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Myocardial perfusion scintigraphy is a noninvasive modality with high sensitivity for the diagnosis and evaluation of coronary artery disease. Physiologically significant coronary stenoses may be evaluated in populations with known or suspected coronary disease, after therapeutic interventions, preoperatively for risk assessment, and for prognostication after acute ischemia or infarction.

A more recent application of this technique has been made to the patients presenting to the ED with chest pain. In a subset of patients with an intermediate or low probability of coronary artery disease and chest pain (unstable angina), the missed diagnosis of coronary artery disease has been reported as high as 5 to 8 percent.12 and 3 As many as a third of patients with acute myocardial infarction do not have electrocardiographic (ECG) changes suggestive or diagnostic of ischemia, many of which have baseline ECG abnormalities.

Several centers around the country have used myocardial perfusion scintigraphy to further classify this subset into high-risk and low-risk categories to reduce the incidence of missed acute ischemic coronary syndromes and the number of unnecessary hospital admissions for noncardiac chest pain. In a large study at the Medical College of Virginia involving 1187 patients, 99mTc-sestamibi perfusion imaging was used in defining the critical pathways in this population. 4 Used with established clinical criteria, the cardiac event rate at 1-year follow-up for patients with abnormal scan findings was 42 percent versus 3 percent (revascularization) for those with a normal scan findings. In those with abnormal scan findings, 11 percent experienced myocardial infarction and 8 percent suffered cardiac death; in those with normal scan findings, none had myocardial infarction or death. other centers around the country are reporting similarly favorable results. 56

The nuclear perfusion imaging protocol performed in the ED is very similar to conventional myocardial perfusion stress protocols with the exception that the injections are performed at rest during chest pain. Preliminary reports indicate that timing of injection during chest pain may improve diagnostic sensitivity; however, other centers have reported good results with injections performed up to within 12 h of the chest pain. 7 99mTc-sestamibi or tetrofosmin are used because of their favorable imaging properties of minimal redistribution and lower radiation dosimetry compared with 201Tl chloride. After intravenous injection, these 99mTc tracers are highly extracted and retained for several hours within the myocardium in a distribution proportional to coronary blood flow. This permits imaging several hours later after additional ED evaluation or intervention. Because of the more favorable dosimetry of 99mTc tracers, a higher dosage approaching 7 to 10 times the injected dose of 201Tl is typically used. This permits high-quality tomographic imaging (single-photon emission computed tomograpy or SPECT) and ECG gating, which provides additional information, including assessment of wall motion, wall thickening, and left ventricular ejection fraction. In patients with a normal findings on resting perfusion study, further evaluation with a stress myocardial perfusion study may be performed with them as outpatients. Preliminary studies have shown the cost effectiveness of this risk stratification, and further studies are currently in progress. FigurĀ§..l.5Z.-.6, Figure..57z7 (.Pla.t.e...Z), and Figure..,.5.7z8 (PIate.8) illustrate the utility of myocardial perfusion scintigraphy in a patient with acute chest pain.

FIG. 57-6. A 59-year-old white hypertensive man who arrived at the emergency department with 6 h of intermittent chest pain. Findings on physical examination and electrocardiography were unremarkable. Initial cardiac enzyme levels (CK-MB, myoglobin, and troponin T) were normal. 99mTc-sestamibi SPECT perfusion images show a moderate area of hypoperfusion in the middle and proximal inferolateral wall. The patient went directly to catheterization, which showed a 95 percent circumflex marginal stenosis that was successfully treated by angioplasty. (Courtesy of Ethan Spiegler, MD.)

FIG. 57-6. A 59-year-old white hypertensive man who arrived at the emergency department with 6 h of intermittent chest pain. Findings on physical examination and electrocardiography were unremarkable. Initial cardiac enzyme levels (CK-MB, myoglobin, and troponin T) were normal. 99mTc-sestamibi SPECT perfusion images show a moderate area of hypoperfusion in the middle and proximal inferolateral wall. The patient went directly to catheterization, which showed a 95 percent circumflex marginal stenosis that was successfully treated by angioplasty. (Courtesy of Ethan Spiegler, MD.)

Inferolateral HypokinesisInferolateral Hypokinesis

FIG. 57-8. (Plate8). Bull's-eye representation of gated SPECT data. Hypoperfusion of the proximal inferolateral wall as well as mild hypokinesis and diminished wall thickening. There is preserved global left ventricular function.

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