Equations Estimating the Predissected Diameter of the Ascending Aorta for Acute Type A Aortic Dissection.

Background: A successful endovascular treatment for acute type A dissection has been recently reported. However, there has been no consensus regarding the appropriate stent graft size based on the estimated predissected aortic diameter for this pathology.

Methods: We developed new equations for estimating the predissected ascending aorta and aortic arch by investigating computed tomography images that had been scanned less than 3 years before dissection. From 684 patients with type A AAD, 28 were matched for the study. We measured the predissected whole circumference length (pre-wCL), postdissected whole circumference length (post-wCL), postdissected true lumen circumference length (post-tCL), postdissected major diameter (post-Dma), and postdissected minor diameter (post-Dmi) of the acutely dissected aorta. This was followed by the calculation of (post-tCL + post-wCL)/2 and (post-Dma + post-Dmi)/2. Six equations (linear function) and modified equations were derived from each of the abovementioned parameters.

Results: Four equations (post-wCL, post-Dma, [post-tCL + post-wCL]/2, and [post-Dma + post-Dmi]/2) had nearly the same bias and accuracy (<9.42 mm). For clinical use, we also developed one modified equation using the post-wCL (y = 0.9x) among four parameters because of its simplicity and decreased the possibility of measurement error. The biases of circumference length and accuracy were 5.5 ± 4.9 mm and 84.6%, respectively, and they improved to 4.4 ± 3.3 mm and 93.4% in cases with a ratio of post-tCL/post-wCL of 0.66 or more.

Conclusions: Our newly developed equation can be used to calculate the predissected ascending aortic diameter and aortic arch diameter in cases of acute type A dissection.