Myocardial Perfusion Imaging

Robert Corne and I. David Greenberg Introduction

Coronary artery disease (CAD) is the leading cause of death in North America. Atherosclerosis is by far the major cause of CAD. CAD can range from asymptomatic luminal irregularities to sudden total occlusion leading to myocardial infarction.

Atherosclerotic CAD involves an intimal inflammatory reaction. Endothelial cell injury associated with coronary risk factors (smoking, hypertension, diabetes mellitus, hyperlipidemia) results in the entry into the subendothelial space of cellular elements (monocytes) and plasma constituents (notably LDL cholesterol). Monocytes transform into macrophages which engulf LDL cholesterol that has been oxidized in the subendothelial space ("minimally modified" LDL). Activated macrophages produce cytokines which direct smooth cell proliferation and migration into the subendothelial space and produce metalloproteinases and tumor necrosis factor (TNF). Both of these substances can lead to connective tissue degradation, plaque rupture (Fig. 1) and acute coronary syndromes (unstable angina, acute myocardial infarction).

Plaque growth results in progressive coronary stenosis which may cause transient myocardial ischemia (clinically manifested as angina pectoris) when there is an increase in myocardial oxygen demand such as with exercise or emotional stress. The detection of coronary stenosis by nuclear medicine techniques is based on the assessment of relative coronary blood blow at rest and during stimuli that normally increase coronary flow.

Physiologic and Technical Considerations

Physiologic Evaluation of Coronary artery disease

Whereas coronary angiography provides information about the anatomic extent and severity of CAD, myocardial perfusion imaging (MPI) assesses the physiologic or hemodynamic significance of coronary stenosis by inducing heterogeneity in coronary flow. Resting coronary flow is maintained until there is approximately a 90% reduction of coronary arterial diameter. However, the ability to attain maximum flow (termed coronary flow reserve) is impaired with approximately a 50% coronary stenosis (Fig. 2). Increases in coronary flow can be achieved by increasing oxygen demand with exercise (treadmill or bicycle) or beta adrenergic agonists (dobutamine) and by direct vasodilators (adenosine, dipyridamole).

Treadmill Exercise

Graded exercise testing (GXT) in conjunction with myocardial perfusion imaging is most commonly performed on a treadmill. GXT is preferred over pharmaco-

Nuclear Medicine, edited by William D. Leslie and I. David Greenberg. ©2003 Landes Bioscience.

A normal wall

The Donts of Treadmill Buying

The Donts of Treadmill Buying

Though competitive runners are advised to run on the road, there are several reasons why you should buy treadmills anyway. You might have a family which means that your schedule does not have the flexibility it once had.

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