This review highlights recent advances in myocardial perfusion imaging in echocardiography, single-photon-emission computed tomography, positron-emission tomography, cardiac computed tomography, and cardiac magnetic resonance imaging. The future of non-invasive cardiac imaging is trending toward comprehensive studies combining different modalities to evaluate both cardiac anatomy and its functional status.
Coronary artery disease (CAD) represents a tremendous financial and health burden as the leading cause of death in the US.1 Acute coronary syndrome and its subsequent manifestations, including heart failure and need for cardiac transplantation, are associated with significant morbidity and mortality. Hypertension, dyslipidemia, tobacco abuse, diabetes, chronic kidney disease, and family history of CAD are important risk factors for the development and progression of CAD. Sensitive, accurate, and reproducible tests to detect CAD are therefore important for risk stratification to optimize patient outcome and contain rapidly escalating medical care costs through pre-morbid diagnosis and treatment.
The development of myocardial ischemia begins with coronary stenoses, which lead initially to a reduction in perfusion, followed by diastolic dysfunction, regional systolic wall motion abnormality, ST-segment depression on electrocardiography (ECG), and, finally angina—a sequence known as the ischemic cascade. Detecting disease at its earliest stage will allow for medical intervention and reduce future cardiovascular events. However, atherosclerosis and consequent regional perfusion disparities due to endothelial dysfunction may occur at the microvascular level prior to the development of significant stenoses seen on coronary angiography or wall motion abnormalities on stress echocardiography. Coronary remodeling progresses by outward compensatory expansion of atherosclerosis while preserving the lumen area in minimal and moderate CAD; this is followed by luminal narrowing in severe CAD.2 Use of coronary intravascular ultrasound has demonstrated outward remodeling of the elastic external membrane of the diseased segment while keeping the luminal area the same as the nearby disease-free segment.3 In addition, several studies have shown that the majority of myocardial infarctions (MIs) are associated with non-flow-limiting, unstable plaques.4 Delcour et al. showed that patients with normal coronary angiography but abnormal myocardial perfusion imaging (MPI) may predict a higher likelihood of future cardiovascular events.5 Invasive evaluation of perfusion such as fractional flow reserve (FFR) is associated with peri-procedural complications of infection, bleeding, coronary dissection, and stroke. In low- to intermediate-risk populations, the risks may outweigh the benefits of an invasive procedure. Non-invasive evaluation of myocardial perfusion is therefore preferred in these settings.
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