Optimizing left atrial appendage imaging: the diagnostic value of left lateral decubitus cardiac CT angiography

Background Cardiac computed tomography angiography (CCTA) is widely used to detect left atrial appendage (LAA) thrombus before catheter ablation; however, the conventional biphasic supine (BS) CCTA doubles radiation exposure. This study evaluated whether single-phase left lateral decubitus (LLD) CCTA can maintain diagnostic accuracy while reducing radiation dose. Methods We retrospectively included 114 patients with atrial fibrillation who underwent CCTA between December 2022 and December 2024 (BS group, n = 57; LLD group, n = 57). Transesophageal echocardiography served as the reference standard. Two experienced radiologists independently reviewed each phase of the CCTA images for thrombus detection. We assessed the distribution pattern of contrast enhancement in the LAA during the arterial phase in the supine position and compared LAA filling, diagnostic performance, and effective radiation dose between the BS and LLD protocols. Result In the early arterial phase of the BS group, contrast attenuation in the LAA progressively decreased from the base toward the apex. The LLD position significantly improved contrast agent filling in the left atrial appendage apex (median 444.8 HU vs. 70.3 HU, Z = 8.10, p < 0.001) and reduced the early filling defect rate from 28% to 8.8% ( p < 0.001) compared to the arterial phase in the BS group. TEE confirmed LAA thrombus in 13 patients (11%). For LLD-CCTA, sensitivity was 100% (95% CI, 61–100), specificity was 0.94 (95% CI, 0.87–0.97), PPV was 0.70 (95% CI, 0.40–0.89), and NPV was 1.00 (95% CI, 0.92–1.00)—performance that was not statistically inferior to the biphasic protocol ( p = 0.35). The mean effective dose was nearly halved, from 7.84 ± 2.44 mSv to 3.89 ± 1.26 mSv ( p < 0.001). Conclusion Single-phase LLD-CCTA maintains diagnostic accuracy while reducing radiation exposure by approximately 50% and streamlining workflow. These advantages support prospective, multicenter validation before considering routine clinical adoption.