458 BELL SYSTEM TECHNICAL JOURNAL 



ventricular muscle fibers in contrast to their normal coordinated and 

 rhythmic contraction. It results from an abnormal stimulation rather 

 than from damage to the heart. In the fibrillating condition, the heart 

 seems to quiver rather than to beat; no heart sounds can be heard with 

 a stethoscope; the pumping action of the heart ceases; failure of circu- 

 lation results in an asphyxial death within a, few minutes. The 

 medical profession long has recognized that ventricular fibrillation once 

 set up in man is unlikely to cease naturally before death. The value 

 of current just under the threshold for ventricular fibrillation, there- 

 fore, may be taken as the maximum current to which man safely may 

 be subjected, because regardless of rescue or after-treatment, death 

 is liable to result from greater current. 



This experimental investigation, therefore, was directed chiefly 

 toward determining the minimum current that would initiate ventri- 

 cular fibrillation and the variation of this threshold current with 

 several factors which enter into the practical application of the results 

 in the development of protective devices and measures. From the 

 standpoints of both physiology and engineering, it was important to 

 determine the influence on this threshold of: 



1. Species and size of animal. 



2. Path of current through the body (determined by points of contact). 



3. Frequency of the current. 



4. Time of occurrence of short shocks in relation to the cardiac cycle. 



5. Duration of shock. 



Thresholds were determined for seven species of animals: the guinea 

 pig, rabbit, cat, dog, sheep, pig, and calf. Standard reference condi- 

 tions included the use of 60-cycIe alternating current for a duration of 

 3 seconds with electrodes on the right fore leg and left hind leg. These 

 conditions typify those of many accidental shocks to man and are very 

 dangerous from the point of view of ventricular fibrillation because the 

 heart is almost directly in the current path. 



Three significant records were made by an oscillograph for each 

 shock. These are illustrated in Figs. lA and IB. They include elec- 

 trocardiograms before and after shock and oscillograms of shock cur- 

 rent and voltage. An electrocardiogram is a graphical record of the 

 time variation of the voltage that is always associated with the action of 

 the heart. The character of the variations in this voltage indicate 

 certain facts as to the heart's condition, the electrocardiogram of a 

 fibrillating heart being very different from that of a normal heart. 

 The group of Fig. lA shows a shock followed by coordinate beating. 

 The group of Fig. IB shows a shock which resulted in ventricular 



