Key points
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Stress MPI remains the most common imaging modality used in patients with known or suspected CAD.
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The improvement in hardware and software and the availability of multiple stress modalities and imaging protocols have contributed to the continued growth and success of stress MPI.
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There is an increasing awareness of the radiation risk and the means to minimize it.
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There are appropriateness criteria and guidelines that define the proper indications for stress MPI.
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Stress MPI provides comprehensive information on myocardial perfusion and regional and global LV function that have incremental diagnostic and prognostic information.
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The results of stress MPI have had a major impact on the role of coronary angiography as the “gold standard” for sensitivity and specificity reporting.
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The terms “false negative” and “false positive” in regard to MPI results should be reconsidered in lieu of the serious limitations of coronary angiography in predicting myocardial blood flow.
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The size of the perfusion defect has stood the test of time in predicting patient outcome and the presence of either fixed defects (scar) or reversible defects (ischemia) are important.
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The presence of additional non-perfusion data may be helpful in managing patients with conditions such as stunning, transient dilatation, and RV dysfunction.
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Not all patients with multivessel disease will have perfusion defects in all diseased territories—not unlike the results of functional assessment of coronary stenoses by flow or pressure wire. which showed not all diseased vessels are physiologically important.
Background
CAD represents a major worldwide health problem. It is estimated that in the United States, 17.6 million individuals have CAD. Around 8.5 million individuals have a history of MI, and 10.2 million individuals have angina pectoris. The lifetime risk of developing CAD is 49% for males and 32% for females aged > 40 years. Although the CAD mortality has been declining, it is anticipated that the prevalence of CAD will continue to increase. Stress testing with MPI is one of the most commonly used noninvasive modalities for evaluation of individuals who have or are suspected of having CAD. Stress MPI is generally indicated for diagnosing CAD, risk-stratifying patients with known CAD, assessing therapeutic interventions and progression/regression of CAD, and assessing the physiological significance of an intermediate coronary stenosis. Appropriateness criteria and national guidelines have been published to assist in the proper use of stress MPI ( Table 6-1 ).
| Score | |
|---|---|
| 1. Detection of CAD | |
| • Symptomatic patients | |
| • Low CAD pretest probability + uninterpretable ECG or cannot exercise | 7 |
| • Intermediate CAD pretest probability + uninterpretable ECG and can exercise | 7 |
| • Intermediate CAD pretest probability + ECG or cannot exercise | 9 |
| • High CAD pretest probability regardless of ECG or ability to exercise | 8 |
| 2. Detection of CAD/Risk Assessment | |
| • Asymptomatic patients | |
| • High ATP III CHD risk | 7 |
| • Miscellaneous cardiac conditions | |
| • New CHF with LV dysfunction + no prior CAD evaluation and nor planned coronary angiography (without ischemia equivalent symptoms) | 8 |
| • Ventricular tachycardia + low ATP III CHD risk | 7 |
| • Ventricular tachycardia + intermediate or high ATP III CHF risk | 8 |
| • Syncope + intermediate or high ATP III CHF risk | 7 |
| 3. Risk Assessment in Asymptomatic or Stable Symptoms | |
| • Equivocal, discordant, or borderline stress testing results with concern for presence of obstructive CAD | 8 |
| • New or worsening symptoms + abnormal coronary angiography or abnormal prior stress test | 9 |
| • Coronary stenosis or abnormality of indeterminate significance | 9 |
| • Asymptomatic patient + high CHD risk with Agatston score 100-400 | 7 |
| • Asymptomatic patient + Agatston score > 400 | 7 |
| • Intermediate risk Duke treadmill score | 7 |
| • High risk Duke treadmill score | 8 |
Exercise and pharmacologic stress agents increase MBF, although via different mechanisms. The peak, or hyperemic, MBF is inversely related to the degree of coronary stenosis but the relationship is not linear. Several studies have shown considerable discordance between the percent diameter stenosis, a measure of anatomic significance of coronary stenosis, and FFR, a measure of the physiologic significance of coronary stenosis in patients with one-, two-, and three-vessel disease. This crucial observation casts doubt on prior studies that used coronary angiography as the “gold standard” to assess the performance of stress MPI (sensitivity and specificity). There is one more overlooked fact—that FFR does not provide data on the extent of a perfusion abnormality or on the nature of the abnormality (scar, ischemia, or mixed). These latter data combined with LVEF and volume have been proven to be powerful predictors of outcome in patients with known or suspected CAD.
The accuracy of stress MPI (or any testing modality) for the diagnosis of CAD depends on the disease severity and the test’s characteristics. Despite the limitations of coronary angiography, in a meta-analysis of 27 studies involving around 3200 patients who underwent exercise MPI, the weighted respective sensitivities and specificities of exercise SPECT for CAD detection were 87% and 64%. The normalcy rate of exercise SPECT MPI for detecting CAD in patients with low likelihood of CAD was 90% in 10 pooled studies involving 628 patients. The mean sensitivities and specificities of vasodilator SPECT MPI for detection of CAD were 86% and 73%, respectively, from pooled studies of about 2500 patients. In a meta-analysis of nine adenosine SPECT MPI studies involving about 1200 patients, the respective mean sensitivity and specificity for CAD detection were 90% and 75%, respectively, with a normalcy rate of 90% in patients with low likelihood of disease. In a meta-analysis of 24 studies involving about 1200 patients, the respective sensitivity, specificity, and accuracy of dobutamine SPECT MPI for CAD detection were 85%, 72%, and 77%, respectively. The use of gating and attenuation correction in one study of adenosine SPECT imaging significantly improved the sensitivity and normalcy rates to > 90%.
Case 6-1
Stress Testing After MI ( Figure 6-1 )
An 81-year-old African American woman with history of HTN, dyslipidemia, end-stage renal disease status post renal transplantation, osteoporosis, and GERD had a non–ST-elevation MI 6 months ago at an outside facility. She did not undergo coronary angiography because of concerns about her renal function. She underwent regadenoson MPI for evaluation of dyspnea on exertion 6 months after her MI. The stress MPI showed normal perfusion ( Figure 6-1, A, B ), LVEF, and wall motion/thickening ( Figure 6-1, C ).
