Left bundle branch block in hypertrophic cardiomyopathy: marker of a more severe phenotype and worse outcome

Background

In hypertrophic cardiomyopathy current guidelines mention left bundle branch block (LBBB) only in end-stage HCM (ES-HCM), where it may guide cardiac resynchronization therapy. However, the clinical and prognostic significance of LBBB in earlier stages of HCM remains undefined.

Purpose

To evaluate the association between LBBB, clinical phenotype, and long-term prognosis in patients with HCM.

Methods

The study included 404 consecutive HCM patients and normal left ventricular (LV) ejection fraction (LVEF) (>50%) at baseline. MACE was considered as the first occurrence of sudden death (SD), ES-HCM, heart transplantation (HT), heart failure (HF)-related death

Results

Compared with patients without LBBB, the 32 patients (8%) with LBBB were older had larger left atrial diameter (Lad), greater maximal wall thickness (MWT) and a higher prevalence of significant LV outflow tract obstruction (≥30 mmHg) (overall p<0.05). During a mean follow-up of 9±7 years, 64 patients experienced MACE. These patients were younger (43±19 vs, 48±17, p=0.026) exhibited more frequent family history of SD (75 vs 46%, 0.007), more frequent LBBB (20 vs 5%, p<0.001), had larger Lad ( 48±9 vs 44±7 mm, p<0.001), and greater MWT (23±6 vs 20±5 mm, p<0.001), than those not experiencing Mace

On multivariable Cox regression analysis, Lad (HR 1.101, p<0.001), family history of SD (HR 1.186, p=0.026), and LBBB (HR 3.575, p<0.001) were independent predictors of MACE (Figure 1).

When endpoints were analyzed separately, LBBB was not associated with SD (n=27), which was independently predicted by Lad (HR 1.091, p=0.007) and MWT (HR 1.092, p=0.008) (Figure 2 , left panel). In contrast, LBBB was a strong independent predictor of HF–related outcomes (ES-HCM, HT, or HF death; n=37), with a sixfold increased risk (HR 6.025, p<0.001), together with Lad (HR 1.111, p<0.0001) (Figure 2, Right panel.

Conclusions

In patients with HCM and normal ejection fraction, LBBB identifies a distinct subgroup with a more advanced disease phenotype. Although not associated with arrhythmic events, LBBB was independently associated with a markedly increased risk of HF progression, conferring a sixfold higher risk of ES-HCM, heart transplantation, or heart failure–related death over long-term follow-up.Figure 1Figure 2