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).