While anoxic hearts of normothermic dogs can be uniformly defibrillated by a single 220 v. shock of 0.10 second duration, defibrillation by the same technique is not so readily accomplished in hypothermic dogs, as shown by previous studies in this laboratory1,2 (Table 1). Defibrillation by repeated shocks was always possible, however, and an effective heart beat was restored in all instances, though not without difficulties in some.
Swan and co-workers,3,4,5 found "that the fibrillating hypothermic heart could rarely be converted to a normal rhythm by massage and electric shock. However, when the coronary arteries of the fibrillating heart were perfused with potassium chloride (1 mEq. per ml.) the fibrillation could usually be converted directly or by use of electric shock."
The object of this experiment was to compare the effectiveness of potassium chloride and electric shock in defibrillating the hearts of hypothermic dogs.
KYLE RH, KIRBY CK. The Use of Potassium Chloride for Defibrillation of the Ventricles of the Hypothermic Dog. AMA Arch Surg. 1957;74(1):136-138. doi:10.1001/archsurg.1957.01280070140017