ECG - SIMLabHAW/SIMLab-Emergency-Simulator GitHub Wiki
On this page an overview of electrocardiography is given. Thereby, the mode of operation is explained together with a demonstration of the implementation of the simulation in the ES.
Electrocardiography (ECG) describes a process which records the electrical activity of the heart. This measurement is based on the fundamental phenomena of the contraction of the heart: the generation of electrical dipoles generated by the depolarisation and repolarisation of the heart's muscle cells. Due to the overall resulting shift of the electrical charge, electrical fields are detectable on the skin's surface. The ECG is commonly used to identify cardiac irregularities of any kind.
An ECG is a composite recording of all the action potentials produced by the nodes and cells of the myocardium. Each wave or segment of the ECG corresponds to an event of the cardiac electric cycle. This cycle repeats itself with every heartbeat.
The P wave is the first impulse of an ECG. When the atria are full of blood, the sinoatrial node fires. The generated electrical signals spread throughout the atria and cause them to depolarise. Therefore, the P wave represents the atrial systole contraction pulse.
Source: Lang, F. and Lang, P. (2007). Basiswissen Physiologie. 2nd ed. Berlin, Heidelberg: Springer Medizin Verlag Heidelberg, p.50.
The atrial contraction starts approximately 100ms after the P wave begins. It is typically represented by an isometric line which connects the P wave to the downward deflecting Q wave. The PQ interval displays the time in which the signals travel from the sinoatrial nodes to the atrioventricular (AV) node.
Source: Lang, F. and Lang, P. (2007). Basiswissen Physiologie. 2nd ed. Berlin, Heidelberg: Springer Medizin Verlag Heidelberg, p.50.
The QRS complex marks the firing of the AV node and represents ventricular depolarisation. The Q wave corresponds to the depolarisation of the intraventricular septum. The R wave is produced by depolarisation of the main mass of the ventricles and is the peak of the ventricular contraction.
Source: Lang, F. and Lang, P. (2007). Basiswissen Physiologie. 2nd ed. Berlin, Heidelberg: Springer Medizin Verlag Heidelberg, p.50.
The S wave constitutes the last phase of ventricular depolarisation at the base of the heart. Atrial repolarisation also occurs during this time, but the signal is obscured by the large QRS complex. The ST segment reflects the plateau in the myocardial action potential. This is when the ventricles contract and pump blood.
Source: Lang, F. and Lang, P. (2007). Basiswissen Physiologie. 2nd ed. Berlin, Heidelberg: Springer Medizin Verlag Heidelberg, p.50.
The T wave represents ventricular repolarisation immediately before ventricular relaxation or ventricular diastole.
Source: Lang, F. and Lang, P. (2007). Basiswissen Physiologie. 2nd ed. Berlin, Heidelberg: Springer Medizin Verlag Heidelberg, p.50.
For additional details of the anatomy of the heart, the cardiac conduction system, and to watch an ECG come alive by animation - just follow the links below:
- Anatomy of the heart
- ECG interpretation explained easy and simple
- Animation of the cardiac conduction system and ECG.
Electrodes are applied to muscle cells by attaching them to a patient's limbs and chest. When the heart is at rest, no potential difference is detectable between the electrodes (a). However, if the muscle fibers are activated (yellow), a positive right-sided potential is generated (b). This potential remains mostly constant during its conduction (c) and dissolves once the muscle fibre is fully activated (d). During the regression of the activation, a potential in the opposite direction is created (e).
Source: Lang, F. and Lang, P. (2007). Basiswissen Physiologie. 2nd ed. Berlin, Heidelberg: Springer Medizin Verlag Heidelberg, p.48.
The ECG simulation in the Emergency Simulator provides different user-interface depending on whether the person is logged in as trainer or trainee. Having each their individual role during the simulation, both the trainer and trainee have specific set of parameters that can be modified or controlled in order to achieve the best experience out of the simulation.
The trainer has several options to adjust the ECG which is simulated for the trainee. First of all, the ECG signal can be turned off and on as to be seen in the clip below.
The heart rate can be varied by changing the number indicated in the white input field by either using the small arrows next to the number or manually entering the desired beats per minute. The newly entered values must be confirmed by pushing the blue "OK"-button on the top right corner of the screen. The waveform will then adapt accordingly. Likewise, the pacer energy threshold may be adapted.
In addition, the ES provides the trainer with the option to modify the ECG waveform with a cardiopulmonary resuscitation (CPR) by simply activating the "CPR"-button on the right hand side of the input fields. For further information on the CPR mode just follow the embedded link.
The trainee's view displays an original screen of an ECG emergency device as presented below.
In order to simulate the scenario as realistic as possible, the heart rate is subject to minor fluctuation instead of an entirely stable value. For the same reason, the trainee's view adapts to changes made by the trainer incrementally rather than immediately. If the heart rate drops below the critical value of 50 bpm or exceeds 120 bpm, the trainee is alerted by a red frame around the heart rate display. However, this is only the default setting. The critical value for the alarm signals can be modified by using the button on the bottom right. To get an overview of the other adjustment options, continue reading on the General Features page.
This alarm does not only appear visually, but also audible in form of an alarm tone. In situations where this may be unwanted, the alarm tone can be muted by the trainee by activating the button presented below. In this case, the button turns green and the alarming sound is muted for two minutes. The ongoing time of mute is displayed within the button itself. By simply clicking the mute button again, the alarm tone is reactivated.
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