Left bundle branch area pacing in CRT: importance of preserving paced QRS with LBBAP morphology to ensure better response to therapy

Background

Conduction system pacing through the left bundle branch area (LBBAP) has emerged as an effective alternative to biventricular pacing (BiVp) for cardiac resynchronization therapy (CRT). Although multiple studies have demonstrated its non-inferiority or even superiority over BiVp, the long-term impact of maintaining a paced QRS with LBBAP morphology has not been systematically evaluated.

Methods

We retrospectively analyzed 49 CRT patients who received successful LBBAP in the CONSYST-CRT trial, either by randomization or by crossover after failed BiVp. Paced QRS morphology was assessed on 12-lead ECG at 15 days, 6 months, and 12 months.

LBBAP morphology was defined as a paced QRS showing qR, Qr, or rsR′ in V1, or a narrow QRS (<120 ms) when these patterns were absent. Paced QRS not meeting these criteria were classified as DSP morphology (Figure 1). CRT response was defined as >5% absolute LVEF increase without death or transplantation; worsening was defined as heart failure-related death or ≥5% LVEF reduction at 12 months.

Results

At 12-month follow-up, 39 patients (80%) maintained an LBBAP QRS morphology and 10 (20%) presented DSP. The proportion of DSP morphology increased over time: 6/49 (12%) at 15 days, and 10/49 (20%) at both 6 and 12 months. Mean ΔLVEF was similar in the LBBAP group (15±10 ms) compared with DSP (10±13 ms; p = 0.3). At 12 months, the percentage of ventricular pacing was 98±2% for both groups.

At 12 months, CRT response was significantly higher in patients maintaining LBBAP morphology (34/39, 87%) than in those with DSP (5/10, 50%; OR 6.8, 95% CI 1.03–45, p = 0.02). Worsening occurred in 1/39 LBBAP patients (3%) vs 3/10 DSP (30%; OR 11.7, 95% CI 1.4–101, p = 0.023).

Conclusion

Loss of LBBAP QRS morphology may occur within the first six months after implantation. Preserving this morphology is crucial to maintain CRT efficacy and optimize clinical outcomes. Patients developing DSP morphology during follow-up should be closely monitored to assess clinical and echocardiographic response and determine the need for device reprogramming or lead revision.Baseline CharacteristicLBBAP (left) DSP (right)