Models of myocardial stunning

The use of animal models is a valuable approach to the elucidation of the pathophysiology of myocardial stunning. Coronary occlusion followed by reperfusion produces stunning experimentally, mimicking a myocardial infarction followed by thrombolysis, angioplasty, or coronary bypass. Timing of occlusion and duration to avoid necrosis is critically dependent on the animal species used. For example, 10 minutes of occlusion is required in pigs, 20 minutes in canine models, and sheep or rabbits may require ischemic times somewhere in between. Alternatively, two to six cycles of occlusion followed by reperfusion (repetitive occlusion) may be used. In addition, global ischemia with the heart vented and on cardiopulmonary bypass may simulate myocardial stunning. In this case, 30 minutes produces 50% reductions in myocardial contractility in dogs while 10 minutes is needed in pigs. Animal models have also included the study of a stunned heart in an in vitro apparatus. In these models, discontinuation of perfusion for 10 to 15 minutes is needed to produce stunning in rats, 20 minutes in rabbits, and probably longer periods in dogs and pigs. Myocyte cell cultures may also be valuable for studying responses to ischemia and reperfusion at the cellular level. It is generally agreed that cardioplegic protection, antioxidants, metabolic enhancements, and blockade of calcium overload are some of the strategies that can minimize or eliminate myocardial stunning.