In an endeavour to develop a safe and easy technique for operating on the open heart, profound hypothermia was induced in dogs by means of an extra-corporeal circulation with pump oxygenator and heat exchanger until the temperature in the pharynx reached 150 C. The circulation was then arrested completely for up to 45 minutes before warming was commenced. The success of these experiments lead to the use of the method in fourteen patients. During the cycle of cooling, complete circulatory arrest, and warming, the changes in the electrical activity of the myocardium were found to follow a regular pattern which is described in this paper.
METHODSHypothermia was induced by means of a low-flow partial cardio-pulmonary bypass through a modified de Wall bubble oxygenator (De Wall et al., 1956;Cooley et al., 1958) and a heat exchanger (Brown et al., 1958) the blood being taken from the right atrium and returned to the patient through a cannula placed in the external iliac artery. If the atrial septum was intact the left atrium was decompressed by draining its blood into the venous reservoir of the machine whenever cardiac action was impaired.Anesthesia was induced with thiopentone, and maintained with intratracheal nitrous oxide and oxygen, with d-tubocurarine to facilitate the control of respiration. During the bypass no anaesthetic agent was given, pure oxygen was administered through the endo-tracheal tube, and a mixture of 95 per cent oxygen and 5 per cent carbon dioxide was used in the bubble oxygenator.Temperatures were measured with glass thermometers in the pharynx and in the pericardial cavity adjacent to the myocardium. The lowest pharyngeal temperatures varied between 130 C and 180 C. and the lowest temperatures measured in the pericardial cavity between 50 and 140 C. (Fig. 1). When the pharyngeal temperature was in the vicinity of 150 C. circulatory arrest was obtained by turning off the pump oxygenator and occluding the vent cavl. The longest period of circulatory arrest was 53 minutes, and the shortest 12 minutes.A continuous electrocardiographic record was made throughout the phases of cooling, arrest, and warming in 11 cases using a Sanborn twin viso direct writer, running at paper speeds of either one, ten, or twenty-five millimetres per second. Incomplete records were obtained in the other three cases using an N.E.P. photographic recorder.Of the fourteen patients, eight had atrial septal defects of the secundum type and two of these had associated partial anomalous pulmonary venous drainage; one patient had an atrial septal defect of the 'primum' type and a separate secundum defect. Two patients had Fallot's tetralogy, and one of these also had an absent left pulmonary artery. Of the remaining three, one had rheumatic 265 group.bmj.com on April 12, 2015 -Published by http://heart.bmj.com/ Downloaded from
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