Background: We investigated the effects of intra-cardiopulmonary resuscitation (CPR) hypothermia with and without volume loading on return to spontaneous circulation and infarction size in an ischemic model of cardiac arrest.
Methods and results: Using a distal left anterior descending artery occlusion model of cardiac arrest followed by resuscitation with a total of 120 minutes of occlusion and 90 minutes of reperfusion, we randomized 46 pigs into 5 groups and used myocardial staining to define area at risk and myocardial necrosis. Group A had no intervention. Immediately after return of spontaneous circulation, group B received surface cooling with cooling blankets and ice. Group C received intra-CPR 680+/-23 mL of 28 degrees C 0.9% normal saline via a central venous catheter. Group D received intra-CPR 673+/-26 mL of 4 degrees C normal saline followed by surface cooling after return of spontaneous circulation. Group E received intra-CPR and hypothermia after return of spontaneous circulation with an endovascular therapeutic hypothermia system placed in the right atrium and set at a target of 32 degrees C. Intra-CPR volume loading with room temperature (group C) or iced saline (group D) significantly (P<0.05) decreased coronary perfusion pressure (group C, 12.8+/-4.78 mm Hg; group D, 14.6+/-9.9 mm Hg) compared with groups A, B, and E (20.6+/-8.2, 20.1+/-7.8, and 21.3+/-12.4 mm Hg). Return of spontaneous circulation was significantly improved in group E (9 of 9) compared with groups A plus B and C (10 of 18 and 1 of 8). The percent infarction to the area at risk was significantly reduced with intra-CPR hypothermia in groups D (24.3+/-4.2%) and E (4+/-3.4%) compared with groups A (72+/-5.1%) and B (67.3+/-4.2%).
Conclusions: Intra-CPR hypothermia significantly reduces myocardial infarction size. Elimination of volume loading further improves outcomes.