Effects of Permanent Left Bundle Branch Area Pacing on QRS Duration and Short-Term Cardiac Function in Pacing-Indicated Patients with Left Bundle Branch Block
Left bundle branch block (LBBB) is a common cardiac conduction disorder that can lead to prolonged QRS duration (QRSd), impaired cardiac function, and increased risks of atrial fibrillation (AF), heart failure, and mortality. Traditional treatments such as biventricular pacing (BiV-CRT) have shown benefits in patients with LBBB and heart failure, but a significant proportion of patients do not respond to this therapy or are unsuitable candidates due to anatomical limitations. His bundle pacing (HBP) has emerged as an alternative, but it has limitations such as higher pacing thresholds and lower R-wave amplitudes. Left bundle branch area pacing (LBBAP) has recently been introduced as a promising technique to address these challenges. This study investigates the effects of LBBAP on QRSd and short-term cardiac function in pacing-indicated patients with LBBB.
Background and Rationale
The relationship between QRSd and cardiac function has been well-established. In 1986, Burkhoff and Sagawa observed that left ventricular pressure decreased linearly as QRSd increased in a pacing experiment. Subsequent studies confirmed that LBBB or right ventricular pacing could prolong QRSd, leading to adverse cardiac outcomes. BiV-CRT has been the standard treatment for patients with LBBB and heart failure, but 30% to 40% of patients do not respond to this therapy, and an additional 10% are unsuitable candidates due to anatomical constraints. HBP has been explored as an alternative, but it has inherent limitations, including higher pacing thresholds and the inability to correct LBBB in patients with distal conduction system disease.
In 2017, Huang et al. reported the first successful case of LBBAP in a patient with LBBB and heart failure who had failed both BiV-CRT and HBP. This case demonstrated significant clinical improvement over one year of follow-up. Since then, LBBAP has been increasingly studied in patients with normal QRS complexes and symptomatic bradycardia, but its effectiveness in patients with LBBB has not been widely evaluated. This study aims to fill this gap by assessing the impact of LBBAP on QRSd and cardiac function in pacing-indicated patients with LBBB.
Methods
Consecutive pacing-indicated patients with LBBB were prospectively enrolled from the First Affiliated Hospital of Nanjing Medical University between October 2017 and December 2019. The study protocol was approved by the Hospital Institutional Review Board, and all patients provided written informed consent. The LBBAP procedure was performed as described in previous reports, with successful LBBAP defined as a unipolar paced QRS morphology presenting as a right bundle branch block pattern and QRSd ≤130 ms. Patients with successful LBBAP were implanted with dual-chamber sensing and pacing devices, while those who failed LBBAP after five attempts or exceeded 30 minutes of fluoroscopy were switched to left ventricular septum pacing (LVSP). If BiV-CRT was still indicated, a CRT pacemaker was implanted.
Baseline and LBBAP-paced electrocardiograms (ECGs) were interpreted by two cardiologists. The stimulus to peak left ventricular activation time (SPLVAT) was measured as the duration between the ventricular stimulation signal and the R peak in lead V5. Echocardiography was performed before and after the procedure to assess left atrial dimension (LAD), left ventricular end-diastolic diameter (LVEDD), left ventricular end-systolic diameter (LVESD), and left ventricular ejection fraction (LVEF). The implant depth and distance to the tricuspid attachment of the LBBAP lead were also measured.
Statistical analysis was performed using SPSS version 20.0 software. Continuous variables were expressed as mean ± standard deviation (SD) and compared using analysis of variance (ANOVA) or paired t-tests. Categorical variables were expressed as observed numbers and percentages and compared using chi-square or Fisher exact tests. All P values were two-tailed, and P values < 0.05 were considered significant.
Results
A total of 39 LBBB patients underwent attempted LBBAP, with successful LBBAP achieved in 31 (79.5%) cases. Eight patients failed LBBAP and were switched to LVSP, with two requiring CRT devices due to paced QRSd >150 ms. Among the 31 successful LBBAP patients (average age 66 ± 13 years, 16 male), the thickness of the interventricular septum (IVS) was 10 ± 1 mm. Sixteen patients had LVEF <50%, and 15 had LVEF ≥50% (7 with sinus sick syndrome [SSS] and 8 with atrioventricular block [AVB]).
In patients with LVEF <50%, QRSd significantly decreased from 175 ± 18 ms to 115 ± 8 ms (P < 0.001), and SPLVAT was 75 ± 11 ms. Patients with normal LVEF also showed significant QRSd reduction. All successful LBBAP patients were implanted with dual-chamber sensing and pacing devices, with 28 receiving both triggered and inhibited devices and 3 receiving ventricle sensing and pacing devices due to persistent AF. One patient (3.2%) experienced lead micro-perforation requiring repositioning, but no acute complications such as chest pain, pneumothorax, or pericardial effusion were encountered. The depth of the 3830 lead was 9 ± 2 mm in the IVS, and the distance from the lead tip to the tricuspid valve attachment was 21 ± 6 mm.
During a mean follow-up of 6 ± 3 months, no complications associated with LBBAP were observed. Clinical outcomes and echocardiography parameters showed significant improvement in LBBAP patients with LVEF <50%. LBBB was corrected in all LBBAP patients, with a mean QRSd reduction of 60 ± 10 ms. New York Heart Association functional class improved from 2.4 ± 0.8 to 1.7 ± 0.6, and amino-terminal pro-brain natriuretic peptide decreased from 1823 ± 1641 ng/L to 829 ± 222 ng/L (all P < 0.05). Super-response to LBBAP was observed in 6/16 patients (37.5%). Among 15 LBBAP patients with baseline normal LVEF and 8 LVSP patients with LVEF <50%, cardiac function parameters also improved, although not significantly.
Discussion
This study demonstrates that LBBAP significantly shortens QRSd and improves cardiac function in pacing-indicated patients with LBBB, particularly those with reduced LVEF. The average QRS narrowing of 60 ms in LBBAP patients surpasses the average 19 ms narrowing observed in BiV-CRT responders. The increase in LVEF in LBBAP patients (from 34.6 ± 7.9% to 45.8 ± 12.4%) also exceeds the 2% to 11% increases reported in large BiV-CRT trials. Furthermore, 37.5% of LBBAP patients with heart failure achieved super-response, compared to 16% in BiV-CRT trials.
LBBAP offers several advantages over traditional pacing methods. Unlike BiV-CRT, which combines pacing of the left ventricular epicardium and right ventricular endocardium, LBBAP utilizes the heart’s intrinsic conduction system, resulting in faster pulse propagation and superior efficacy. HBP, while also utilizing the conduction system, has limitations such as higher capture thresholds and lower R amplitudes, which LBBAP overcomes. Additionally, LBBAP can be performed with single- or dual-chamber devices, offering a better cost-effectiveness ratio.
The safety of LBBAP was also confirmed in this study. Only one patient experienced lead micro-perforation, which was successfully managed with lead repositioning. No late complications were observed during follow-up, consistent with previous reports of low complication rates in LBBAP procedures.
Conclusion
LBBAP significantly shortens QRSd and improves cardiac function in pacing-indicated patients with LBBB, particularly those with reduced LVEF. The high success rate, significant QRS narrowing, and improvement in cardiac function make LBBAP a promising alternative to traditional pacing methods. Further studies with larger sample sizes and longer follow-up periods are needed to confirm these findings and establish LBBAP as a standard treatment for patients with LBBB and heart failure.
doi.org/10.1097/CM9.0000000000001380
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