Calculating ECG Heart Rate Using R-R Intervals

Steps:

• Identify consecutive R waves on the ECG strip.
• Count large squares (0.2 seconds each) between R waves.
• Apply formula: heart rate = 300 / number of large squares.
• Compare calculated rate to 75 bpm.

Why B is correct:

• Option B shows 4 large squares between R waves; 300 / 4 = 75 bpm, matching the 6-second rule for standard paper speed.

Why the others are wrong:

• A: 3 large squares yield 300 / 3 = 100 bpm, too fast.
• C: 5 large squares yield 300 / 5 = 60 bpm, too slow.
• D: 6 large squares yield 300 / 6 = 50 bpm, too slow.

Final answer: B