Electrocardiography (ECG) (Nursing)

00:01 The way we measure this is by electrocardiography.

00:06 An electrocardiograph can detect the electrical currents that are generated by the heart.

00:14 An electrocardiogram is the graphing record of that electrical activity.

00:21 It's important to note or understand that the peaks and the electrocardiogram, the peaks and valleys do not correspond to actual membrane potentials because it's going to be a culmination of all of the action potentials that are happening over the entire heart.

00:42 In this process, electrodes are placed at various points on the body in order to measure the voltage differences.

00:51 So how does this work? The main features of an electrocardiogram include a P wave which is going to correspond to the depolarization of the SA node and the atria.

01:06 From there, we have the P to R interval which is the beginning of atrial excitation all the way to the beginning of ventricular excitation.

01:18 We also have the QRS complex.

01:22 This is going to correspond to ventricular depolarization as well as atrial repolarization.

01:32 Also, we have the QT interval which is the beginning of ventricular depolarization through the ventricular repolarization.

01:44 the ST segment of the electrocardiogram is going to be the entire ventricular myocardium being depolarized.

01:53 And finally, we have our T waves which corresponds to ventricular repolarization.

02:03 In a normal ECG trace, when we have sinus rhythm, you notice that for about a second, you have a P wave followed by your to QRS peak followed by the T wave and in a second you usually can get about two of these occurring.

02:24 Sometimes when you do a trace you'll notice that there is some abnormalities.

02:29 For example if the AV node fails to conduct some SA node impulses, what you'll find is that you have multiple P waves per QRS wave.

02:43 This lets you know that there's some type of blockage and usually in this circumstance, you see two P waves per QRS wave instead of one P wave per QRS wave.

02:58 Sometimes in ventricular fibrillation, we can see just a disorganized tracing where are the electrical activity is just kind of all over the place.

03:09 This is because action potentials are occurring randomly throughout the ventricle.

03:14 This is a grossly abnormal ECG deflection and this is what you can see sometimes in acute heart attacks or after an electrical shock.