Quick Tip: How to Calculate Heart Rate in Atrial Fibrillation on ECG
Sep 12, 2025Atrial fibrillation (AF) gives an irregularly irregular ventricular response, so the usual single-cycle methods (300/large-boxes, 1500/small-boxes) are inaccurate. The simplest, most reliable bedside method when you have a 10-second rhythm strip is:
Count the number of QRS complexes in the 10-second strip and multiply by 6 → beats per minute (bpm).
Why this works: 10 seconds × 6 = 60 seconds. This averages the variability over a longer interval and gives a clinically useful ventricular rate.
Step-by-step method
10-second count (best for AF)
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Identify and count every QRS complex in the 10-second strip.
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Include all QRS complexes (junctional/ventricular beats count as beats).
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If a QRS is partly cut off at the strip edge, count it if the R-wave peak is visible.
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Multiply the count by 6 → ventricular rate in bpm.
Example: you count 14 QRS complexes.
Compute: 14 × 6 = (10×6) + (4×6) = 60 + 24 = 84 bpm.
Use this when the rhythm is clearly irregular (AF) — it gives a good average rate.
Example 1
Example 2
Example 3
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