Equations for Estimating the Predissected Diameter of the Descending Aorta From Computed Tomographic Images at the Onset of Aortic Dissection

BACKGROUND: Estimation of the predissected descending aortic diameter is important for deciding on the size of a stent graft in cases of acute aortic dissection. However, no equations for estimating this diameter have been previously reported. METHODS AND RESULTS: We developed and validated new equations by investigating computed tomography images that were scanned within 3 years before dissection and those that were scanned immediately after the onset of dissection. Among 1127 patients with acute aortic dissection (425 type A and 702 type B), 36 were matched for the study from October 2005 to March 2017 at 4 centers. New equations were developed in 17 patients and validated in 19 patients. We measured the predissected whole circumference length (CL) and postdissected whole CL, true lumen CL, the major diameter, and the minor diameter of the acutely dissected aorta, followed by calculation of (post‐trueCL+post‐wholeCL)/2 and (post–major diameter+post—minor diameter)/2. Six equations (linear function) and modified equations were derived from each of the above‐mentioned parameters. In the derivation sets, equations that used the parameter of (post‐trueCL+post‐wholeCL)/2 were strongly correlated with pre‐wholeCL (Y=0.9433x+5.0147; R (2)=0.9001) and showed significantly less bias compared with the other 5 equations (P<0.0001). In validation sets using this equation, the mean bias of the circumference length and diameter was 2.7±2.8 and 0.85±0.89 mm, respectively. A total of 99.2% of the calculated values were within 3 mm in diameter or less. CONCLUSIONS: Our newly developed equations can be used to calculate the predissected aortic diameter in cases of acute aortic dissection and might help to decide the size of the stent graft.