What are the advantages of coronary CTA over nuclear stress perfusion imaging? Nuclear stress perfusion imaging is based on a decrease in myocardial blood flow (ie, perfusion) in a specific coronary artery territory resulting from a more proximal obstructive atherosclerotic lesion. The myocardium in the region of the obstructed coronary artery will have a decreased uptake of isotope, causing an ischemic pattern to appear. However, if atherosclerotic disease affects all 3 coronary arteries (right, left anterior descending, and circumflex), there may be no relative area of perfusion defect, presenting a false-negative normal perfusion pattern. This finding is referred to as balanced ischemia. Similarly, atherosclerosis of the proximal right coronary artery and the left main coronary artery can yield a normal-appearing perfusion pattern of balanced ischemia during nuclear stress perfusion imaging. Because cardiac CTA directly visualizes the lumen of the coronary arteries, balanced ischemia is not a confounding factor for this imaging modality. The shadowing artifact often seen on the nuclear perfusion images of patients who are obese or who have large breasts results in false-positive findings, potentially leading to unnecessary invasive coronary arteriography. Coronary CTA may be a better option for such patients, provided that they meet appropriate use criteria.
Each year in the United States, approximately 6 million patients are seen in the emergency department with chest pain.
15 Many of these patients have normal cardiac examination results, 12-lead ECG findings, and cardiac biomarker levels, but they are still admitted to the cardiac unit or a similar hospital facility for nuclear stress perfusion imaging studies to avoid misdiagnosis of the 2% of these patients who have actually had an acute myocardial infarction. This practice usually results in a hospital stay with an average duration of 40.5 hours
16 and considerable associated costs. Recent trials of the use of coronary CTA for patients in the emergency department with acute chest pain have shown decreases in both the length and the cost of hospitalization.
16 Randomized trials based on cost-effectiveness models are currently under way to determine whether this strategy improves patient outcomes.
17 Admitting patients with chest pain from the emergency department, cycling myocardial enzymes, and waiting 12 hours before performing a nuclear stress perfusion study currently adds $10 to $12 billion per year to health care costs in the United States.
17 Certainly, it is reasonable to assume that use of cardiac CTA to establish that a patient's coronary arteries are free of atherosclerosis would eliminate further unnecessary hospitalizations for evaluation of chest pain. With further improvements in cardiac CT scanning (eg, the development of 320-slice scanners that can produce images of the heart in 1 gantry rotation, thereby eliminating heart rate and arrhythmia factors) and low-dose radiation protocols (eg, the step-and-shoot protocol), it is not difficult to envision that, in the near future, cardiac CTA will be the preferred diagnostic imaging modality for patients in the emergency department who have chest pain. Well-designed prognostic models support this approach.
17