The Termination of Cardiac Arrythmias by Direct Current Shock.

THE use of DC, shock in the treatment of cardiac arrhythmias has been pioneered by Lown and his associates 1(1962). We are reporting our first 100 patients treated by this method. For those unfamiliar with this technique a short historical and technical introduction is appended. Introduction In 1899 Prevost and Batelli showed that the passage of a small current through the heart muscle (shock) provoked ventricular fibrillation and that the flow of a very strong current over a short period stopped fi;brillation (counter-shock). They used both Alternating Current (AC) and Capacitator Discharge (Direct Current-DC) for defibrillating the heart. This discovery remained unexploited until the advent of cardiac surgery. Ventricular fibrillation in the human heart was first successfully terminated with AC shock by Beck, Pritchard and Feil (1947) in the exposed heart (internal defibrillation) and (1956) through the intact chest'(external defibril-lation). DC shock i(capacitator discharge) was compared with AC in the treatment of ventri-cular fibrillation by Kouwenhoven and Milnor (1956) who considered it inferior, but Lown, Neuman, Amarasingham and Bertovitz who restudied the problem in 1962, convincingly demonstrated the superiority of DC. There are two differences between AC and DC shocks '(Fig. 1). The former consists of alternating positive and negative waves of electricity , the latter of a very brief undirectional pulse. An AC shock lasts 100-200 milliseconds, a DC shock approximately 4 milliseconds. Both the peak voltage and current of a DC shock are very high (about 4,000 volts and 80 amps) so that a very large amount of energy is released in a very short time. An AC shock of similar defibrillating efficiency would have a much smaller current and voltage, but because of very much longer duration the total energy would be rather larger. The effectiveness of a DC shock can be improved by altering the wave-form from the exponential pattern of simple capacitor discharge to a more rounded form by means of an inductance in the circuit. Zoll and others (1956) showed that AC shock would terminate supraventricular arrhy-thmias including atrial flutter and fibrillation, but in a proportion of cases ventricular fibril-lation was produced. Abe and Harken (1963) explored the mamma-lian cardiac cycle in a number of species using a DC shock of 2.5 milliseconds duration and found that there was a 'vulnerable period' of 20-40 milliseconds duration just before the peak of the T wave (Fig. 2). A shock delivered during this period would initiate …