Feasibility and safety of regional myocardial hypothermia during myocardial ischemia and infarction in pigs

Abstract

Mild systemic hypothermia has been shown to be feasible and safe in patients during acute myocardial infarction (AMI). Regional myocardial hypothermia of the ischemic myocardium only may be more effective in myocardial salvage with fewer side effects compared with systemic hypothermia. The purpose of this study was to evaluate the feasibility and safety of regional myocardial hypothermia in pigs. Open-chest pigs with (n=5) or without (n=4) myocardial infarction underwent left anterior descending coronary artery (LAD) ligation followed by intracoronary infusion of lactated Ringer's solution (at room temperature and at 15 degrees C between 20-35 ml/min for 3 min) via the central lumen of a specially designed balloon catheter at the time of reperfusion. Intramyocardial temperatures via thermocouples at the ischemic zone (LAD territory) and non-ischemic zone (circumflex territory) as well as systemic temperature were constantly recorded, as were the hemodynamics. Each pig acted as its control regarding the myocardial temperature response to both solutions. In addition, intracoronary versus intramyocardial temperatures were compared with thermocouples in both territories during infusion. There was no hemodynamic compromise or arrhythmia seen during the intracoronary infusion of either temperature solution. There was a linear relationship between the infusion solution temperature and infusion rate versus intramyocardial temperature response, with the cooled solution providing 2 degrees C lower temperature and faster infusion resulting in lower intramyocardial temperature. There was no change in the non-ischemic zone or systemic temperature. On average, 6-8 degrees C reduction in tissue temperature, potential target temperature range for hypothermic therapy, was achieved in all animals. In addition, intracoronary temperature in distal LAD measured by intracoronary thermocouples correlated with the intramyocardial temperature (2 degrees C lower temperature in the coronary artery). It is feasible and safe to achieve regional myocardial hypothermia by intracoronary infusion of cooled solution in pigs.