The Significance of Changes in the Electrocardiogram in Hypothermia

Death from ventricular fibrillation is the gravest risk that attends the current use of hypo- thermia in surgery of the heart and brain.Any reliable warning of its approach would clearly be important.In 1938 Tomaszewski published electrocardiograms from an accidentally frozen patient that showed an extra, slowly inscribed deflection between the QRS complex and the early part of the S-T segment.This deflection was produced experimentally in dogs in 1943 by Grosse-Brockhoff and Schoedel, and has been described by several workers since, both in patients and in animals deliberately cooled.Osborn (1953) considered that it represented a current of injury caused by the acidosis that develops in hypothermic animals allowed to breathe spontaneously: he thought that it heralded ventricular fibrillation and was a very bad prognostic sign.This opinion has been repeatedly quoted and very recently Fleming and Muir (1957) considered that the association of the deflection with ventricular fibrillation was confirmed.This view received theoretical backing from the work of Hegnauer and his colleagues (Covino and Williams, 1955; Covino and Hegnauer, 1955).They thought that during the time occupied by the deflection, the threshold of cardiac muscle to artificial stimulation was strikingly reduced.Hegnauer has, however, recently stated that these conclusions were invalid, since the experiments were carried out by a technique that gave rise to artefacts unrecognized at the time (Hegnauer and Covino, 1956).Although there is a danger that this cardiographic sign may be regarded as a warning of the onset of ventricular fibrillation, there have been few reports of the effect of deliberate hypothermia on the cardiogram of patients without heart disease (Lougheed et al., 1955; Gunton et al., 1956; Villamil et al., 1955, 1957; Emslie-Smith, 1956).Further, in the published accounts of the effects of hypothermia on the human cardiogram most workers seem to have followed changes in a single lead only, and the reported incidence of the characteristic deflection is very variable.The changes described in the S-T segment of the hypothermic dog are also varied and confusing.In order to assess the significance of this deflection more carefully it has been studied in hypo- thermic patients with normal hearts, and by the use of direct epicardial electrodes in hypothermic dogs. METHODSHypothermia in Human Subjects.Five anasthetized patients, four of whom had no heart disease, were cooled by ice bags laid on the skin in preparation for craniotomy to arrest subarachnoid haemorrhage.There were 4 women and 1 man, aged 35 to 49 years.While the temperature fell the multiple-lead cardio- gram was continuously monitored in a cathode ray oscilloscope, and recorded when any change was seen.The technical details were described in a previous paper (Emslie-Smith, 1956) and the further subjects of