Abstract 175: Cerebral and Myocardial Mitochondrial Injury Differ in a Rat Model of Cardiac Arrest

Abstract

Introduction: Neurologic and myocardial dysfunction after successful resuscitation is prominent and mitochondrial dysfunction is predicted to be a key determinant of poor outcomes. Mitochondria contribute a critical role as effectors and targets of reperfusion injury. However, the onset and severity of mitochondrial dysfunction during cardiac arrest (CA) is not fully understood. The present study was done to explore whether changes in cerebral and myocardial mitochondria differ after cardiac arrest and cardiopulmonary resuscitation (CPR). Hypothesis: Mitochondrial injury is more severe in the brain compared to the heart during and following cardiac arrest and CPR. Methods: Sprague-Dawley rats weighing between 450 - 550 g were randomized into 4 groups (n=6): 1) sham (surgery, no ventricular fibrillation (VF) or CPR), 2) VF (VF 8 mins, no CPR); 3) VF and CPR (VF 8 mins and CPR 8 mins, no defibrillation); ROSC 1 h (VF 8 mins, CPR 8 mins, defibrillation, and observe 1 h after ROSC). VF was induced through a guide wire advanced from the right jugular vein into the right ventricle. Brain and heart mitochondria were extracted by differential centrifugation and used to measure oxidative phosphorylation and calcium retention capacity (CRC). Results: Compared with sham, brain mitochondrial CRC in VF, VF+CPR and ROSC 1 h were decreased (110±11 vs. 70±13, 62±24, 50±6 nmol Ca 2+ /mg protein, p<0.05). However, the CRC of the heart mitochondria was decreased only 1 h after ROSC compared to sham (1000±150 vs. 1000±84, 993±78, 600±76 nmol Ca 2+ /mg protein). Brain mitochondrial oxidative phosphorylation with complex I substrate glutamate in VF, VF+CPR and ROSC 1 h were all decreased compared to sham (127 + 8 vs 92±17, 84±12, and 92±15, p<0.05). This contrasted myocardial mitochondria oxidative phosphorylation which had no impairment (324±3 vs 338±46, 379±29, and 323±45). Conclusions: Mitochondria in the brain are more sensitive to injury during CA and CPR compared to heart mitochondria. With markedly decreased CRC, mitochondria are likely to contribute to cerebral reperfusion injury during CPR and ROSC. Preservation of cerebral mitochondrial activity and mitochondrial function during cardiac arrest may improve post-resuscitation neurological function.