Management of Patients with Right Bundle Branch Block (RBBB) and Myocardial Perfusion Scintigraphy (MPS)
Patients with RBBB should undergo careful evaluation of myocardial perfusion scintigraphy results due to the high risk of false-positive findings in the inferolateral segments. 1
Diagnostic Considerations for MPS in RBBB Patients
Interpretation Challenges
- RBBB can lead to false-positive perfusion defects on MPS, particularly in the inferolateral segments, due to functional changes produced by dissynchronous ventricular activation 1
- Unlike LBBB (where anteroseptal defects are common false positives), RBBB-related artifacts typically appear in the inferolateral wall
- These perfusion defects occur in approximately 23% of patients with RBBB who have normal coronary arteries 1
Risk Stratification
- RBBB is not a benign finding and carries prognostic significance:
- Associated with increased all-cause mortality (HR 1.5) and cardiovascular mortality (HR 1.7) even in patients without known cardiovascular disease 2
- Patients with RBBB show decreased functional aerobic capacity and slower heart rate recovery during exercise testing 2
- RBBB is associated with similar or worse outcomes compared to LBBB in patients with suspected myocardial infarction 3
Management Algorithm for RBBB Patients Undergoing MPS
Step 1: Pre-Test Evaluation
- Determine if RBBB is new or pre-existing
- Assess for symptoms suggesting underlying cardiac disease (syncope, presyncope, chest pain)
- Evaluate for presence of other conduction abnormalities (e.g., left anterior fascicular block) that may indicate bifascicular block 4
- Consider baseline echocardiography to assess for structural heart disease 4
Step 2: MPS Protocol Selection
- Use pharmacological stress (vasodilator) rather than exercise stress when possible
- Pharmacological stress reduces the likelihood of rate-dependent conduction abnormalities affecting interpretation 5
- Vasodilator stress is preferred over dobutamine in RBBB patients
Step 3: Image Interpretation
- Pay special attention to inferolateral wall perfusion defects, which may represent RBBB-related artifacts 1
- Use both visual and quantitative assessment methods
- Consider the following when interpreting MPS results:
Step 4: Risk Assessment and Follow-up
- Patients with RBBB and normal MPS or only RBBB-related perfusion defects have a good prognosis (annual cardiac death rate <1%) 6
- Patients with RBBB and perfusion defects extending beyond the typical RBBB-related artifact areas have significantly worse prognosis (annual cardiac death rate ~6.4%) and warrant aggressive coronary evaluation 6
Special Considerations
RBBB in Acute Settings
- In patients with suspected myocardial infarction, RBBB carries similar risk to LBBB and should prompt consideration of urgent coronary angiography 3
- RBBB is present in approximately 6.2% of AMI patients and is associated with a 64% increased odds ratio of in-hospital death 7
- Evidence-based therapies are often underutilized in patients with RBBB 7
RBBB and Cardiac Resynchronization Therapy
- Patients with RBBB generally do not benefit from standard cardiac resynchronization therapy (CRT) unless they have evidence of left ventricular mechanical dyssynchrony 7
- Assessment of mechanical dyssynchrony may be valuable in RBBB patients with heart failure to identify potential CRT responders 7
Pitfalls to Avoid
- Do not dismiss RBBB as a benign finding, especially in symptomatic patients
- Avoid overreliance on MPS without considering the potential for false-positive results in RBBB patients
- Do not assume that all perfusion defects in RBBB patients are artifacts; defects extending beyond typical RBBB-related areas likely represent true coronary disease
- Do not automatically apply the same interpretation criteria used for LBBB to RBBB patients
By following this structured approach, clinicians can more accurately interpret MPS findings in patients with RBBB and make appropriate management decisions based on the true risk of coronary artery disease.