Detection of left atrial thrombus in patients with mitral stenosis and atrial fibrillation: retrospective comparison of two-phase computed tomography, transoesophageal echocardiography and surgical findings.

Objective: This retrospective study aims to assess the accuracy of two-phase computed tomography (CT) and transoesophageal echocardiography (TEE) for the detection of left atrial (LA) thrombus in patients with mitral stenosis (MS) and atrial fibrillation (AF), by using intraoperative findings as the reference standard.

Methods: Preoperative two-phase CT and intraoperative TEE were performed in 106 patients with MS and AF. The ratio (LAA/AAL) of Hounsfield units (HU) in the LA appendage (LAA) to the ascending aorta (AA) was calculated on the late-phase CT image.

Results: LA echodense masses on TEE and LA filling defects on two-phase CT were observed in 29 and 39 patients, respectively. Thirty-five LA thrombi were identified at surgery in 27 patients. Compared with the intraoperative findings, per-patient sensitivity, specificity, positive and negative predictive values of two-phase CT were 100 %, 85 %, 69 % and 100 %, and those by using TEE were 93 %, 95 %, 86 % and 97 % in detecting LAA thrombus. After adopting the cut-off value of 0.5 for the LAA/AAL HU ratio, the specificity and positive predictive value of two-phase CT were increased to 96 % and 90 %, respectively.

Conclusion: Two-phase CT with a cut-off value of LAA/AAL HU ratio of 0.5 provides high performance for the detection of LAA thrombus.

Key Points: • Accurate detection of left atrial appendage (LAA) thrombus is extremely important. • However artefacts from flow effects influence both CT and ultrasound findings. • Two-phase ECG-gated CT offers new insight into thrombus detection. • Analysis of aortic/atrial opacification helps differentiate LAA thrombus from artefact at CT.