Skip to 0 minutes and 10 secondsIn week one of the course, we looked at the normal electrical conduction of the heart, known as sinus rhythm, and how this is linked to coordinated contraction and movement of blood. We now need to think about how the electrical activity is represented on an ECG as waves and complexes. A normal sinus beat starts with the generation of an electrical impulse at the sinus node and the spread of this impulse as what is called a wave of depolarisation across the atria. This event is represented on the ECG as a smooth, rounded wave form called a p-wave. The second step in the process is the impulse moving through the atrioventricular node and the bundle of his.

Skip to 0 minutes and 57 secondsThis does not produce a deflection on the ECG, so it's represented by a gap between the end of the p-wave and the beginning of the next wave form. Following this, the impulse travels down both bundle branches and depolarises the ventricles. This is represented by the QRS complex, which can vary in its shape, but is often of two or three deflections. After depolarisation, repolarisation of the ventricles occurs. And this is represented by an asymmetric t-wave.

Relationship between sinus rhythm and the ECG waveforms

In this video, we look, in greater detail, at the relationship between sinus rhythm and the ECG waveforms.

As this is a powerpoint presentation, we’ve also created an illustrated transcript for you to download in the download section.

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This video is from the free online course:

ECG Assessment: an Introduction for Healthcare Providers

St George's, University of London