Dimensions of the left atrium (LA) are contingent upon specific phase of the cardiac cycle. Most cardiac CT protocols enable visualization of the left ventricle and associated structures rather than the left atrium. [1-3]However, atrial systole and diastole are not the same as the corresponding ventricular phases. We therefore aimed to: 1) assess optimal reconstruction phases for visualization of LA and left atrial appendage (LAA), and 2) evaluate differences in atrial dynamics among patients with paroxysmal versus persistent atrial fibrillation (A.Fib).

Patients were retrospectively identified who underwent multiphase ECG-gated cardiac CT for A.Fib catheter ablation or LAA occlusion device planning. All CT were performed on dual-source SOMATOM Definition scanners (Siemens Healthcare). Reconstructions were performed throughout the cardiac cycle (0-95%) at 5% increments. Quantitative measurements were performed utilizing TeraRecon Aquarius workstation (iNtuition, Ver.4.4.13) (Fig. 1). The LAA ostium was defined as the plane connecting the pulmonary vein ridge superiorly to the inferior junction of the left atrium or LAA at the left circumflex artery. Maximal and minimal...

A total of 36 patients (mean age: 75.7±11.1 years, 72% males) were included, with either paroxysmal (n=24) or persistent (n=12) A.Fib. Optimal CT reconstruction phases for visualization of the LA/LAA were observed during 40-50% and 0-10% R-R interval for atrial diastole and systole, respectively, among most patients (Fig. 2). These are very different from optimal phases in standard cardiac CT that targets coronary arteries and left ventricle. Moreover, a significant variability in LAA dimensions was observed among patients with paroxysmal versus persistent A.Fib (p <0.05)...

CT scanning protocols for planning of LAA occlusion should be designed to target the expected phases of atrial systole and diastole.

1. Oda S, Honda K, Yoshimura A, et al.256-Slice coronary computed tomographic angiography in patients with atrial fibrillation: optimal reconstruction phase and image quality.Eur Radiol2016;26:55-63. 2. Meyer M, Haubenreisser H, Schoepf UJ, et al.Radiation Dose Levels of Retrospectively ECG-Gated Coronary CT Angiography Using 70-kVp Tube Voltage in Patients with High or Irregular Heart Rates.Acad Radiol2017;24:30-7. 3. Lee AM, Beaudoin J, Engel LC, et al.Assessment of image quality and radiation dose of prospectively ECG-triggered adaptive dual-source coronary computed tomography angiography (cCTA) with arrhythmia rejection algorithm in...