ECG Heart Rate Calculator (Irregular Rhythm)
Count the number of R-waves inside the strip duration.
6 Seconds (30 Large Squares)
10 Seconds (50 Large Squares)
3 Seconds (15 Large Squares)
Custom Duration
Calculated Heart Rate:
0 BPM
Ventricular Rate Class:
–
How to Calculate Heart Rate from ECG in Atrial Fibrillation
Calculating heart rate from an Electrocardiogram (ECG) when a patient is in Atrial Fibrillation (AFib) requires a different approach than normal sinus rhythm. In standard rhythms, the "300 rule" or "1500 rule" relies on the consistency of the R-R interval (the distance between heartbeats). However, the defining characteristic of AFib is an "irregularly irregular" rhythm, meaning the R-R intervals vary constantly.
Key Concept: You cannot use the distance between two specific beats to calculate the rate in AFib because the next beat might come sooner or later. Instead, you must calculate the average rate over time.
The 6-Second Method (The Gold Standard for AFib)
The most accurate manual method for calculating ventricular rate in atrial fibrillation is the "6-Second Method." This technique takes a snapshot of the heart's activity over a fixed period to determine the average Beats Per Minute (BPM).
Step-by-Step Calculation:
- Identify the Timeframe: On standard ECG paper, 5 large squares represent 1 second. Therefore, a 6-second strip consists of 30 large squares.
- Count the QRS Complexes: Count the number of R-waves (the tall spikes representing ventricular contraction) that fall within these 30 large squares.
- Tip: If a QRS complex falls exactly on the start or end line, count it as half, or consistently count only the starting one.
- Multiply by 10: Since you have counted the beats in 6 seconds, multiply that number by 10 to get the rate for 60 seconds (1 minute).
Example: If you count 11 QRS complexes in a 6-second strip:
- Calculation: 11 beats × 10 = 110 BPM.
Why Not Use the 300 or 1500 Rule?
The standard methods involve dividing 300 by the number of large squares between two R-waves, or 1500 by the number of small squares. In AFib:
- Interval 1: Might be 3 large squares (Rate = 100 BPM).
- Interval 2: Might be 5 large squares (Rate = 60 BPM).
- Interval 3: Might be 2 large squares (Rate = 150 BPM).
Using just one of these intervals would give a vastly incorrect clinical picture. The 6-second method averages these fluctuations out.
Interpreting the Results: Controlled vs. Uncontrolled AFib
Once you have calculated the heart rate, it helps classify the severity of the condition, specifically regarding the ventricular response (how often the ventricles are actually beating).
- Controlled Ventricular Response: Heart rate is between 60 and 100 BPM (at rest). This is often the therapeutic goal.
- Rapid Ventricular Response (RVR): Heart rate exceeds 100 BPM (or 110 BPM depending on guidelines). This requires medical attention to slow the rate and prevent hemodynamic instability.
- Slow Ventricular Response (Bradycardia): Heart rate is below 60 BPM. This can occur due to excessive rate-control medication or conduction system disease.
Accuracy of ECG Paper Speeds
This calculator assumes the standard paper speed of 25 mm/sec. At this speed:
- 1 Small Square = 0.04 seconds
- 1 Large Square = 0.20 seconds
- 5 Large Squares = 1.0 second
- 30 Large Squares = 6.0 seconds
Always verify the paper speed printed on the bottom of the ECG strip before calculating.