MYOCARDIAI. 



ITARILITY— HEGNAUER and COVINO 



339 



A 4 



I i I 

 Control ECG at 25** C 



B 



25**^ fmin. after start of infusion 



Fig. 6. — Progressive ECG changes in hypothermic dogs during continuous infusion of isotonic 



calcium chloride. 



pH reversal at low temperature ; but the latter, at any rate, appears so at normal 

 temperature.^' (b) Reversal of the ECG to normal is readily accomplished by 

 revvarming even before pH restoration is advanced (luipublished data), (c) Several 

 investigators have commented upon the fact that spontaneous fibrillation rarely if 

 ever occurs above the 25° to 26° temperature. First note was made in connection 

 with "rewarming"' death^ which is also fibrillary, and which to date has not been 

 seen above 25°. During cooling, fibrillation is anticipated in a proportion of dogs 

 when the 25° to 26° level has been reached or passed.^- ^' ^- The development of an 

 acidotic state, too, is gradual and progressive, and one may with equal logic pro- 

 pose that the critical pH for fibrillation is reached at 25° imder the experimental 

 conditions described. Despite this, our own impressions favor temperature, as the 

 important factor, (d) The degree of acidosis required to produce diastolic threshold 

 changes in normothermic dogs is greater than that in hypothermic (6.5-6.9 vs. 

 7.1-7.2).'"' (e) The increased sensitivity to exogenous calcium is apparently a 

 temperature effect. 



REFERENCES 



1. Hegnauer, A. H., D'Amato, H. E., and Flynn, J. : Influence of intraventricular catheters on 



course of immersion hypothermia in the dog, Am. J. Physiol. 167 : 63, 1951. 



2. Covino, B. G., Charleson, D., and D'Amato, H. E. : Ventricular fibrillation in the hypo- 



thermic dog. Am. J. Physiol. 178: 148, 1954. 



