What is the normal QRS (QRS complex) length?

Normal QRS Duration

In adults, a normal QRS duration is ≤110 ms, with a QRS duration ≥120 ms considered wide and indicative of intraventricular conduction delay. 1

Age-Specific Normal QRS Duration Values

The normal QRS duration varies by age:

Adults:

• Normal QRS: ≤110 ms
• Borderline/Incomplete conduction delay: 110-119 ms
• Wide QRS/Complete conduction delay: ≥120 ms 1, 2

Children:

• Ages 4-16 years: Normal QRS <100 ms
• Ages <4 years: Normal QRS <90 ms 2, 1

Clinical Significance of QRS Duration

QRS duration reflects ventricular depolarization time and has important clinical implications:

• Normal QRS duration (≤110 ms) generally indicates normal ventricular conduction
• Prolonged QRS duration (≥120 ms) suggests intraventricular conduction delay, which may be associated with:
  • Bundle branch blocks (RBBB or LBBB)
  • Nonspecific intraventricular conduction delay
  • Increased heart size 1
  • Left ventricular dysfunction 3

Common QRS Patterns and Their Criteria

Complete Right Bundle Branch Block (RBBB)

• QRS ≥120 ms in adults
• rsr', rsR', or rSR' pattern in V1/V2
• S wave duration > R wave or >40 ms in leads I and V6
• Normal R peak time in V5/V6 but >50 ms in V1 2

Complete Left Bundle Branch Block (LBBB)

• QRS ≥120 ms in adults
• Broad notched/slurred R wave in leads I, aVL, V5, V6
• Absent q waves in leads I, V5, V6
• R peak time >60 ms in V5/V6
• ST and T waves usually opposite to QRS direction 2

Measurement Considerations

For accurate QRS measurement:

• Measure the widest QRS complex from earliest deflection to latest deflection in any lead
• Global intervals (from earliest onset to latest offset in all leads) are longer than single-lead measurements
• QRS duration is typically wider in precordial leads than in limb leads 1

Common Pitfalls in QRS Measurement

• Incorrect measurement technique: Not measuring the widest QRS complex across all leads
• Failure to consider age-appropriate norms: Using adult criteria for pediatric ECGs
• Overlooking borderline values: QRS durations between 110-119 ms in adults may have clinical significance
• Ignoring QRS morphology: The specific pattern provides additional diagnostic information beyond just duration 1

A QRS duration >110 ms should prompt further evaluation for potential cardiac pathology, as prolonged QRS duration has been associated with increased mortality in various cardiac conditions 3, 4.