The effectiveness of topical cardiac hypothermia.

The effectiveness of cooling the subendocardial myocardium by five different methods was evaluated in a group of 100 patients. The most effective and consistent method to cool the heart was by total body hypothermia with the heat exchanger in the cardiopulmonary bypass system. Myocardial temperature became equal to vena caval blood temperature after only a one minute lag. The least effective methods of myocardial cooling were those in which a bath of chilled fluid enveloped the outside surface of the heart, with and without aortic cross-clamping. The drop in ventricular septal temperature was so small that topical hypothermia, by itself, may be worthless. Two methods in wich chilled fluid was perfused through the coronary system produced a significant lowering of myocardial temperature. One of these methods employs coronary perfusion with a cold cardioplegic solution in addition to total body hypothermia. It is our current choice for myocardial protection during cross-clamping of the ascending aorta.