How do you calculate heart rate on a 6-second ECG strip?

• A. Count the number of Q waves in 6 seconds and multiply by 10 to get bpm.
• B. Count the number of P waves in 6 seconds and multiply by 6.
• C. Count the number of R waves in 6 seconds and multiply by 10 to get bpm.
• D. Measure PR interval and convert to bpm.

Answer: (C)

The main idea is to count the number of ventricular contractions, indicated by R waves, on a 6-second ECG strip and then multiply by 10 to convert that count into beats per minute. Each R wave corresponds to one heartbeat (ventricular depolarization), so tallying how many R waves appear in a 6-second window gives the number of heartbeats in that window. Since there are ten 6-second blocks in a minute, multiplying by 10 yields the heart rate in bpm.

This method works quickly and is reliable for a standard ECG tracing, especially when the rhythm is regular. If the rhythm is irregular, you still get an estimate by counting the R waves in the 6-second strip, but for a precise rate you’d prefer a longer recording (or a full 1-minute count).

Why the other ideas don’t fit: P waves reflect atrial activity, not the total number of heartbeats, so counting P waves won’t give heart rate. Q waves are just part of the QRS complex and don’t occur once per beat in a way that reliably marks every heartbeat. Measuring the PR interval assesses conduction time from atria to ventricles, not the rate.