Depression is a recognized risk factor for coronary heart disease (CHD) and, by studying pairs of twins, researchers from Emory and Yale believe they have found a mechanism that explains this link. In research announced today at the American College of Cardiology's 53rd Scientific Sessions in New Orleans, the scientists say they found a decrease in heart rate variability (HRV) in those twins who were depressed as compared to their non-depressed siblings.
The scientists studied 50 pairs of male twins between the ages of 47 and 57 who were free of symptomatic CHD. Twenty-four hour ambulatory electrocardiograms (ECGs) of these research subjects were analyzed and depressive symptoms were measured with the Beck Depression Inventory. The lifetime history of major depression of each man was also assessed with the Structured Clinical Interview for Psychiatry Disorders .
"Within each pair of twins we studied, HRV parameters were strongly related with the severity of depressive symptoms. A lifetime history of major depression was related to HRV only in presence of current depressive symptoms -- but people with depressive symptoms had decreased HRV also in absence of a lifetime history of major depression. These findings are important because decreased HRV is a heart disease risk factor," says Emory Heart Center cardiologist Viola Vaccarino MD, Ph.D., lead author of the study. "And these results are even more remarkable for the fact that they are derived from twin study design, which is semi-experimental and allows tight control for extraneous factors. "
She explains that HRV reflects the beat-to-beat fluctuations in heart rate noted on the EKG that are governed by the autonomic nervous system ( the portion of the nervous system that controls the body's visceral functions, including action of the heart). "Autonomic dysfunction, as reflected by decreased HRV, is a plausible mechanism linking depression to CHD because it can raise the risk of arrhythmias and sudden death," Dr. Vaccarino says.
She adds that the results of the twin study are important not only because they provide an explanation for how depression increases CHD risk in persons without CHD initially, but also because they underscore the clinical significance of minor depression in addition to major depression. "The data suggest that treatment of clinical depression, and perhaps also minor forms of depression, should reduce the risk of CHD via normalization of HRV," Dr. Vaccarino states. "Hopefully, there will be future clinical trials to test this idea in a controlled, randomized fashion. "
Other members of the research team include Rachel Lampert MD and Forrester Lee MD of the Yale School of Medicine, New Haven, CT, J. Douglas Bremner MD, Jerome L. Abramson PhD, Nancy Murrah RN, Nadeem Afzal MD, and Faiz Cheema MD of the Emory University School of Medicine, Atlanta, GA, and Jack Goldberg PhD, of the Seattle VA ERIC/VET Registry, Seattle, WA.
The study was sponsored by the National Heart, Lung and Blood Institute (NHLBI).