Used for high-speed ECG recordings (Pediatrics/Tachycardia)
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How to Calculate Heart Rate at 50mm/sec
Most standard ECGs are recorded at a paper speed of 25 mm/sec. However, in specific clinical scenarios like pediatrics or extreme tachycardia, the speed is increased to 50 mm/sec to stretch out the waveform for better visualization.
When the paper speed doubles, the traditional constants used for calculation also double:
The 600 Rule: Divide 600 by the number of large squares between two R peaks.
The 3000 Rule: Divide 3000 by the number of small squares between two R peaks.
Step-by-Step Calculation Guide
Identify two consecutive R waves (the tall peaks).
Count the number of large squares (5mm each) or small squares (1mm each) between them.
At 50mm/sec, use the formula: Heart Rate (BPM) = 3000 / Total Small Squares.
Examples for 50mm/sec Paper Speed
Large Squares
Small Squares
Heart Rate (BPM)
2
10
300 BPM
4
20
150 BPM
6
30
100 BPM
10
50
60 BPM
Why use 50 mm/sec?
Doubling the paper speed is particularly useful for identifying P-waves in fast rhythms or measuring intervals more precisely in infants, whose heart rates are naturally much higher than adults. Note that at this speed, the complexes look twice as wide as they would at standard speed, so do not mistake a normal QRS for a wide QRS complex.
function calculateHeartRate() {
var largeSquares = document.getElementById("largeSquares").value;
var smallSquares = document.getElementById("smallSquares").value;
var resultDiv = document.getElementById("ecg-result");
var output = document.getElementById("hr-output");
var bpm = 0;
if (smallSquares > 0) {
bpm = 3000 / smallSquares;
document.getElementById("largeSquares").value = (smallSquares / 5).toFixed(1);
} else if (largeSquares > 0) {
bpm = 600 / largeSquares;
document.getElementById("smallSquares").value = largeSquares * 5;
} else {
alert("Please enter the number of large or small squares.");
return;
}
if (bpm > 0 && isFinite(bpm)) {
resultDiv.style.display = "block";
var category = "";
if (bpm > 100) category = " (Tachycardia)";
else if (bpm < 60) category = " (Bradycardia)";
else category = " (Normal Range)";
output.innerHTML = "Estimated Heart Rate: " + Math.round(bpm) + " BPMCalculated at 50mm/sec speed" + category + "";
} else {
alert("Please enter a valid numeric value.");
}
}