Statistical Analysis
In this matched case-control study, the exposures consist of two clusters of variables. The first cluster includes 4 variables associated with the ostial area: OA at 0 and 90 degrees, OA at 45 and 135 degrees, OA calculated using the largest radius in the 4 TEE planes and the orthogonal radius, and aggregate OA. The other cluster includes two variables: Maximum LAA depth and LAA Exit Velocity. The outcome is a binary variable called LAA thrombus (Yes vs. No). The patients with thrombus were identified as cases. The patients without thrombus were considered as the candidate controls. The propensity score method was utilized to determine the matched controls while accounting for confounding from prognostic variables. The matching variables included age, LVEF, and sinus rhythm at the time of TEE. The greedy nearest neighbor technique was used to achieve the 1:1 matched design to produce the slightest within-pair difference. Patients were matched only if the difference in the logits of the propensity scores for pairs of patients were less than or equal to 0.5 times the pooled estimate of the standard deviation (see Figure 2). Another variable, therapeutic anticoagulation at the time of TEE, was exactly matched. Thus, the possibility of investigating the independent effects of those variables on the outcome can be effectively eliminated. 61 matched pairs were identified in the analysis data set (Figure 1).