Abstract
Introduction: The most significant change to the latest AHA CPR guidelines is the recommendation of CPR first followed by defibrillation, for un-witnessed arrests. We tested the hypothesis that global myocardial ischemia during ventricular fibrillation (VF) decreases activation rate and short duration of reperfusion would normalize activation rates. Methods: We studied 6 Langendorff perfused human hearts which were explanted from cardiomyopathic patients who underwent transplantation. Tyrode solution was used for perfusion and flow was maintained at 0.9 to 1.1 ml/g/min. Multi-electrode mapping was performed for the entire epicardium (112 electrodes sock array) and the LV endocardium (112 electrodes balloon array). VF was induced by applying a 9-volt battery on the epicardium. As soon as the VF episode was induced, perfusion was turned off for 200 seconds mimicking global ischemia. At the end of this period the perfusion system was turned back on at a flow similar to baseline for an additional 140 seconds, mimicking a state of reperfusion. The hearts were then defibrillated and this protocol was repeated twice after a rest period of 5 minutes. For the analysis, 20 s electrograms located on the LV freewall (both endo and epi) were recorded at t = 0, 90, 180, 260 and 320s, for a total of 11520 electrograms. Local Activation Rates (LAR) for each electrogram was determined as the dominant frequency (DF) corresponding to the highest value in the power spectrum between 1.5 and 8 Hz. Results: Activation rate decreased from 4.962±0.020 Hz to 3.704±0.022 Hz (p<0.0001) during the 200 seconds of global ischemia. During the 140 seconds of reperfusion the activation rate increased to 4.882±0.024 Hz (p<0.0001). This value was comparable to what was measured at the onset of VF (p = 0.011). These changes of rates were similar for both endocardium and epicardium data (p = 0.0236). Conclusions: During long episodes of human VF, global myocardial ischemia leads to slowing of activation rate on the epicardium and endocardium. Two minutes of re-perfusion leads to reversal of this effect. These findings may support the recent change in CPR guidelines.
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