Prosthetic replacement of the ascending aorta increases wall tension in the residual aorta.

BACKGROUND: Prosthetic replacement of the ascending aorta with nonelastic vascular grafts impairs the local Windkessel function. Whether this increases wall tension in the remaining aorta is still a not completely investigated hypothesis but is of clinical relevance with respect to postprocedural development of aneurysms and dissections, especially in the proximal descending aorta.
METHODS: Fresh porcine thoracic aortas, including the root, were set up in a mock circulation before and after prosthetic replacement of the ascending aorta. Cyclic changes in aortic dimensions were measured by ultrasonic micrometers at defined positions at the proximal part of the descending aorta. At the same positions, aortic pressures were recorded simultaneously using Millar tip manometers. Wall thickness was measured after pulsatile testing, and the resulting wall tension was calculated from the Laplace law.
RESULTS: After prosthetic replacement of the ascending aorta, peak systolic pressure in the proximal descending aorta increased from 117.6 +/- 6.1 mm Hg to 129.2 +/- 6.3 mm Hg, resulting in a rise of wall tension by 12.4% +/- 4.2% (p = 0.001). The maximum rate of pressure rise (dp/dt(max)) increased by 42.6% +/- 16.4% (p < 0.001).
CONCLUSIONS: Replacement of the ascending aorta with noncompliant prosthetic material significantly increases wall tension and rate of pressure rise in the residual aorta. This may have clinical impact with respect to a sudden and sustained rise of mechanical load, especially at the vulnerable proximal descending aorta.