Background The number of entry tears impacts the development and prognosis of type B aortic dissection (TBAD).
Objective To analyze the influence of different entry tears 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 were 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 were 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) consisted 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 was possible to simulate the blood flow condition of real TBAD patients. The hemodynamic parameters at each breach were measured by Doppler ultrasound, and the blood flow direction change time (RT) and velocity time integral (VTI) were obtained to describe the blood flow changes of TBAD breach.
Results In group A1, the blood from the proximal breach flowed into the false lumen first and then flowed out, mainly presented as inflow (VTI: 19. 39 ± 5.88 vs 9.89 ± 3.41, P=0.013), and for the distal breach, the blood flowed out first and then flowed in, mainly presented as outflow (VTI: 22.61 ± 11.81 vs 7.67 ± 3.26, P=0.024). In group A2, the diameter of the proximal breach was reduced, and the VTI rate (the ratio of VTI after the change of direction of blood flow in the breach to VTI in the whole cycle) was decreased (33.70% ± 4.22% vs 51.00% ± 4.80%, P=0.046), and there was no statistical difference in the distal breach VTI rate. In group A3, the distal breach diameter was reduced, and the VTI rate was reduced (30.10% ± 7.75% vs 15.30% ± 3.19%, P=0.045), and the blood flow change time RT was longer (0.54 ± 0.08 s vs 0.71 ± 0.01 s, P=0.023). In group B1, we found that blood would flow from the true lumen to the false lumen through the middle breach in systole, and from the false lumen to the true lumen in diastole. The blood flow from the false lumen to the true lumen accounted for 64.19% ± 5.30% of the whole cardiac cycle. There was no significant difference between the blood flow from the proximal breach into the false lumen and the blood flow from the middle and distal breach out of the false lumen (VTI: 22.68 ± 6.76 vs 22.89 ± 7.69, P=0.800). In group B2, the diameter of the middle breach decreased, the VTI rate increased (36.39% ± 5.84% vs 87.00% ± 5.66%, P＜0.001), and the RT reflux time decreased (0.27 ± 0.06 s vs 0.21 ± 0.04 s, P=0.341). In group B3, the VTI rate of the middle breach decreased (36.39% ± 5.84% vs 16.61% ± 0.86%, P=0.004) after the stent was placed to block the proximal first breach.
Conclusion The number and diameter of the breach and whether the stent is placed or not will affect the blood flow direction and blood flow parameters of different breaches in multi breach TBAD, resulting in different effects on the progression of dissection. In clinical practice, treatment strategies should be formulated according to the blood flow characteristics of different breaches, so as to achieve better prognosis.
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