Ventricular fibrillation threshold in the three-toed sloth (Bradypus tridactylus).

The ventricular fibrillation threshold (VFT) can be defined as the minimum electrical value able to trigger fibrillation. The objective was to determine the threshold fibrillatory current in the three-toed sloth, animal which may show spontaneous defibrillation. Ten specimens were used (average weight 3.9 kg, SD 0.28). Two electrodes of the spoon type were laterally applied to the ventricles, stimulating with a nonsynchronized train of rectangular pulses, variable amplitude, until fibrillation was established. Applied voltage and current were displayed on a storage oscilloscope. The average VFT current was 2.3 mA/g of heart (SD 0.4). Each threshold was obtained as the mid-range value between the maximum current which did not fibrillate and the minimum one which did fibrillate. Out of 98 fibrillations, 40% showed spontaneous reversal before 60 sec of fibrillation were completed. Beyond that time, electrical defibrillation was instituted. Three puppies (average weight 5.2 kg, SD 1.4) yielded an average VFT of 0.59 mA/g of heart (SD 0.14) using the same procedure. When the two VFT were compared (unpaired "t"-test), a significant difference was found (t 6.35; p less than 0.001), concluding that sloths would appear as more difficult to fibrillate than dogs of comparable body size.