Count all R-waves within the strip duration (including the first one, exclude if strictly outside).
Standard rhythm strips are usually 6 seconds (30 large boxes at 25mm/sec).
Estimated Ventricular Rate
0 BPM
function calculateAfibRate() {
var qrsInput = document.getElementById('qrsCount');
var durationInput = document.getElementById('stripDuration');
var resultBox = document.getElementById('resultBox');
var bpmDisplay = document.getElementById('bpmResult');
var interpretationDisplay = document.getElementById('interpretation');
var qrsCount = parseFloat(qrsInput.value);
var duration = parseFloat(durationInput.value);
// Validation
if (isNaN(qrsCount) || qrsCount <= 0) {
alert("Please enter a valid number of QRS complexes.");
return;
}
if (isNaN(duration) || duration <= 0) {
alert("Please enter a valid strip duration in seconds.");
return;
}
// Calculation: (Count / Seconds) * 60 = BPM
var bpm = (qrsCount / duration) * 60;
bpm = Math.round(bpm);
// Interpretation Logic for Afib
var message = "";
var messageColor = "#333";
var bgColor = "#f1f3f5";
if (bpm = 60 && bpm 100 && bpm <= 110) {
message = "Tachycardic (Moderate Rapid Ventricular Response)";
bgColor = "#fff3cd"; // Light yellow
messageColor = "#856404";
} else {
message = "Rapid Ventricular Response (RVR) – Uncontrolled";
bgColor = "#f8d7da"; // Light red
messageColor = "#721c24";
}
// Output
bpmDisplay.innerText = bpm + " BPM";
interpretationDisplay.innerText = message;
interpretationDisplay.style.backgroundColor = bgColor;
interpretationDisplay.style.color = messageColor;
resultBox.style.display = "block";
}
How to Calculate Rate in Afib (Atrial Fibrillation)
Calculating the heart rate in Atrial Fibrillation (Afib) requires a different approach than normal sinus rhythm due to the irregularly irregular nature of the heartbeat. Standard methods, such as the "300 method" (dividing 300 by the number of large boxes between R-waves), are inaccurate in Afib because the R-R intervals vary constantly.
The Gold Standard: The 6-Second Strip Method
The most accurate and clinically accepted way to calculate the ventricular rate in Atrial Fibrillation is the 6-Second Method. This method provides an average rate that accounts for the irregularity of the rhythm.
Obtain a 6-Second Strip: Most standard ECG paper records time on the horizontal axis. At a standard speed of 25mm/sec, 6 seconds is equal to 30 large boxes (or 150 small boxes). Many ECG strips have "hash marks" every 3 seconds at the top or bottom of the paper. Two of these 3-second intervals make a 6-second strip.
Count the QRS Complexes: Count every QRS complex (the tall spikes indicating ventricular contraction) that falls within this 6-second window.
Tip: If a QRS complex lands exactly on the start line, count it. If it lands on the end line, usually you do not count it (standardize your practice), but generally, count all full complexes visible.
Multiply by 10: Since there are 60 seconds in a minute, and you have measured 6 seconds, multiply your count by 10 to get the Beats Per Minute (BPM).
Example Calculation:
You look at a 6-second strip of a patient in Afib.
You count 13 QRS complexes. Math: 13 × 10 = 130 BPM. Interpretation: This is Atrial Fibrillation with Rapid Ventricular Response (RVR).
Why is this important?
In Atrial Fibrillation, the atria are quivering rather than contracting effectively. The clinical concern is often the Ventricular Rate (how fast the ventricles are pumping). Interpretation falls into three main categories:
Controlled Afib: Heart rate is between 60 and 100 BPM. This is the goal of rate-control therapy (e.g., using Beta-blockers or Calcium Channel Blockers).
Afib with RVR (Rapid Ventricular Response): Heart rate is > 100 BPM. This can lead to hemodynamic instability, hypotension, or heart failure if sustained.
Slow Ventricular Response: Heart rate is < 60 BPM. This may indicate too much AV nodal blocking medication or intrinsic conduction disease.
Alternative: The 10-Second Method
For even greater accuracy, especially if the rate is very slow, you can count the QRS complexes in a 10-second strip (usually the entire length of a standard 12-lead ECG) and multiply by 6. The calculator above allows you to change the duration to 10 seconds if you prefer this method.