Endografting of the descending thoracic aorta increases ascending aortic input impedance and attenuates pressure transmission in dogs.
OBJECTIVE
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 55 mm 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 (Gamma) were calculated from the pressure wave transfer functions.


RESULTS
The Z0 (0.25+/-0.05 vs 0.41+/-0.06 mmHg/ml s(-1), P<.05) was increased and C was decreased (0.45+/-0.07 vs 0.28+/-0.04 ml/mmHg, P<0.001) following endograft placement. SVR tended to increase (P=.06) and ascending aortic Gamma was unchanged. The PWV increased (418+/-67 vs 755+/-135 cm/s, P<.05) and the distal Gamma 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 Gamma 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.
Department of Anesthesia and Surgery, University of Calgary, Calgary, Alta., Canada. gary.dobson@calgaryhealthregion.ca
G
G
Dobson
J
J
Flewitt
J V
JV
Tyberg
R
R
Moore
M
M
Karamanoglu
D000818:Animals; D001013:Aorta, Thoracic / Q000503:physiopathology* / Q000601:surgery; D001783:Blood Flow Velocity / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology*; D004285:Dogs; D017097:Electric Impedance; D005260:Female; D006327:Heart Block / Q000139:chemically induced / Q000503:physiopathology; D008297:Male; D008365:Manometry; D011673:Pulsatile Flow / Q000502:physiology; D015607:Stents