Prior to atrial fibrillation (AF) ablation, computed tomography angiography (CTA) is increasingly used for left atrial appendage (LAA) thrombus detection. LAA filling defects on CTA may represent thrombus or incomplete contrast mixing with blood. A pre-bolus of contrast material with delay before the CTA contrast bolus can help distinguish between thrombus and incomplete contrast mixing. We present results from a double-contrast, single-phase CTA protocol used in our daily clinical practice. In patients who underwent AF ablation between 2011 and 2015, double-contrast, single-phase CTA was performed prior to ablation. Two contrast boluses (30 and 70 ml) with 25-s interbolus delay were administered followed by prospectively triggered cardiac CTA. Only patients with left atrial (LA) or LAA filling defects underwent transesophageal echocardiography (TEE) to rule out thrombus. Prior to ablation, 605 CTA-scans were performed (median radiation dose: 3.1 mSv). In 579 CTA-scans (95.7 %), the LA and LAA completely filled with contrast. In 26 CTA-scans (4.3 %) the LAA showed a filling defect whereby thrombus could not be excluded. In 2 of those 26 patients (7.7 % and 0.3 % of the total population), TEE verified LAA thrombus. Low-risk LAA filling defects on CTA (n = 7/26) with an inhomogeneous aspect, Houndsfield Unit values >100, and an indefinite border were all caused by incomplete contrast mixing. No thromboembolic complications occurred perioperatively or during 6 months follow-up. Prior to AF ablation, incidence of LAA filling defects on double-contrast, single-phase CTA is low. TEE remains warranted in all but low-risk filling defects to rule out thrombus.
Keywords: Atrial fibrillation; Catheter ablation; Computed tomography angiography; Left atrial appendage thrombus.