Long-term impact of combat-related traumatic injury on heart rate variability: findings from the ADVANCE study

INTRODUCTION: Combat-related traumatic injury (CRTI) has been associated with adverse cardiovascular outcomes in veterans. However, the long-term impact of contemporary CRTI on heart rate variability (HRV, a marker of autonomic function) has never been investigated in combat veterans and personnel. This analysis aimed to examine the association between CRTI and short-term HRV in a contemporary cohort of British servicemen. METHODS: This analysis used the first follow-up data from the ArmeD serVices trAuma rehabilitatioN outComE (ADVANCE) prospective cohort study. Participants comprised 469 injured (those who sustained serious physical CRTI while on deployment in Afghanistan) and 506 uninjured servicemen [those who were uninjured and were frequency-matched to the injured based on age, sex (male), rank and deployment: Afghanistan 2003-2014 at recruitment]. Resting HRV was measured (5 min ECG) in the supine position. Root mean square of successive differences (RMSSD) and the sympathetic nervous system (SNS) index were reported as measures of parasympathetic and sympathetic activity, respectively. Multiple linear regression models reported the association between CRTI and HRV, adjusting for age, rank and ethnicity. RESULTS: Participants' median age was 37.5 years. The time from CRTI/deployment was approximately 11 years. Median RMSSD was significantly lower in the injured versus uninjured [37.7 ms (IQR: 25.3 to 55.9) vs 41.9 ms (IQR: 27.7 to 62.2); p=0.01]. After confounder adjustment, CRTI was significantly associated with lower RMSSD [geometric mean ratio: 0.92 (95% CI 0.85 to 0.99)] and relatively higher SNS index [coefficient: 0.19 (95% CI 0.05 to 0.34)] in the injured versus uninjured. Blast injury and traumatic amputation were associated with significantly lower RMSSD and greater SNS activity. CONCLUSION: CRTI is associated with greater relative autonomic imbalance. These findings may help understand the recovery pathway following CRTI in wounded combat veterans and personnel.