Mixed Results from Cardiac Resynchronization Trials Challenge Left Bundle Branch Pacing as BiV Alternative
Key Insights
Recent randomized controlled trials present conflicting evidence on left bundle branch area pacing (LBBAP) versus traditional biventricular pacing for cardiac resynchronization therapy, with operator experience emerging as a critical factor.
The LECART trial demonstrated superior outcomes with LBBAP, primarily driven by reduced device-related complications requiring surgical reintervention, while the LEFT-BUNDLE-CRT trial failed to establish noninferiority.
Extended follow-up data from multiple studies suggest that while conduction-system pacing shows promise, biventricular pacing remains the established first-line therapy with the strongest evidence base.
Three pivotal studies presented at the European Heart Rhythm Association (EHRA) Congress 2026 in Paris have provided new insights into left bundle branch area pacing (LBBAP) as an alternative to conventional biventricular pacing for cardiac resynchronization therapy (CRT), revealing both promise and limitations for this emerging technique.
The evidence continues to evolve around conduction-system pacing, with recent trials offering nuanced rather than definitive conclusions about its role in clinical practice. According to Elena Arbelo, MD, PhD, from Hospital Clínic de Barcelona and chair of EHRA's advocacy and quality improvement committee, "We now have randomized data showing that [LBBAP] is a very credible CRT option, with procedural advantages in some settings and clinical outcomes that are at least broadly comparable to BiV-CRT in selected populations."
LECART Trial Shows Procedural Advantages
The LECART trial, conducted at 11 Belgian centers with extensive experience in both conduction-system and biventricular pacing, enrolled 168 patients with heart failure with reduced ejection fraction, wide QRS, and no right bundle branch block. Patients were randomized to receive either LBBAP using stylet-driven leads or conventional biventricular pacing.
Results demonstrated a significant advantage for LBBAP in the primary composite endpoint of all-cause death, hospitalization for heart failure, device-related complications requiring surgical reintervention, or failure to deliver CRT at one year. The endpoint occurred in 12% of LBBAP patients compared to 25% in the biventricular pacing group (HR 2.14; 95% CI 1.01-4.52).
The benefit was primarily driven by fewer complications requiring reintervention—2% with LBBAP versus 15% with biventricular pacing (OR 6.76; 95% CI 1.48-30.97). LBBAP also demonstrated procedural efficiency advantages, with shorter median procedure time (76 vs 98 minutes) and fluoroscopy time (9 vs 12 minutes; P = 0.007 for both).
Jean-Benoît le Polain de Waroux, MD, PhD, from AZ Sint-Jan (search) in Bruges, who presented the findings, concluded that "Left bundle branch area pacing appears to provide an effective and practical strategy for cardiac resynchronization."
LEFT-BUNDLE-CRT Falls Short of Noninferiority
The LEFT-BUNDLE-CRT trial, conducted at 11 Spanish centers and published simultaneously in the European Heart Journal, randomized 175 patients with left bundle branch block and class I or IIa guideline indications for CRT. The study aimed to establish noninferiority of LBBAP compared to biventricular pacing.
At six months, CRT response—defined as improved clinical composite score or at least 15% reduction in left ventricular end-systolic volume—was observed in 90% of LBBAP patients and 95% of biventricular pacing patients (RR 0.95; 95% CI 0.88-1.02). However, this difference failed to meet noninferiority criteria (P = 0.12) because the lower bound of the confidence interval fell below the predetermined 0.90 margin.
Notably, an on-treatment analysis accounting for high crossover rates did demonstrate noninferiority of LBBAP. Clinical outcomes including heart failure hospitalizations, cardiovascular events, ventricular arrhythmias, and mortality showed no significant differences between groups.
Long-term His-Bundle Pacing Data
Extended follow-up from the His-Alternative I pilot study, with median duration of 5.3 years, provided important insights into the durability of conduction-system pacing. The analysis included 50 patients with symptomatic heart failure, LVEF ≤35%, and left bundle branch block.
His-bundle pacing was associated with more lead revisions (37% vs 3%; P = 0.003) and generator replacements (47% vs 10%; P = 0.005) compared to biventricular pacing overall. However, patients with low implant thresholds (≤2.5 V per millisecond) achieved results similar to biventricular pacing.
Long-term mortality or heart failure hospitalization risk showed no difference between groups (HR 0.32; 95% CI 0.07-1.49), with similarly high echocardiographic response rates in both His-bundle and biventricular pacing groups (89% and 90%, respectively).
Conflicting Evidence from Recent RCTs
The complexity of interpreting conduction-system pacing evidence was further highlighted by two additional randomized trials published in JAMA Cardiology—HeartSync-LBBP and PhysioSync-HF—which produced conflicting results.
The Chinese HeartSync-LBBP trial showed left bundle branch pacing reduced the risk of all-cause death or heart failure hospitalization versus biventricular pacing (8% vs 28%; HR 0.26; 95% CI 0.12-0.57) over 36 months of follow-up. In contrast, the Brazilian PhysioSync-HF trial demonstrated worse outcomes with conduction-system pacing, failing to meet noninferiority criteria and showing higher mortality rates.
Kenneth Ellenbogen, MD, from Virginia Commonwealth University and a HeartSync-LBBP co-author, attributed the divergent results primarily to operator experience. In PhysioSync-HF, 42.8% of procedures were performed by operators with fewer than 40 prior conduction-system pacing cases, while HeartSync-LBBP operators had performed more than 285 procedures each.
Clinical Implications and Future Directions
Despite growing evidence, current European Society of Cardiology guidelines maintain that "especially in CRT candidates with LBBB, biventricular pacing has more solid evidence of efficacy and safety, and therefore remains first-line therapy."
Arbelo emphasized caution in interpreting current evidence: "These trials are important, but they do not yet justify a one-size-fits-all conclusion that LBBAP should replace conventional CRT across the board." She noted the need for "larger studies with longer-term follow-up and 'proper outcomes' (CV mortality, HF admissions, etc)."
The expert consensus suggests the field is evolving toward individualized CRT approaches. "The real future is probably individualized CRT, where the best modality depends on anatomy, conduction pattern, operator expertise, and the ability to achieve a durable result," Arbelo explained.
Biventricular pacing continues to play an important role as "the best-established CRT strategy with the longest evidence base," remaining appropriate for many patients and centers. The emerging paradigm positions conduction-system pacing as taking "a growing share, especially in centers with strong expertise, but not toward elimination of BiV-CRT."
As the evidence base continues to mature, the success of conduction-system pacing appears highly dependent on technical expertise and patient selection, with operator experience emerging as a critical determinant of outcomes.