ECG Heart Rate Calculator
Understanding ECG Heart Rate Calculation
Electrocardiograms (ECGs or EKGs) are vital diagnostic tools that record the electrical activity of the heart. A key piece of information derived from an ECG is the heart rate, which indicates how many times the heart beats per minute. There are several methods to calculate heart rate from an ECG strip, depending on the information available.
Methods for Calculating Heart Rate from an ECG:
1. Using the R-R Interval (in Seconds):
This is the most straightforward method if you know the duration between two consecutive R waves (the tallest peak in the QRS complex). The R-R interval represents one cardiac cycle.
Formula: Heart Rate (bpm) = 60 / R-R Interval (seconds)
Example: If the R-R interval measured on the ECG strip is 0.8 seconds, the heart rate is calculated as: 60 / 0.8 = 75 beats per minute (bpm).
2. Using the R-R Interval (in Small Boxes):
Most standard ECG machines run at a paper speed of 25 mm/second. Each small box on the ECG grid is typically 1 mm wide. Therefore, 25 small boxes represent 1 second.
Formula: Heart Rate (bpm) = 1500 / Number of Small Boxes between R-R intervals
Explanation: Since 1500 (60 seconds * 25 small boxes/second) is the total number of small boxes in one minute at a standard paper speed, dividing this by the number of small boxes between two R waves gives you the heart rate.
Example: If there are 20 small boxes between two consecutive R waves, the heart rate is: 1500 / 20 = 75 beats per minute (bpm).
3. Using the R-R Interval (in Large Boxes):
Large boxes on an ECG grid are typically formed by 5 small boxes (5 mm wide).
Formula: Heart Rate (bpm) = 300 / Number of Large Boxes between R-R intervals
Explanation: Since 300 (60 seconds * 5 large boxes/second) is the total number of large boxes in one minute at a standard paper speed, dividing this by the number of large boxes between two R waves gives you the heart rate. This method is a quick estimation.
Example: If there are 4 large boxes between two consecutive R waves, the heart rate is: 300 / 4 = 75 beats per minute (bpm).
4. Using ECG Paper Speed (Generalization):
For ECGs not run at the standard 25 mm/s, you can adapt the formulas.
Formula: Heart Rate (bpm) = 60 / (R-R Interval in Small Boxes * (1 mm / Paper Speed in mm/s))
This simplifies to: Heart Rate (bpm) = (60 * Paper Speed in mm/s) / R-R Interval in Small Boxes
Example: If the R-R interval is 20 small boxes and the paper speed is 50 mm/s: Heart Rate (bpm) = (60 * 50) / 20 = 3000 / 20 = 150 bpm.
It's important to note that these calculations are most accurate for regular heart rhythms. For irregular rhythms, averaging the R-R intervals over a longer period or using other methods might be necessary for a more precise heart rate estimation.