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The available imaging arsenal for the detection and management of ischemic heart disease has never been larger. Many new noninvasive imaging techniques have obviated the need for many invasive diagnostic procedures and offer risk stratification of patients with known and newly detected disease. Imaging allows the stratification of patients with preclinical disease, beyond that of clinical risk factors. Finally, in cases of invasive diagnostic workups, new imaging modalities now offer highly accurate quantification and adjunctive information that was previously not possible.
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Given the often overwhelming array of imaging modalities and potential findings from each given imaging test, a framework with which to categorize imaging findings is useful. The "ischemic cascade" that follows coronary artery occlusion (Fig. 20–1), as first described by Nesto and Kowalchuk,1 provides such a framework. By establishing the progression from clinically unrecognized parameters to myocardial infarction, the concept of the ischemic cascade allows the physician to recognize and categorize the potential findings from a given imaging study and interpret them along a clinically meaningful spectrum.
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The progression along the continuum of detectable abnormalities of the myocardium is preceded by detectable precursors affecting the coronary arteries, namely atherosclerotic changes, although simple coronary arterial disease may not lead to ischemic consequences. In the presence of a discrete coronary artery stenosis or generalized arteriopathy significant enough to cause significantly decreased myocardial blood flow at rest or during stress (exercise or pharmacologically induced), perfusion defects can be initially detected. Diastolic myocardial dysfunction follows and then systolic dysfunction. Eventually, electrocardiogram (ECG) changes and infarction can be detected. Various imaging tests can detect or infer the presence of myocardial ischemia or infarct. These findings are summarized in Table 20–1.
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Therefore, in this chapter, we discuss each imaging modality and outline the potential findings offered by each modality ...