Exercise Stress Exercise stress is the gold standard for stress MPI. Exercise is ideal for dilating the coronary vessels to assess whether myocardial blood perfusion is adequate or whether ischemia is present during stress. However, in order to achieve accurate, diagnostic MPI results, the patient must be able to reach an adequate level of exercise (ie, at least 85% of his or her predicted maximum heart rate). Performing MPI during submaximal exercise reduces the sensitivity of the test and can lead to false negative results.68 Injecting the radionuclide tracer at submaximal exercise levels can have negative consequences for both the patient and the medical staff, including the need for reimaging (usually on another day), double radiation exposure for the patient, scheduling disruptions, delay in obtaining diagnostic information, and lost revenue, as only 1of the procedures may be covered by insurance.68 Exercise-Limiting Factors Although exercise remains the preferred method of stress for cardiac imaging, many patients are unable to complete a maximal exercise stress test for a variety of reasons.69 Various medical conditions, motivational issues, use of certain medications, and age can all affect the ability to exercise to target heart rates. Table 7 lists many of the factors that can render a patient unable to perform a maximal stress test. Table 7. Factors That Prevent or Limit Patients' Ability to Exercise Adequately70-72

Non-Stress Testing Stress Testing Exercise vs. Pharmacologic Stress

Diabetics, patients with metabolic syndrome, and African-American women also often tend to have a lower ability to exercise adequately. Pharmacologic Stress Because patients often have conditions or factors that limit their ability to exercise adequately, almost 50% of MPI studies performed in the US are done with pharmacologic stress.69 The commonly used pharmacologic stress agents include adenosine, dipyridamole, and dobutamine. Adenosine and dipyridamole are generally used for nuclear MPI, while dobutamine is primarily used in echocardiography. Adenosine is the most commonly used pharmacologic stress agent in MPI procedures in the US.73 The clinical utility of pharmacologic stress MPI is well established. MPI results obtained with adenosine stress have been shown to be concordant with results obtained with exercise stress.74,75 Adenosine and dipyridamole have similar sensitivity and specificity for CAD diagnosis.76  The American Society of Nuclear Cardiology Task Force on Women and Heart Disease have recommended that women who are unable to perform 5 metabolic equivalents (METs) are candidates for pharmacologic stress.7 Pharmacologic stress MPI has been shown to have a higher diagnostic accuracy than exercise ECG for detecting CAD in women.7 To view a cardiac testing algorithm that demonstrates the roles of both exercise and pharmacologic stress imaging, see the Stress Testing section of this Web site.