function calculateAfibRate() {
var qrsInput = document.getElementById('qrsCount');
var durationInput = document.getElementById('stripDuration');
var resultSection = document.getElementById('resultSection');
var bpmDisplay = document.getElementById('bpmResult');
var classDisplay = document.getElementById('classificationResult');
var interpretDisplay = document.getElementById('interpretationText');
var qrsCount = parseFloat(qrsInput.value);
var durationSeconds = parseFloat(durationInput.value);
if (isNaN(qrsCount) || qrsCount <= 0) {
alert("Please enter a valid number of QRS complexes.");
return;
}
// Calculation: (Count / Seconds) * 60
var bpm = (qrsCount / durationSeconds) * 60;
bpm = Math.round(bpm);
// Display BPM
resultSection.style.display = "block";
bpmDisplay.innerHTML = bpm + " BPM";
// Classification Logic for AFib
var classification = "";
var className = "";
var interpretation = "";
if (bpm = 60 && bpm 100 && bpm <= 110) {
classification = "Moderate Rapid Ventricular Response";
className = "class-tachy";
interpretation = "The heart rate is slightly elevated.";
} else {
classification = "Uncontrolled AFib (Rapid Ventricular Response)";
className = "class-danger";
interpretation = "The heart rate is significantly elevated (RVR). This may lead to hemodynamic instability or symptoms like palpitations and shortness of breath.";
}
classDisplay.textContent = classification;
classDisplay.className = "result-classification " + className;
interpretDisplay.textContent = interpretation;
}
How to Calculate Heart Rate in Atrial Fibrillation (ECG)
Calculating the heart rate accurately from an electrocardiogram (ECG) is a fundamental skill in cardiology. However, when a patient is in Atrial Fibrillation (AFib), the standard rules of calculation change. Because AFib is characterized by an "irregularly irregular" rhythm, the intervals between beats (R-R intervals) vary continuously, making standard methods like the "300 rule" inaccurate.
Key Takeaway: In Atrial Fibrillation, you cannot calculate heart rate based on a single gap between beats. You must calculate the average rate over a set period of time using the "6-Second Method."
Why the Standard "300 Method" Fails in AFib
For regular rhythms (like Normal Sinus Rhythm), medical professionals often use the 300 Method: counting the number of large grid squares between two consecutive R waves and dividing 300 by that number.
In Atrial Fibrillation, the distance between R waves changes with every beat. If you use the 300 method on two beats that are close together, you might calculate a rate of 150 BPM. If you use the next two beats which are far apart, you might calculate 60 BPM. Neither represents the true ventricular rate.
The Gold Standard: The 6-Second Method
The most reliable way to calculate heart rate in the presence of an irregular rhythm is to count the number of electrical impulses conducted to the ventricles over a fixed time duration.
Step-by-Step Calculation Guide
Obtain a Rhythm Strip: Print out an ECG strip. Most standard ECG papers have time markers at the bottom or top (often small tick marks every 3 seconds).
Identify a 6-Second Interval: Count out a duration of 6 seconds. On standard ECG paper (running at 25mm/sec), 6 seconds equals 30 large squares.
Count the QRS Complexes: Count every QRS complex (the tall spikes representing ventricular contraction) that falls completely within that 6-second window. Do not count P waves or fibrillation waves.
Multiply by 10: Since there are 60 seconds in a minute, multiply your count by 10 to get the Beats Per Minute (BPM).
Example: If you count 11 QRS complexes in a 6-second strip, the heart rate is 11 × 10 = 110 BPM.
Interpreting the Results in AFib
Once you have calculated the ventricular rate, it is categorized clinically to determine treatment urgency:
Heart Rate (BPM)
Classification
Clinical Implication
< 60 BPM
Slow Ventricular Response
May cause dizziness or syncope. Check for excessive medication dosing.
60 – 100 BPM
Controlled Response
Ideal therapeutic target for resting heart rate.
> 100 BPM
Rapid Ventricular Response (RVR)
Heart is beating too fast to fill properly. Can lead to heart failure or hypotension.
Alternative Methods
While the 6-second method is standard, you can improve accuracy by using a longer duration if the strip allows:
10-Second Method: Used often with full 12-lead ECGs. Count QRS complexes in the entire 10-second tracing and multiply by 6.
60-Second Method: Counting the apical pulse or telemetry history for a full minute is the most accurate method but requires more time.
Frequently Asked Questions
Does this calculator work for Atrial Flutter?
Yes. If the Atrial Flutter has a variable block (irregular response), use the 6-second method described above. If the block is fixed (e.g., exactly 2:1 or 4:1), you can use the standard 300 method, but the 6-second method remains accurate for both.
What are the grid sizes on ECG paper?
Standard ECG paper moves at 25mm/second.
Small square: 1mm x 1mm = 0.04 seconds.
Large square: 5mm x 5mm = 0.20 seconds.
Therefore, 5 large squares = 1 second, and 30 large squares = 6 seconds.
Why is Heart Rate important in AFib?
In AFib, the atria are quivering rather than pumping efficiently. If the ventricles also beat too fast (RVR), cardiac output drops significantly, potentially causing blood clots, stroke, or heart failure. "Rate Control" is a primary pillar of AFib management.