Prevalence of left atrial appendage thrombi and associated risks in patients referred for atrial flutter ablation

Atrial flutter (AFL) is a common supraventricular arrhythmia, often associated with an increased risk of thromboembolic events. Current guidelines recommend catheter ablation of the cavotricuspid isthmus as first-line therapy. However, thrombotic risk assessment remains essential, particularly through transesophageal echocardiography (TEE) to detect left atrial appendage (LAA) thrombi prior to ablation. This study aimed to determine the prevalence of LAA thrombi in patients with AFL undergoing pre-ablation TEE and to identify clinical, laboratory, and echocardiographic variables associated with thrombus formation.

This retrospective, single-center, cohort study analyzed TEE reports of patients with AFL treated between 2015 and 2022 at a tertiary referral center in Brazil. Demographic, clinical, laboratory, and echocardiographic data were collected and analyzed using chi-square tests, Student's t-tests, and multivariate logistic regression. A clinical score incorporating key predictive variables was developed to improve risk stratification. Receiver operating characteristic (ROC) curves, net reclassification improvement (NRI), and five-fold stratified cross-validation were used for performance assessment.

A total of 528 patients were included (mean age: 63.9±14.2 years; 69.9% male). Pre-ablation TEE identified LAA thrombi in 18.8% of cases. Independent predictors of thrombus formation included heart failure, prior stroke/TIA, left atrial enlargement, and reduced glomerular filtration rate. The clinical score demonstrated 85.4% sensitivity (95% CI: -), 53.2% specificity (95% CI: -), and an area under the curve (AUC) of 0.726, indicating improved discriminative ability compared to the CHA₂DS₂-VASc score (87.6% sensitivity [95% CI: -], 22.2% specificity [95% CI: -]). The model achieved a positive NRI of 28.8% compared with the CHA₂DS₂-VASc score.

The prevalence of LAA thrombus was higher than previously reported in similar populations. The newly developed clinical score showed improved discriminative performance relative to the CHA₂DS₂-VASc score and may help identify high-risk patients who could benefit from pre-ablation TEE in the context of AFL.