Abstract 18: Coronary Perfusion Pressure in VF and in PEA/A Cardiac Arrest Animals

We hypothesized that equivalent chest compressions are less effective at perfusing the heart in pulseless electrical activity/asystole (PEA/A) cardiac arrest than in ventricular fibrillation (VF) cardiac arrest. We tested this hypothesis in two swine models of cardiac arrest. Two groups of pigs (33+4 kg) were anesthetized and instrumented to measure coronary perfusion pressure (CPP). CPP was calculated as aortic minus right atrial pressure measured just before the initiation of a chest compression. Group 1 underwent 5 minutes of unsupported electrically induced ventricular fibrillation. Group 2 animals were ventilated with a 12% oxygen and balance nitrogen mixture until aortic pulsations were less than 2 mmHg. Animals remained unsupported for an additional 6 minutes. Both groups were resuscitated with chest compressions (100/min) and ventilations (100% O2, 10/min). After 7 minutes, Group 1 animals were defibrillated. Resuscitation continued until either return of spontaneous circulation occurred or 20 minutes elapsed. Return of spontaneous circulation occurred in 6 of 7 Group 1 and 2 of 6 Group 2 pigs. CPP during resuscitation started at ~5 mmHg for both groups. Group 1 CPP increased to 13 mmHg in the first 3 minutes of chest compressions while the CPP in Group 2 remained at 5 mmHg. Decompression central venous pressure was the same for both groups (7 mmHg). CPP correlated with decompression aortic pressure in both groups. CPP was lower in Group 2 animals than in Group 1 animals and this difference was reflected in the number of animals who had return of spontaneous circulation. This data would suggest that one reason why PEA/A patients survive cardiac arrest less frequently than VF patients is that chest compressions perfuse the heart less effectively in PEA/A patients than in VF patients.