Assessing PET MPI for Microvascular Disease

Key Parameters to Evaluate

The American College of Cardiology recommends calculating the myocardial blood flow reserve (MBFR or MFR) to assess microvascular disease, with values <1.9-2.0 indicating microvascular dysfunction, even in the absence of visible perfusion defects 1, 2, 3
The American Heart Association suggests that absolute myocardial blood flow (MBF) values should be quantified for both rest and stress (hyperemic) conditions 4
The myocardial flow reserve (MFR) should be calculated as the ratio of stress to rest absolute myocardial blood flow, with normal MFR being ≥2.0, and values <2.0 suggesting impaired coronary flow reserve 2, 4
A uniform reduction in MFR across multiple coronary territories is characteristic of microvascular disease, rather than focal epicardial stenosis 3, 4
The left ventricular ejection fraction (LVEF) reserve should be evaluated, as abnormal LVEF reserve provides incremental value in predicting microvascular dysfunction 5, 6

PET offers superior spatial resolution compared to SPECT, improving diagnostic accuracy, particularly in women and obese patients 2, 3
PET allows for the calculation of absolute blood flow across coronary vessels, essential for detecting microvascular dysfunction 2, 3
The diagnostic accuracy of PET is approximately 20% higher than SPECT MPI (88% versus 67%, p=0.009) 3

A normal MFR (≥2.0) indicates normal coronary vasodilatory capacity 4
A mildly reduced MFR (1.8-2.0) suggests early microvascular dysfunction, requiring optimization of medical therapy 4
A moderately to severely reduced MFR (<1.8) indicates significant microvascular dysfunction 4

MFR findings should be correlated with patient symptoms, particularly in women, who have a higher prevalence of non-obstructive CAD and microvascular dysfunction 2, 3
The presence of risk factors for microvascular disease, such as diabetes, hypertension, and smoking, should be considered when interpreting borderline MFR values 4

Rb-82 and N-13 ammonia are the most commonly used radioisotopes for PET MPI 5
Hybrid PET/CT can be used to evaluate both functional and anatomical aspects of coronary circulation 2, 7

Sole reliance on visual assessment of perfusion defects should be avoided, as microvascular disease may not produce visible perfusion abnormalities 2, 4
Globally reduced MFR should not be misinterpreted as technical error, as it may represent diffuse microvascular disease or balanced multi-vessel epicardial disease 2, 4
Reduced MFR has prognostic value, independently predicting adverse cardiovascular events, even in patients with normal perfusion images 4