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Different graft flow patterns due to competitive flow or stenosis in the coronary anastomosis assessed by transit-time flowmetry in a porcine model

^a Department of Circulation and Medical Imaging, Norwegian University of Science and Technology, N-7489 Trondheim, Norway
^b Department of Cardiothoracic Surgery, St. Olavs University Hospital, Trondheim, Norway
^c Institute of Surgical Sciences, The Medical Faculty, University of Bergen, Bergen, Norway

Received 31 August 2008; received in revised form 17 February 2009; accepted 23 February 2009.

^_* Corresponding author. Tel.: +47 91717994; fax: +47 73867029. (Email: haavardnordgaard{at}gmail.com).

Objective: To assess whether coronary graft flow patterns are affected differently by native coronary competitive flow or by stenosis of the coronary anastomosis. Methods: Nine pigs (65–70 kg) underwent off-pump grafting of the left internal mammary artery to the left anterior descending artery (LAD). Transit-time flow patterns in the mammary grafts were recorded under four different conditions: (1) baseline flow (proximal LAD occluded), (2) full competitive flow, (3) partial competitive flow and (4) after creation of a stenosis in the anastomosis. Competitive flow was achieved by an adjustable occluder on the left anterior descending artery. The mean luminal stenosis of the anastomosis was 75 ± 11%, calculated by epicardial ultrasound. Mean flow, systolic and diastolic antegrade and retrograde flow during different flow conditions were calculated as ratios of baseline flow and compared. Different derived flow indexes were calculated and compared in the same manner. Friedman's test and post hoc analyses by Wilcoxon signed-ranks were performed without correction for multiple comparisons. Results: Mean graft flow was more reduced by competitive flow than by a stenotic anastomosis of 75 ± 11%. Competitive flow significantly decreased diastolic antegrade flow and both diastolic and systolic maximum peak flows, but increased retrograde flow, compared with baseline and stenosis. Furthermore, competitive flow and stenosis could be distinguished by analysis of several derived indexes. Pulsatility index (maximum – minimum flow/mean flow) and insufficiency percent (retrograde flow as fraction of total flow) was increased significantly more by competitive flow than by stenosis. Diastolic filling percent was significantly reduced at competitive flow compared with stenosis and baseline. Conclusions: The mammary graft flow was significantly reduced by native coronary competitive flow, but marginally decreased by a stenotic anastomosis of 75% mean luminal stenosis. Reduction of graft flow due to competition was particularly evident in diastole. A detailed flow pattern analysis may differentiate between competitive flow and stenosis of the anastomosis.

Key Words: Heart surgery • CABG • Anastomosis • Coronary graft assessment • Transit-time flow measurement • Epicardial ultrasound