The importance of monitoring intramyocardial temperature during hypothermic myocardial protection.

In 50 patients undergoing cardiac operation, hypothermic cardioplegic solution was infused into the root of the aorta immediately after aortic cross-clamping. Cardiac standstill was achieved within 1 to 3 minutes. However, monitoring of intramyocardial temperature with a needle thermistor revealed that such core cooling is unpredictable (the intramyocardial temperature achieved ranged from 7 degrees to 33 degrees C), unstable (this temperature can rise at more than 0.5 degrees C per minute), and uneven (a difference of up to 17 degrees C was observed between the intramyocardial temperature of the anterior and posterior left ventricular sites). The area supplied by the stenotic coronary artery was least protected. Monitoring of intramyocardial temperature enables one to know when supplementary cooling is indicated. We conclude that widespread differences in this temperature during cardiac operation make monitoring advisable for optimal myocardial protection.