Reduced heart rate volatility: an early predictor of death in trauma patients

Abstract

Objective: To determine if using dense data capture to measure heart rate volatility (standard deviation) measured in 5-minute intervals predicts death.

Background: Fundamental approaches to assessing vital signs in the critically ill have changed little since the early 1900s. Our prior work in this area has demonstrated the utility of densely sampled data and, in particular, heart rate volatility over the entire patient stay, for predicting death and prolonged ventilation.

Methods: Approximately 120 million heart rate data points were prospectively collected and archived from 1316 trauma ICU patients over 30 months. Data were sampled every 1 to 4 seconds, stored in a relational database, linked to outcome data, and de-identified. HR standard deviation was continuously computed over 5-minute intervals (CVRD, cardiac volatility-related dysfunction). Logistic regression models incorporating age and injury severity score were developed on a test set of patients (N = 923), and prospectively analyzed in a distinct validation set (N = 393) for the first 24 hours of ICU data.

Results: Distribution of CVRD varied by survival in the test set. Prospective evaluation of the model in the validation set gave an area in the receiver operating curve of 0.81 with a sensitivity and specificity of 70.1 and 80.0, respectively. CVRD predict death as early as 24 hours in the validation set.

Conclusions: CVRD identifies a subgroup of patients with a high probability of dying. Death is predicted within first 24 hours of stay. We hypothesize CVRD is a surrogate for autonomic nervous system dysfunction.

FIGURE 1. SIMON physiologic parameter Web display (24 hours).

FIGURE 2. Daily SIMON ICU unit summary report (5/14 beds shown) sent to ICU director, nurse manager, and chief resident.

FIGURE 3. Patient inclusion criteria for test and validation sets.

FIGURE 4. Distribution of short-term heart ratevolatility over ICU stay by mortality in the 923 patient test set. Percent < 0.5 was used to define cardiac volatility related dysfunction (CVRD) measurement. Bin size = 0.01.

FIGURE 5. Mean CVRD in first 24 hours of ICU stay versus age, injury severity score, ventilator days, and units of blood transfused. Combined dataset (N = 1316). P values using ANOVA.

FIGURE 6. Percent mortality versus cardiac volatility related dysfunction (CVRD) in the First 24 hours of ICU stay. Age and ISS not incorporated. Data for test and validation set (N = 1316).

FIGURE 7. Logistic regression model ROC curves for test and validation sets. P value shown is comparing test and validation set curves. P value for both curves < 0.0001.

FIGURE 8. True positives (patients predicted to die who die) and false negatives (patients predicted to live who die) rates versus days to death. combined test and validation sets (N = 1316).