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ECG Heart Rate Calculation Methods:
Regular Rhythm: 300 ÷ number of large squares between R-R
Irregular Rhythm: (Number of R waves in 30 large squares) × 10
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There are two primary methods for calculating heart rate from an ECG, depending on whether the rhythm is regular or irregular.
Regular Rhythm Method: When the heart rhythm is regular (equal spacing between R waves), count the number of large squares between two consecutive R waves and divide 300 by this number.
Irregular Rhythm Method: When the rhythm is irregular, count the number of R waves in a 30 large square span (6 seconds) and multiply by 10.
Details: Accurate heart rate determination is essential for diagnosing arrhythmias, assessing hemodynamic stability, and guiding treatment decisions in cardiac emergencies.
Tips: Select the appropriate method based on rhythm regularity. For regular rhythms, enter the number of large squares between R waves. For irregular rhythms, count R waves in 30 large squares (6 seconds).
Q1: What defines a regular vs irregular rhythm?
A: Regular rhythm has consistent R-R intervals (variation <10%). Irregular rhythm has varying intervals.
Q2: Why 300 for regular rhythm calculation?
A: Standard ECG paper speed is 25mm/sec (5 large squares/sec). 300 = 60 seconds × 5 large squares.
Q3: When should I use the irregular method?
A: For atrial fibrillation, multifocal atrial tachycardia, or any rhythm with irregular R-R intervals.
Q4: What if the rate is very fast (>150 bpm)?
A: For rates >150, count small squares (1500 ÷ number of small squares between R-R).
Q5: How accurate are these methods?
A: Regular method is precise for regular rhythms. Irregular method gives average rate over 6 seconds.