How to Calculate Atrial and Ventricular Rate on Ecg
by
ECG Heart Rate Calculator
Calculate Atrial and Ventricular Rates accurately
Large Square Method (Fastest)
Small Square Method (Most Precise)
6-Second Strip Method (For Irregular Rhythms)
Atrial Rate
—
BPM
Ventricular Rate
—
BPM
How to Calculate Atrial and Ventricular Rate on ECG
Understanding the difference between atrial and ventricular rates is crucial for identifying cardiac arrhythmias, such as heart blocks or atrial fibrillation. The atrial rate is derived from the P-P interval, while the ventricular rate is derived from the R-R interval.
1. The Large Square Method (The 300 Rule)
This is the fastest method for regular rhythms. Count the number of large squares (5mm blocks) between two consecutive complexes.
Formula: 300 ÷ Number of Large Squares
Example: If there are 3 large squares between R-waves, the ventricular rate is 100 BPM (300/3).
2. The Small Square Method (The 1500 Rule)
This provides the most precision for regular rhythms, especially at high heart rates.
Formula: 1500 ÷ Number of Small Squares (1mm blocks)
Example: If there are 20 small squares between P-waves, the atrial rate is 75 BPM (1500/20).
3. The 6-Second Strip Method
Crucial for irregular rhythms like Atrial Fibrillation. Count the complexes on a 6-second portion of the strip (which is 30 large squares long).
Formula: Number of complexes in 6 seconds × 10
Example: If you count 9 R-waves in a 6-second strip, the ventricular rate is 90 BPM.
Note: In a healthy heart, the atrial and ventricular rates are identical. If they differ, it may indicate pathology like AV Dissociation or Third-Degree Heart Block.
function updateFields() {
var method = document.getElementById("calcMethod").value;
var regularFields = document.getElementById("regularFields");
var irregularFields = document.getElementById("irregularFields");
var atrialLabel = document.getElementById("inputLabelAtrial");
var ventricularLabel = document.getElementById("inputLabelVentricular");
if (method === "large") {
regularFields.style.display = "block";
irregularFields.style.display = "none";
atrialLabel.innerHTML = "Large Squares between P-P:";
ventricularLabel.innerHTML = "Large Squares between R-R:";
} else if (method === "small") {
regularFields.style.display = "block";
irregularFields.style.display = "none";
atrialLabel.innerHTML = "Small Squares between P-P:";
ventricularLabel.innerHTML = "Small Squares between R-R:";
} else {
regularFields.style.display = "none";
irregularFields.style.display = "block";
}
}
function calculateECG() {
var method = document.getElementById("calcMethod").value;
var atrialRate = 0;
var ventricularRate = 0;
var interpretation = "";
if (method === "large") {
var aIn = parseFloat(document.getElementById("atrialInput").value);
var vIn = parseFloat(document.getElementById("ventricularInput").value);
if (aIn > 0) atrialRate = 300 / aIn;
if (vIn > 0) ventricularRate = 300 / vIn;
} else if (method === "small") {
var aIn = parseFloat(document.getElementById("atrialInput").value);
var vIn = parseFloat(document.getElementById("ventricularInput").value);
if (aIn > 0) atrialRate = 1500 / aIn;
if (vIn > 0) ventricularRate = 1500 / vIn;
} else {
var aCount = parseFloat(document.getElementById("atrialCount6").value);
var vCount = parseFloat(document.getElementById("ventricularCount6").value);
if (!isNaN(aCount)) atrialRate = aCount * 10;
if (!isNaN(vCount)) ventricularRate = vCount * 10;
}
if (atrialRate > 0 || ventricularRate > 0) {
document.getElementById("ecgResults").style.display = "block";
document.getElementById("atrialResult").innerHTML = Math.round(atrialRate);
document.getElementById("ventricularResult").innerHTML = Math.round(ventricularRate);
if (Math.abs(atrialRate – ventricularRate) > 5) {
interpretation = "Noticeable dissociation between atrial and ventricular rates.";
} else if (ventricularRate 100) {
interpretation = "Tachycardia detected.";
} else {
interpretation = "Heart rate within normal sinus range (60-100 BPM).";
}
document.getElementById("interpretation").innerHTML = interpretation;
} else {
alert("Please enter valid positive numbers for calculation.");
}
}