Abstract 127: The Induction of Mild Hypothermia Does Not Induce Further Sympathetic Activation After Ventricular Fibrillation / Resuscitation in Pigs
Background: The induction of mild hypothermia (MH, 32–34 °C) has become guideline therapy after cardiac arrest, and experimental data indicate a positive inotropic effect of MH. However, cooling causes sympathetic activation (increased noradrenalin levels, shivering) in awake and anaesthetized patients, which might be an adverse side effect of MH after cardiac arrest. Whether or not MH further activates the sympathetic nervous system after resuscitation has not been investigated, yet.
Methods: In 16 anaesthetized pigs (64±2 kg), ventricular fibrillation (VF, 5 min) was induced electrically. After resuscitation including a single bolus of adrenaline (1 mg), pigs were assigned either to normothermia (38 °C, n=8, NT) or to MH (33 °C, n=8, intravascular cooling device). At control conditions and at 10 min, 1 h, 2 h, 4 h, and 6 h after return of spontaneous circulation (ROSC), the heart rate variability (HRV) of a 15-min-ECG-sample was analyzed, and blood samples were drawn. The high-frequent-fraction (HF, 0.07–0.5 Hz) of HRV represented parasympathetic tone, the ratio between low-frequent-fraction (LF, 0.01–0.07 Hz) and HF represented sympathetic tone. Catecholamine-levels (adrenaline, noradrenaline and dopamine) were assessed by commercial RIA-kits.
Results: HF decreased in both groups at 10 min after ROSC (MH: 41±6 vs 68±5, p<0.05; NT: 29±4 vs 64±7, p<0.05). At 2 h after ROSC, HF was already higher in MH than in NT (76±3 vs 37±5, p<0.05), and LF/HF was already lower in MH than in NT (0.21±0.05 vs 1.75±0.43, p<0.05). At 6 h after ROSC, HF and LF/HF were back to control values in both groups. There was no difference between both groups in the concentration of catecholamines at any time point.
Conclusions: Both HRV and catecholamine levels indicate that the induction of MH does not lead to a further sympathetic activation after VF and resuscitation. Thus, beneficial effects of MH on cardiac function do not rely on an increased sympathetic tone.
- © 2010 by American Heart Association, Inc.