EKG Heart Rate Calculator
Understanding EKG Heart Rate Calculation
Electrocardiograms (EKGs or ECGs) are vital tools for assessing the electrical activity of the heart. One of the most common calculations performed with EKG tracings is determining the heart rate. There are several methods to achieve this, depending on the information available from the EKG strip.
Method 1: Using the RR Interval (Most Accurate for Regular Rhythms)
The 'RR interval' is the time between two consecutive R waves on the EKG, which represent ventricular depolarization. This is the most accurate method when the heart rhythm is regular.
The formula is: Heart Rate (bpm) = 60 / RR Interval (seconds)
For example, if the RR interval is measured to be 0.80 seconds, the heart rate would be 60 / 0.80 = 75 beats per minute (bpm).
Method 2: Using Large Boxes (Good Approximation for Regular Rhythms)
EKG paper is typically printed on a grid where each large box represents 0.20 seconds (at a standard paper speed of 25 mm/sec). If the rhythm is regular, you can count the number of large boxes between two consecutive R waves.
The formula is: Heart Rate (bpm) = 300 / Number of Large Boxes between R waves
For example, if there are 4 large boxes between two R waves, the heart rate is 300 / 4 = 75 bpm.
Method 3: Using Small Boxes (Most Precise for Regular Rhythms)
Each large box on EKG paper is further divided into 5 small boxes. Therefore, each small box represents 0.04 seconds (25 mm/sec / 5 small boxes/large box). This method is the most precise when the rhythm is regular.
The formula is: Heart Rate (bpm) = 1500 / Number of Small Boxes between R waves
For example, if there are 20 small boxes between two R waves, the heart rate is 1500 / 20 = 75 bpm.
Method 4: Using Paper Speed and Interval (General Calculation)
This calculator also allows for a more generalized calculation if you know the paper speed and the measured interval in terms of large and small boxes.
First, calculate the total interval in seconds: Total Interval (sec) = (Number of Large Boxes * 0.20) + (Number of Small Boxes * 0.04) (assuming 25 mm/sec paper speed). Note that 0.20 sec = 1 large box and 0.04 sec = 1 small box at 25mm/sec. If the paper speed is different, these values change. For a paper speed of 50 mm/sec, large boxes are 0.10 sec and small boxes are 0.02 sec.
Then, calculate the heart rate: Heart Rate (bpm) = 60 / Total Interval (sec)
Example: If there are 3 large boxes and 5 small boxes, and the paper speed is 25 mm/sec:
Total Interval = (3 * 0.20) + (5 * 0.04) = 0.60 + 0.20 = 0.80 seconds.
Heart Rate = 60 / 0.80 = 75 bpm.
Important Note: The methods using large and small boxes assume a regular heart rhythm. For irregular rhythms, other methods like the '6-second strip method' (counting QRS complexes in a 6-second strip and multiplying by 10) are more appropriate.