Select the ratio of atrial beats (F-waves) to ventricular beats (QRS complexes).
Atrial Flutter Rate:0 bpm
Ventricular Rate:0 bpm
Cycle Length (CL):0 ms
Interpretation:
function calculateFlutterRate() {
// Inputs
var boxes = document.getElementById('fWaveDistance').value;
var ratio = document.getElementById('conductionRatio').value;
var resultDiv = document.getElementById('results');
// Validation
if (!boxes || boxes <= 0) {
alert("Please enter a valid number of small boxes (greater than 0).");
resultDiv.style.display = "none";
return;
}
// Calculations
// Standard paper speed: 25mm/sec
// 1 small box = 0.04 seconds = 40ms
// Rate = 1500 / small boxes
var boxesVal = parseFloat(boxes);
var atrialRate = 1500 / boxesVal;
var cycleLengthMs = boxesVal * 40;
var ventRateDisplay = "";
if (ratio === "variable") {
// If variable, typically ranges between 2:1 and 4:1
var rate2 = Math.round(atrialRate / 2);
var rate4 = Math.round(atrialRate / 4);
ventRateDisplay = rate4 + " – " + rate2 + " bpm (Avg)";
} else {
var ratioVal = parseFloat(ratio);
var vRate = atrialRate / ratioVal;
ventRateDisplay = Math.round(vRate) + " bpm";
}
// Interpretation Logic
var interpretation = "";
if (atrialRate 350) {
interpretation = "Above typical flutter range (Possible A-Fib or 1:1 Flutter).";
} else {
interpretation = "Consistent with Typical Atrial Flutter (240-350 bpm).";
}
// Display Results
document.getElementById('atrialRateResult').innerHTML = Math.round(atrialRate) + " bpm";
document.getElementById('ventricularRateResult').innerHTML = ventRateDisplay;
document.getElementById('cycleLengthResult').innerHTML = Math.round(cycleLengthMs) + " ms";
document.getElementById('interpretationText').innerHTML = interpretation;
resultDiv.style.display = "block";
}
How to Calculate Atrial Flutter Rate
Atrial flutter is a macro-reentrant atrial arrhythmia characterized by a rapid, regular atrial rhythm. Accurately calculating the atrial flutter rate is essential for diagnosing the arrhythmia and distinguishing it from other supraventricular tachycardias (SVTs). Unlike chaotic Atrial Fibrillation, Atrial Flutter presents with distinct "sawtooth" F-waves on an electrocardiogram (ECG).
The 1500 Method
The most precise way to manually calculate the atrial rate on a standard ECG (running at 25 mm/sec) is the "1500 method." This involves measuring the distance between the specific flutter waves.
Formula: Atrial Rate = 1500 รท Number of Small Boxes between F-waves
Because the atrial flutter circuit typically circulates around the tricuspid valve annulus (in typical Type I flutter), the rate is highly consistent, usually falling between 240 and 340 beats per minute (bpm), with 300 bpm being the classic textbook presentation.
Determining Ventricular Rate and AV Block
In atrial flutter, the AV node usually cannot conduct every single atrial impulse to the ventricles because the atrial rate is too fast (physiological refractory period). The AV node creates a "block" to protect the ventricles.
To calculate the ventricular rate (the pulse rate you would feel on the patient), you divide the atrial rate by the conduction ratio:
2:1 Block (Most Common): For every 2 atrial F-waves, 1 QRS complex passes through. If the atrial rate is 300 bpm, the ventricular rate will be roughly 150 bpm.
3:1 Block: For every 3 F-waves, 1 QRS passes. Atrial rate 300 bpm results in a ventricular rate of 100 bpm.
4:1 Block: Often seen after treatment with AV nodal blocking agents (like beta-blockers). Atrial rate 300 bpm results in a ventricular rate of 75 bpm.
Typical Measurements
On a standard ECG grid:
1 Small Box: 0.04 seconds (40 ms)
1 Large Box: 0.20 seconds (200 ms)
Typical Flutter Cycle Length: Usually around 200ms (5 small boxes), which equates to exactly 300 bpm.
Clinical Significance
Calculating the exact rate helps confirm the diagnosis. A regular narrow complex tachycardia at exactly 150 bpm should immediately raise suspicion of Atrial Flutter with 2:1 block. If the calculated atrial rate is significantly below 240 bpm, the rhythm might be Atrial Tachycardia rather than Flutter. If it is faster than 350-400 bpm, the rhythm may be degenerating into Atrial Fibrillation.