Changes in viscoelasticity of the myocardium during cardioplegic arrest

To evaluate the efficacy of myocardial preservation during open heart surgery, we measured the viscoelasticity of the canine myocardium during cardioplegic arrest. A transfer function method was used for the measurement with a monitoring system consisting of a vibrator, a function generator, accerometers and a signal processor. Six mongrel dogs were put on cardiopulmonary bypass and after measurement of control hemodynamics, they were subjected to cardioplegic arrest at myocardial temperatures ranging from 4 to 32 degrees C. Viscoelasticity was measured at every 15 min and the cardioplegic solution was added every 30 min. After two hr of cardioplegic arrest, the myocardium was reperfused and postischemic hemodynamics were measured after 30 min of non-working beating. Satisfactory myocardial function returned in 3 hearts with the myocardial temperatures below 24 degrees C with myocardial viscoelasticity within the control range. Moderately decreased myocardial contractility was noted in a heart kept at temperature of 27 degrees C and its viscoelasticity remained in the control range of 90 min of ischemia and then began to decrease. In 2 hearts kept at temperatures higher than 29 degrees C, severely depressed myocardial contractility was noted, and viscoelasticity decreased transiently at 45 to 60 min and then returned to control levels. These results suggested usefulness of continuous monitoring of the viscoelasticity in early detection of its degenerative alterations due to impaired myocardial preservation during open heart surgery.