Role of myocardial protection for coronary artery bypass grafting on the beating heart

Background. Minimal invasive coronary artery bypass grafting is often performed on the warm, beating heart. This setting requires special measures for protection of the myocardium during acute regional ischemia under normothermic conditions. Methods. A first possibility to enhance the tolerance to ischemia during short episodes of coronary artery occlusion is based on a pharmacologic approach. A second possibility is mechanical unloading of the ischemic heart during and after regional ischemia. Results. To interfere with the ionic imbalances leading to necrosis, blockade of the Na+-H+ exchanges can be induced. It is shown that the selective Na+-H+ exchange inhibitor HOE 694 is able to prevent ischemic contracture in the experimental setting. Another pharmacologic approach is the use of endogenous adenosine accumulation in the ischemic myocardium. This can be achieved by the use of nucleoside transport inhibitors (lidoflazine or nitrobenzylthioinosine) having the ability to accumulate adenosine at the site of its production. Adenosine has a strong cardioprotective effect via adenosine A1 receptor stimulation and induces bradycardia by opening K+ channels and increasing the potassium current. It is also shown that left ventricular unloading by an axial flow pump (Hemopump) improves postischemic myocardial dysfunction (stunning) in an experimental model of short regional ischemia and reperfusion. Conclusions. Further clinical investigation of both pharmacologic and mechanical techniques for cardioprotection during minimally invasive coronary artery bypass grafting is required.