On an ECG, which statement about tachycardia based on the R-R interval is correct?

On an ECG, which statement about tachycardia based on the R-R interval is correct?

• A. The heart rate is greater than 100 bpm when the R-R interval is closer than 3 large boxes.
• B. The heart rate is between 60 and 100 bpm when the R-R interval is between 3 and 5 large boxes.
• C. The heart rate is less than 60 bpm when the R-R interval is wider than 5 large boxes.
• D. The heart rate is exactly 75 bpm when the R-R interval spans 4 large boxes.

Answer: (A)