Tear size and location impacts false lumen pressure in an ex vivo model of chronic type B aortic dissection

BackgroundFollow-up mortality is high in patients with type B aortic dissection (TB-AD) approaching one in four patients at 3 years. A predictor of increased mortality is partial thrombosis of the false lumen which may occlude distal tears. The hemodynamic consequences of differing tear size, location, and patency within the false lumen is largely unknown. We examined the impact of intimal tear size, tear number, and location on false lumen pressure.MethodsIn an ex-vivo model of chronic type B aortic dissection connected to a pulsatile pump, simultaneous pressures were measured within the true and false lumen. Experiments were performed in different dissection models with tear sizes of 6.4 mm and 3.2 mm in the following configurations; model A: proximal and distal tear simulating the most common hemodynamic state in patients with TB-AD; model B: proximal tear only simulating patients with partial thrombosis and occlusion of distal tear; and model C: distal tear only simulating patients sealed proximally via a stent graft with persistent distal communication. To compare false lumen diastolic pressure between models, a false lumen pressure index (FPI%) was calculated for all simulations as FPI% = (false lumen diastolic pressure/true lumen diastolic pressure) × 100.ResultsIn model A, the systolic pressure was slightly lower in the false lumen compared with the true lumen while the diastolic pressure (DP) was slightly higher in the false lumen (DP 66.45 ± 0.16 mm Hg vs 66.20 ± 0.12 mm Hg, P < .001, FPI% = 100.4%). In the absence of a distal tear (model B), diastolic pressure was elevated within the false lumen compared with the true lumen (58.95 ± 0.10 vs 54.66 ± 0.17, P < .001, FPI% = 107.9%). The absence of a proximal tear in the presence of a distal tear (model C) diastolic pressure was also elevated within the false lumen versus the true lumen (58.72 ± 0.24 vs 56.15 ± 0.16, P < .001, FPI% 104.6%). The difference in diastolic pressure was greatest with a smaller tear (3.2 mm) in model B. In model B, DBP increased by 13.9% (P < .001, R2 0.69) per 10 beat per minute increase in heart rate (P < .001) independent of systolic pressure.ConclusionsIn this model of chronic type B aortic dissection, diastolic false lumen pressure was the highest in the setting of smaller proximal tear size and the lack of a distal tear. These determinants of inflow and outflow may impact false lumen expansion and rupture during the follow-up period.

Clinical RelevanceFollow-up mortality rates are high in patients discharged from the hospital after an acute type B aortic dissection. Previous data has suggested that patients with complete thrombosis of the false lumen have improved outcomes, whereas those with a patent false lumen have an increased risk of aortic expansion and death. Recent data indicates that partial thrombosis of the false lumen (the presence of both flow and thrombus) is a strong independent predictor of mortality in these patients. A potential mechanism of poor outcomes in these patients may relate to the obstruction of distal tears by thrombus from the false lumen to the true lumen resulting in restricted outflow and a subsequent increase in false lumen pressure. Our model examines this hypothesis by measuring the pressures in the true and false lumen in an ex-vivo model of aortic dissection by varying the determinants of inflow and outflow.