Investigation of Heart Rate Variability after Cardiopulmonary Resuscitation and Subsequent Hypothermia

Abstract

The time between cardiac arrest and cardiopulmonary resuscitation (CPR) determines the intensity of neuronal cell damage. Induction of mild hypothermia (cooling the body kernel to 33°C for about. 24 hours) directly after cardiopulmonary reanimation improves the patient’s neurological outcome. Therefore, the objective of this study was to investigate if there are different patterns of heart rate regulation in cardiopulmonary resuscitated patients during mild hypothermia differentiating between survivors (rated by the Glasgow outcome score, GOS 4–5) and deceased patients (GOS 1). Long-term ECG was monitored for 30 minutes from patients in intensive care unit directly after normothermia achievement. 18 CPR patients (5 patients with GOS 4, age 59.8±19.1 and 4 patients with GOS 5, age 56.2±14.5 vs. 9 patients with GOS 1, age 66.7±7.7) with stable cardiovascular circulation and cardiac sinus rhythm were enrolled in this study. Autonomic regulation was assessed applying heart rate variability (HRV) analysis. Six HRV parameters were calculated and revealed significant differences in the autonomous regulation of heart rate between both groups during the hypothermia period directly after thermal recovery: sdNN (40.2±19.5 vs. 10.9±4.1, p=0.013), cvNN (0.06±0.03 vs. 0.02±0.007, p=0.01), sdaNN1 (21.2±9.3 vs. 7.5±2.7, p=0.008), renyi0.25 (4.2±0.6 vs. 2.8±0.4, p=0.01), renyi2 (3.5±0.6 vs. 1.9±0.4, p=0.008) and finally, shannon (3.7±0.6 vs. 2.2±0.4, p=0.008). Applying HRV analysis in this study we could demonstrate the occurrence of different patterns in the autonomic cardiovascular regulation in cardiopulmonary resuscitated patients after mild hypothermia treatment. Reduced HRV was recognised in deceased patients, which suggests an association with the final neurological outcome. Therefore, the HRV measures might support the prognosis of beneficial effects of mild hypothermia and thus, the prediction of the patient’s outcome.