Clinical comparisons of methods of myocardial protection.

Currently, numerous methods are in use for myocardial hypothermia as a myocardial preservation modality for cardiac operations. During cardiac ischemia we have compared myocardial surface cooling with topical cold saline (Group I, N = 9), crystalloid cardioplegia plus topical cold saline (Group II, N = 8) and cardioplegia with a specially designed cooling jacket (Group III, N = 8) in patients undergoing aortic or mitral valve replacement, or both. Temperatures were assessed and recorded continuously in standardized locations for the right and left ventricular epicardium and endocardium. In Group I the rate of cooling was significantly slower than in the other two groups. Also, excessive gradients were developed across the left and right ventricular walls. In Group II the rate and depth of cooling were adequate and initial temperature gradients were eliminated. However, over the period of ischemia, significant rewarming occurred. In Group III temperatures were reduced rapidly and uniformly and maintained at or below 10 degrees C for the duration of the ischemic period. These differences are statistically significant (p less than 0.05). For optimal myocardial hypothermia, we recommend the following: separate cannulation of the superior and inferior venae cavae with caval snares; venting of the pulmonary artery (if inadequate, pulmonary vein occlusion or direct left atrial venting); induction of myocardial hypothermia with crystalloid or cold blood cardioplegia; and maintenance of hypothermia by the cooling jacket described herein. It is also desirable to continuously monitor temperatures of the right and left ventricular endocardial and epicardial surfaces.