Preclinical emergency management is frequently associated with a combination of physical and psychological stress.

This stress is known to lead to a broad variety of changes in the physiology even extending in the cardiovascular system. Both physical and psychological stress induces ECG changes. These changes include not only arrhythmias but also deviations in ST-T segment representing the phase of repolarization.

Information about changes in ST-T segment are missing until now. The investigators hypothesise that ST-T deviations occur in emergency physicians during shift at an emergency response car.

In order to show changes in ST-T segment a prospective observational trial will be conducted. By using a 12 lead ECG Holter the investigators will obtain ECGs during shifts of emergency physicians at an emergency response vehicle.

During 12-hour shifts emergency physicians will be attached to the 12 lead Holter ECG. ECGs will be analysed after blinding of names and reason of call (code) to the investigators. The primary outcome will be ST-T segment changes greater than 0.1mV in two corresponding leads for more than 30 seconds per 100 calls.

As secondary outcomes, other ECG changes such as ST-T segment changes <0.1mV, T wave inversion or HRV will be analysed. Furthermore, surrogate parameter of stress will be measured using NASA-Task Load Index and cognitive appraisal and correlated to ST-T segment changes. Correlations between different phases of calls, different indications of calls and ECG changes will be assessed. Furthermore, correlation between alarm codes apriori defined as stressfull using a delphi process and ST-T segment changes as well es surrogate parameters of stress will be assessed.

Inclusion Criteria:

• Healthy emergency physicians doing shifts at the Medical University of Vienna's emergency response car

Exclusion Criteria:

• Known pregnancy
• Pre-existing cardiac diseases (valvular heart disease > I°, any form of cardiomyopathy, history of coronary artery disease, history of myocarditis, any channelopathy, known high degree (>1% of all beats within 24h) premature atrial or ventricular beats or atrial fibrillation or conduction disturbance.
• Any antiarrhythmic therapy
• Any implanted cardiac device
• Manifest Hyperthyroidism
• Termination of exercise testing due to the commonly used criteria26 or not reaching 85% of maximal predicted load.

Emergency physicians working at the Medical University of Vienna's emergency response cars will be invited to take part in this trial. Participants will be recruited by personalised phone contact, via email or direct approach and will not financially benefit for participation. The emergency physicians are anaesthesiologists and emergency medicine consultants and senior anaesthesia or emergency medical residents with prehospital emergency medicine credentials.