False lumen/true lumen wall pressure ratio is increased in acute non-A non-B aortic dissection

Acute non-A non-B aortic dissection (AD), a new concept of aortic pathology, is characterized morphologically by confinement of the dissection to the aortic arch or arch involvement either by the most proximal tear or by retrograde extension without extending to the ascending aorta [1, 2]. OBJECTIVES We aimed to determine whether non-A non-B aortic dissection (AD) differs in morphologic and haemodynamic properties from type B AD. METHODS We simulated and compared haemodynamics of patients with acute type B or acute non-A non-B AD by means of computational fluid dynamics. Wall pressure and wall shear stress (WSS) in both the true lumen (TL) and false lumen (FL) at early, mid- and late systole were evaluated. Morphology, WSS and the FL/TL wall pressure ratio were compared between groups. RESULTS Nineteen patients (type B, n = 7; non-A non-B, n = 12) were included. The median age (51 [46, 67] vs 53 [50, 63] years; P = 0.71) and a complicated course (14% vs 33%; P = 0.6) did not differ between the type B group and the non-A non-B group. However, the median entry tear width was increased in the non-A non-B group (9.7 [7.3, 12.7] vs 16.3 [11.9, 24.9] mm; P = 0.010). Streamlines showed, in patients with non-A non-B AD, blood from the TL flowed into the FL via the entry tear. Prevalence of a FL/TL wall pressure ratio >1.0 (type B versus non-A non-B) at early, mid- and late systole was 57% vs 83% (P = 0.31), 43% vs 83% (P = 0.13) and 57% vs 75% (P = 0.62), respectively. WSS did not differ between the groups. CONCLUSIONS The increased FL/TL wall pressure ratio observed during systole in non-A non-B AD may beget a complicated presentation.