function calculateECGHeartRate() {
var rrMs = document.getElementById('rr_ms').value;
var largeSq = document.getElementById('large_sq').value;
var smallSq = document.getElementById('small_sq').value;
var resultDiv = document.getElementById('ecg-result');
var output = document.getElementById('hr-output');
var category = document.getElementById('hr-category');
var bpm = 0;
if (rrMs > 0) {
bpm = 60000 / rrMs;
} else if (largeSq > 0) {
bpm = 300 / largeSq;
} else if (smallSq > 0) {
bpm = 1500 / smallSq;
} else {
alert('Please enter a value in one of the fields.');
return;
}
bpm = Math.round(bpm);
resultDiv.style.display = 'block';
output.innerHTML = 'Heart Rate: ' + bpm + ' BPM';
if (bpm 100) {
category.innerHTML = 'Classification: Tachycardia';
category.style.color = '#e67e22';
} else {
category.innerHTML = 'Classification: Normal Sinus Rhythm';
category.style.color = '#27ae60';
}
}
Which Interval is Used to Calculate Heart Rate in an ECG?
In electrocardiography (ECG), the heart rate is primarily calculated using the R-R interval. This interval represents the time between two consecutive R waves (the tallest peaks of the QRS complex), which signifies the time between successive ventricular contractions.
Common Calculation Methods
Depending on the rhythm regularity and the available equipment, clinicians use three primary methods to determine heart rate from an ECG strip:
The 1500 Method: Used for regular rhythms. Since standard ECG paper moves at 25 mm/sec, there are 1,500 small squares (1mm each) in one minute. By dividing 1,500 by the number of small squares between two R waves, you get an exact beats-per-minute (BPM) count.
The Sequence Method (300 Method): A quicker version of the 1500 method. You divide 300 by the number of large squares (5mm each) between R waves. For example, if there are 4 large squares, the HR is 300 / 4 = 75 BPM.
The 6-Second Method: Essential for irregular rhythms like Atrial Fibrillation. You count the number of QRS complexes in a 6-second strip (30 large squares) and multiply that number by 10.
Examples of Heart Rate Calculations
Interval Measured
Calculation
Result (BPM)
15 Small Squares
1500 / 15
100 BPM
3 Large Squares
300 / 3
100 BPM
1000ms R-R Interval
60,000 / 1000
60 BPM
Why the R-R Interval?
The R-R interval is used because the R wave is the most prominent and easily identifiable spike on an ECG. While the P-P interval can also be used to calculate the atrial rate, the R-R interval specifically determines the ventricular rate, which is the most clinically significant metric for assessing cardiac output and identifying conditions like bradycardia or tachycardia.