Endografting of the Descending Thoracic Aorta Increases Ascending Aortic Input Impedance and Attenuates Pressure Transmission in Dogs

Abstract 

Objectives

Endografting is being used to manage aneurysms, dissections and acute traumatic disruptions of the thoracic aorta. The acute effects of such interventions on ventricular afterload and on pressure wave transmission characteristics are not well known.

Methods

In five dogs, a 55mm endograft was introduced into the descending aorta, just distal to the left subclavian artery, with oversizing of 20%. Following formaldehyde induced complete heart block, the hearts were paced (30–120bpm). The ascending aortic pressures and flows were recorded using Millar micro-tip manometers and ultrasonic flowmeters, respectively. Arterial pressures proximal and distal to the stent site were also recorded. For each heart rate, parameters of a modified Windkessel (SVR: systemic vascular resistance, Z₀: characteristic impedance, C: total arterial compliance) were estimated. The pulse wave velocity (PWV) and reflection coefficient (Γ) were calculated from the pressure wave transfer functions.

Results

The Z₀ (0.25±0.05 vs 0.41±0.06mmHg/mls⁻¹, P<.05) was increased and C was decreased (0.45±0.07 vs 0.28±0.04ml/mmHg, P<0.001) following endograft placement. SVR tended to increase (P=.06) and ascending aortic Γ was unchanged. The PWV increased (418±67 vs 755±135cm/s, P<.05) and the distal Γ decreased (0.09±0.10 vs −0.49±0.07, P<.05).

Conclusions

Endografting in the proximal descending aorta cause unfavorable changes in the ascending aortic input impedance and an increase in the PWV through the grafted segment, consistent with an increase in the modulus of elasticity. The grafts produce a negative Γ at the distal end, an uncommon occurrence in the systemic circulation. Whether this change is of sufficient magnitude to result in post-graft dilation is unknown.

Keywords: Stents, Pressure wave transmission, Arterial impedance, Pulse wave velocity