What does a mild decrease in Myocardial Blood Flow Reserve (MBFR) on Right Coronary Artery (RCA) territory indicate on a PET CT scan?

Understanding Mild Decrease in MBFR on RCA Territory on PET CT

A mild decrease in Myocardial Blood Flow Reserve (MBFR) on the Right Coronary Artery (RCA) territory indicates possible coronary artery disease affecting smaller branches or distal segments of the RCA, which requires clinical correlation with patient symptoms and risk factors to determine appropriate management.

What MBFR Means and Its Clinical Significance

• MBFR (Myocardial Blood Flow Reserve) is a quantitative measure obtained during PET imaging that reflects the ratio of stress to rest absolute myocardial blood flow, providing information about coronary vasodilatory capacity 1
• Normal MBFR is generally considered to be ≥2.0, while values <2.0 suggest impaired coronary flow reserve 1, 2
• Reduced MBFR reflects abnormalities of flow within the epicardial coronary arteries, microvasculature, or both, and independently predicts risk of major coronary artery disease events 1

Interpretation of Mild Decrease in MBFR in RCA Territory

• A mild decrease in MBFR specifically in the RCA territory suggests:

  • Possible stenosis in smaller branches of the RCA rather than the main vessel 3
  • Potential disease in the distal segments of the RCA that may not be visible on conventional angiography 1
  • Possible early coronary microvascular dysfunction in the territory supplied by the RCA 1

• This finding is clinically significant because:

  • It can identify hemodynamically significant coronary disease even when anatomical imaging appears normal or shows only mild stenosis 1, 4
  • It provides prognostic information beyond what is available from visual perfusion assessment alone 4, 2

Clinical Implications and Management Considerations

• Risk stratification:

  • Patients with reduced MBFR (<2.0) have higher risk of adverse cardiovascular events compared to those with normal MBFR 4, 2
  • The 2023 AHA/ACC guidelines recommend incorporating MBFR information into risk assessment for patients with chronic coronary disease 1

• Management approach based on MBFR findings:

  • For patients with MBFR ≤1.8, early revascularization may provide a survival benefit regardless of the level of ischemia on conventional perfusion imaging 4
  • For mild reductions in MBFR (between 1.8-2.0), optimization of guideline-directed medical therapy is recommended 1
  • Clinical correlation with symptoms is essential, as the significance of reduced MBFR should be interpreted in the context of the patient's clinical presentation 1

Important Considerations and Caveats

• The finding should be interpreted in the context of:

  • Patient symptoms (presence/absence of angina) 1
  • Other cardiac risk factors 1
  • Results from other diagnostic tests 1

• Potential pitfalls in interpretation:

  • Elevated resting rate-pressure product can cause artificially reduced MBFR despite normal peak stress myocardial blood flow 2
  • Technical factors such as patient motion or attenuation artifacts can affect MBFR measurements 5
  • The residual activity correction algorithm used in time-efficient protocols can significantly impact MBFR calculations 5

• When MBFR is mildly reduced but perfusion appears normal:

  • This may represent early disease that has not yet progressed to cause visible perfusion defects 1
  • It could indicate microvascular dysfunction, especially in women 1
  • Follow-up testing may be warranted, particularly if symptoms persist 1

Next Steps After Finding Mild Decrease in MBFR

• Clinical correlation with symptoms and risk factors 1
• Consider invasive coronary angiography if:
  • Patient has significant symptoms despite medical therapy 1
  • There are other high-risk features present 1
• If angiography is performed, consider assessment of fractional flow reserve (FFR) for intermediate lesions 1
• Optimize medical therapy for coronary artery disease 1
• Regular follow-up to monitor for progression of disease 6