBB correction at lower outputs (panel (H)). HBED: His bundle electrogram (distal); HBEP: His bundle electrogram (proximal). Sweep speed 100 mm/s.

Figure 3

Different capture patterns during LBBAP-CRT in a patient with non-ischemic cardiomyopathy and baseline wide QRS (panel (A)). During the procedure, LVSP (panel (B)), NS-LBBP (panel (C)) and S-LBBP (panel (D)) could be observed during unipolar pacing at different outputs. Bipolar pacing with AV Interval adjusted to favor intrinsic conduction through the RBB resulted in further QRS narrowing (panel (E)). Panels (F,G) show the final lead position in the LAO (40°) and RAO (35°) projections, respectively. COI: Current of injury; DF: Defibrillation; LB: Left bundle; LVSP: Left ventricular septal pacing; NS-LBBP: Non-selective left bundle branch pacing; S-LBBP: Selective left bundle branch pacing. Sweep speed 100 mm/s.

Figure 4

Patient with dilated cardiomyopathy undergoing LBBAP-CRT. Panel (A) shows the baseline QRS (188 ms); panel (B) shows NS-LBBP and panel (C) shows S-LBBP; panel (D) shows the final paced QRS after adjusting the programmed AV delay in the device to allow intrinsic conduction through the intact patient’s RBB resulting in further QRS narrowing; panels (E,F) show the RAO and LAO 30° view of the final lead location; panel (G) shows a four-chamber echocardiographic view with the LBBAP lead tip in the subendocardium of the left ventricular septum. COI: Current of injury; DF: Defibrillation; LAO: Left anterior oblique view; LB: Left bundle; LBBAP: Left bundle branch area pacing; RAO: Right anterior oblique view; RBB: Right bundle branch. Sweep speed 100 mm/s.

Figure 5

Patient with non-ischemic cardiomyopathy undergoing HOT-CRT. Baseline LBBB (panel (A)) could be only partially corrected with HBP (panel (B)). S-HBP without bundle branch correction could be seen at low outputs (panel (C)). Adding a CS lead and pacing from the His lead 20 ms earlier than from the CS lead, a further reduction in QRS duration could be obtained (panel (E)). Panel (D) shows the paced QRS morphology from the CS lead only. Panels (F,G) show the final lead locations in the LAO and RAO views, respectively. CS: Coronary sinus; HBED: His bundle electrogram (distal). HOT-CRT: His-Optimized cardiac resynchronization therapy. Sweep speed 25 mm/s.

Figure 6

Principal studies reporting data on BiVP-CRT, HBP-CRT, and LBBAP-CRT with the total number of patients included. Asterisks indicate randomized studies [7,8,9,10,11,12,13,14,15,17,18,19,20,21,22,23,24,25,34,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,83,88,96].