Role of reduced heart rate volatility in predicting death in trauma patients

Associating frailty and dynamic dysregulation between motor and cardiac autonomic systems

Frailty is a geriatric syndrome associated with the lack of physiological reserve and consequent adverse outcomes (therapy complications and death) in older adults. Recent research has shown associations between heart rate (HR) dynamics (HR changes during physical activity) with frailty. The goal of the present study was to determine the effect of frailty on the interconnection between motor and cardiac systems during a localized upper-extremity function (UEF) test. Fifty-six individuals aged 65 or above were recruited and performed the previously developed UEF test consisting of 20-s rapid elbow flexion with the right arm. Frailty was assessed using the Fried phenotype. Wearable gyroscopes and electrocardiography were used to measure motor function and HR dynamics. In this study, the interconnection between motor (angular displacement) and cardiac (HR) performance was assessed, using convergent cross-mapping (CCM). A significantly weaker interconnection was observed among pre-frail and frail participants compared to non-frail individuals (p < 0.01, effect size = 0.81 ± 0.08). Using logistic models, pre-frailty and frailty were identified with sensitivity and specificity of 82%-89%, using motor, HR dynamics, and interconnection parameters. Findings suggested a strong association between cardiac-motor interconnection and frailty. Adding CCM parameters in a multimodal model may provide a promising measure of frailty.

Test-retest reliability of short- and long-term heart rate variability in individuals with spinal cord injury

STUDY DESIGN

Cross-sectional.

OBJECTIVES

To investigate test-retest reliability of heart rate variability (HRV) metrics in SCI without restriction of activity over long (24-h) and shorter durations (5-min, 10-min, 1-h, 3-h and 6-h).

SETTINGS

University hospital in Khon Kaen, Thailand.

METHODS

Forty-five participants (11 with tetraplegia and 34 with paraplegia) underwent two 24-h recordings of RR-intervals to derive time and frequency HRV metrics. Relative reliability was assessed by intraclass correlation coefficient (ICC) and absolute reliability by coefficient of variation (CV) and Bland-Altman limits of agreement (LoA).

RESULTS

For 5- and 10-min durations, eight of eleven HRV metrics had moderate to excellent reliability (ICC 0.40-0.76); the remaining three were poor (ICC < 0.4). HRV values from 1-h and 3-h durations showed moderate to excellent reliability (ICC of 0.46-0.81), except for 1-h reliability of ULF and TP (ICC of 0.06 and 0.30, respectively). Relative reliability was excellent (ICC of 0.77-0.92) for 6-h and 24-h durations in all HRV metrics. Absolute reliability improved as recording duration increased (lower CVs and narrower LoAs). Participants with high AD risk (SCI level at or above T6) showed lower test-retest reliability of HF and LF values than participants with low AD risk.

CONCLUSION

Relative reliability of HRV was excellent for 6-h and 24-h. The best absolute reliability values were for 24-h duration. Time-domain outcomes were more reliable than frequency domain outcomes. Participants with high risk of AD, particularly those with tetraplegia, showed lower reliability, especially for HF and LF.

Frailty assessment using a novel approach based on combined motor and cardiac functions: a pilot study

BACKGROUND

Previous research showed association between frailty and an impaired autonomic nervous system; however, the direct effect of frailty on heart rate (HR) behavior during physical activity is unclear. The purpose of the current study was to determine the association between HR increase and decrease with frailty during a localized upper-extremity function (UEF) task to establish a multimodal frailty test.

METHODS

Older adults aged 65 or older were recruited and performed the UEF task of rapid elbow flexion for 20 s with the right arm. Wearable gyroscopes were used to measure forearm and upper-arm motion, and electrocardiography were recorded using leads on the left chest. Using this setup, HR dynamics were measured, including time to peak HR, recovery time, percentage increase in HR during UEF, and percentage decrease in HR during recovery after UEF.

RESULTS

Fifty-six eligible participants were recruited, including 12 non-frail (age = 76.92 ± 7.32 years), and 40 pre-frail (age = 80.53 ± 8.12 years), and four frail individuals (age = 88.25 ± 4.43 years). Analysis of variance models showed that the percentage increase in HR during UEF and percentage decrease in HR during recovery were both 47% smaller in pre-frail/frail older adults compared to non-frails (p < 0.01, effect size = 0.70 and 0.62 for increase and decrease percentages). Using logistic models with both UEF kinematics and HR parameters as independent variables, frailty was predicted with a sensitivity of 0.82 and specificity of 0.83.

CONCLUSION

Current findings showed evidence of strong association between HR dynamics and frailty. It is suggested that combining kinematics and HR data in a multimodal model may provide a promising objective tool for frailty assessment.

Incidence and Outcomes of Critical Illness-Related Corticosteroid Insufficiency in Trauma Patients

The spectrum of critical illness-related corticosteroid insufficiency (CIRCI) in trauma is not fully defined. This study describes our trauma experience with hydrocortisone-treated patients experiencing CIRCI. We conducted a 5-year retrospective analysis from a Level II trauma center using biochemical and clinical criteria for adrenal insufficiency. Seventy patients met the inclusion criteria for CIRCI. There was a 34 per cent mortality rate despite therapy. Nonsurvivors were older with larger admission base deficits and experienced higher rates of sepsis, bacteremia, and pneumonia. Nonsurvivors had prolonged vent days (mean 53 ± 64 days) when compared with survivors (mean 30 ± 22 days; P = 0.029). Renal replacement therapy was a strong predictor of mortality. Spinal cord-injured patients had high Injury Severity Scores (mean 34 ± 18), elevated baseline Cortisol levels (mean 56 ± 84 vs 18 ± 14; P = 0.004), and required prolonged duration of steroid therapy (30 ± 52 vs 15 ± 15 days; P = 0.080) when compared with the nonspinal cord-injured group. Our data suggest that CIRCI in trauma is associated with significant mortality and morbidity even when patients are treated appropriately.

Clinical applications of heart rate variability in the triage and assessment of traumatically injured patients

Heart rate variability (HRV) is a method of physiologic assessment which uses fluctuations in the RR intervals to evaluate modulation of the heart rate by the autonomic nervous system (ANS). Decreased variability has been studied as a marker of increased pathology and a predictor of morbidity and mortality in multiple medical disciplines. HRV is potentially useful in trauma as a tool for prehospital triage, initial patient assessment, and continuous monitoring of critically injured patients. However, several technical limitations and a lack of standardized values have inhibited its clinical implementation in trauma. The purpose of this paper is to describe the three analytical methods (time domain, frequency domain, and entropy) and specific clinical populations that have been evaluated in trauma patients and to identify key issues regarding HRV that must be explored if it is to be widely adopted for the assessment of trauma patients.

Heart rate variability as a triage tool in patients with trauma during prehospital helicopter transport

BACKGROUND

Prehospital triage of patients with trauma is routinely challenging, but more so in mass casualty situations and military operations. The purpose of this study was to prospectively test whether heart rate variability (HRV) could be used as a triage tool during helicopter transport of civilian patients with trauma.

METHODS

After institutional review board approval and waiver of informed consent, 75 patients with trauma requiring prehospital helicopter transport to our level I center (from December 2007 to November 2008) were prospectively instrumented with a 2-Channel SEER Light recorder (GE Healthcare, Milwaukee, WI). HRV was analyzed with a Mars Holter monitor system and proprietary software. SDNN (standard deviation [SD] of the normal-to-normal R-R interval), as an index of HRV, was correlated with prehospital trauma triage criteria, base deficit, seriousness of injury, operative interventions, outcome, and other data extracted from the patients' medical records. There were no interventions or medical decisions based on HRV. Data were excluded only if there was measurement artifact or technical problems with the recordings.

RESULTS

The demographics were mean age 47 years, 63% men, 88% blunt, 25% traumatic brain injury, 9% mortality. Prehospital SDNN predicted patients with base excess < or = -6, those defined as seriously injured and benefiting from trauma center care, as well as patients requiring a life-saving procedure in the operating room. No other available data, including prehospital en-route vital signs, predicted any of these. The sensitivity, specificity, positive predictive value, and negative predictive value were 80%, 75%, 33%, 96%, respectively, with and an overall accuracy of 76% for predicting a life-saving intervention in the operating room.

CONCLUSIONS

This is the first demonstration that prehospital HRV (specifically SDNN) predicts base excess and operating room life-saving opportunities. HRV triages and discriminates severely injured patients better than routine trauma criteria or en-route prehospital vital signs. HRV may be a useful civilian or military triage tool to avoid unnecessary helicopter evacuation for minimally injured patients. A prospective, randomized trial in a larger patient population is indicated.

A simple non-physiological artifact filter for invasive arterial blood pressure monitoring: a study of 1852 trauma ICU patients

Invasive arterial blood pressure (BP) is a vital sign in hemodynamic monitoring of trauma intensive care unit (ICU) patients. Continuous BP analysis can potentially provide additional information about patient status, predict morbidity and mortality, and automatically populate electronic nurse charting systems than intermittent monitoring. Challenges to routine application in the ICU include integration of complex physiological data collection systems, artifacts, missing data, and the various clinical interventions that may temporarily corrupt the BP signal. We have developed and previously described SIMON (signal interpretation and monitoring), a physiological data collection system in the Trauma ICU at Vanderbilt University. In order to extract useful information from continuous arterial line BP monitoring, it is necessary to remove non-physiological artifacts. In this setting, potential artifacts appear to be caused by resonance, over-damping, and data transmission. We designed a simple filter to identify various sources of non-physiological artifacts using statistical signal processing techniques. We implemented the filter to arterial invasive BP signals of 1852 trauma patients throughout their length of ICU stay. After filtering, the power of BP measures to predict hospital death was enhanced. Therefore, we concluded that our strategy of removing non-physiological artifact was simple, fast and useful for an accurate assessment of BP measures in trauma patients.

Heart rate variability index in trauma patients

BACKGROUND

Heart rate variability (HRV) changes often reflect autonomic dysfunction with high sensitivity, but the specificity is also low. There are several different methods for measuring HRV, but interpretation is often complex, and the units are not interchangeable. For these reasons, HRV monitoring is not routinely used in many clinical situations. We hypothesized that the specificity of HRV as a screening tool for trauma patients could be improved by controlling some of the confounding influences using multiple logistic regression.

METHODS

A prospective observational trial with waiver of consent was performed in 243 healthy student volunteers and 257 trauma patients, in the resuscitation bay and intensive care units of a Level I trauma center, who received computed axial tomography (CT) scans of the head as part of the initial work up. Electrocardiogram results were recorded for 5 minutes. HRV was defined by SD of normal R-R intervals (SDNN5) and by root mean square of successive differences of R-R intervals (RMSSD5). A head CT scan was considered positive (+) if there were abnormalities in the parenchyma (diffuse axonal injury or contusion), vasculature (intraparenchymal, subdural, or epidural hemorrhage), and/or structural or bony components (fractures of the face or cranium).

RESULTS

In volunteers, SDNN5 was 73 +/- 15 (M +/- SD) milliseconds, compared with 42 +/- 22, 31 +/- 19, 28 +/- 17, and 12 +/- 8 milliseconds in, CT(-) patients with no sedation (n = 82), CT(-) with sedation (n = 60), CT(+) with no sedation (n = 55), and CT(+) with sedation (n = 60), respectively. The differences between trauma, sedation, and CT categories were significant (all p < 0.001). RMSSD5 differences were similar and also highly significant (all p < 0.001). For both SDNN5 and RMSSD5, in each category, there was wide overlap in the range of values, and strong inverse correlations with heart rate (all p < 0.001). Using multiple logistic regression in a subset with no missing data (n = 194), an index was derived from ln(SDNN5) adjusted for six confounding factors. With a negative predictive value held constant at 0.90, compared with ln(SDNN5) alone, the stepwise addition of heart rate, sedation, age, gender, and blood pressure progressively improved the specificity of the HRV index from 0.56 to 0.77, positive predictive value from 0.55 to 0.68, and efficiency from 0.68 to 0.80. This index was then normalized (0-100 scale) for ease of interpretation.

CONCLUSIONS

(1) Several factors alter HRV in patients; (2) when HRV was indexed for some of these factors, its specificity and efficiency were improved for predicting a discrete pathologic state in trauma patients, i.e. (+) or (-) cranial CT scans; (3) the algorithm can incorporate other factors to further refine the diagnostic and/or prognostic ability of HRV as a noninvasive clinical tool; (4) this concept should be applicable to any other HRV measurement technique or outcome.

Adrenal insufficiency, heart rate variability, and complex biologic systems: a study of 1,871 critically ill trauma patients

BACKGROUND

Reduction in integer heart rate variability (HRVi), one potential measurement of complex biologic systems, is common in ICU patients and is strongly associated with hospital mortality. Adrenal insufficiency (AI) and reduced HRVi are associated with autonomic dysfunction. Failure of the autonomic nervous system can be associated with loss of biologic complexity. We hypothesize decreased HRVi is associated with AI, and HRVi improves after treatment of AI, suggesting "recomplexification" (resumption of normal stress response to injury).

STUDY DESIGN

Of 4,116 trauma ICU admissions from December 2000 to November 2005, 1,871 patients had sufficient physiologic, laboratory, pharmacy, and demographic data for analysis. Seventy-five patients failing cosyntropin-stimulation testing were defined as AI; the remaining 1,796 were defined as no AI. HRVi was calculated as integer heart rate standard deviation over 5-minute intervals. HRVi 10th, 50th (median), and 90th percentiles were calculated over the 72 hours pre-, or poststeroid, or both administration (AI). HRVi percentiles in non-AI patients were evaluated at the same interval and compared with AI using Wilcoxon's rank-sum test. In patients with AI, daily HRVi was computed 3 days before and after steroid administration, and compared between survivors and nonsurvivors.

RESULTS

There were 2.9 million heart-rate intervals measured. HRVi stratified patients with AI (cosyntropin failure), and without AI. HRVi was similar in AI survivors and nonsurvivors before steroid treatment, but differed after treatment. HRVi increased substantially in survivors after steroid administration, yet did not change in nonsurvivors. HRVi does not increase in patients who are unresponsive to steroids and die.

CONCLUSIONS

Reduced heart-rate variability, a potential measurement of complex biologic systems, is associated with cosyntropin-confirmed AI; improved in patients responding to steroid therapy; and is a noninvasive, real-time biomarker suggesting AI.

Cardiac uncoupling and heart rate variability stratify ICU patients by mortality: a study of 2088 trauma patients

OBJECTIVE

We have previously shown that cardiac uncoupling (reduced heart rate variability) in the first 24 hours of trauma ICU stay is a robust predictor of mortality. We hypothesize that cardiac uncoupling over the entire ICU stay independently predicts mortality, reveals patterns of injury, and heralds complications.

METHODS

A total of 2088 trauma ICU patients satisfied the inclusion criteria for this study. Cardiac uncoupling by outcome was compared using the Wilcoxon rank sum test. Risk of death from cardiac uncoupling and covariates (age, ISS, AIS Head Score, total transfusion requirements) was assessed using multivariate logistic regression models at each ICU day. Univariate logistic regression was used to assess risk of death from uncoupling irrespective of covariates at each ICU day.

RESULTS

A total of 1325 (63.5%) patients displayed some degree of uncoupling over their ICU stay. The difference in uncoupling between survivors and nonsurvivors is both dramatic and consistent across the entire ICU stay, indicating that the presence of uncoupling is unrelated to the cause of death. However, the magnitude of uncoupling varies by day when data is stratified by cause of death.

CONCLUSIONS

Cardiac uncoupling: 1) is an independent predictor of death throughout the ICU stay, 2) has a predictive window of 2 to 4 days, and 3) appears to increase in response to inflammation, infection, and multiple organ failure.