Cardiac Arrhythmias following Condenser Discharges Led through an Inductance: Comparison with Effects of Pure Condenser Discharges.

• Transthoracic defibrillaton of the heart can be accomplished by several types of electric impulses, but more information is needed concerning the most suitable voltage and wave form for such impulses. In an earlier study reported in this journal, we described a method of applying graded condenser discharges during selected phases of the cardiac cycle through the intact chest walls of dogs under thiopental anesthesia. The applied voltages ranged from 0.5 to 6 kilovolts, the condenser capacities from 0.5 to 100 microfarads, and the energies from 0.06 to 1800 watts. It was found that the severity of the arrhythmias caused by these discharges increased progressively as the voltage was increased, and to a lesser degree as the total amount of electrical energy was increased. Arrhythmias were significantly more severe when the shock was delivered during the refractory period (ST interval) than during the excitable stage (P-interval) of the cardiac cycle. Work on this problem has been continued in order to find what forms of condenser discharge would produce the mildest and briefest arrhythmias. The present paper describes the effects on cardiac rhythm of condenser discharges modified by passage through an inductive resistance in series with the condenser. Such an inductance (between the condenser and the animal) changes the shape of the discharge curve; it reduces the voltage, lengthens the duration and changes the wave form (fig. 3, below). This discharge