The PR, QRS, and QT are intervals (a portion of the baseline and at least one wave) that are measured in seconds on an ECG.

PR Interval

The PR Interval is calculated from the beginning of the P wave to the beginning of the QRS complex. It represents the time it takes the heart’s electrical impulse to travel from the atria through the AV node, bundle of His, and left/right bundle branches.

• Normal Duration: 0.12-0.20 seconds (120-200 ms)
• Prolonged PR Intervals represent a conduction delay through the atria or AV node.

QRS Complex

The QRS complex follows the P wave and represents the depolarization (contraction) of the ventricles.

• Normal Duration: 0.06-0.12 seconds (60-120 ms)
• Prolonged QRS complexes represent a conduction defect at the Bundle of His or in the bundle branches.

QT Interval

The QT interval represents the depolarization and repolarization of the ventricles.

• Normal Duration: 0.36-0.44 seconds (360-440 ms)