Electrocardiogram Interpretation – How to Determine the Heart Rate
Estimating the heart rate from an electrocardiogram (EKG) is one of the fundamental steps of EKG interpretation, playing an important role in the diagnosis and treatment of heart disease. With the EKG as a diagnostic tool, the healthcare provider can promptly detect both overt and subclinical deviations from the normal rate and rhythm.
The quick method (used when rhythm is regular):
Look for an R wave coinciding with a bold line. Then, count the number of large squares between this R wave and the next R wave. Determine the rate using the table below.
- 1 large square : 300/1 = 300 per minute
- 2 large square : 300/2 = 150 per minute
- 3 large square : 300/3 = 100 per minute
- 4 large square : 300/4 = 75 per minute
- 5 large square : 300/5 = 60 per minute
- 6 large square : 300/6 = 50 per minute
How to determine the heart rate when the rhythm is irregular:
In a standard EKG tracing, the electrical activity of the heart is measured for 10 continuous seconds. Count the number of QRS complexes in one continuous lead where cardiac activity was monitored for the whole 10 seconds or in contiguous leads encompassing 10 seconds of cardiac activity. Multiply this number by 6 (10 x 6 = 60 seconds = 1 minute) to obtain the number of heartbeats per minute or the average heart rate.
Count the number of QRS-complexes within 30 large squares. This is equivalent to 30 x 200 ms or 6 seconds of cardiac activity. Multiply this number by 10 (6 x 10 = 60 seconds = 1 minute) to get the number of heartbeats per minute or the average heart rate.
This short EKG course provided a simplified approach to determining the heart rate through EKG interpretation. Whichever method one prefers to use, it is important to always correlate findings with the overall clinical picture. For more in-depth discussions and interactive exercises to help you develop your EKG reading skills, please visit CardioCollege.com.