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## St George's, University of London

Skip to 0 minutes and 9 seconds Parameters for normal sinus rhythm. In an earlier step, we have seen how the electrical activity of the heart is represented on an ECG. The presence of a P wave, followed by a QRS complex and a T wave, represents what we call a normal sinus beat, indicating that the impulse has been generated at the sinus node and then spread across the atria and the ventricles. There are a wide variety of different measurements which can be taken to examine the wave forms and their relationships in greater detail; however, we’re just going to briefly look at two of these, which are of particular significance.

Skip to 0 minutes and 51 seconds The first is called the PR interval, which is the distance from the beginning of the P wave to the beginning of the QRS complex. It therefore includes the whole of the P wave and the gap between the P and the QRS. This interval tells us whether or not there is normal conduction between the atria and the ventricles. And a normal PR interval is between three and five small squares in width. The second measurement is the QRS duration, which should be no more than 2.5 small squares in width. A normal QRS duration tells us that the ventricles are depolarising normally.

Skip to 1 minute and 38 seconds A run of continuous sinus beats, as you see here, is called sinus rhythm. When assessing ECG for the presence of sinus rhythm,

Skip to 1 minute and 47 seconds you should look for the following features: Distinct P waves should be present.

Skip to 1 minute and 55 seconds Every P wave should be followed by a QRS complex and a T wave. The P waves, QRS complexes, and T waves should look similar across the rhythm strip. And the PR interval should be constant and within the normal range of three to five small squares. This indicates that the same electrical events are happening over and over again, and there is a normal connection between the atria and the ventricles. The heart rate is also usually regular. And this can be confirmed by looking for consistent intervals between the peaks of neighbouring QRS complexes.

# Parameters for normal sinus rhythm

In this presentation, we look at the parameters for normal sinus rhythm.

This includes a review of the normal waveforms and relationships between them. We will also be looking at two measurements in particular; the PR interval and the QRS duration.