Effect of body hypothermia on transventricular simple-capacitor-discharge defibrillation thresholds

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Abstract
In 260 successful transventricular simple-capacitor-discharge defibrillations performed on 20 mongrel dogs under conditions of body hypothermia, an overall average peak current threshold of 69.5 mA/g of heart (SD 30.4) was found. This value, when compared by the unpaired t-test with previous data obtained under conditions of relative normothermia (89.5 mA/g of heart, SD 32.8, 346 defibrillations, 20 dogs), yielded a highly significant difference (P .mchlt. 0.1%). When comparing the deviation of the regression equation (current vs. temperature) from the horizontal line, the Snedecor F test also gave a high level of significance (P .mchlt. 1%). Body hypothermia evidently significantly reduces transventricular defibrillation thresholds. After normalizing the regression equations, this reduction on the average was equal to 4.1%/.degree. C (SD 1.4) for current and to 5.9%/.degree. C (SD 1.4) for energy over the 20 dogs. In all animals, the coefficient of variation was greater for energy than for current (about twice as much), suggesting that current is a better descriptor of what is needed for electrical defibrillation. The transventricular impedance was rather constant, yielding an overall average of 28.5 .OMEGA. (SD 6.0).

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