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

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.