Observations on flow characteristics of passive external aortic shunts

Extraluminal heparin-bonded shunts have been recommended to support the distal circulation and decompress the proximal vascular bed during procedures that require interruption of flow through the thoracic aorta. Shunts that originate in either the left ventricle or the proximal aorta are generally viewed as hemodynamically similar, despite incomplete documentation of their flow characteristics. The present study was conducted to further define these hemodynamic properties. Identical extraluminal shunts were placed from the left ventricular apex and aortic arch to the distal thoracic aorta in mongrel dogs. Simultaneous pressure and Doppler flow velocities were recorded in the carotid and femoral arteries. Computer-enhanced composite waveforms were used to assist data analysis. When compared to ventricular cannulation, aortic cannulation provided improved proximal decompression and increased mean distal flow. In addition, significant diastolic flow reversal was recorded in the distal circulation when ventricular cannulation was employed. On the other hand, ventricular cannulation was associated with the preservation of pulsatile flow, whereas flow generated by aortic cannulation was linear. It is concluded that extraluminal shunts that originate in the left ventricle and the proximal aorta have distinct hemodynamic properties. These differences may be clinically important in specific situations.