Cerebral metabolic rate of oxygen is correlated to treatment effect of electroconvulsive therapy in patients with depression

Background: Neurobiological understanding of the antidepressant mechanisms of electroconvulsive therapy (ECT) is important to advance the treatment. ECT may work by improving depression-related alterations in the cerebral oxygen metabolism. Methods: 21 in-patients with depression treated with an ECT series were examined 1) within two days before, and 2) a few days (median = 4 days) after the last ECT session. Depression severity was assessed by the six-item Hamilton Depression Rating Scale (HDRS-6). Magnetic resonance imaging (MRI) was used to measure 1) global cerebral blood flow (CBF) by phase contrast mapping technique and 2) global cerebral metabolic rate of oxygen (CMRO₂) by measuring cerebral extraction of oxygen (A-V.O₂) using susceptibility-based oximetry. Statistical analyses were performed using multiple linear regression, adjusting for age and gender. Results: ECT relieved depressive symptoms from HDRS-6 = 13.9 to 5.2 (p < 0.001), as expected. A larger increase in CMRO₂ after ECT was correlated with a better treatment effect (0.5 % reduction in HDRS-6 per 1 % increase in CMRO₂, adjusted R² = 0.24, p = 0.026). The effect was driven by both higher A-V.O₂ and increased CBF. Before ECT, an abnormal decoupling between CMRO₂ and CBF was observed, which was normalized after the treatment (adjusted R² = 0.17, p = 0.03). Conclusions: The treatment effect of ECT for depression was associated with increased CMRO₂. Furthermore, ECT restored the normal coupling between CBF and CMRO₂. The results suggest that the cerebral oxygen metabolism may be abnormally altered in patients with depression and ECT restores such dysfunction.