What is considered a normal, wide, or narrow QRS (Quadrature Amplitude Modulation complex) duration?

Normal, Wide, and Narrow QRS Duration

In adults, a normal QRS duration is ≤110 ms, a wide QRS is ≥120 ms, and a narrow QRS is typically <100 ms. 1

Age-Specific QRS Duration Criteria

The QRS duration varies by age, with specific thresholds for normal and abnormal values:

Adults (>16 years)

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

Children

• Ages 4-16 years:
  • Normal: <100 ms
  • Prolonged: ≥100 ms 1
• Ages <4 years:
  • Normal: <90 ms
  • Prolonged: ≥90 ms 1

Clinical Significance of QRS Duration

Wide QRS (≥120 ms)

• Indicates intraventricular conduction delay
• Common patterns include:
  • Complete RBBB: QRS ≥120 ms with rsr', rsR', or rSR' pattern in V1/V2 1
  • Complete LBBB: QRS ≥120 ms with broad notched/slurred R waves in leads I, aVL, V5, V6 1
  • Nonspecific intraventricular conduction delay: QRS >110 ms without meeting RBBB or LBBB criteria 1

Narrow QRS (<100 ms)

• Generally indicates normal ventricular conduction
• May be associated with smaller heart size 1
• Can be seen in fascicular blocks where QRS duration is typically <120 ms 1

Factors Affecting QRS Duration

1. Measurement method: Global intervals (from earliest onset to latest offset in all leads) are longer than single-lead measurements 1

2. Heart size: QRS duration may increase with increasing heart size 1

3. Lead placement: QRS is typically wider in precordial leads than in limb leads 1

4. Heart rate: An inverse relationship exists between heart rate and QRS duration - for every 10 bpm increase in heart rate, QRS duration decreases by approximately 1.14 ms 2

5. QRS amplitude: A positive relationship exists between QRS amplitude and duration (for durations between 52-105 ms) 2

Clinical Implications

Wide QRS complexes (≥120 ms) have significant prognostic implications:

• Associated with worse left ventricular function and poorer prognosis in heart failure patients 3
• Specific QRS morphologies (particularly LBBB) predict benefit from cardiac resynchronization therapy 4
• QRS duration >100 ms has high specificity (83.6%) for predicting abnormal ejection fraction 5
• Progressively increasing QRS duration correlates with worsening prognosis 3

Common Pitfalls in QRS Duration Assessment

1. Incorrect measurement technique: Always measure the widest QRS complex from the earliest deflection to the latest deflection in any lead

2. Failure to consider age-appropriate norms: What's normal in adults may be abnormal in children

3. Overlooking borderline values: QRS durations between 110-119 ms in adults represent incomplete conduction delays that still have clinical significance

4. Ignoring QRS morphology: Duration alone doesn't tell the complete story - specific patterns (RBBB, LBBB) provide additional diagnostic information

5. Misinterpreting rate-related changes: Tachycardia can artificially narrow the QRS complex