How to recognize atrial fibrillation on an ECG
Other platforms explain it with text and video. In VMS you practice it on the patient.
Atrial fibrillation is the most common sustained arrhythmia and a major cause of stroke. Recognizing it quickly starts rate control and stroke prevention.
Step by step
Check the patient first
Look at the patient and the blood pressure. Low pressure, chest pain or confusion with a fast rate needs urgent help. [1]
Look at R to R spacing
In atrial fibrillation, the spaces between beats vary with no pattern. This is called irregularly irregular. [2]
Look for P waves
There are no clear P waves. The baseline may show small, uneven fibrillation waves, best seen in lead V1. [2]
Check the QRS
The QRS is usually narrow. A wide QRS can mean a bundle branch block or another problem that needs expert review. [2]
Measure the rate
Count QRS complexes in 6 seconds and multiply by 10. A rate over 100 is called rapid ventricular response. [2]
Rule out look-alikes
Atrial flutter shows regular sawtooth waves. Multifocal atrial tachycardia shows three or more different P waves. Shaking can mimic the baseline waves. [2]
Report clearly
Give the rhythm, rate, symptoms and when it started. Onset time and stroke risk guide treatment. [1]
Common errors
- Calling tremor or movement artifact atrial fibrillation.
- Using the 300 rule to find the rate in an irregular rhythm.
- Missing atrial flutter with variable block.
Practice it in VMS
In VMS you do this on the patient, not on paper: every step goes on the checklist with a score, and in Teach mode Blocky tells you what comes next.
VMS cases that train this skill
Sources
Facts and steps follow AAMC Core Entrustable Professional Activities (Core EPAs); NCCPA PANCE Content Blueprint. VMS is not affiliated with these organizations. Updated: 2026-10-11.