What is the normal QRS (QRS complex) length?

Normal QRS Duration

The normal QRS duration is less than 120 milliseconds in adults, less than 100 milliseconds in children 4 to 16 years of age, and less than 90 milliseconds in children under 4 years of age. 1

Normal QRS Duration by Age Group

• In adults: QRS duration is normally less than 120 milliseconds 1
• In children 4-16 years: QRS duration is normally less than 100 milliseconds 1
• In children under 4 years: QRS duration is normally less than 90 milliseconds 1

Borderline QRS Duration

• In adults, QRS duration between 110-119 milliseconds is considered borderline and may represent incomplete bundle branch block 1
• In children 8-16 years, QRS duration between 90-100 milliseconds is considered borderline 1
• In children under 8 years, QRS duration between 80-90 milliseconds is considered borderline 1

Clinical Significance of QRS Duration

• QRS duration represents ventricular depolarization time and should be present in all standard ECG leads in normal cardiac conduction 2
• Prolonged QRS duration (≥120 ms) is a marker of intraventricular conduction delay, which may indicate:
  • Complete right or left bundle branch block 1
  • Nonspecific intraventricular conduction delay 1
  • Potential left ventricular dysfunction 3, 4

Factors Affecting QRS Duration

• Heart rate: For every 10 beat increase in heart rate, QRS duration decreases by approximately 1.14 milliseconds 5
• QRS amplitude: There is a positive relationship between QRS duration and total QRS amplitude for durations between 52-105 milliseconds 5
• Gender: Exceptionally narrow QRS durations (<62 ms) are more common in females (76%) than males (24%) 5

Clinical Implications

• QRS duration >120 ms is associated with:

  • Worse left ventricular function 6, 3
  • Poorer prognosis in heart failure patients 6
  • Higher all-cause mortality compared to narrow QRS complex 6
  • Increased risk of ventricular tachyarrhythmias 6

• In patients with idiopathic pulmonary arterial hypertension, prolonged QRS duration (≥120 ms) is associated with:

  • Worse functional capacity 7
  • 2.5-fold increased risk of death 7

Common Pitfalls in QRS Measurement

• Failure to recognize age-dependent normal values 1
• Not accounting for heart rate effects on QRS duration 5
• Confusing incomplete bundle branch block (QRS 110-119 ms) with normal QRS duration 1
• Overlooking that a progressive increase in QRS duration worsens prognosis in heart failure patients 6

Remember that while QRS duration is an important diagnostic parameter, it should always be interpreted in the context of the patient's clinical presentation and other ECG findings.