Differences Between Right Ventricular Conduction Delay, Right Bundle Branch Block, and Incomplete Right Bundle Branch Block
The main difference between these conditions lies in their QRS duration and morphology criteria, with right ventricular conduction delay being a nonspecific term, complete RBBB having QRS ≥120 ms with specific morphology, and incomplete RBBB having the same morphology but QRS duration between 110-119 ms. 1
Right Bundle Branch Block (RBBB)
Complete RBBB
- QRS duration ≥120 ms
- Characteristic morphology:
- rsr', rsR', rSR', or rarely qR pattern in leads V1 or V2
- R' or r' deflection usually wider than initial R wave
- S wave of greater duration than R wave or >40 ms in leads I and V6
- Normal R peak time in leads V5 and V6 but >50 ms in lead V1 1
Incomplete RBBB (IRBBB)
- Same QRS morphology criteria as complete RBBB but with QRS duration between 110-119 ms 1
- Often presents with RSR' pattern in right precordial leads
- May be a normal variant, especially in athletes, or may represent early conduction disease 2
- Can be differentiated from normal variants by:
- Diminution of S wave depth in V1, V2
- Inversion of ratio where S wave in V1 > S wave in V2
- Slurring of downstroke or upstroke of S wave
- QRS duration ≥100 ms 3
Right Ventricular Conduction Delay
- This is a nonspecific term that falls under the broader category of "nonspecific intraventricular conduction delay"
- QRS duration >110 ms where morphology criteria for RBBB or LBBB are not present 1
- Does not meet specific criteria for either complete or incomplete RBBB
- May represent partial delay in right ventricular activation without meeting formal RBBB criteria
Clinical Significance and Implications
Complete RBBB
- May indicate structural heart disease or be an isolated finding
- Associated with higher risk of progression to high-grade AV block in certain contexts
- May mask left ventricular conduction delays 4
- Requires evaluation for underlying cardiac conditions, especially if new onset
Incomplete RBBB
- Often a benign finding, especially in young adults and athletes
- May require no further evaluation if no other abnormalities are found on clinical exam
- Can be confused with other conditions such as:
- Type-2 Brugada ECG pattern
- Right ventricular enlargement
- Arrhythmogenic right ventricular cardiomyopathy
- Ventricular preexcitation 2
Right Ventricular Conduction Delay
- Nonspecific finding that warrants evaluation for underlying cardiac disease
- May represent early conduction system disease or be related to structural heart disease
Special Considerations
- In patients with RBBB and left ventricular dysfunction, there may be concomitant left ventricular conduction delay that is masked by the RBBB pattern 4
- Some patients with RBBB and heart failure may benefit from cardiac resynchronization therapy, particularly those with "atypical RBBB" showing evidence of delayed left ventricular activation 5
- The presence of anasarca (severe generalized edema) can lead to apparent amelioration of bundle branch blocks due to decreased electrical impedance, potentially causing misclassification 6
Diagnostic Pitfalls
- Electrode placement can affect QRS morphology - higher placement of V1 and V2 electrodes may create an RBBB-like pattern
- Pectus excavatum can create RBBB-like patterns
- RBBB is common in ostium secundum atrial septal defect, so clinicians should be alert to splitting of the second heart sound 2
- QRS duration may be affected by electrolyte abnormalities, medications, and other transient factors
Understanding these differences is crucial for accurate ECG interpretation and appropriate clinical decision-making regarding further evaluation and management of patients with these conduction abnormalities.