Laboratory Evaluation of In t raoperative

The investigative laboratory is the appropriate place to evaluate methods of intraoperative myocardial protection. It is becoming apparent that diseased myocardium is more susceptible to intraoperative injury than is nor- mal heart muscle, and so animal models that simulate human cardiac disease states such as chronic left ventricular hypertrophy should be used to assess various techniques. Long-term studies on animals surviving operation are necessary in order to evaluate the chronic effects of various methods of protec- tion. n order to be successful, an open-heart operation must correct a specific anatomical defect and at the same time should not cause any I impairment of preexisting cardiac function. The best method of protecting the heart during any particular operation has not yet been proved, and most of the techniques presently used have been developed in a clinical situation. Similarly, almost all long-term studies following cardiopulmonary bypass have been per- formed in patients, with the inherent limitations present in any clinical assessment of cardiac function and morphology. New methods of myocardial protection are currently being developed, and the investigative laboratory is the appropriate location for these innovations to be evaluated. The best model for assessing intraoperative myocardial protection varies between laboratories and depends on available facilities, veterinary support, the expertise of a particular investigator, and financial resources. Although many of the great advances in cardiac physiology and biochemistry have been made using small animal preparations, large animals (usually dogs but occasionally calves, pigs, or primates) are necessary to provide a model upon which cardiac surgical procedures similar to those performed clinically can be carried out. Ventricular Hypertrophy One of the most important considerations in evaluating injury to heart muscle duringan operation is the state of the muscle before the procedure. Hypertrophic myocardium has been demonstrated to be much more susceptible than normal myocardium to the detrimental effects of anoxia, ischemia, and ventricular fibril- lation.