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Cardiology Teaching Package

A Beginners Guide to Normal Heart Function, Sinus Rhythm & Common Cardiac Arrhythmias

The ST Segment

There is a brief period between the end of the QRS complex and the beginning of the T wave where there is no conduction and the line is flat. This is known as the ST segment and it is a key indicator for both myocardial ischaemia and necrosis if it goes up or down.

Image: The ST Segment

Diagram of the ST segment of the sinus wave

So now you can see the 3 phases of the cardiac cycle which represents one heart beat. The previous example shows a rhythm strip of sinus rhythm. Here you can clearly see how each heart beat is made up of 3 distinct waves: a p wave; QRS complex, and t wave.

When you have a lot more experience you will be able to evaluate all 5 waves, but for now stick to 3.

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