Affective disorders are associated with an increased risk of cardiovascular disease, which, at least partly, appears to be independent of psychopharmacological treatments used to manage these disorders. Reduced heart rate variability (SDNN) and a low Omega-3 Index have been shown to be associated with increased risk for death after myocardial infarction. Therefore, we set out to investigate heart rate variability and the Omega-3 Index in euthymic patients with bipolar disorders.

We assessed heart rate variability (SDNN) and the Omega-3 Index in 90 euthymic, mostly medicated patients with bipolar disorders (Bipolar-I, Bipolar-II) on stable psychotropic medication, free of significant medical comorbidity and in 62 healthy controls. Heart rate variability was measured from electrocardiography under a standardized 30minutes resting state condition. Age, sex, BMI, smoking, alcohol consumption and caffeine consumption as potential confounders were also assessed.

Heart rate variability (SDNN) was significantly lower in patients with bipolar disorders compared to healthy controls (35.4 msec versus 60.7 msec; P<0.0001), whereas the Omega-3 Index did not differ significantly between the groups (5.2% versus 5.3%). In a linear regression model, only group membership (patients with bipolar disorders versus healthy controls) and age significantly predicted heart rate variability (SDNN).

Heart rate variability (SDNN) may provide a useful tool to study the impact of interventions aimed at reducing the increased risk of cardiovascular disease in euthymic patients with bipolar disorders. The difference in SDNN between cases and controls cannot be explained by a difference in the Omega-3 Index.