Traumatic Brain Injury and CVD: What’s the Link?

The long-term impact of traumatic brain injury (TBI) on neurologic and psychiatric function is well-established, but a growing body of research is pointing to unexpected medical sequalae, including cardiovascular disease (CVD).

A recent review looked at the investigation to date into this surprising connection, not only summarizing study findings but also suggesting potential mechanisms that might account for the association.

“This work offers further evidence that individuals with TBI are at an elevated risk of unfavorable cardiovascular outcomes for an extended period following the initial incident; consequently, they should undergo regular monitoring,” senior author Ross Zafonte, DO, president of Spaulding Rehabilitation Network, Boston, and lead author Saef Izzy, MD, MBChB, a neurologist at the Stroke and Cerebrovascular Center of Brigham and Women’s Hospital, Boston, Massachusetts, told theheart.org | Medscape Cardiology.

“This holds significant importance for healthcare practitioners, as there exist several strategies to mitigate cardiovascular disease risk — including weight management, adopting a healthy diet, engaging in regular physical activity, and quitting smoking,” they stated.

Leslie Croll, MD, American Heart Association volunteer and assistant professor of clinical neurology at the Temple University Lewis Katz School of Medicine, Philadelphia, Pennsylvania, told theheart.org | Medscape Cardiology that it’s “extremely important to learn more about the interplay between TBI, neurologic disease, psychiatric complications, and the cardiovascular system.”

Hopefully, she added, “future research will help us understand what kind of cardiovascular disease monitoring and prevention measures stand to give TBI patients the most benefit.”

Chronic Condition

TBI is “a major cause of long-term disability and premature death,” and is “highly prevalent among contact sports players, military personnel (eg, due to injuries sustained during conflict), and the general population (eg, due to falls and road traffic incidents),” the authors wrote.

Most studies pertaining to TBI have “primarily focused on establishing connections between single TBI, repetitive TBI, and their acute and chronic neurological and psychiatric consequences, such as Parkinson’s disease, Alzheimer’s disease, and chronic traumatic encephalopathy (CTE),” Zafonte and Izzy noted. By contrast, there has been a “notable lack of research attention given to non-neurological conditions associated with TBI.”

They pointed out that recent insights into TBI — particularly the acknowledgment of TBI as an “emerging chronic condition rather than merely an acute aftermath of brain injury” — have come to light through epidemiologic and pathologic investigations involving military veterans, professional American-style football players, and the civilian population. “This recognition opens up an opportunity to broaden our perspective and delve into the medical aspects of health that may be influenced by TBI.”

To broaden the investigation, the researchers reviewed literature published between January 1, 2001, and June 18, 2023. Of 26,335 articles, they narrowed their review down to 15 studies that investigated CVD, CVD risk factors, and cerebrovascular disease in the chronic phase of TBI, including community, military, or sport-related brain trauma, regardless of the timing of disease occurrence with respect to brain injury via TBI or repetitive head impact.

New Cardiovascular Risk

Studies that used national or local registries tended to be retrospective and predominantly conducted in people with preexisting cardiovascular conditions. In these studies, TBI was found to be an independent risk factor for myocardial dysfunction. However, although these studies do provide evidence of elevated cardiovascular risk subsequent to a single TBI, including individuals with preexisting medical comorbidities “makes it difficult to determine the timing of incident cardiovascular disease and cardiovascular risk factors subsequent to brain injury,” they wrote.

However, some studies showed that even individuals with TBI but without preexisting myocardial dysfunction at baseline had a significantly higher risk for CVD than those without a history of TBI.

In fact, several studies included populations without preexisting medical and cardiovascular comorbidities to “better refine the order and timing of CVD and other risk factors in individuals with TBI.”

For example, one study of concussion survivors without preexisting diagnoses showed that cardiovascular, endocrinological, and neuropsychiatric comorbidities occurred at a “significantly higher incidence within 5 years after concussive TBI compared with healthy individuals who were matched in terms of age, race, and sex and didn’t have a TBI exposure.” Other studies yielded similar findings.

Because cardiovascular risk factors and events become more common with age, it’s important to account for age in evaluating the effects of TBI. Although many studies of TBI and subsequent CVD didn’t stratify individuals by age, one 10-year study of people without any known cardiovascular or neuropsychiatric conditions who sustained TBI found that people as young as 18-40 years were more likely to develop hypertension, hyperlipidemia, obesity, and diabetes within 3-5 years following brain injury than matched individuals in the control group.

“Individuals who have encountered TBI, surprisingly even those who are young and in good health with no prior comorbid conditions, face an increased risk of adverse cardiovascular outcomes for an extended duration after the initial event,” Zafonte and Izzy summarized. “Therefore, it’s imperative that they receive regular and long-term screenings for CVD and associated risk factors.”

Bidirectional Relationship

Brain injury has been associated with acute cardiovascular dysfunction, including autonomic heart-brain axis dysregulation, imbalances between the sympathetic and parasympathetic nervous systems, and excessive catecholamine release, the authors noted.

Zafonte and Izzy suggested several plausible links between TBI and cardiovascular dysfunction, noting that they are “likely multifaceted, potentially encompassing risk factors that span the pre-injury, injury, and post-injury phases of the condition.”

• TBI may induce alterations in neurobiological processes, which have been reported to be associated with an increased risk for CVD (eg, chronic dysfunction of the autonomic system, systemic inflammation, and modifications in the brain-gut connection).
• Patients with TBI might develop additional risk factors following the injury, including conditions like posttraumatic stress disorder, depression, and other psychiatric illnesses, which are “known to augment the risk of CVD.”
• TBI can lead to subsequent behavioral and lifestyle changes that place patients at an elevated risk for both cardiovascular and cognitive dysfunction when compared to the general population of TBI survivors.
• There may be additional as yet undefined risks.

They believe there’s a bidirectional relationship between TBI and CVD. “On one hand, TBI has been associated with an elevated risk of CVD,” they said. “Conversely, cardiovascular risk factors such as diabetes, hypertension, hyperlipidemia, and sleep disturbances that have been demonstrated to negatively influence cognitive function and heighten the risk of dementia. Consequently, this interplay can further compound the long-term consequences of the injury.”

Their work aims to try and disentangle this “complex series of relationships.”

They recommend screening to identify diseases in their earliest and “most manageable phases” because TBI has been “unveiled as an underappreciated risk factor for CVD within contact sports, military, and community setting.”

An effective screening program “should rely on quantifiable and dependable biomarkers such as blood pressure, BMI, waist circumference, blood lipid levels, and glucose. Additionally, it should take into account other factors like smoking habits, physical activity, and dietary choices,” they recommended.

Heart-Brain Connection

Croll noted that TBI is “associated with many poorly understood physiologic changes and complications, so it’s exciting to see research aimed at clarifying this chronic disease process.”

In recent years, “we have seen a greater appreciation and understanding of the heart-brain connection,” she said. “Moving forward, more research, including TBI research, will target that connection.”

She added that there are probably “multiple mechanisms” at play underlying the connection between TBI and CVD.

Most importantly, “we are increasingly learning that TBI is not only a discrete event that requires immediate treatment but also a chronic disease process,” and when we “think about the substantial long-term morbidity associated with TBI, we should keep increased risk for CVD on top of mind,” said Croll.

The review received no funding. Izzy reported receiving grants from the US National Institutes of Health (NIH) and 2023 Stepping Strong Innovator Award. Zafonte reported receiving grants from the NIH and royalties from Springer and Demos publishing for serving as a coeditor of Brain Injury Medicine. Zafonte has also served as an advisor to Myomo, Oncare.ai, Nanodiagnostics, and Kisbee. He reported evaluating patients in the Massachusetts General Hospital Brain and Body–TRUST Program, which is funded by the NFL Players Association. The other authors’ disclosures are listed on the original paper. Croll declared no relevant financial relationships.