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

Abstract

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/m² 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/m², 1.27; 95% CI, 1.03-1.57; p = 0.025). AF risk increased across LAVI tertiles (log-rank χ² = 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.