Delayed recovery following hypothermic arrest in rabbit myocardium

The purpose of this investigation was to determine the relationship between the duration of myocardial ischemia at 15 degrees C and the time required for the myocardium to recover maximum contractile function following the ischemia. The isolated blood perfused rabbit heart was used as a model of myocardial ischemia. Hearts from 22 New Zealand white rabbits were divided into four groups. In Group I seven hearts were subjected to 15 minutes of ischemia at 15 degrees C. In Group II five hearts were subjected to 30 minutes of ischemia at 15 degrees C. In Group III and IV the ischemia time was extended to 60 and 120 minutes, respectively. Following the ischemia each heart was reperfused at normothermia and papillary muscle contractility was measured and used as an index of myocardial recovery. Hearts in Group I recovered their maximum contractile function after an average of 22.5 minutes. Those in Groups II, III, and IV were fully recovered after 31.7, 38.2, and 45.5 minutes, respectively. The study indicates that the time required for the maximum recovery of myocardial contractility following myocardial ischemia increases at a decreasing rate with an increase in the duration of the ischemia at 15 degrees C.