Background  The number of entry tears impacts the development and prognosis of Type B Aortic Dissection (TBAD). This study aims to analyze the influence of different entry tear on the occurrence and progression of TBAD by constructing and comparing flow parameters at each entry in two-entry and three-entry porcine TBAD models, thereby illustrating changes in blood flow direction and volume.

Methods  Adult porcine aortas were acquired and processed to expose the intima. A special scraper was used to separate the intima and media to create a dissection, with the length of the dissection controlled at 20cm. Subsequently, surgical knives were used to create different tears in the intima. The artery was then flipped again to construct models of TBAD with either two or three entry tears. Among them, the two-entry models are categorized as Group A: A1 with two entry tears of the same diameter, A2 with a smaller proximal entry tear, A3 with a smaller distal entry tear; the three-entry models are categorized as Group B: B1 with three entry tears of the same size, B2 with a smaller middle entry tear, B3 with the first proximal entry tear sealed by a stent graft. The mock circulation loop (MCL) consists of a control system, pulsatile pump, one-way valves, and a reservoir tank to mimic the human circulatory system. A 40% glycerol water solution was used to simulate blood, with a simulated heart rate of 60 bpm, and nylon particles served as ultrasound contrast agents. By integrating the completed model with the MCL, it is possible to simulate the blood flow condition of real TBAD patients. Doppler ultrasound measurements were conducted to assess blood flow variations at each entry and obtain hemodynamic parameters such as blood flow velocity.

Results  In three-entry TBAD, there were no changes in blood flow direction at the proximal and distal entry tears, but characteristic alterations were observed in the intimal flap and blood flow at the middle entry tear. During the systolic phase, blood flowed from the true lumen into the false lumen (36% ± 5.3%), while during diastole, blood moved fro0.m false lumen into true lumen, with a flow reversal time of 0.27 ± 0.058 seconds. The majority of blood, approximately 64% ± 5.3%, flowed from false lumen into true lumen, and there was a statistically significant difference in flow volumes between inflow and outflow from false lumen (7.1 vs 13.2, P ＜ 0.05). The blood flow volume entering false lumen from the proximal tear and exiting false lumen through the middle and distal tears showed no difference (VTI: 22.68 ± 6.76 vs 22.89 ± 7.69, P=0.800). In two-entry TBAD, at the proximal entry tear, blood initially entered false lumen before exiting, with inflow dominating (19.4 vs 9.9, P ＜ 0.05). For the distal entry tear, blood initially exited before entering, with outflow dominating (22.6 vs 7.6, P ＜ 0.05). There is no difference in the blood flow volume entering false lumen from the proximal tear and exiting false lumen from the distal tear (VTI: 9.50 ± 3.44 vs 14.93 ± 11.43, P=0.254). Additionally, changes in blood flow direction occurred earlier at the proximal entry tear (0.52 s vs 0.62 s, P ＜ 0.05).

Conclusion  In cases of two-entry tear TBAD, reducing the diameter of the proximal entry tear, which serves as the inflow pathway, will decrease the blood flow into the false lumen. Conversely, reducing the diameter of the distal entry tear, which serves as the outflow pathway, will increase blood flow into the false lumen, potentially increasing the risk of disease progression. In three-entry tear TBAD, lowering systolic pressure may have the potential to reduce the blood flow through the mid-entry tear into the false lumen, subsequently reducing the pressure within the false lumen. This could slow down the progression of acute TBAD and the rate of arterial dilation. However, this theory requires further experimental and clinical validation.