Normal Electrocardiography (ECG) Intervals 

Updated: Nov 14, 2019
  • Author: Buck Christensen; Chief Editor: Buck Christensen  more...
  • Print

Normal Electrocardiography Intervals

Electrocardiography (ECG) has become one of the most useful diagnostic tests in clinical medicine. The ECG is now routine in the evaluation of patients with implanted defibrillators and pacemakers. It is also used to detect myocardial injury, ischemia, and the presence of prior infarction. In addition to its usefulness in ischemic coronary disease, the ECG, in conjunction with ambulatory ECG monitoring, is of particular use in the diagnosis of disorders of the cardiac rhythm and the evaluation of syncope. Other common uses of the ECG include evaluation of metabolic disorders, effects and side effects of pharmacotherapy, and the evaluation of primary and secondary cardiomyopathic processes, among others. [1, 2]

Normal values for waves and intervals are as follows:

  • RR interval: 0.6-1.2 seconds

  • P wave: 80 milliseconds

  • PR interval: 120-200 milliseconds

  • PR segment: 50-120 milliseconds

  • QRS complex: 80-100 milliseconds

  • J-point: N/A

  • ST segment: 80-120 milliseconds

  • T wave: 160 milliseconds

  • ST interval: 320 milliseconds

  • QT interval: 420 milliseconds or less if heart rate is 60 beats per minute (bpm)