What is the difference between right ventricular conduction delay and right bundle branch block (RBBB)?

Right Ventricular Conduction Delay vs. Right Bundle Branch Block: Key Differences

Right ventricular conduction delay (RVCD) is a less severe form of conduction abnormality with QRS duration between 110-119 ms, while right bundle branch block (RBBB) is a complete block with QRS duration ≥120 ms, with specific morphological criteria that indicate complete interruption of conduction through the right bundle branch.

Diagnostic Criteria

Right Ventricular Conduction Delay

• QRS duration between 110-119 ms
• Incomplete RBBB pattern
• Does not meet all morphological criteria for complete RBBB
• May show some terminal R' wave in V1-V3 but less pronounced
• Sometimes referred to as "nonspecific intraventricular conduction delay" when morphology criteria for bundle branch blocks are not fully present 1

Right Bundle Branch Block (Complete)

• QRS duration ≥120 ms in adults
• Terminal R' wave in right precordial leads (V1-V3)
• Wide, slurred S wave in leads I, aVL, V5, and V6
• Secondary ST-T wave changes (ST depression and T-wave inversion) in right precordial leads
• Normal R peak time in leads V5 and V6 but prolonged in leads V1-V3 1

Electrophysiological Differences

The fundamental difference lies in the degree of conduction impairment:

• RVCD: Represents delayed (but not completely blocked) conduction through the right bundle branch
• RBBB: Represents complete block of the right bundle branch, forcing electrical activation to spread from the left ventricle to the right ventricle through myocardial tissue rather than the specialized conduction system 1

Clinical Significance

Prevalence

• Complete RBBB occurs in approximately 0.6% of males and 0.3% of females under age 40 1
• RVCD/incomplete RBBB is more common but exact prevalence varies by population

Prognostic Implications

• RVCD: Generally benign with minimal clinical significance in otherwise healthy individuals
• Complete RBBB:
  • In healthy individuals without structural heart disease, typically benign with no adverse long-term prognosis 2
  • In heart failure patients, associated with increased mortality risk similar to LBBB 3
  • May indicate underlying structural heart disease requiring further evaluation 1

Mechanical Dyssynchrony

• Complete RBBB causes less mechanical dyssynchrony than LBBB in failing hearts 4
• Some patients with RBBB may have concomitant delayed left ventricular activation, showing an "atypical RBBB" pattern that may benefit from cardiac resynchronization therapy 5, 6

Evaluation Approach

When either RVCD or RBBB is detected:

1. Assess for symptoms: Both are usually asymptomatic but may be markers of underlying disease
2. Look for structural heart disease: Consider echocardiography, especially if there are concerning clinical features 1
3. Evaluate for other conduction abnormalities: Particularly if RBBB is associated with left axis deviation (suggesting bifascicular block) 1
4. Consider ambulatory monitoring: If symptoms suggest intermittent bradycardia or higher-degree block 1

Management Implications

• Isolated RVCD generally requires no specific treatment
• Isolated RBBB in asymptomatic individuals without structural heart disease typically requires no specific treatment
• In heart failure patients:
  • RBBB with evidence of concomitant left ventricular activation delay may benefit from cardiac resynchronization therapy 5
  • Standard RBBB shows less response to biventricular pacing compared to LBBB 4
  • Right ventricular-only pacing may be as effective as biventricular pacing in pure RBBB 4

Pitfalls to Avoid

1. Don't assume all QRS prolongations are pathological - isolated RBBB and RVCD can be benign findings
2. Don't overlook the possibility of bifascicular block when RBBB is accompanied by left axis deviation
3. Don't assume all RBBB patterns respond poorly to cardiac resynchronization therapy - those with concomitant LV activation delay may benefit 5
4. Don't confuse RVCD with early repolarization or other normal variants that may cause QRS notching

Remember that the clinical context is crucial when interpreting the significance of these conduction abnormalities, as their implications vary significantly between healthy individuals and those with underlying cardiac disease.