Diagnosis of left atrial appendage thrombus using cardiac computed tomography: new insights from thrombi locations

Background Cardiac computed tomography (CCT) is an emerging non-invasive modality for assessing left atrial appendage (LAA) thrombus, but the results were conflicting. Our study aims to evaluate the accuracy of CCT for detecting LAA thrombus in patients undergoing catheter ablation of atrial fibrillation (AF), using transesophageal echocardiography (TEE) as the reference standard. Methods From May 2017 to December 2022, 726 patients (male: 60.2%, age: 61±11 years) who had both TEE and CCT before catheter ablation of AF were retrospectively included. The CCT protocol consisted of one angiographic phase and one delayed scan 30 seconds later. LAA thrombi were defined as solid masses on TEE or persistent defects on CCT. The thrombus dimension and location, the LAA filling and emptying flow velocity were assessed by TEE. Results Of the 57(7.9%) patients with LAA thrombi identified by TEE, 29(50.9%) were located at the LAA ostium, and 28(49.1%) were in the LAA. The former showed higher motility following blood flow and heartbeats than the latter. The CCT detected 14(48.3%) of the LAA-ostium thrombi but 25(89.3%) of those in the LAA ( p = 0.001). The LAA-ostium thrombi with the LAA mean flow velocity higher than 0.35m/s and maximum diameters shorter than 10mm were more prone to have CCT false-negative results. Conclusion For patients undergoing catheter ablation for AF, CCT with a 30s delay scan is less sensitive to LAA thrombi than TEE, especially LAA-ostium thrombi with smaller sizes and higher LAA flow velocity. Clinical perspective section What are new? Over half of the LAA thrombi were located at the LAA ostium. The CCT was less sensitive to the LAA-ostium thrombi with smaller sizes and higher LAA flow velocity. What is the clinical implication? 1. The CCT using a 30s delay scan did not reliably exclude the LAA thrombi for the patients scheduled for pulmonary vein isolation, especially those located at the LAA ostium.