Effect of stent-graft compliance on endotension after EVAR.

PURPOSE: To investigate whether, and to which extent, the type of graft has influence on the pressure in the aneurysm sac. METHODS: The study consisted of a dynamic and a static experiment. In the dynamic experiment, a latex aneurysm was inserted into an in-vitro circulation model, with variable (80-180 mmHg) systemic systolic pressure and a pulse pressure of 40 mmHg. Seven types of devices were used to exclude the aneurysm: a latex reference graft, 3 stentless grafts made of different fabrics, and 3 different types of commercially produced stented grafts used for endovascular aneurysm repair (EVAR). The systolic and diastolic intra-aneurysm pressures (IAP) were measured, along with the pulse pressure. The mean IAP and pulse pressures were compared for each category of graft (stented/stentless) and for each graft. In the static experiments, the compliance of each graft and the latex aneurysm were determined by measuring the change in volume necessary to obtain a change in pressure. Furthermore, the IAP with each graft was measured in a nonpulsatile situation under systolic pressures varying between 60 and 140 mmHg. RESULTS: The experiments showed that, with increasing systemic pressures, there was a small pressure (<5 mmHg) increase in the aneurysm, but there was no significant difference among grafts in the dynamic or the static experiments (p = 0.12 and p = 0.17, respectively). With the 3 stented EVAR grafts, there was less pressure transmission than with the 3 stentless grafts, but this difference was not significant (p>0.05). CONCLUSION: This in-vitro study demonstrated that there is a clinically irrelevant pressure transmission through the graft wall and no significant difference in the pressure transmission between stented and stentless grafts.

Aneurysm sac pressure monitoring: does the direction of pressure measurement matter in fibrinous thrombus?

PURPOSE: This study was conducted to clarify the effect of the direction of pressure measurement on the pressure readout in fibrinous thrombus of the abdominal aortic aneurysm. METHODS: Three weights of 468 g (weight 1), 578 g (weight 2), and 675 g (weight 3) were molded. A specimen of human fibrinous thrombus was positioned under the weights. Because the surface area of the weights and the thrombus was 400 mm(2), weights 1, 2, and 3 caused pressures of 88, 108, and 127 mm Hg, respectively. Pressure measurements were performed at different angles between the sensor and the applied force (0 degrees , 22.5 degrees , 30 degrees , 45 degrees , 60 degrees , 67.5 degrees , 90 degrees ) Thrombi of 10 different patients were analyzed. Pressure measurements in the thrombi at different angles were statistically compared by a linear mixed model analysis. RESULTS: The measurements at 90 degrees differed statistically from the measurements at 0 degrees , 22.5 degrees , 30 degrees , 45 degrees , 60 degrees , and 67.5 degrees (P < .001). The pressure readout was only similar to the applied pressure when the pressure sensor was positioned at 90 degrees to the applied force. Pressure measurements in other sensor positions resulted in lower pressure measurements. Pressure changes were detected in all sensor positions. There appeared to be no significant difference between the pressure measurements taken at same angles in the 10 thrombi (P > .05). CONCLUSION: In fibrinous thrombus of abdominal aortic aneurysm, the direction of pressure measurement influenced the pressure readout.