CT protocols and image analysis
CT was performed within the 3 weeks before CA. Early and late-phase cardiac CT was conducted in the prone position using a 128-section helical CT scanner (Somatom Definition AS, Siemens Healthcare GmbH, Erlangen, Germany). Contrast material (Iopamiro®, 370 mg of iodine/ml, Bracco Imaging, Milan, Italy) was injected intravenously at a dose of 25.9 mg/kg body weight/s for 12-14 s. Early-phase prone-position CT (early-pCT) was initiated 5 s after the region of interest in the ascending aorta reached 160 Hounsfield units. Late-pCT was started 30 s later. Once the contrast was visualized, a breath-hold instruction was provided to the patient, and CT was initiated. After CT, the patients were observed for at least 15 min for the detection of any contrast medium-related side effects, such as a rash, nausea, or abnormal blood pressure. Three-dimensional CT images were reconstructed for the left atrium (LA) and LAA. All CT images were reviewed by two experienced cardiologists and one radiologist.
If no contrast defect (CD) was observed in the LAA by late-pCT, CA was performed as planned. If CDs were detected only during early-pCT but not late-pCT, CA was performed on schedule. The performance of CA was postponed in patients with CDs who were found on late-pCT; in these patients, we changed or increased the anticoagulant dose and performed a careful follow-up at our outpatient clinic. CT angiography was repeated after several months of altered anticoagulation therapy. If the subsequent late-pCT revealed the absence of CDs in the LAA, CA was performed.