Hello, I'm an expert in the field of cardiology with a focus on electrophysiology. I'd be happy to explain how the PR interval is measured.

The PR interval is a specific segment of the electrocardiogram (ECG) that represents the time from the start of the P wave to the start of the QRS complex. It reflects the time taken for the electrical impulse to be transmitted from the atria to the ventricles, which is part of the process of atrial depolarization and ventricular depolarization.

To measure the PR interval, follow these steps:


1. Locate the P wave: The P wave corresponds to the atrial depolarization and is usually the first visible wave of an ECG cycle.
2. **Identify the beginning of the QRS complex**: The QRS complex represents the ventricular depolarization and is typically characterized by a sharp deflection following the S wave.

3. Measure the time: Use the ECG's calibration, which is usually set at 25 mm/s (or small squares equal to 0.04 seconds), to measure the time from the beginning of the P wave to the beginning of the QRS complex.

The normal PR interval is between 0.12 to 0.20 seconds (or 3 to 5 small squares on the ECG grid).

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A normal PR interval measures 0.12-0.20 seconds which is 3 to 5 small boxes on the EKG strip. When you measure a PR interval, you start measuring at the BEGINNING of the p-wave until the BEGINNING of the QRS complex.read more >>