Is a QRS (quasi-random signal) duration of 90 milliseconds with an rSr′ pattern in lead V1 a normal or abnormal finding on an electrocardiogram (ECG)?

Normal Finding

A QRS duration of 90 ms with an rSr′ pattern in lead V1 is a normal variant and does not represent pathology. 1

QRS Duration Assessment

• The QRS duration of 90 ms falls well below the threshold for abnormality, which is >110 ms in adults over 16 years of age 1
• In adult males, normal QRS duration ranges from 74-114 ms with an average of 95 ms, making 90 ms clearly within normal limits 1
• For children less than 4 years of age, QRS duration ≥90 ms would be considered prolonged, but this does not apply to adults 1

The rSr′ Pattern in V1

• An rSr′ pattern in V1/V2 with normal QRS duration (<110 ms) is explicitly recognized as a normal variant in children and does not represent incomplete right bundle branch block (RBBB) 1
• The American Heart Association/American College of Cardiology guidelines specifically state that this ECG pattern may be present in the absence of heart disease, particularly when lead V1 is recorded in a higher or more rightward position 1
• The terms "rsr′" and "normal rsr′" should not be used to describe pathological patterns because their meaning can be variously interpreted 1

Distinguishing from Incomplete RBBB

• Incomplete RBBB requires QRS duration between 110-120 ms in adults, which is not met in this case 1, 2
• In children, incomplete RBBB may be diagnosed when the terminal rightward deflection is ≥20 ms but <40 ms, but even then requires QRS duration between 86-90 ms in children less than 8 years of age 1
• Since the QRS duration is only 90 ms, this does not meet criteria for incomplete RBBB in adults 3

Clinical Significance

• In asymptomatic individuals without structural heart disease, this finding is benign and requires no further workup 4, 3
• Asymptomatic patients with normal QRS duration (<110 ms) and rSr′ pattern require no specific treatment, only routine follow-up 4
• This pattern is particularly common in young athletes and does not represent pathological cardiac disease 3

Common Pitfalls to Avoid

• Do not misinterpret this normal variant as incomplete RBBB—the QRS duration must be ≥110 ms in adults for that diagnosis 3
• Verify correct lead placement, as improper V1 positioning can create or exaggerate this pattern 1, 4
• Do not order unnecessary cardiac workup in asymptomatic patients with this finding and no family history of sudden cardiac death or structural heart disease 4, 3