Understanding ECG and Heart Rate Calculation
Electrocardiogram (ECG or EKG) is a vital diagnostic tool that records the electrical activity of the heart. It provides a graphical representation of the heart's rhythm and can help detect various cardiac abnormalities. One of the most fundamental pieces of information derived from an ECG is the heart rate.
Methods for Calculating Heart Rate from an ECG:
There are several common methods to calculate heart rate from an ECG tracing, each suited to different scenarios and levels of regularity of the heart rhythm. These calculations primarily rely on measuring the time between successive R-waves (the peak of the QRS complex), which represent ventricular depolarization.
1. Using the R-R Interval in Seconds:
This is the most direct method and is used when you can accurately measure the time between two consecutive R-waves. The formula is:
Heart Rate (bpm) = 60 / R-R Interval (seconds)
For example, if the R-R interval is measured to be 0.8 seconds, the heart rate is 60 / 0.8 = 75 beats per minute (bpm).
2. Using Large Boxes (Thick Lines):
Standard ECG paper is typically calibrated so that each large box (5 small boxes wide) represents 0.20 seconds. This method is useful for regular rhythms. The formula is:
Heart Rate (bpm) = 300 / Number of large boxes between R-R intervals
If there are, for instance, 3 large boxes between two R-waves, the heart rate is 300 / 3 = 100 bpm.
3. Using Small Boxes (Thin Lines):
This method offers greater precision, especially for irregular rhythms or when the R-R interval doesn't fall neatly on large box lines. Standard ECG paper has 25 mm/sec speed, meaning each small box represents 0.04 seconds. The formula is:
Heart Rate (bpm) = 1500 / Number of small boxes between R-R intervals
If you count 15 small boxes between two R-waves, the heart rate is 1500 / 15 = 100 bpm.
4. Using ECG Paper Speed (Generalization):
The above methods assume a paper speed of 25 mm/sec. If the paper speed is different, you can adjust the formulas. The general principle is that the heart rate is the number of beats in a minute. We know the duration of one cardiac cycle (R-R interval) and the paper speed.
Heart Rate (bpm) = (60 / R-R Interval in seconds)
Where R-R Interval in seconds can be calculated from the number of boxes and the paper speed:
R-R Interval (seconds) = (Number of small boxes * 0.04 seconds/small box) if paper speed is 25 mm/sec.
Or more generally:
R-R Interval (seconds) = (Number of small boxes / Paper Speed in mm/sec) * 0.04 seconds
This calculator allows you to input various parameters to determine the heart rate, providing flexibility for different ECG interpretations.
function calculateHeartRate() {
var rrInterval = parseFloat(document.getElementById("rrInterval").value);
var paperSpeed = parseFloat(document.getElementById("paperSpeed").value);
var largeBoxes = parseFloat(document.getElementById("largeBoxesPerRInterval").value);
var smallBoxes = parseFloat(document.getElementById("smallBoxesPerRInterval").value);
var heartRate = NaN;
var calculationMethod = "";
if (!isNaN(rrInterval) && rrInterval > 0) {
heartRate = 60 / rrInterval;
calculationMethod = `Calculated using R-R Interval: 60 / ${rrInterval.toFixed(2)} sec`;
} else if (!isNaN(largeBoxes) && largeBoxes > 0) {
heartRate = 300 / largeBoxes;
calculationMethod = `Calculated using Large Boxes: 300 / ${largeBoxes}`;
} else if (!isNaN(smallBoxes) && smallBoxes > 0 && !isNaN(paperSpeed) && paperSpeed > 0) {
// Assuming standard 0.04 sec per small box for 25 mm/sec paper speed is the base
// If paper speed is different, we need to re-calculate R-R interval in seconds first
var rrIntervalFromBoxes = (smallBoxes / paperSpeed) * 0.04;
heartRate = 60 / rrIntervalFromBoxes;
calculationMethod = `Calculated using Small Boxes (at ${paperSpeed} mm/sec): 1500 / ${smallBoxes} (approximately ${rrIntervalFromBoxes.toFixed(2)} sec)`;
}
var resultDiv = document.getElementById("result");
if (!isNaN(heartRate)) {
resultDiv.innerHTML = `
`;
} else {
resultDiv.innerHTML = `Please enter valid numbers for the inputs.`;
}
}
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font-family: sans-serif;
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text-align: center;
color: #333;
margin-bottom: 20px;
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