In a 27‑year‑old asymptomatic adult with an rSR′ pattern in lead V1 on ECG, what is the most likely diagnosis and recommended management?

RSR' Pattern in Lead V1 in a 27-Year-Old

In an asymptomatic 27-year-old with an rSR' pattern in V1, this is most likely a normal variant and requires no further workup if the QRS duration is less than 110 ms. 1

Diagnostic Approach

The critical first step is to measure the QRS duration precisely, as this determines whether the finding is benign or requires further evaluation 1:

If QRS Duration <110 ms (Normal Variant)

• This represents a normal variant in young adults and requires no further investigation 2, 1
• The AHA/ACCF/HRS guidelines explicitly state that an rSr' pattern in V1 and V2 with normal QRS duration is a normal variant 2
• This may represent late activation of the crista supraventricularis (CSV), a right ventricular crest that is one of the last structures depolarized 3
• No echocardiogram or additional testing is needed in asymptomatic patients 1

If QRS Duration 110-119 ms (Incomplete RBBB)

• This meets criteria for incomplete right bundle branch block (IRBBB) in adults 2
• Obtain an echocardiogram to evaluate for structural heart disease, including atrial septal defect, right ventricular pressure/volume overload, or conduction system disease 1
• IRBBB can be benign but may indicate underlying pathology, particularly right ventricular diastolic overload from conditions like atrial septal defect 4

If QRS Duration ≥120 ms (Complete RBBB)

• This represents complete right bundle branch block 2
• Echocardiography is mandatory to assess for structural abnormalities 1
• Additional criteria for complete RBBB include: S wave duration greater than R wave or >40 ms in leads I and V6, and R peak time >50 ms in V1 2

Key Distinguishing Features to Assess

Beyond QRS duration, evaluate these additional ECG characteristics:

• Check lead V2: In true incomplete RBBB, the terminal vector directs forward causing an r' in V2 as well as V1, whereas normal variants typically show the pattern only in V1 4
• Examine the S wave in leads I and V6: If S wave duration is <40 ms with QRS ≤100 ms, this favors CSV pattern (normal variant) over pathological IRBBB 5
• Verify proper lead placement: V1 recorded too high or too far right can create a false rSR' pattern 2, 1

Conditions to Exclude (If Symptomatic or Abnormal Exam)

While the question specifies an asymptomatic patient, be alert for these pathological patterns that can mimic benign rSR':

• Brugada syndrome type 2 pattern: Look for coved or saddleback ST elevation in V1-V2 3, 6
• Arrhythmogenic right ventricular cardiomyopathy: Consider if family history of sudden death or ventricular arrhythmias 3, 6
• Atrial septal defect: Listen for fixed split S2 on physical exam; this is a common cause of IRBBB 3
• Right ventricular hypertrophy or strain: Assess for signs of pulmonary hypertension 6

Common Pitfalls to Avoid

• Do not use the terms "rSR'" and "normal rSR'" interchangeably, as the AHA/ACCF/HRS guidelines specifically advise against this due to variable interpretation 2, 1
• Do not order unnecessary testing in truly asymptomatic patients with QRS <110 ms, as this represents physiologic variation 1
• Do not miss incorrect lead placement as a technical cause of the pattern 1

Bottom Line for This Case

Given the patient is 27 years old and asymptomatic, if the QRS duration is <110 ms, reassure the patient this is a normal variant and no further action is needed. 2, 1 If QRS is ≥110 ms or if any symptoms or abnormal physical findings are present, proceed with echocardiography 1.