Abstract 8: Effects of Timing of Intra-CPR and Post Resuscitation Hypothermia on Myocardial Infarction Size in a Porcine Model of Ischemic Cardiac Arrest
Background: Intra-CPR hypothermia (HTM) has been shown to decrease infarction size in a STEMI/cardiac arrest animal model. Myocardial protection is greatest when no-volume HTM is applied early during CPR and target temperature of <33°C is achieved before coronary reperfusion is established. We hypothesized that myocardial protection with HTM is dependent upon two factors: a) time to achieve target temperature and b) initiation of HTM during systemic reperfusion with CPR.
Methods: In a porcine model of STEMI/cardiac arrest, the mid LAD was occluded in 27 animals. Five minutes of untreated ventricular fibrillation were followed by 5 minutes of vest-CPR followed by defibrillation and standard ACLS protocol. In group A, intra-CPR HTM was initiated with 5ml/kg/min of 4°C NS during CPR and followed by external hypothermia until the end of the experiment. An endovascular device that cools with no volume loading was used in Groups B and C and was started during CPR and 30 minutes after return of spontaneous circulation respectively. The target temperature in all groups was 33°C. Resuscitated animals had the intracoronary balloon deflated after a total of 120 minutes of ischemia. 90 minutes of reperfusion were followed with euthanasia and myocardial infarction staining.
Results: Groups B and C had significantly higher coronary perfusion (22±4 and 21±3) compared to group A (14.4±3 mmHg) during CPR (p<0,05). Groups A, B and C had 5/9, 9/9 and 5/9 survivors respectively. Time to reach target temperature was 81±14, 16.6±7, 38±10 and min (p<0.01). The respective infarction to area at risk was 28±7, 8±5, 44±15 (p<0.05). Ejection fraction at 60 min post ROSC was 17.7±2, 33±5 and 26±6 (p<0.05 A vs B).
Conclusions: Intra CPR HTM with and without volume loading significantly decreased myocardial infarction size compared to post ROSC no-volume intravascular HTM. Systemic reperfusion (CPR after cardiac arrest) with cold blood appears to magnify the protection offered by hypothermia. The protection is not only dependent on time to reach target temperature but also on the initiation of HTM during CPR.
- © 2010 by American Heart Association, Inc.