Diagnosis of left atrial appendage thrombus in patients with atrial fibrillation: delayed contrast-enhanced cardiac CT.

OBJECTIVES: The current reference standard for diagnosing LAA thrombi is transesophageal echocardiography (TEE), a semi-invasive technique. We aimed to devise an optimal protocol for cardiac computed tomography (CCT) in diagnosing left atrial appendage (LAA) thrombus in patients with atrial fibrillation (AF), using TEE as reference standard. METHODS: Two hundred sixty consecutive patients referred for radiofrequency ablation for AF were prospectively enrolled. All patients underwent CCT and TEE within 2 hours. The CCT protocol included one standard angiographic phase and three delayed acquisitions at 1-, 3-, and 6-min after contrast injection. Thrombi were defined as persisting defects at 6-min delayed acquisition. RESULTS: TEE demonstrated spontaneous contrast in 52 (20%) patients and thrombus in 10 (4%). In 63 patients (24%), CCT demonstrated LAA early filling defects at angiographic phase. Among them, 15 (6%) had a persistent defect at 1-min, 12 (5%) at 3-min, and 10 (4%) at 6-min. All 10 thrombi diagnosed on TEE were correctly identified by delayed CCT, without any false positives. For all phases, sensitivity and negative predictive were 100%. Specificity increased from 79% for the angiographic phase to 100% at 6-min. Positive predictive value increased from 16% to 100%. Estimated radiation exposure was 2.08 ± 0.76 mSv (mean ± standard deviation) for the angiographic phase and 0.45 ± 0.23 mSv for each delayed phase. CONCLUSION: A CCT protocol adding a 6-min delayed phase to the angiographic phase can be considered optimized for the diagnosis of LAA thrombi, with a low radiation dose. KEY POINTS: • In patients with persistent atrial fibrillation referred for ablation procedures, a cardiac CT examination comprising an angiographic-phase acquisition and, in case of filling defects, a 6-min delayed phase may help reduce the need for transesophageal echocardiography. • Cardiac CT would provide morphological and volumetric data, along with the potential to exclude the presence of thrombi in the left atrial appendage.

Feasibility of ultra-low contrast 64-slice computed tomography angiography before transcatheter aortic valve implantation: a real-world experience.

AIMS: To investigate the feasibility, image quality, and clinical implications of an ultra-low-dose contrast injection computed tomography angiography (CTA) protocol in patients scheduled for transcatheter aortic valve implantation (TAVI). METHODS AND RESULTS: Images obtained with 64-slice CT were retrospectively evaluated in 162 TAVI candidates with a body mass index (BMI) of ≤29 kg/m(2). A multiphasic, low iodine dose and BMI-adapted CM protocol was administered in all patients (BMI <22 kg/m(2): 40 mL; BMI 22-29 kg/m(2): 55 mL). All images were evaluated for image quality, vessel attenuation, and estimated radiation dose. The anatomy, diameters, perimeter, and area of the aortic annulus were assessed. Anatomy and diameters of peripheral vessels were also evaluated. Image quality of the aortic root and ilio-femoral vessels was diagnostic in all patients. Vascular attenuation was >200 HU at any vessel level. The mean diameters of the aortic annulus were 22 ± 3 mm (range: 16-28 mm) × 26 ± 3 mm (range: 20-33 mm); the mean perimeter was 77.0 ± 7.1 mm. After CTA, a total of 137 patients (84.6%) underwent TAVI. Mean estimated radiation dose was 20.2 ± 4.6 mSv. CONCLUSION: With our protocol, we achieved images of the aortic annulus and aorto-iliac anatomy of sufficient quality to allow patient selection and procedural planning for TAVI, with a substantial reduction of the amount of injected CM.