PR interval

In electrocardiography, the PR interval is measured from the beginning of the P wave to the beginning of the QRS complex. It is usually 120 to 200 ms long. On the usual 25 mm/s ECG tracing, this corresponds to 3 to 5 small boxes. The PR interval reflects the time the electrical impulse takes to travel from the sinus node through the AV node and entering the ventricles. The PR interval is therefore a good estimate of AV node function.

In case a Q wave was measured with an ECG, the PR interval is also commonly named "PQ interval" instead.

Interpretation

Variations in the PR interval can be associated with certain medical conditions:

• Duration
  • A long PR interval (of over 200 ms) may indicate a first degree heart block.^[1] Prolongation can be associated with hypokalemia or acute rheumatic fever.^[2] or Lyme disease. ^[3]

• • A short PR interval may indicate a pre-excitation syndrome via an accessory pathway that leads to early activation of the ventricles, such as seen in Wolff-Parkinson-White syndrome.
  • A variable PR interval may indicate other types of heart block.
• PR segment depression may indicate atrial injury or pericarditis.^[4]
• Variable morphologies of P waves in a single ECG lead is suggestive of an ectopic pacemaker rhythm such as wandering pacemaker or multifocal atrial tachycardia

References