What is the management and diagnosis of a patient with an Rsr' pattern in lead V1 on an electrocardiogram (EKG)?

Management and Diagnosis of Rsr' Pattern in V1

An Rsr' pattern in lead V1 requires assessment of QRS duration to distinguish between complete right bundle branch block (RBBB), incomplete RBBB, or a benign normal variant, with the key threshold being QRS duration ≥120 ms in adults for complete RBBB versus <110 ms for a normal variant. 1

Diagnostic Algorithm

Step 1: Measure QRS Duration

Complete RBBB (requires all criteria):

• QRS duration ≥120 ms in adults, >100 ms in children ages 4-16 years, or >90 ms in children <4 years 1
• Rsr', rsR', rSR', or rarely qR pattern in V1 or V2 (the R' deflection is typically wider than the initial R wave) 1
• S wave duration greater than R wave or >40 ms in leads I and V6 1
• R peak time >50 ms in lead V1 but normal in V5 and V6 1

Incomplete RBBB:

• QRS duration 110-119 ms in adults (90-100 ms in children 4-16 years, 86-90 ms in children <8 years) 1
• Same morphology criteria as complete RBBB 1
• In children, terminal rightward deflection <40 ms but ≥20 ms may indicate incomplete RBBB 1

Normal Variant:

• QRS duration <110 ms in adults 2, 3
• Rsr' pattern in V1 and V2 is considered a normal variant in children 1, 2
• Common in young patients, athletes, and individuals with flat chest 3, 4

Step 2: Evaluate Lead V2

Examine whether the r' extends to V2:

• If r' is present in both V1 and V2 with prolonged QRS, this suggests true incomplete or complete RBBB and may indicate advanced right ventricular overload 4
• If r' is only in V1 with normal QRS duration, this favors a normal variant 4

Step 3: Assess S Wave Characteristics in V1 and V2

Critical distinguishing features:

• Diminished S wave depth in V1 compared to V2 (SV1/SV2 ratio >1.0) suggests true conduction disease rather than normal variant 5
• Slurring of the S wave downstroke or upstroke indicates pathologic RBBB 5
• Patients with SV1/SV2 >1.0 are significantly older (mean 60 vs 33 years) and more likely to progress to complete RBBB 5

Clinical Context and Management

Benign Scenarios (No Further Workup Needed):

• Children or young adults with Rsr' in V1-V2 and normal QRS duration (<110 ms) 1, 2, 3
• Athletes with isolated Rsr' pattern and normal QRS duration 3
• Asymptomatic individuals with QRS <110 ms and no other ECG abnormalities 3, 6

Requires Further Evaluation:

• New-onset complete or incomplete RBBB warrants echocardiography to assess for structural heart disease, right ventricular pressure/volume overload, or conduction system disease 1, 4
• Rsr' with ST elevation in V1-V3 raises concern for Brugada syndrome and requires cardiology referral 6, 7
• QR pattern (not Rsr') in V1 with RBBB in the setting of acute dyspnea or hemodynamic instability has high positive predictive value for massive pulmonary embolism and may warrant empiric thrombolysis before imaging confirmation 8
• Progressive widening of QRS or development of symptoms (syncope, dyspnea, palpitations) requires comprehensive cardiac evaluation including echocardiography and possibly electrophysiology study 6, 5

Common Pitfalls to Avoid

• Do not use the terms "Rsr'" or "normal Rsr'" interchangeably, as they can be variously interpreted and lead to confusion 1, 2
• Do not assume all Rsr' patterns are benign without measuring QRS duration and assessing clinical context 6
• Do not overlook lead V2 - failure to examine whether the pattern extends beyond V1 may miss true RBBB 4
• Do not dismiss Rsr' in patients with syncope or cardiac arrest - this pattern can be seen in life-threatening conditions like Brugada syndrome or arrhythmogenic right ventricular dysplasia 6, 7
• Incorrect lead placement (V1 recorded too high or too far right) can create a false Rsr' pattern 1