Association Between Heart Rate Variability and ECG Changes in On-Duty Prehospital Physicians

Mathias Maleczek^1,2Karl Schebesta^1,3*Thomas Hamp⁴Balthasar Laussner¹Thomas Pezawas⁵Mario Krammel^4,6Bernhard Roessler^1,2

• ¹Department of Anaesthesia, Intensive Care Medicine and Pain Medicine, Medical University of Vienna, Ebene, Austria
• ²Academic Simulations Center Vienna, Vienna, Austria
• ³Department of Anaesthesia and Intensive Care Medicine, Orthopaedic Hospital Vienna – Speising, Vienna, Austria, Vienna, Austria
• ⁴Emergency Medical Service Vienna, Vienna, Austria
• ⁵Department of Cardiology, University Clinic for Internal Medicine II, Medical University of Vienna, Vienna, Vienna, Austria
• ⁶PULS – Austrian Cardiac Arrest Awareness Association, Vienna, Austria

Background/Objectives: Prehospital emergency physicians work in physically and psychologically stressful environments. During their shifts, changes in electrocardiogram (ECG) attributable to stress have been described previously. Alterations in heart rate variability (HRV) as well as in ST-T segments have been reported. Nevertheless, the association between those two parameters still remains unclear in this setting. Methods: A retrospective analysis of data collected in a previous prospective trial was conducted. The primary objective was the association of HRV metrics with the risk of ST-T abnormalities during five-minute intervals and on a mission basis. Therefore, the root mean square of successive differences (RMSSD) and standard deviation of normal-to-normal (SDNN) intervals were analysed. Additionally, variations in HRV during different phases of a mission were investigated. Results: Data of 20 physicians was analysed. SDNN was positively associated with ST-T abnormalities both on a 5 minute basis (OR: 1.04, 95%CI: 1.03-1.04) and a mission basis while RMSSD was negatively associated with ST-T abnormalities evaluated per mission (OR: 0.73, 95%CI: 0.57-0.93). pNN50 was not associated with ST-T abnormalities. During patient care and patient transport HRV was significantly lower than during alarm and en-route of a rescue mission. Conclusion: No reliable correlation between HRV values and the occurrence of ST-T segment changes during missions in prehospital emergency physicians were found. Therefore, it is questionable whether HRV alone is sufficient to detect ischemia-like changes during stressful events.