What is the approach to a patient with a normal QRS (quantitative QRS) complex presenting with an rS pattern?

Approach to rS Pattern in a Patient with Normal QRS

The rS pattern in a patient with normal QRS duration (<120 ms) most commonly indicates a left anterior fascicular block, left posterior fascicular block, or a normal variant depending on which leads demonstrate this pattern. 1

Diagnostic Approach Based on Lead Location

rS Pattern in Precordial Leads (V1-V2)

• Normal variant - common finding in healthy individuals
• Right ventricular conduction delay (incomplete RBBB) - when accompanied by:
  • QRS duration between 110-119 ms
  • rSr' morphology in V1-V2
  • S wave duration > R wave in leads I and V6 1

rS Pattern in Limb Leads

• Left Anterior Fascicular Block (LAFB) - when found in leads II, III, and aVF with:

  • QRS duration <120 ms
  • Left axis deviation (-45° to -90°)
  • qR pattern in lead aVL
  • R-peak time in lead aVL ≥45 ms 1

• Left Posterior Fascicular Block (LPFB) - when found in leads I and aVL with:

  • QRS duration <120 ms
  • Right axis deviation (90° to 180°)
  • qR pattern in leads III and aVF 1

Clinical Evaluation Algorithm

1. Determine lead location of rS pattern

   • Precordial (V1-V2) vs. Limb leads

2. Measure QRS duration

   • Confirm normal QRS (<120 ms)
   • If 110-119 ms, consider incomplete bundle branch block 1

3. Calculate frontal plane axis

   • Left axis deviation (-45° to -90°): Consider LAFB
   • Right axis deviation (90° to 180°): Consider LPFB
   • Normal axis: Likely normal variant 1

4. Examine for associated patterns

   • qR pattern in aVL: Supports LAFB
   • qR pattern in III and aVF: Supports LPFB
   • rSr' in V1-V2: Suggests incomplete RBBB 1

5. Rule out pathological causes

   • Assess for symptoms (syncope, palpitations)
   • Check for structural heart disease
   • Review prior ECGs for progression 2

Clinical Significance and Management

• Isolated LAFB or LPFB with normal QRS duration:

  • Generally benign if asymptomatic
  • Monitor for progression to more advanced conduction disease
  • No specific therapy required if isolated finding 2

• Incomplete RBBB with rS pattern:

  • Usually benign in absence of symptoms or structural heart disease
  • Regular follow-up with serial ECGs recommended 2

• Progressive conduction disease:

  • Serial ECGs to monitor for widening QRS
  • Consider cardiac evaluation if symptoms develop 1, 2

Important Caveats

• An rS pattern alone is insufficient for diagnosis - must consider axis deviation and other ECG features
• Don't confuse rS pattern in normal QRS with wide complex tachycardias (which may show similar patterns but with QRS ≥120 ms)
• The presence of rS pattern in multiple leads may indicate more significant conduction disease requiring closer follow-up
• Isolated fascicular blocks rarely require intervention but may be markers for underlying cardiac disease 2