Study population
The study population consisted of 252 consecutive patients presenting for outpatient coronary computed tomography angiography (CCTA) for exclusion of coronary artery disease at 2 tertiary centers in Egypt during the period from January to July 2017. The research protocol was approved by the ethics committee, and informed consent was obtained from all patients.
The following baseline data was collected: age, gender, history of valvular heart disease, heart failure, atrial fibrillation, and history of stroke or transient ischemic attack. Echocardiograms were reviewed for left ventricular function and presence of valvular heart disease, and electrocardiograms (ECGs) were reviewed for heart rate and rhythm. Exclusion criteria for performing CCTA included contrast allergy, renal impairment (creatinine > 2 mg/dl), active asthma, and weight greater than 140 kg. Patients with a history of atrial fibrillation or frequent premature beats on ECG that may result in image artifacts were excluded from the study, as well as patients with a history of heart failure, ejection fraction less than 50%, and moderate-to-severe valvular heart disease. CT images with motion artifacts that prevented adequate analysis of the left atrium were also excluded.
Imaging
Cardiac MDCT imaging was performed using a 64-slice MDCT scanner (Aquilion 64, Toshiba Medical Systems, Japan) according to standard clinical protocol. Patients were examined in supine position, in a single breath hold, at a controlled heart rate of less than 70 beats per minute. Scanning parameters included tube current 400 mAs, potential 120 kV, rotation time 400 ms, and collimation 64 × 0.5 mm. All examinations were ECG-gated, and were conducted after administration of 50-80 ml of non-ionic iopromide contrast medium (Ultravist) at a rate of 4-6 ml/s. Axial source images were acquired in spiral mode, and two and three-dimensional reconstruction images were created at four segments at 40 to 70% of the R to R interval. The reconstructed images were processed on a separate work station (Vitrea) with multi-planar formatting and volume rendering to visualize individual heart structures with high detail. All images were analyzed by 2 expert cardiologists, who were blinded to patient history.
All images were evaluated for LA diameter and volume, as well as LAA volume, length, orifice position, and morphology. LA diameter was measured in its maximum anteroposterior dimension in axial images. LA and LAA volumes were measured from three-dimensional reconstruction images. The LAA orifice was identified as the narrowest part of the LAA opening, and its position was classified in relation of its superior aspect to the opening of the upper left pulmonary vein into high, medium, and low (above, in-line with, and below the opening of upper left pulmonary vein respectively). The LAA morphology was categorized based on Wang et al. and Kimura et al.’s previous classifications (5)(6) into 4 distinct morphological variants: windsock (having a dominant central lobe of length > 40 mm, and either secondary lobes arising in one direction or bending over 100°), chicken wing (having a dominant lobe > 40 mm with an acute bend of less than 100° in its proximal or middle part), cactus (having a dominant central lobe of length < 40 mm and secondary lobes arising in both superior and inferior directions), and cauliflower (having a length of < 40 mm with complex internal structure).
Statistical analysis
The IBM SPSS software was used for statistical analysis. Continuous variables were presented as mean ± standard deviation while categorical variables were presented as numbers and percentages. Differences in the LA and LAA dimensions in the 4 morphologic types were compared using one-way analysis of variance (ANOVA) for continuous variables and chi-square test for categorical variables. Differences in the LA and LAA dimensions as well as LAA morphological types were then compared in males and females using Student’s t test for continuous variables and chi-square test for categorical variables.