If two R waves are closer than 3 large boxes, the rate is

If two R waves are closer than 3 large boxes, the rate is

• A. Greater than 100 bpm
• B. Normal 60-100 bpm
• C. Less than 60 bpm
• D. Cannot be determined

Answer: (A)

Estimating heart rate from an ECG relies on the R–R interval. Each large box on ECG represents 0.2 seconds, so a quick rule of thumb is 300 divided by the number of large boxes between consecutive R waves. If the R waves are closer than 3 large boxes, the interval is under 0.6 seconds, giving a rate greater than 300/3, which is 100 bpm. So the rate is faster than 100 bpm. This places it in tachycardia territory rather than normal. In a regular rhythm, this estimation holds well; if rhythms are irregular, you’d average over several beats.

Estimating heart rate from an ECG relies on the R–R interval. Each large box on ECG represents 0.2 seconds, so a quick rule of thumb is 300 divided by the number of large boxes between consecutive R waves. If the R waves are closer than 3 large boxes, the interval is under 0.6 seconds, giving a rate greater than 300/3, which is 100 bpm. So the rate is faster than 100 bpm. This places it in tachycardia territory rather than normal. In a regular rhythm, this estimation holds well; if rhythms are irregular, you’d average over several beats.