Computed Tomography–Derived Left Atrial Intramyocardial Fat and Low‐Voltage Zones in Atrial Fibrillation

Introduction Left atrial low‐voltage zones (LVZs) are associated with atrial fibrosis and arrhythmia recurrence after atrial fibrillation (AF) ablation and are thought to underlie many recurrences despite durable pulmonary vein isolation. However, noninvasive markers of the arrhythmogenic atrial substrate remain poorly characterized. We sought to investigate the association between computed tomography (CT)–derived left atrial intramyocardial fat (inFAT) and electroanatomically defined LVZs. Methods and Results In this single‐center retrospective study, 145 consecutive patients undergoing first‐time radiofrequency AF ablation underwent preprocedural dual‐source CT and high‐density left atrial voltage mapping in sinus rhythm. LVZs were defined as contiguous regions with bipolar voltage < 0.5 mV. ADAS 3D post‐processing was used to quantify total inFAT, dense inFAT, and fat–myocardial admixture. LVZs were identified in 51 patients (35.2%). Compared with patients without LVZs, those with LVZs had a higher prevalence of persistent AF (58.8% vs. 17.0%; p < 0.001) and a greater left atrial volume index (LAVi) (74.41 [64.87–99.50] vs. 62.99 [52.78–74.73] mL/m 2 ; p < 0.001). Patients with LVZs also demonstrated larger volumes of total inFAT, dense inFAT, and fat–myocardial admixture, accompanied by lower radiodensity values of total and dense inFAT. In multivariable logistic regression analysis, persistent AF (adjusted odds ratio [OR]: 5.389; 95% confidence interval [CI]: 2.162–13.433; p < 0.001) and dense inFAT volume (adjusted OR: 3.439; 95% CI: 1.107–10.677; p = 0.033) remained independently associated with the presence of LVZs, whereas LAVi did not. Among the CT‐derived fat metrics, only dense inFAT retained an independent association with LVZs after adjustment for clinical covariates. Conclusion CT‐derived dense inFAT was independently associated with left atrial LVZs and may represent a novel noninvasive marker of the arrhythmogenic atrial substrate in AF. Prospective studies are warranted to determine its role in substrate‐guided ablation strategies and risk stratification.