To estimate the atrial rate, how do you calculate using the number of P waves?

To estimate the atrial rate from an ECG tracing, you count the number of P waves present in a specific time frame and then multiply this number by a factor that corresponds to the time interval in which the P waves were counted. In the context of a standard 6-second strip, the convention is to multiply by 10.

This calculation is derived from the fact that a 6-second strip contains a total of 30 small squares (where each small square represents 0.04 seconds on the ECG). Therefore, when you count the number of P waves found in this section (for example, in a 6-second strip), multiplying that count by 10 gives you the estimated atrial rate in beats per minute.

Choosing the factor of 10 reflects this standard measurement method, making it the correct choice for estimating the atrial rate based on P wave counts within a 6-second interval.