Atrial Fibrillation (Afib) Rate Calculator
.afib-calculator-wrapper {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
max-width: 800px;
margin: 20px auto;
padding: 20px;
background-color: #f9fbfd;
border: 1px solid #e1e4e8;
border-radius: 8px;
}
.afib-calc-header {
text-align: center;
margin-bottom: 30px;
}
.afib-calc-header h2 {
color: #2c3e50;
margin-bottom: 10px;
}
.afib-calc-header p {
color: #6c757d;
font-size: 0.95em;
}
.calc-input-group {
background: #ffffff;
padding: 25px;
border-radius: 8px;
box-shadow: 0 2px 4px rgba(0,0,0,0.05);
margin-bottom: 25px;
border-left: 5px solid #007bff;
}
.form-row {
display: flex;
flex-wrap: wrap;
gap: 20px;
margin-bottom: 20px;
}
.input-col {
flex: 1;
min-width: 250px;
}
.input-label {
display: block;
font-weight: 600;
margin-bottom: 8px;
color: #343a40;
}
.input-field {
width: 100%;
padding: 12px;
border: 1px solid #ced4da;
border-radius: 4px;
font-size: 16px;
transition: border-color 0.15s ease-in-out;
}
.input-field:focus {
border-color: #007bff;
outline: 0;
}
.calc-btn {
display: block;
width: 100%;
padding: 14px;
background-color: #007bff;
color: white;
border: none;
border-radius: 4px;
font-size: 18px;
font-weight: bold;
cursor: pointer;
transition: background-color 0.2s;
}
.calc-btn:hover {
background-color: #0056b3;
}
.result-box {
background-color: #ffffff;
border: 1px solid #e9ecef;
border-radius: 8px;
padding: 25px;
text-align: center;
margin-top: 20px;
display: none;
}
.bpm-display {
font-size: 48px;
font-weight: 800;
color: #2c3e50;
margin: 10px 0;
}
.bpm-unit {
font-size: 18px;
font-weight: normal;
color: #6c757d;
}
.status-badge {
display: inline-block;
padding: 8px 16px;
border-radius: 50px;
font-weight: 600;
font-size: 14px;
margin-top: 10px;
}
.status-normal { background-color: #d4edda; color: #155724; }
.status-brady { background-color: #fff3cd; color: #856404; }
.status-tachy { background-color: #f8d7da; color: #721c24; }
.article-content {
margin-top: 40px;
line-height: 1.6;
color: #333;
}
.article-content h3 {
color: #2c3e50;
margin-top: 25px;
}
.info-box {
background-color: #e2e6ea;
padding: 15px;
border-left: 4px solid #6c757d;
margin: 20px 0;
font-size: 0.9em;
}
.method-grid {
display: grid;
grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
gap: 20px;
margin-top: 20px;
}
.method-card {
background: #fff;
padding: 15px;
border: 1px solid #ddd;
border-radius: 6px;
}
Estimated Ventricular Rate
0 BPM
How to Calculate Heart Rate in Atrial Fibrillation
Calculating the heart rate (specifically the ventricular rate) during Atrial Fibrillation (Afib) poses a unique challenge compared to normal sinus rhythm. Because Afib is characterized by an "irregularly irregular" rhythm, the distance between R-waves (the R-R interval) varies constantly. This renders standard calculation methods, such as the "300 method" or "1500 method," inaccurate.
Clinical Note: The standard approach for Afib rate calculation is determining the average ventricular rate over a set period, typically 6 seconds.
The 6-Second Method
The most reliable way to calculate the heart rate from an ECG strip showing Atrial Fibrillation is the 6-Second Method. This method provides a mean heart rate that accounts for the irregularity of the rhythm.
- Obtain the Strip: Ensure you have a 6-second strip of the ECG rhythm. On standard ECG paper, 6 seconds is equivalent to 30 large boxes.
- Count the R-Waves: Count the number of complete QRS complexes (R-waves) that fall within the 6-second markers. Do not count partial complexes at the very beginning or end of the strip unless they are predominantly within the markers.
- Multiply by 10: Since 6 seconds is one-tenth of a minute, multiply your count by 10 to get the Beats Per Minute (BPM).
Interpreting the Results
Controlled Response
60 – 100 BPM
In a stable patient, a ventricular rate between 60 and 100 beats per minute is considered "controlled Afib." This is often the goal of rate-control therapy.
Rapid Ventricular Response (RVR)
> 100 BPM
A rate exceeding 100 BPM is tachycardia. In the context of Afib, rates significantly above 110-120 BPM are often termed Afib with RVR, which can lead to hemodynamic instability.
Slow Ventricular Response
< 60 BPM
A rate below 60 BPM indicates bradycardia. This may be due to excessive AV nodal blocking drugs or intrinsic conduction disease.
Why the 300 Method Fails for Afib
The "300 method" involves dividing 300 by the number of large squares between two consecutive R-waves. Since the R-R interval in Afib changes with every beat, using this method on two specific beats will give you an instantaneous rate that does not reflect the patient's actual average heart rate. For example, two beats might be very close together (simulating 150 BPM) while the next two are far apart (simulating 60 BPM).
Disclaimer: This calculator is for educational and informational purposes only. It is not a medical device and should not be used for clinical diagnosis or treatment. Always consult a qualified healthcare professional for medical advice.
function calculateAfibRate() {
// 1. Get input values
var durationInput = document.getElementById('stripDuration');
var countInput = document.getElementById('rWaveCount');
var duration = parseFloat(durationInput.value);
var rWaves = parseFloat(countInput.value);
// 2. Clear previous results classes
var resultContainer = document.getElementById('resultContainer');
var bpmDisplay = document.getElementById('bpmResult');
var statusBadge = document.getElementById('clinicalStatus');
var explanation = document.getElementById('resultExplanation');
// 3. Validation
if (isNaN(rWaves) || rWaves < 0) {
alert("Please enter a valid number of R-Waves.");
return;
}
if (isNaN(duration) || duration (8/6)*60 = 80 BPM.
// Simplified: if 6s strip, count * 10.
var bpm = (rWaves / duration) * 60;
// Round to nearest integer for standard clinical reporting
bpm = Math.round(bpm);
// 5. Determine Clinical Status
var statusText = "";
var statusClass = "";
var explText = "";
if (bpm = 60 && bpm 100) {
statusText = "Tachycardia / Rapid Ventricular Response (RVR)";
statusClass = "status-tachy";
explText = "The ventricular rate is elevated (>100 BPM), indicating Rapid Ventricular Response.";
}
// 6. Update DOM
bpmDisplay.innerHTML = bpm + '
BPM';
// Reset classes
statusBadge.className = "status-badge";
statusBadge.classList.add(statusClass);
statusBadge.innerText = statusText;
explanation.innerText = explText;
// Show result box
resultContainer.style.display = "block";
// Scroll to result slightly
resultContainer.scrollIntoView({behavior: "smooth", block: "nearest"});
}