Fransthoracic Ventricular Defibrillatlon with Square-wave Stimuli: ONE-HALF CYCLE,

• In 1960 Kouwenhoven, Jude, and Knickerbocker reported that adequate circulation of the blood could be achieved by means of closed chest cardiac massage. This technique is said to permit the oxygen demands of the myocardium to be satisfied by external means and thereby makes practical the utihzation of transthoracic electric shock for the reversal of ventricular fibrillation. However, Del Guerico et al.,have observed low cardiac output in three patients undergoing external cardiac massage. Alexander et al. reported successful treatment of ventricular tachycardia by transthoracic electric shock in 1961. Their paper was followed by others, particularly from Lown's group *~° which described the successful use of transthoracic shock for terminating a variety of other cardiac arrhythmias. As a result of both these developments, the use of electric shocks applied by means of electrodes held on the surface of the chest has assumed an appreciably increased clinical importance in the treatment of cardiac arrhythmias. With this increased importance and use has come a renewal of interest in evaluating the effectiveness of different types of electric shocks in order to find the most satisfactory waveform. This interest has led to the development of several types of external defibrillators which deliver capacitor discharges.