Introduction: Transesophageal echocardiography (TEE) is routinely performed before catheter ablation of atrial tachyarrhythmias to rule out the presence of possible left atrial thrombi. However, data to support this practice are scarce.

Methods: We analyzed consecutive pre-procedural TEE in a high-volume electrophysiology center for the presence of left atrial thrombi and a relevant flow reduction in the left atrial appendage (LAA) defined as LAA sludge or pronounced spontaneous echo contrast. Possible predictors of reduced flow were recorded and compared in a multivariate logistic regression analysis.

Results: 1676 TEE in 1670 consecutive individual patients were included (1122 before pulonary vein isolation (PVI), 436 before atrial flutter ablation, 166 before other EP studies in patients with a history of atrial tachyarrhythmias). 555 patients (33%) were female, mean age was 63 ± 12 years and BMI was 27 ± 5 kg/m2. Nine patients (0.5%) had an LAA thrombus on pre-procedural TEE. Ninety-five further patients (5.7%) had a relevant reduction in LAA flow as characterized by LAA sludge or spontaneous echo contrast. While a higher CHA₂DS₂-VaSc-Score was associated with the presence of LAA sludge and LAA thrombus (p=0.01), no further clinical parameters such as cardiac comorbidities or choice of oral anticoagulation agent were independently predictive of reduced flow velocities or thrombus in a logistic regression model. Importantly, LAA thrombi also occurred in patients with a CHA₂DS₂-VaSc-Score ≤ 1 (n=1) or in sinus rhythm (n=2). Of note, 6 out of 9 patients with a LAA thrombus were anticoagulated with phenprocoumon.

Conclusion: LAA thrombus is a rare occurrence before an elective catheter ablation. In patients with CHA₂DS₂-VaSc-Score ≤ 1 the likelihood of LAA thrombus is so low (0.2%) that it may be considered to give up routine TEE before an EP study/ablation.