QRS Interval of 90 ms on EKG: Normal Ventricular Conduction
A QRS interval of 90 ms on an EKG represents normal ventricular conduction in adults, as it falls well within the normal range of QRS duration (less than 110 ms) according to established cardiology guidelines. 1
Normal QRS Duration by Age Group
The QRS complex represents ventricular depolarization, and its duration varies by age:
- Adults: Normal QRS duration is considered ≤110 ms 1
- Children 4-16 years: Normal QRS duration is <100 ms 1
- Children <4 years: Normal QRS duration is <90 ms 1
In adults, QRS duration typically ranges from 74 to 114 ms, with an average of 95 ms according to studies of normal males over 18 years of age 1.
Clinical Interpretation of 90 ms QRS Duration
A 90 ms QRS interval indicates:
- Normal ventricular depolarization - The electrical impulse is traveling through the ventricles at an appropriate speed
- Intact conduction system - No evidence of bundle branch blocks or fascicular blocks
- Absence of ventricular hypertrophy - Severe hypertrophy often leads to QRS prolongation
Differentiating from Conduction Abnormalities
Not Bundle Branch Block
- Complete RBBB requires QRS ≥120 ms in adults plus specific morphological features 1, 2
- Complete LBBB requires QRS ≥120 ms in adults plus specific morphological features 1
- Incomplete RBBB requires QRS between 110-119 ms in adults 1
- Incomplete LBBB requires QRS between 110-119 ms in adults 1
Not Fascicular Block
- Left anterior/posterior fascicular blocks require QRS <120 ms but have specific axis deviation patterns not determined by QRS duration alone 1
Clinical Significance
A normal QRS duration of 90 ms suggests:
- Efficient electrical conduction through the ventricular myocardium
- Synchronous ventricular contraction which optimizes cardiac output
- Absence of structural abnormalities that would delay ventricular activation
Important Caveats
- QRS duration alone doesn't provide complete information about cardiac electrical function
- The method of measurement affects QRS duration (global intervals from all leads are preferred) 1
- QRS morphology and axis should also be evaluated alongside duration
- Normal QRS duration doesn't exclude all cardiac pathologies (e.g., coronary artery disease, cardiomyopathies without conduction abnormalities)
Conclusion
A QRS duration of 90 ms falls within normal limits for adults and indicates normal ventricular depolarization without evidence of conduction system disease. This finding is reassuring from an electrophysiological standpoint but should be interpreted in the context of the complete clinical picture.