Rhythm and Blues: Using Heart Rate to Diagnose Depression

Jackie Rocheleau

March 30, 2021

Depression might be a disorder of the brain, but its harms aren't confined to the cranium. Prolonged depression has been linked with a slew of health problems, from impaired immune function to gastrointestinal dysfunction. It's also been linked with cardiovascular disease (CVD), even increasing the risk for heart attack and a disrupted heart rate. Now, researchers are exploring whether heart function could be a valuable biomarker in informing depression diagnosis and treatment.

Major depressive disorder has proven difficult to diagnose and treat, and biomarkers that indicate a depressive episode or suggest specific interventions would be an attractive solution to its clinically nebulous nature.

Currently, diagnosing depression relies on the patient effectively communicating their symptoms. If the patient does receive a diagnosis, treating it remains a matter of trial and error. It takes weeks to know whether a treatment is working, and in only one third of cases does the condition go into remission after the patient is initially prescribed an antidepressant. Even after successful treatment, it's challenging to identify who might be at risk for relapse, and when. Research now shows that cardiac biomarkers may be a way improve this picture. Clinicians could use changes in heart rate to both inform depression diagnosis and gauge a patient's predicted response to treatment.

Given the increased risk for CVD among people with depression and the link between heart rate changes and CVD risk, these biomarkers could have implications for heart health, too. "We need more than just the current toolkit," said Amit Shah, MD, a cardiologist and assistant professor of epidemiology at Emory University, Atlanta, Georgia. "Ultimately, what we're trying to do is develop interventions not only for depression but also for the associated physical health problems related to depression, in particular, cardiovascular disease," he said. These overlapping interests ― and the prospect of clinically considering both conditions in tandem ― mean this research is "really worth its weight in gold," adds Shah.

The Data on Heart Rate Biomarkers

Patients with depression are often found to have lower heart rate variability (HRV) and higher heart rates. Scientists don't know the mechanisms underpinning this relationship but think changes in the autonomic nervous system during depression, as well as stress generally, have a role.

Rébecca Robillard, PhD, is the head scientist of the Clinical Sleep Research Platform at the Royal's Institute of Mental Health Research, Ottawa, Canada. In a 2019 study published in BMC Psychiatry, Robillard's team used electrocardiogram recordings from sleep studies to see whether heart rate abnormalities were associated with depression. Using a profiling algorithm to analyze heart rate and HRV data, the team identified persons with depression with 80% accuracy among 174 people with sleep complaints.

"It's still early days, but our work certainly suggests that [HRV and heart rate] could serve as potential biomarkers," Robillard said.

In another study, Stephan Claes, MD, PhD, psychiatrist and professor of psychiatry at Katholieke Universiteit Leuven, Leuven, Belgium, and his group tested the biomarker potential of heart rate and HRV data that were continuously recorded over several days. They too used an algorithm to distinguish 16 people with treatment-resistant depression from 16 without depression. Within the depression group, they used the algorithm to distinguish patients who had received ketamine treatment from those who had not.

The algorithm could differentiate between the depressed and nondepressed groups with 90% accuracy. Those with depression had higher overall heart rates, particularly at night, and lower HRV. Claes noted that, unlike in other studies, "the most reliable parameter that we had for this prediction was the heart rate, not the HRV." After treatment, heart rates improved, but HRV remained the same.

Although their study has not yet been peer reviewed and more research is needed, Claes thinks that increased heart rate, especially during the night, could eventually serve as a warning sign of depression relapse. "That would allow a quicker referral to care and better care because of earlier intervention," he said.

Finding a Signal Amid the Noise

But heart rate and HRV aren't foolproof biomarkers. Some studies have found that antidepressant use lowers HRV and that HRV changes aren't unique to depression. There's the added complication that depression often overlaps with other mental disorders.

"I think we've been very disappointed about the success of using particular biomarkers for particular disorders, because the majority of mental disorders are very heterogeneous," said Andrew Kemp, PhD, psychology professor at Swansea University, Swansea, United Kingdom. "A particular biomarker will, at the end of the day, be just one particular aspect of the overall profile that clinicians will have on particular individuals."

The clinical utility of a heart rate–depression connection may go both ways.

For instance, depression could serve as a warning sign for atrial fibrillation, according to research from Parveen Garg, MD, an associate professor of clinical medicine at the University of Southern California Keck School of Medicine, Los Angeles, California. In a study involving more than 6000 people, Garg showed that higher scores on depression scales correlated with a higher risk for the occurrence of atrial fibrillation over a follow-up period of about 13 years.

Depression is associated with other heart conditions as well. "A lot of data seem to suggest that just the presence of depression can increase risk for a whole range of cardiovascular problems," said Garg. Epidemiologic studies have found associations between depression and the development of coronary heart disease and a modest increased risk for stroke.

"Things going on in your brain also have effects on the rest of your body," said Garg. "Just recognizing this link, that maybe mental illness has an effect on other illnesses or diseases that can affect other parts of your body ― I think that's something we can share now."

Jackie Rocheleau is a freelance journalist covering health and science. Her work has appeared in Forbes, Knowable, Scientific American, and other publications.

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