ECG Tips on Differentiating Between the Different Rhythms

Atrial flutter⁸ is identified by the presence of:

• Loss of isoelectric line
• Regular atrial activity ~300 beats/minute
• Saw-tooth pattern of inverted flutter waves (II, III, aVF)
• Upright flutter waves in V1 (these may be mistaken for P waves)

In atrial flutter with a fixed AV conduction ratio, the ventricular rate is a fraction of the atrial rate, for example in a 3:1 block  the ventricular rate would be ~100bpm (1/3 of atrial rate ~300bpm).

Atrial flutter with a variable AV conduction ratio, there may be alternating 2:1, 3:1 and 4:1 ratios, creating an irregular ventricular response which mimics atrial fibrillation.

Multifocal atrial tachycardia⁹ is identified by the presence of:

• HR >150 beats/minute (can be as high as 250bpm, usually ~100-150bpm)
• Irregularly irregular rhythm
• Varying PP/PR/RR intervals
• 3 different P wave morphologies in same lead
• No flutter waves

Atrial fibrillation¹⁰ is identified by the presence of:

• Irregularly irregular rhythm
• Loss of isoelectric line
• No P waves
• Narrow (<120ms) QRS complex (unless BBB/accessory pathway/rate-related aberrancy)
• Fine or coarse fibrillatory waves.