Low heart rate variability (HRV), as a measure of disrupted autonomic nervous system functioning, has been associated with an increased risk of developing posttraumatic stress disorder (PTSD).
In a prospective, longitudinal study, marines whose HRV was low before they were deployed were significantly more likely to be diagnosed with PTSD after deployment.
"We found that marines and sailors who had lower HRV shortly before deployment to a combat situation were more likely to return home with PTSD," study leader Arpi Minassian, PhD, clinical professor of psychiatry, University of California, San Diego, told Medscape Medical News.
"Our results don't necessarily suggest that lower HRV causes PTSD, rather that it's a harbinger or a signal that the body's stress response system is not functioning optimally and that may put the individual at greater risk of developing PTSD once he or she has been exposed to a trauma," Dr Minassian said.
"The results suggest that we need to continue to pay attention to the biological factors that are associated with PTSD, which might better inform our prevention and treatment efforts," she added.
The study was published online September 9 in JAMA Psychiatry.
Dr Minassian noted that her group and many others have found that lower HRV is related to a higher prevalence of PTSD when both are measured cross-sectionally.
What they knew less about was whether lower HRV, which is theorized to be indicative of a less well-functioning autonomic nervous system, may indicate who might be at risk for PTSD after exposure to trauma.
"A prospective study like the Marine Resiliency Study [MRS] allowed us to start answering that question. PTSD is a major public health problem among returning service members and veterans. Psychological and psychiatric treatments for PTSD can be helpful for some, but not all, veterans who suffer from its symptoms," Dr Minassian said.
"The MRS is a collaboration between the Marine Corps, Navy, Veterans Affairs Health Services Research and Development, and researchers to study risk and resilience factors in PTSD by assessing military service members before a combat deployment and reassessing them after they return," she explained.
Between July 14, 2008, and May 24, 2012, Dr Minassian and her team assessed 2160 active-duty Marines 1 to 2 months before a combat deployment and again 4 to 6 months after their return, as part of the MRS.
In the first phase of the MRS, 59 of 1415 male Marines were found to develop PTSD after deployment.
In the second phase of the MRS, 25 of 745 male Marines were found to develop PTSD after deployment.
The investigators measured HRV using a finger plethysmograph, an optical technique that detects a pulse, for a 5-minute period while the individual was awake and resting.
They then analyzed the interbeat intervals of the heart using algorithms that perform a mathematical transformation of heart rate and divide it into low-frequency (LF) and high-frequency (HF) components.
"Generally speaking, the LF component is thought to reflect the functioning of the sympathetic nervous system, while the HF component is thought to reflect the parasympathetic nervous system.
"Thus, when we examine the ratio between the LF and HF components of heart rate, we can derive an estimate of the balance between these two systems. A higher ratio might mean that the parasympathetic nervous system may not be working well enough to adequately 'calm' the sympathetic nervous system," Dr Minassian explained.
When they correlated predeployment HRV with the prevalence of postdeployment PTSD, the researchers found that lower HRV before deployment was associated with an increased risk for PTSD after deployment (odds ratio [OR], 1.47; 95% confidence interval [CI], 1.10 - 1.98; P = .01).
Of the 2122 Marines whose HRV was in the normal range, 3.7% (78) developed PTSD after deployment, compared with 15.8% (6) of the 38 Marines whose HRV was low.
"Recent meta-analyses suggest that psychological treatments for PTSD are effective for many, but not all, people who struggle with this debilitating disorder. If we could turn our attention to the factors, perhaps biological, that place some at greater risk for developing PTSD, our efforts at prevention will be better informed," Dr Minassian said.
She added that these results need to be replicated by other researchers.
"Additionally, we need to have a better understanding of other biological factors that place people at risk for PTSD, such as markers of inflammation, genes, the brain's response to stress and fear, etc," she said.
In an accompanying editorial, Amit Shah, MD, and Viola Vaccarino, MD, PhD, from Emory University School of Medicine, Atlanta, Georgia, agree that more studies are needed to clarify the role of HRV as a risk biomarker for PTSD.
In an interview with Medscape Medical News, Dr Vaccarino noted that not all individuals exposed to trauma develop PTSD, "so efforts to find biomarkers of susceptibility are important to identify vulnerable persons who may be targeted for prevention."
"This is the first longitudinal study identifying autonomic dysregulation, measured by heart rate variability before trauma exposure, as a predictor of PTSD. However, results will need to be confirmed by future studies, since the reported effects are relatively small, not entirely consistent, and may be accounted for by unmeasured factors."
Dr Minassian, Dr Shah, and Dr Vaccarino report no relevant financial relationships.
Medscape Medical News © 2015 WebMD, LLC
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Cite this: Low Heart Rate Variability Predicts PTSD - Medscape - Sep 28, 2015.