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KEY POINTS
Limitations of relative perfusion imaging alone include missed “balanced ischemia,” left main coronary artery disease (CAD), microvascular disease, and in cases of pharmacologic stress inability to identify lack of induced vasodilation. Measurement of myocardial blood flow reserve (MBFR) potentially resolves those issues.
A normal result of both positron emission tomography (PET) myocardial perfusion and MBFR confers a lower risk of CAD and microvascular disease and lower risk of long-term major adverse cardiac events compared to spatially-relative perfusion alone.
A reduced global MBFR incrementally predicts those at a higher risk of future adverse cardiovascular events, independent of perfusion defect and left ventricular ejection fraction (LVEF) assessment.
All patients with reduced MBFR should be appropriately treated medically regardless of the presence of multivessel disease, given the association with high cardiovascular risk.
MBFR helps guide post-test revascularization decisions
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Traditionally, perfusion assessment with single-photon emission computed tomography (SPECT) and positron emission tomography (PET) has been the cornerstone of the noninvasive assessment of symptomatic patients with known or suspected coronary artery disease (CAD) using radionuclide myocardial perfusion imaging (MPI), providing important diagnostic and risk stratification data.1–3 Yet, clinicians are well aware that CAD can be identified at subsequent cardiac catheterization despite a normal perfusion result, and even with an abnormal result, catheterization may demonstrate more severe disease than identified. As perfusion assessment is relative in comparison to other areas, there are several limitations of this technique. This includes potentially missing diagnosis of high-risk CAD in patients where there is a balanced reduction of flow across multiple coronary artery territories, or left main CAD.4 Additionally, for both PET and SPECT, patients undergoing pharmacologic stress imaging, a normal result may be due to lack of effective vasodilation of the agent in the presence of CAD. Furthermore, the visual assessment of relative perfusion images makes it more susceptible to inter-reader and intra-reader variability, further negatively affecting its diagnostic and prognostic utility. Quantitative myocardial blood flow (MBF) assessment helps address these limitations, identify missed CAD, and provide a more comprehensive assessment of future cardiovascular risk. An important additional aspect of MBF assessment is the ability to identify patients with isolated microvascular disease, which is an independent predictor of cardiovascular events. This chapter details the role of quantitative MBF assessment in the diagnosis, prognosis, and management of symptomatic patients with suspected or known CAD. As flow quantitation with cardiac PET is currently available for clinical use and is frequently a part of a clinical program (in contrast to SPECT), this chapter focuses on cardiac PET MBF assessment.
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WHAT IS MYOCARDIAL BLOOD FLOW ASSESSMENT AND HOW IS IT PERFORMED?
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Accurate MBF assessment requires measurement of the timing of radiotracer activity delivered by the arterial blood to the myocardium at rest and stress. Terms used to describe blood flow quantitation include absolute rest MBF (measured in ml/min/g of myocardial tissue), absolute stress MBF (measured in ml/min/g of myocardial ...