How to Calculate Heart Rate in Atrial Fibrillation on Ecg

Atrial Fibrillation (AFib) ECG Heart Rate Calculator

Quickly calculate the average ventricular rate for irregular rhythms like AFib using the rhythm strip method.

Count every R-wave spike within the selected time period.

6 Seconds (30 Large Boxes) 10 Seconds (Full Standard ECG) 3 Seconds (15 Large Boxes)

Calculated Heart Rate:

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Beats Per Minute (BPM)

function calculateAFibHR() { var qrs = document.getElementById("qrsCount").value; var seconds = document.getElementById("stripLength").value; var resultDiv = document.getElementById("afib-hr-result-container"); var resultDisplay = document.getElementById("afibResult"); var interpretation = document.getElementById("afibInterpretation"); if (qrs === "" || qrs <= 0) { alert("Please enter a valid number of QRS complexes."); return; } var hr = Math.round((parseFloat(qrs) / parseFloat(seconds)) * 60); resultDisplay.innerHTML = hr; resultDiv.style.display = "block"; var category = ""; if (hr = 60 && hr 100 && hr <= 110) { category = "This is a leniently controlled ventricular response."; } else { category = "This indicates tachycardia (Rapid Ventricular Response – RVR)."; } interpretation.innerHTML = "Note: In Atrial Fibrillation, the heart rate is naturally irregular. " + category; }

How to Calculate Heart Rate in Atrial Fibrillation on ECG

Calculating the heart rate (ventricular rate) in Atrial Fibrillation (AFib) is significantly different from calculating a normal sinus rhythm. Because AFib is "irregularly irregular," you cannot use standard methods like the "300 rule" or counting small boxes between two R-waves, as the distance (R-R interval) changes with every beat.

The 6-Second Method (Standard Practice)

The most accurate way to determine the heart rate in an irregular rhythm is the 6-second strip method. This provides the average number of beats per minute.

1. Obtain a rhythm strip: Ensure you have a strip representing 6 seconds of time. On a standard ECG (moving at 25mm/sec), 6 seconds equals 30 large squares.
2. Count the QRS complexes: Count every "spike" (R-wave) within that 6-second window.
3. Multiply by 10: Since there are 10 six-second intervals in one minute (60 seconds), multiplying your count by 10 gives you the beats per minute (BPM).

The 10-Second Method

Most modern 12-lead ECG printouts are 10 seconds long. If you are looking at a full standard ECG page:

• Count the total number of QRS complexes on the rhythm strip at the bottom (usually Lead II).
• Multiply that number by 6.
• Example: If you count 15 beats in a 10-second strip, the heart rate is 15 x 6 = 90 BPM.

Why the "300 Rule" Fails in AFib

The "300 / Number of Large Squares" rule relies on a constant R-R interval. In AFib, the atria are quivering randomly, leading to erratic conduction to the ventricles. One beat might have a 4-square gap (75 BPM), while the next has a 2-square gap (150 BPM). Using only one interval would give a false reading of the patient's actual clinical status.

Clinical Note: When documenting heart rate for an AFib patient, it is best practice to record a range (e.g., "Ventricular rate 70-110 BPM") or specifically state it is an "Average Ventricular Rate."

Quick Reference Table

Strip Length	Multiplier	Formula
3 Seconds (15 Large Boxes)	x 20	Beats * 20
6 Seconds (30 Large Boxes)	x 10	Beats * 10
10 Seconds (Full Page)	x 6	Beats * 6