Changes in cardiac rhythm and in the form of the electrocardiogram resulting from induced hypothermia in man

Electrocardiograms were recorded in twenty-nine adult patients during hypothermia which was induced for the performance of cerebrovascular surgery. Twenty-four of the patients had no clinical or electrocardiographic evidence of heart disease. At body temperatures of 28 to 30°C. electrocardiographic abnormalities appeared in many of the patients. The heart rate slowed; the P-R and Q-T intervals and the duration of the QRS complex were lengthened; S-T segment and T-wave changes appeared. Auricular fibrillation or other auricular arrhythmias occurred in nineteen patients. Ventricular fibrillation occurred in two patients. Cardiac massage was followed by recovery in one of these. The change in impulse origin and conduction and the auricular arrhythmias did not produce serious hemodynamic disturbances. Postoperatively at normal body temperature, the electrocardiograms revealed a return to sinus rhythm. In a few cases the S-T segment and T-wave changes persisted or appeared in the first few days after operation. It is concluded that auricular fibrillation is a frequent occurrence when the body temperature of human subjects without heart disease is lowered to 28 to 30°C. Usually this arrhythmia is benign, restricted in time to the period of hypothermia, and is not followed by a disturbance of heart function.