Ectopy in trauma patients: Cautions for use of heart period variability in medical monitoring

Introduction: Heart period variability measurements have been proposed for use in early prediction of mortality or the requirement for lifesaving interventions in trauma patients. However, the presence of even one ectopic beat (EB) and/or electromechanical noise compromises the accurate calculation of heart period variability. We tested the hypothesis that ECGs from trauma patients exhibit a greater frequency of EBs than healthy human research subjects. Methods: Continuous ECGs were recorded in 20 healthy human subjects at rest, 108 healthy human subjects undergoing experimentally induced progressive central hypovolemia (via lower body negative pressure, LBNP), and 245 trauma patients. The proportions of subjects/patients with at least one EB were identified in each group. Results: ECG waveforms from 20% and 18% of healthy human subjects at rest or undergoing LBNP, respectively, contained at least one EB. ECG waveforms from 36% of the trauma patients were found to contain either EBs (35%) or electromechanical noise (1%). Conclusions: A significant number of EBs occur in healthy subjects both at rest and during progressive reduction in central blood volume, and trauma is associated with a near doubling of this incidence. As both EBs and noise result in invalid heart period variability calculations, these metrics as currently calculated could not be used in approximately 36% of trauma patients. The limited use in nearly two of every five trauma patients indicate that it is unlikely that continuous heart period variability measurements could substantially improve pre-hospital or emergency room decision-support in trauma.