Understanding ECG Heart Rate Calculation
The heart rate is the number of times your heart beats in one minute. In electrocardiography (ECG), the heart rate can be estimated by measuring the time between consecutive R waves (R-R interval) or by counting the number of small or large boxes on the ECG paper between R waves.
Methods for Calculation:
-
Using R-R Interval (in seconds): This is the most accurate method if the R-R interval is precisely measured. The formula is:
Heart Rate (BPM) = 60 / R-R Interval (seconds)
-
Using Large Boxes: ECG paper is typically printed with small squares (1mm x 1mm) and larger squares formed by 5 small squares (5mm x 5mm). If the paper speed is 25 mm/sec, one large box represents 0.2 seconds. The formula is:
Heart Rate (BPM) = 300 / Number of Large Boxes between R-R intervals
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Using Small Boxes: If the paper speed is 25 mm/sec, one small box represents 0.04 seconds. The formula is:
Heart Rate (BPM) = 1500 / Number of Small Boxes between R-R intervals
Our calculator primarily uses the R-R interval in seconds. However, you can derive the R-R interval from the box counts if needed. For example, if there are 5 large boxes between R waves on a 25 mm/sec strip, the R-R interval is 5 boxes * 0.2 sec/box = 1.0 second. If there are 25 small boxes, the R-R interval is 25 boxes * 0.04 sec/box = 1.0 second.
Example:
If the R-R interval measured from an ECG strip is 0.75 seconds:
Heart Rate = 60 / 0.75 = 80 BPM
If there are 4 large boxes between R waves on a 25 mm/sec strip:
Heart Rate = 300 / 4 = 75 BPM
If there are 20 small boxes between R waves on a 25 mm/sec strip:
Heart Rate = 1500 / 20 = 75 BPM
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function calculateHeartRate() {
var rrInterval = parseFloat(document.getElementById("rrInterval").value);
var ecgStripSpeed = parseFloat(document.getElementById("ecgStripSpeed").value);
var smallBoxSize = parseFloat(document.getElementById("smallBoxSize").value);
var largeBoxSize = parseFloat(document.getElementById("largeBoxSize").value);
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = ""; // Clear previous results
if (isNaN(rrInterval) || rrInterval <= 0) {
resultDiv.innerHTML = "Please enter a valid R-R interval in seconds.";
resultDiv.style.color = "red";
return;
}
if (isNaN(ecgStripSpeed) || ecgStripSpeed <= 0) {
resultDiv.innerHTML = "Please enter a valid ECG paper speed.";
resultDiv.style.color = "red";
return;
}
if (isNaN(smallBoxSize) || smallBoxSize <= 0) {
resultDiv.innerHTML = "Please enter a valid small box size.";
resultDiv.style.color = "red";
return;
}
if (isNaN(largeBoxSize) || largeBoxSize <= 0) {
resultDiv.innerHTML = "Please enter a valid large box size.";
resultDiv.style.color = "red";
return;
}
// Calculate using R-R interval in seconds
var heartRateFromRR = 60 / rrInterval;
var heartRateDisplay = "
ECG Heart Rate Calculation:
";
heartRateDisplay += "
Method 1 (R-R Interval):";
heartRateDisplay += "Heart Rate = 60 / " + rrInterval + " seconds =
" + heartRateFromRR.toFixed(2) + " BPM";
// Calculate number of large boxes from R-R interval
var largeBoxes = rrInterval / (largeBoxSize / ecgStripSpeed);
heartRateDisplay += "
Derived from R-R Interval:";
heartRateDisplay += "Number of Large Boxes between R-R intervals:
" + largeBoxes.toFixed(2) + "";
if (largeBoxes > 0) {
var heartRateFromLargeBoxes = 300 / largeBoxes;
heartRateDisplay += "
Method 2 (Large Boxes): Heart Rate = 300 / " + largeBoxes.toFixed(2) + " =
" + heartRateFromLargeBoxes.toFixed(2) + " BPM";
}
// Calculate number of small boxes from R-R interval
var smallBoxes = rrInterval / (smallBoxSize / ecgStripSpeed);
heartRateDisplay += "
Derived from R-R Interval:";
heartRateDisplay += "Number of Small Boxes between R-R intervals:
" + smallBoxes.toFixed(2) + "";
if (smallBoxes > 0) {
var heartRateFromSmallBoxes = 1500 / smallBoxes;
heartRateDisplay += "
Method 3 (Small Boxes): Heart Rate = 1500 / " + smallBoxes.toFixed(2) + " =
" + heartRateFromSmallBoxes.toFixed(2) + " BPM";
}
resultDiv.innerHTML = heartRateDisplay;
resultDiv.style.color = "#28a745"; // Green for success
}