In majority of patients with atrial fibrillation (AF), thrombus forms in the left atrial appendage (LAA).However the relation of LAA morphology with LAA thrombus is unknown. Most studies have shown that CHADS2 , CHA2DS2-VASc scores, left ventricular systolic dysfunction, dense spontaneous echo contrast (SEC), low LAA peak flow velocities, and complex aortic plague are related to thromboembolic risk.

This study(1) demonstrates that complex LAA morphology as assessed by 3D-TEE (3-dimensional trans-esophageal echocardiogram) imaging is associated with the presence of LAA thrombus This increased risk is present even after adjusting for other clinical risk factors and blood stasis suggesting that that LAA morphology might be a congenital risk factor for LAA thrombus formation in patients with AF.

564 Patients who were candidates for catheter ablation for symptomatic drug-resistant AF were enrolled in the study. On the day before ablation, TEE examinations were performed, with a sequential TEE 1 year later in patients who had maintained sinus rhythm for at least 1 year after catheter ablation. In this time frame, patients maintained a therapeutic INR.

Transthoracic echocardiogram measured the following: left ventricular end-diastolic volume, end-systolic volume, and ejection fraction (LVEF, modified Simpson’s). TEE measured the following: spontaneous echo contrast (SEC), LAA emptying flow and LAA emptying flow velocity. LAA morphology was measured using 3D TEE. Blood samples were also obtained to measure plasma high sensitivity CRP, BNP concentration, and pro-thrombin time/INR at the time of the TEE.

The number of LAA lobes was significantly higher than that in patients without LAA thrombus. Majority of patients with LAA thrombus had 3 or more LAA lobes. There was also a higher degree of SEC and lower LAA emptying velocity in patients with 3 or more LAA lobes. This study showed that, in comparison with 1 or 2 lobes, an LAA with 3 lobes was 8.6 times (OR 8.6, 95 CI 1.9 – 39.8, P =0.006), 4 or 5 lobes was 10 times (OR 10, 95% CI 2.2 – 42.1, P = 0.004) and 3 or more lobes was 9.2 times (OR 9.2, 95 CI 2.0 – 41.1, P 0.004) more likely to have thrombus.

It is interesting to note that SEC and lower LVEF were identified as significant predictors for LAA thrombus formation whereas LAA volume was not a significant predictor. This study also showed that complex LAA morphology is a congenital characteristic and is not influenced by LA remodeling. This was demonstrated on sequential TEEs which revealed remodeling of the LA but there was no change in lobes.

In summary, this study showed that complex LAA morphology as assessed by 3D-TEE is associated with increased risk of LAA thrombus. In the future, analysis of LAA morphology may provide additional information in the diagnosis of LAA thrombus which would refine the formulation of medical strategies including anti-coagulation management.

Reference: 1. Yamamoto M, Seo Y, Kawamatsu N et al. Complex Left Atrial Appendage Morphology and Left Atrial Appendage Thrombus Formation in Patients With Atrial Fibrillation. Circulation Cardiovascular imaging 2014.