Normal QRS Duration
The normal QRS duration in adults is ≤110 ms, with values between 110-119 ms considered borderline or incomplete conduction delay, and ≥120 ms indicating complete conduction delay or bundle branch block. 1
Normal QRS Duration by Age Group
- Adults: ≤110 ms
- Children 4-16 years: <100 ms
- Children <4 years: <90 ms
Abnormal QRS Duration Classifications
Incomplete Conduction Delays
- Incomplete RBBB: QRS duration between 110-119 ms with RBBB morphology 2
- Incomplete LBBB: QRS duration between 110-119 ms with LBBB morphology 2
Complete Conduction Delays
- Complete RBBB: QRS duration ≥120 ms with specific RBBB morphology 2
- Complete LBBB: QRS duration ≥120 ms with specific LBBB morphology 2
- Nonspecific intraventricular conduction delay: QRS duration >110 ms without meeting criteria for RBBB or LBBB 2
Clinical Significance of QRS Duration
QRS duration has important prognostic implications:
QRS ≥120 ms is associated with:
QRS ≥170 ms with LBBB is strongly associated with significant left ventricular systolic dysfunction (mean EF of 24%) 5
Progressive increases in QRS duration correlate with worsening prognosis 3
Measurement Technique
For accurate QRS measurement:
- Measure from the earliest onset to the latest offset in any lead
- Use the widest QRS complex for assessment
- Consider that global intervals (across all leads) are longer than single-lead measurements
Common Pitfalls
- Failure to consider age-appropriate norms
- Incorrect measurement technique
- Not recognizing that QRS duration may increase with increasing heart size
- Overlooking that fragmented QRS (notched R or S waves with normal duration) may also indicate myocardial pathology 6
QRS prolongation is a valuable diagnostic and prognostic marker in various cardiac conditions, with specific thresholds (110 ms and 120 ms) serving as important clinical decision points.