Cluster analysis of acute ascending aortic dissection provides novel insight into mechanisms of distal progression.

BACKGROUND: Whether primary tear size impacts extent of type A dissection is unclear. Using statistical groupings based on dissection morphology, we examined its relationship to primary tear area. METHODS: We retrospectively reviewed 108 patients who underwent acute ascending dissection repair from 2000-2016. Dissection morphology was characterized using 3-dimensional (3D) reconstructions of computed tomography (CT) scan images. Two-step cluster analysis was performed to group the dissections by examining the true lumen area as a fraction of the total aortic area at various levels. RESULTS: Cluster analysis defined two distinct categories. This first grouping corresponds to DeBakey type I (n=71, 65.7%) with a dissection extending from the ascending aorta to the aortic bifurcation. The second grouping conforms more closely to DeBakey type II dissection (n=37, 34.3%). It differs however from the classic type II definition as the dissection may extend up to the distal arch from the ascending aorta. Compared to type I, this "extended" DeBakey type II had no malperfusion (P<0.05), a larger primary tear area (6.6 vs. 3.7 cm2, P=0.009), and a greater burden of atherosclerotic coronary artery disease (P<0.05). A smaller aortic valve annulus (P=0.025) and a smaller root false lumen area (P=0.017) may explain less aortic valve insufficiency (P<0.05) in extended type II dissections. No differences in complications or survival were seen. CONCLUSIONS: In this series, limited distal extension of DeBakey type II dissections appears to be related to a larger primary tear area and greater atherosclerotic disease burden. It is also associated with less malperfusion and aortic valve insufficiency.