ECG Basics · Lesson 6 · Reading the paper
Three ways to count heart rate
Pick the method that suits the rhythm: box counting for regular rhythms, a 6-second count when beats are irregular.
The methods
- 300 rule: divide 300 by the number of large boxes between two R waves. 1 box = 300, 2 = 150, 3 = 100, 4 = 75, 5 = 60, 6 = 50. Quick, but only for regular rhythms.
- 1500 rule: divide 1500 by the number of small boxes between two R waves. More precise for regular rhythms.
- 6-second count: count QRS complexes in 6 seconds (30 large boxes) and multiply by 10. Works for irregular rhythms such as atrial fibrillation. On a 10-second strip, multiply the count by 6.
On the AF strip, read the RR labels under the trace: every pair of beats gives a different box count, so a box rule from one pair can be far off. The widget averages all pairs on the strip, which is close to what the 6-second count does for you. That is why irregular rhythms are counted, not measured from one interval.
Naming the rate
| Term | Adult rate |
|---|---|
| Bradycardia | < 60 /min (some guidelines use < 50) |
| Normal | 60–100 /min |
| Tachycardia | > 100 /min |
If atrial and ventricular rates differ (AV block, flutter), count each one separately.
References
- Mason JW, Hancock EW, Gettes LS, et al. Recommendations for the standardization and interpretation of the electrocardiogram, Part II: electrocardiography diagnostic statement list. Circulation 2007;115:1325–1332.
- Kusumoto FM, et al. 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay. Circulation 2019;140:e382–e482.