Fibrillation

Fibrillation is chaotic, with the affected part of the heart all trying to depolarise from many different origins. This results in a quivering (fairly useless) part of the heart. Fibrillation can either affect the atria (Atrial Fibrillation) or the ventricles (Ventricular Fibrillation).

• Atrial Fibrillation is irregular with absent P waves.
• Ventricular Fibrillation is totally chaotic.

Flutter

Flutter is a bit more organised, with regular flutter waves spreading out from the affected part of the heart. Flutter waves are usually very fast at about 300 beats / min. Like fibrillation, flutter can affect either the atria (Atrial Flutter) or the ventricles (Ventricular Flutter, but this is rare).

• Atrial Flutter has regular flutter waves instead of P waves, which can make the baseline look like a sawtooth. Because the AV node normally can't conduct at this extremely fast rate, it usually only lets some of these impulses through to the ventricles.
• Ventricular Flutter is much more unusual. It almost turns the whole trace into a giant sawtooth!

Narrow complex rhythm

Narrow complex rhythms have QRS complexes that are less than 100 msec wide (2.5 small squares at standard settings). Common Narrow complex rhythms include Normal Sinus Rhythm, Sinus Tachycardia, Atrial Fibrillation and Atrial Flutter. These rhythms must originate from somewhere above the ventricles, because the only way to achieve a sharp narrow QRS complex is by travelling through the ventricles completely normally on the fast normal conduction highways.

Wide complex rhythms

Wide complex rhythms have QRS complexes that are more than 100 msec wide (2.5 small squares at standard settings). These rhythms can either start within the ventricles, or if they do start above the ventricles they may encounter a conduction block that prevents them from using the normal conduction highways through the ventricles. Examples of wide complex rhythms include Ventricular Tachycardia, Left or Right Bundle Branch Blocks.

Real AF

Real AF is an irregularly irregular rhythm with no P waves. The baseline may show fine or coarse fibrillatory waves. Patients with new AF need to discuss anticoagulation, have investigations to check for contributing factors and have a strategy for rate or rhythm control.

Fake AF: P Waves Hiding in Artefact

If the baseline is fuzzy it can hide the P waves. AF is less likely if the QRS complexes are regularly spaced apart. Look closely for the P waves – leads II, V1 and V2 are often the best leads to see them in. If in doubt, repeat the ECG and try to reduce the artefact.

Fake AF: Regularly Irregular rhythms

Not all that is irregular is AF. Look closely for grouped beats (QRS complexes occurring together in repeating patterns). This can occur with second degree AV blocks. You might need a longer rhythm strip to see this pattern. If there are P waves, it’s not AF!

Fake AF: Subtle P waves

P waves can be very small and subtle. Occasionally you may also notice a rhythm with P waves that change shape (called Wandering Atrial Pacemaker). The computer is not great at picking up these P waves and may call it AF. It’s not!

Fake AF: Regular Rhythm + Ectopic Beats

Even if the rhythm is irregularly irregular, it may not be AF. Extra (ectopic) beats can interrupt an underlying regular rhythm and make it appear irregular. If there is baseline artefact it also makes this more difficult. Again, a longer strip of recording makes this easier to see.

Make your own Calipers

The easiest way to work out if a rhythm is regular is by marking the QRS complexes on a spare bit of paper and sliding this pattern along the ECG to see if the remaining beats march out evenly.