ECG Quest > Basics > Regularity


To interpret abnormal ECG rhythms, the first skill you need is to know the difference between regular, grouped and irregular rhythms. We call this the regularity.


If the rhythm is regular, then the QRS complexes are evenly spaced apart.


If the rhythm is grouped, there will be regular groups of beats with gaps between them of different lengths. Sometimes grouped rhythms are also known as ‘regularly irregular’.


If the rhythm is irregular, the QRS complexes will be unevenly spaced apart with no clear pattern. Sometimes these irregular rhythms are called ‘irregularly irregular’.

Assessing the regularity can sometimes be very difficult with only short strips of recording. A longer rhythm strip is often printed along the bottom of the ECG to make this interpretation easier. Calipers are also useful tools for deciding if a rhythm is regular or not. On paper ECGs, physical calipers can be marched out across the page to check if the complexes are evenly spaced apart. On the computer, calipers can either be dragged across the screen or set by clicking on the ECG.

Of these variations, it is probably the hardest to pick grouped rhythms. They are often mistaken for irregular rhythms and sometimes you need a longer strip of recording to be able to pick the repeating pattern. So, keep an eye out for grouped rhythms.

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