Increased QT Interval Variability in 3 Recently Concussed Athletes: An Exploratory Observation

Abstract

Context:The QT interval variability index (QTVI) is a noninvasive measure of beat-to-beat fluctuations of the QT interval as seen from a single electrocardiographic lead. It represents the relationship between the respective variabilities of the QT and R-R intervals. Recently, the QTVI was demonstrated to be an index of vagal cardiac autonomic modulation in resting conditions.Objective: To determine whether QTVI varied in athletes at 48 hours, 1 week, and 2 weeks after a concussive head injury.Design: Case series. Setting: Testing facility. Patients or Other Participants:Three athletes with recent concussions and 3 uninjured athletes with similar demographic factors.Main Outcome Measure(s): Continuous 3-lead electrocardiograms were obtained in a seated, resting position over 2 successive weeks. Separate, unpaired t tests were performed to determine whether group-visit differences were present in the QTVI at 48 hours, 1 week, or 2 weeks.Results: No demographic differences were present between groups. At 48 hours, the QTVI was greater in the concussion group than in the matched controls. At weeks 1 and 2, the QTVI in the concussion group was lower than at 48 hours and not different from that of the control group. Conclusions:Vagal cardiac autonomic modulation, as quantified by the QTVI, appeared to be negatively affected in concussed athletes within 48 hours of injury, resolved within 1 week, and remained at control group levels 2 weeks later. Serial assessments of QTVI may be of clinical utility in identifying suspected cases of acute concussion and may provide helpful information for determining when an athlete can return to play safely.Key Words: autonomic nervous system, heart, cardiovascular system, return to play Key Points• The QT interval variability index was higher at rest in concussed participants than in the control group.• This resting change suggests that vagal cardioautonomic modulation was impaired in recently concussed participants.• The QT interval variability index change resolved within 1 week of injury.B y definition, a sport concussion is a complex pathophysiologic process affecting the brain that is induced by traumatic biomechanical forces. l The nature of the brain injury results in a number of short-term and, in some cases, long-term symptoms. The primary assessment and management of concussion has included comprehensive evaluations designed to identify symptoms from the cognitive, vestibular, and somatic realms; these evaluations are often used in the subsequent determination of playing status. 2 To date, the respective assessment techniques have routinely demonstrated efficacy across multiple groups of athletes.An underexplored area that may have utility in the identification of acute concussion injury is assessment of cardiovascular autonomic function. Linear and nonlinear computations of heart rate variability (HRV), a measure of the autonomically mediated periodicity in a mean heart rate,3 have demonstrated transient, abnormal autonomic responses to exercise or lowintensity provocati...

The Effect of Exertion on Heart Rate and Rating of Perceived Exertion in Acutely Concussed Individuals

“…This study allowed us to directly observe the influence of concussion on regulation of the cardiac rhythm in symptomatic athletes. Comparable research has limited the evaluation of regulatory dysfunction to patients already asymptomatic [5,6], during isometric exercise [10] or while the individual is at rest [13]. In addition, while other studies have explored the capacity of the autonomic system to adjust and respond to prolonged steady-state exercise, our study specifically evaluated the anticipatory response to exercise and adjustment to a change in exertion level over time, which is more representative of athletic performance.…”

“…La Fountaine et al [10] demonstrated that autonomic activity at rest could differentiate concussed from non-concussed controls and that vagal dysfunction after concussion resulted in an increase in vagal activity at 48 hours post-injury despite evidence for sympathetic hyperactivity one week and two weeks later [13]. Similarly, an animal model of brain injury showed a significantly lower resting HR in concussed rats on the day of injury when compared with sham-treated rats [7], suggesting that the nature of autonomic system dysfunction after injury is time dependent, with vagal dysfunction from a state of sluggish withdrawal to one of disordered engagement or re-engagement.…”

“…For instance, some studies suggest increases in parasympathetic influence (or lack of parasympathetic withdrawal) in the very early stages after acute injury [9,13]. Similarly, an animal study in 2013 by Griesbach et al [7] found reduced resting HRs in rats on the day of injury.…”

A Physiological Approach to Prolonged Recovery From Sport-Related Concussion

“…49 Autonomic tests may be effective in identifying concussion or PCS. La Fountaine et al 27,28 showed that 2 measures of cardiac vagal modulation, the QT interval variability index at rest and HR complexity during isometric hand-grip exercise, were altered within 48 hours of head injury, resolved within 1 week, and remained at control levels 2 weeks later, consistent with vagal dysfunction early after concussion. In a controlled study of HRV in university athletes who were judged to be clinically recovered from concussion (a mean of 95 days postinjury), Abaji et al 50 found that during the isometric hand-grip exercise, but not at rest, athletes with a history of concussion had less HF power and a greater LF : HF ratio than age-and teammatched controls with no history of concussion.…”

“…Concussion affects the autonomic nervous system (ANS) 27,28 and the control of both cerebral blood flow (CBF) [29][30][31][32] and cardiac rhythm. 33,34 The primary ANS control center may be damaged in concussion, particularly if a rotational force was applied to the upper cervical spine, 35 as supported by results from a diffusion tensor imaging study 36 that showed changes to brainstem white matter neurons after concussion.…”