Use the "6-second method" (or a custom duration) to calculate the heart rate for irregular rhythms like Atrial Fibrillation.
6 Seconds (Standard)
10 Seconds
3 Seconds
Estimated Heart Rate:
0 BPM
Understanding Heart Rate Calculation in Irregular Rhythms
When an ECG rhythm is regular, clinicians often use the "300 Method" or the "1500 Method" by counting small or large boxes between R-waves. However, in an irregular rhythm—such as Atrial Fibrillation (AFib) or premature ventricular contractions (PVCs)—the distance between R-waves (the R-R interval) varies. This makes standard box-counting inaccurate.
The 6-Second Method Explained
The most reliable way to estimate the heart rate in an irregular rhythm is the 6-second method. On a standard ECG printout running at 25 mm/sec, 30 large squares represent 6 seconds. Most ECG strips have markings (usually small vertical lines at the top) every 3 seconds.
Steps to calculate manually:
Identify a 6-second segment on the ECG strip.
Count the total number of QRS complexes (the spikes) within that 6-second window.
Multiply that number by 10 to get the beats per minute (BPM).
Example Calculation
If you count 8 QRS complexes in a 6-second strip, the calculation is:
8 complexes × 10 = 80 BPM
If you are using a 10-second strip (common in many digital readouts), you would multiply the number of complexes by 6 instead.
Clinical Significance
An irregular heart rate is often a sign of an underlying cardiac condition. A normal resting heart rate is between 60 and 100 BPM. Rates below 60 are considered bradycardia, and rates above 100 are considered tachycardia. In cases of irregular rhythms, calculating an average rate over a longer period (like 6 or 10 seconds) provides a more clinically relevant "mean" heart rate than focusing on a single beat-to-beat interval.
function calculateIrregularHR() {
var qrs = document.getElementById("qrsCount").value;
var seconds = document.getElementById("stripSeconds").value;
var resultBox = document.getElementById("ecg-result-box");
var hrDisplay = document.getElementById("hrResult");
var interpretationDisplay = document.getElementById("hrInterpretation");
if (qrs === "" || qrs <= 0) {
alert("Please enter a valid number of QRS complexes.");
return;
}
// Formula: (Number of Beats / Seconds) * 60 seconds in a minute
var bpm = Math.round((parseFloat(qrs) / parseFloat(seconds)) * 60);
hrDisplay.innerHTML = bpm + " BPM";
resultBox.style.display = "block";
var interpretation = "";
if (bpm = 60 && bpm <= 100) {
interpretation = "Interpretation: Normal resting heart rate range";
} else {
interpretation = "Interpretation: Tachycardia (Fast heart rate)";
}
interpretationDisplay.innerHTML = interpretation;
}