Effect of intraluminal thrombus on pressure transmission in the abdominal aortic aneurysm.

OBJECTIVE: To clarify the effect of intraluminal thrombus on pressure transmission.
METHODS: A saccular aneurysm was inserted into an artificial circulation system. Subsequently, the saccular aneurysm was filled with eight different human aortic aneurysm thrombus samples. Starch solution in an empty aneurysm was used as a control. A pressure sensor measured the pressure in the circulation, and a second piezoelectric sensor measured the pressure in the saccular aneurysm at 3, 2, and 1 cm from the endoluminal surface (23 locations). The influence of the elastic characteristics of the aneurysm wall on the extent of pressure reduction was evaluated by experiments performed with aneurysms made of rubber and paraffin.
RESULTS: The pressures measured in the empty aneurysm were identical to those measured in circulation (P > .05). The pressure measured in the thrombus was significantly lower than the pressure measured in the circulation (P < .05). The mean pressure ratio between the systolic thrombus pressure and systolic circulation pressure at 1, 2, and 3 cm was 0.90 +/- 0.09, 0.86 +/- 0.10, and 0.81 +/- 0.09, respectively. However, there was a clear correlation between the pressure in the circulation and in the thrombus (Pearson correlation coefficient: mean, r = 0.997; range, 0.975-0.999; P < .01). The change in circulatory pressure was followed by an almost identical change in thrombus pressure (regression coefficient: mean, beta = .997; range, .983-1.000; P < .01). In stiff aneurysms, the pressure reduction is less than in more compliant ones (P < .05).
CONCLUSIONS: In an in vitro model, pressure in the aneurysmal sac is reduced by fibrinous thrombus. CLINICAL RELEVANCE: Endovascular aneurysm repair (EVAR) aims at reducing the pressure in the aneurysmal sac. Therefore, it seems attractive to use pressure monitoring in the aneurysmal sac as a follow-up after EVAR. This study contributes to the development of the rationale of pressure monitoring in the aneurysmal sac as a follow-up method after EVAR. The aneurysmal sac is filled with thrombus. To interpret pressure measurements in the thrombus, we have to learn about the effect of the thrombus on pressure transmission and on the pressure measurements themselves. Our study demonstrates that reduction of pressure occurs as it is transmitted through a human aortic thrombus.