New research in the US suggests that a simple 15-minute electrocardiogram could help a doctor determine whether a patient has major depression or bipolar disorder.

Bipolar disorder often is misdiagnosed as major depression. But while the symptoms of the depressive phase of bipolar disorder are similar to that of major depression, the treatments are different and often challenging for the psychiatrist. Treatment for the depressed phase of bipolar includes an antidepressant along with a safeguard such as a mood stabilizer or antipsychotic drug to prevent a switch to a manic episode. A doctor who misdiagnoses bipolar disorder as major depression could inadvertently trigger a manic episode by prescribing an antidepressant without the safeguard of an accompanying mood stabilizing drug.

Researchers at Loyola University found that heart rate variability, as measured by an electrocardiogram, indicated whether subjects had major depression or bipolar disorder (heart rate variability is a variation in the time interval between heartbeats). The study, led by Professor Angelos Halaris, was published in the World Journal of Biological Psychiatry.

"Having a non-invasive, easy-to-use and affordable test to differentiate between major depression and bipolar disorder would be a major breakthrough in both psychiatric and primary care practices," Dr. Halaris said.

In measuring heart rate variability, researchers computed what is known to cardiologists as respiratory sinus arrhythmia (RSA). At the baseline (beginning of the study), the subjects with major depression had significantly higher RSA than those with bipolar disorder.

In a secondary finding, researchers found that patients with bipolar disorder had higher blood levels of inflammation biomarkers than patients with major depression. Inflammation occurs when the immune system revs up in response to a stressful condition such as bipolar disorder.

Though these initial results are promising, the study only enrolled 64 adults with major depression and 37 with bipolar disorder so further research is needed to confirm the study's findings and determine their clinical significance.

Reference: Brandon Hage, Briana Britton, David Daniels, Keri Heilman, Stephen W. Porges, Angelos Halaris. Low cardiac vagal tone index by heart rate variability differentiates bipolar from major depressionThe World Journal of Biological Psychiatry, 2017; 1 DOI: 10.1080/15622975.2017.1376113