Left Atrial Volume Index, Left Ventricular Outflow Tract Gradient, and Incident Atrial Fibrillation in Hypertrophic Cardiomyopathy

Background Atrial fibrillation (AF) is a common complication of hypertrophic cardiomyopathy (HCM). Whether left atrial volume index (LAVI) or resting left ventricular outflow tract (LVOT) gradient better identifies patients who develop AF is unresolved. Objectives To compare baseline LAVI and resting LVOT gradient as predictors of incident AF in HCM. Methods We retrospectively studied 777 patients with HCM identified by ICD‐10 code I42.1 (obstructive hypertrophic cardiomyopathy). Patients with pre‐existing AF or atrial flutter were excluded, leaving 547 patients. The primary exposure was baseline LAVI (available in 167 patients; 25 incident AF events), analyzed per 10‐mL/m 2 increment. Incident AF was defined as new AF, AF hospitalization, or cardioversion after the index date, and evaluated using Cox models. Secondary analyses assessed LVOT gradient, LAVI tertiles, time‐varying mavacamten exposure, and competing risks. Results During a median follow‐up of 2.31 years, 60 patients developed incident AF. LAVI was independently associated with incident AF in the prespecified model adjusted for age, sex, and hypertension (adjusted HR per 10 mL/m 2 , 1.27; 95% CI, 1.03–1.57; p = 0.025). AF risk increased across LAVI tertiles (log‐rank χ 2 = 9.48; p = 0.0087). Resting LVOT gradient was also independently associated with incident AF after the same adjustment (HR per 10 mm Hg, 1.07; 95% CI, 1.00–1.15; p = 0.042; n = 190, 26 events). In a head‐to‐head model, neither association remained significant. Conclusions In HCM, LAVI and resting LVOT gradient were each independently associated with incident AF, and neither remained significant when modeled together. LAVI may serve as a practical echocardiographic marker to refine AF risk assessment.