Interatrial block in hypertrophic cardiomyopathy: Associations with left atrial remodeling and adverse atrial outcomes

Background Interatrial block (IAB) has been associated with atrial fibrillation (AF) and stroke in broader cardiovascular populations. Whether these associations extend to hypertrophic cardiomyopathy (HCM) and how IAB relates to underlying left atrial (LA) remodeling remain unknown. Objective This study aimed to investigate the prevalence, morphofunctional correlates, and prognostic value of IAB in patients with HCM. Methods This multicenter study included 259 patients with HCM without a history of AF/stroke. IAB was defined by a P-wave duration of >120 ms. Associations between morphologic and functional parameters of the LA and IAB were assessed using cardiac magnetic resonance imaging. The primary composite endpoint was new-onset AF, transient ischemic attack, or ischemic stroke. Results IAB was present in 10% of the cohort. Patients with IAB exhibited larger LA diameter (median 47.4 vs 43.2 mm; <ani:em>P</ani:em> =.022), larger indexed maximum LA volume (median 52.5 vs 46.9 mL/m²; <ani:em>P</ani:em> =.043), impaired LA ejection fraction (median 48% vs 51%; <ani:em>P</ani:em> =.043), reduced LA reservoir strain (median 22.0% vs 29.3%; <ani:em>P</ani:em> =.018), and reduced LA conduit strain (median 8.3% vs 12.1%; <ani:em>P</ani:em> =.012). During a median 5.8-year follow-up, IAB was independently associated with a 2-fold increased risk of the composite endpoint (hazard ratio 2.11; 95% confidence interval 1.13–3.95; <ani:em>P</ani:em> =.019) and new-onset AF (hazard ratio 2.10; 95% confidence interval 1.07–4.16; <ani:em>P</ani:em> =.031). Conclusion In patients with HCM, IAB is associated with significant LA structural and functional impairments, indicative of advanced atrial cardiomyopathy. Its presence was independently associated with an increased risk of incident AF and stroke, suggesting its value as a simple, accessible electrocardiographic marker for enhanced risk stratification.