I. Development of an in vitro model of myocardial cooling: a study of the effect of cardiac size on cooling rate.

A physical model for the study of local cardiac hypothermia was developed using excised animal hearts. The validity of the model was established by showing close similarity between cooling curves of dog hearts in vivo and in the model. The model was then used to compare the cooling rates of three groups of excised hearts using cold saline irrigation. Groups 1, 2, and 3 had mean left ventricular weights of 166, 379, and 1,429 gm, respectively, and mean left ventricular wall thicknesses of 1.5, 2.0, and 3.1 cm, respectively. For the same 10 degrees C temperature fall, Group 1 took 25 +/- 2.8 minutes, Group 2 took 54 +/- 9.2 minutes, and Group 3 took 117 +/- 21 minutes. To avoid slow cooling and consequent ischemic damage in the hypertrophic ventricle, it may be desirable to initiate cooling using coronary perfusion with cold blood or cold cardioplegic solutions.