What are the normal electrocardiogram (ECG) intervals and wave durations in a healthy adult?

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Normal ECG Intervals and Wave Durations in Healthy Adults

In healthy adults, the normal QRS duration is ≤110 ms, the PR interval ranges from 120-200 ms, and the normal QRS axis lies between -30° and +90°. 1

QRS Complex Duration

The upper limit of normal QRS duration in adults over 16 years of age is 110 ms. 1 This threshold applies to both males and females, though males may occasionally demonstrate durations up to 110 ms as a normal variant. 1 The QRS complex represents ventricular depolarization and is measured from the earliest onset to the latest offset across all leads. 1

Key Technical Considerations:

  • Global interval measurements (from spatial vector magnitude or superimposed complexes) are the preferred standard and will be longer than single-lead measurements 1
  • QRS duration may increase with increasing heart size 1
  • The QRS complex appears wider in precordial leads compared to limb leads 1

PR Interval

The normal PR interval in adults ranges from 120-200 ms (0.12-0.20 seconds). 2 This interval reflects conduction time from the onset of atrial depolarization through the AV node to the beginning of ventricular depolarization.

Heart Rate Dependency:

  • The PR interval demonstrates moderate heart rate dependency, being less rate-dependent than the QT interval (approximately 36% of linear QT/RR slopes) 3
  • PR interval adaptation to heart rate changes differs significantly by sex: females require 114.9 ± 81.1 seconds for 95% adaptation versus 65.4 ± 64.3 seconds in males 3
  • The PR/cycle-length relationship is highly curvilinear, with significantly more curvature in females than males 3

Abnormal PR Values:

  • PR interval <120 ms suggests ventricular preexcitation (as seen in Wolff-Parkinson-White syndrome) 2
  • PR interval >200 ms indicates first-degree AV block

P Wave Parameters

Normal P wave duration in healthy adults averages 106.8-110.2 ms, with females having marginally shorter durations than males. 3

Reference Values by Sex:

  • Females: 106.8 ± 8.4 ms (rate-corrected) 3
  • Males: 110.2 ± 7.9 ms (rate-corrected) 3

Additional P Wave Characteristics:

  • P wave duration is minimally heart rate dependent (only 9 ± 10% of linear QT/RR slopes) 3
  • All P wave indices (maximum, mean, lead II duration, and dispersion) increase significantly with advancing age 4
  • Men consistently demonstrate longer P wave indices compared to women across all age groups 4
  • P wave indices show strong correlation with PR interval duration 4

Population-Specific Reference Ranges:

The Multi-Ethnic Study of Atherosclerosis established that significant age, sex, and race differences exist in P wave parameters, necessitating stratified reference ranges. 5 Middle-aged adults (45-64 years) have shorter P wave durations than seniors (65-84 years), and these differences persist after adjusting for anthropometric and clinical factors. 5, 4

QRS Axis

The normal QRS axis in adults ranges from -30° to +90°. 1

Axis Deviation Definitions:

  • Left axis deviation: Beyond -30° 1
    • Moderate: -30° to -45° 1
    • Marked: -45° to -90° (often associated with left anterior fascicular block) 1
  • Right axis deviation: 1
    • Moderate: +90° to +120° 1
    • Marked: +120° to +180° (often associated with left posterior fascicular block) 1
  • Indeterminate axis: When no dominant QRS deflection is present (equiphasic QRS complex) 1

Physiologic Factors:

  • The QRS axis shifts leftward with increasing age 1
  • Body habitus influences the mean frontal plane electrical axis 1

R Wave Peak Time

Normal R peak time (intrinsicoid deflection) is ≤50 ms in leads V5 and V6. 1 This measurement represents the interval from QRS onset to the peak of the R wave in leads without a small initial r wave. 1

Clinical Pitfalls:

  • R peak time >60 ms in leads V5-V6 suggests left ventricular conduction delay or left bundle branch block 1
  • R peak time >50 ms in lead V1 is a criterion for right bundle branch block 1

QT Interval Considerations

While not explicitly detailed in the provided guidelines for normal values, the QT interval requires heart rate correction for accurate interpretation. 6 The QT interval is measured from the beginning of the QRS complex to the end of the T wave and demonstrates significant heart rate dependency. 6 Accurate manual assessment requires careful attention to lead choice, U-wave presence, and proper identification of T wave termination. 6

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

4
Research

P-wave indices: derivation of reference values from the Framingham Heart Study.

Annals of noninvasive electrocardiology : the official journal of the International Society for Holter and Noninvasive Electrocardiology, Inc, 2010

6
Research

The measurement of the QT interval.

Current cardiology reviews, 2014

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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