High resolution ECG changes in survivors of out-of-hospital cardiac arrest during and after mild therapeutic hypothermia

Our aims were to determine whether mild therapeutic hypothermia (MTH) is associated with ECG changes similar to those observed in accidental hypothermia, and to use advanced ECG parameters to further characterize any electrophysiological changes associated with MTH. The study included 46 patients (35 after primary, 9 after secondary, and 2 after heart arrest of undetermined type), treated with MTH. In all patients, a 5-minute 12-lead high fidelity ECG was recorded during MTH and in normothermia, with core body temperatures 33.0 ± 0.6 and 37.2 ± 0.6 °C, respectively. Custom software programs were used to calculate several conventional and advanced ECG parameters. During MTH, changes in standard ECG parameters included significantly increased RR, PR and QTc intervals, as already described in the literature. Utilizing advanced ECG, we also found significantly increased HRV, QRS vector amplitude and spatial ventricular gradient, but decreased QTV and narrower spatial QRS-T angle. We conclude that hypothermia significantly affects electro physiological characteristics of heart muscle and suggest that recovery from MTH is associated with increased sympathetic drive.