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Effects of local epicardial cooling/warming on the complexity of the ventricular fibrillatory pattern

In ten Langendorff-perfused rabbit hearts localized cooling/warming were induced by a specific device in a ventricular epicardium area (modified zone, MZ) during ventricular fibrillation (VF). Epicardial electrical activity was mapped in MZ and another area of the same ventricle (NMZ), during basal temperature (37 oC), MZ-hypothermia (32 oC, 27 oC, 22 oC) and MZ-hyperthermia (42 oC). We analyzed: 1) the mean fibrillatory interval (VV) at each temperature step, and 2) the complexity of the activation maps (I, II and III classification, in increasing order) at basal temperature, hypothermia-22 oC and hyperthermia. In MZ, VF was decelerated by hypothermia (VV: 65 ± 16 vs 52 ± 10 ms, p<;0.05) and accelerated by hyperthermia (VV: 44 ± 7 vs 52 ± 7 ms, p<;0.05), in a reversible manner. VV changes with temperature in MZ fitted to a lineal model (r=-0.52, p<;0.0001). In NMZ, no significant differences were observed. Epicardial hypothermia induced a significant variation in the complexity of the VF activation maps in MZ respect NMZ, with type III increments and type II decrements (MZ-22 oC: I = 7%, II = 31%, III = 62%; NMZ-22 oC: I = 7%, II = 47%, III = 46%, p<;0.01). We conclude that local myocardial warming accelerates VF, and local myocardial cooling decelerates VF and increases the complexity of the VF activation pattern.