Preconditioning and proximal ligation did not influence the outcome of direct internal mammary artery bypass grafting in a canine model

The aim of this study was to assess the need for preconditioning and/or exclusion of competitive flow in minimally invasive coronary bypass grafting procedures (MICAB), to prevent early graft occlusion. Eight mongrel dogs (+/- 25 kg) were operated on under intravenous anaesthesia (sodium thiopenthal 15 mg/kg) and maintained with Halothan 1-2% and Pancurorium. A direct anastomosis between the left internal mammary artery and the left anterior descending coronary artery was performed, via anterior distal sternotomy, on the beating heart. Four dogs were preoperatively randomly conditioned by intravenous bolus injection of Diltiazem (0.0025 g/kg) prior to the procedure and after (meanwhile the left internal mammary artery takedown, the proximal coronary artery was snared during 15 min). In the absence of ECG changes or rhythm disturbances, a direct anastomosis of the left internal mammary artery and the left anterior descending coronary artery was performed. In four control dogs, direct MICAB procedure was done without preconditioning. The proximal left anterior descending coronary artery was occluded upstream of the arteriotomy in two dogs from both groups to exclude competitive flow from the native coronary artery. All the procedures were successful, except for one conditioned dog that sustained preoperative transmural anterior myocardial infarction. Cardiac enzymes (CK and CKMB) rose in all groups immediately after the procedure; this was not statistically significant between groups. All survivors were angiographically controlled after 6 to 8 weeks. They showed good patency of all grafts (mean thrombolysis in myocardial infarction-flow equals 2.86). There was perfect matching between the left internal mammary artery and left anterior descending coronary artery in the conditioned and proximal occluded group, which was contrary to the competitive flow in the control groups between the open left anterior descending coronary artery and the left internal mammary artery graft. Permeability of the left internal mammary artery grafts are not influenced by preconditioning nor exclusion of competitive flow in the MICAB technique for the canine model. Graft diameter and flow are merely the result of outflow conditions. In one case, preconditioning was followed by fatal myocardial infarction.