1. In this retrospective study, traumatic brain injury in any capacity amongst United States army veterans was associated with an increased risk of cardiovascular disease.
2. Nearly all severities of traumatic brain injury were significantly associated with increased risk of all components of the composite outcome of cardiovascular disease.
Level of Evidence Rating: 2 (Good)
Study Rundown: Millions of Americans have served in the United States (US) army, involved in combat in regions including Afghanistan and Iraq. Approximately 1 in 5 veterans suffer traumatic brain injury (TBI) ranging in severity between mild, moderate/severe and penetrating injury during their time on duty. This history of TBI is associated with significant morbidity and mortality, including an increased risk for disability secondary to neurological and mental health conditions. Previous studies have demonstrated a potential association between traumatic brain injury and risk of cardiovascular disease (CVD), although the population of interest was older adults. This study sought to determine whether a history of TBI increases CVD risk in US veterans who have served post-9/11.
A total of 1,559,928 individuals were included in the study. 19.3% (301,169) veterans had a documented TBI history. Participants were mostly young (67.8% under 35 years) and male (81.9%). Those with a TBI history were especially likely to be young males and cigarette smokers, and less likely to have any postsecondary education, while those without a TBI history were more likely to have certain comorbidities associated with CVD. All severities of TBI were significantly associated with increased risk of CVD. Furthermore, other than penetrating TBI and CVD death (no association), all severities of TBI were significantly associated with increased risk of all components of the composite outcome of CVD.
This retrospective cohort study by Stewart et al demonstrates an increased risk of CVD following TBI amongst mostly young army veterans in the United States. This information is helpful in designing interventions to protect military persons from TBI and detect its sequelae early on. A strength of this study includes the large sample size, as well as the suggestion of a dose-response relationship which strengthens the conclusions described here. However, this study is susceptible to confounding due to its retrospective nature and multifactorial nature of both the exposure and the outcome. Further study should be conducted to understand the pathogenesis of the association between TBI and CVD, as well as describing clinical interventions to improve patient outcomes.
In Depth [retrospective cohort]: A retrospective cohort study was completed at the University of Utah. Several databases were consulted to gather data including the US Department of Veterans Affairs (VA) and Department of Defense (DoD) Identity Repository (VADIR), the VA Corporate Data Warehouse (CDW), the DoD and VA Infrastructure for Clinical Intelligence (DaVINCI), the Theater Data Management Store (TMDS), the DoD Trauma Registry (DoDTR), and the National Death Index (NDI).
Participant data was gathered from an ongoing study cohort (the Long-term Impact of Military-Relevant Brain Injury Consortium–Chronic Effects of Neurotrauma Consortium Phenotype study). Eligible patients were aged 18 years or older, had at least 3 years of healthcare data available between 1999 and 2016 and had no prior diagnosis of CVD. The outcome of interest (CVD) was a composite of the following: coronary artery disease, stroke, peripheral arterial disease, and CVD death, which were diagnosed as an inpatient or on two separate occasions as an outpatient.
Patients with TBI history were more likely to have the following characteristics (standardized mean difference): smoking history (0.37), substance use disorder (0.16), obesity (0.004), obstructive sleep apnea (0.06), insomnia (0.32), post-traumatic stress disorder (0.58), depression (0.32) and anxiety (0.30). However, the following were more likely in non-TBI veterans: hyperlipidemia (-0.08), kidney disease (-0.01), hypertension (-0.02) and diabetes (-0.04). All severities of TBI were associated with an increased risk of CVD (hazard ratio; 95% confidence interval): mild (1.18; 1.15-1.21), moderate/severe (2.10; 2.02-2.20) and penetrating (3.97; 3.70-4.25). There was a trend towards a dose-dependent relationship, in that greater severity of TBI seemed to be associated with a higher risk of CVD in the secondary analysis.
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