Key points
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Exercise (treadmill or bicycle) is the preferred stress modality in patients who can exercise and achieve adequate exercise endpoints.
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Vasodilator stress is reserved for patients who have exercise limitations, left bundle branch block, or electronically paced rhythms.
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Dobutamine stress is reserved for patients who have exercise limitations and who have contraindications to vasodilator stress.
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The non-ST changes during exercise stress testing provide useful prognostic information.
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The site of ST depression during stress testing does not predict the site of coronary stenosis/ischemia location.
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The site of ST elevations during stress testing in leads without Q waves often is accurate in localizing the site of coronary stenosis/ischemia.
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Hybrid protocols are available, such as combination of dobutamine and atropine and exercise with vasodilators.
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The ST responses are characterized as positive, negative, or nondiagnostic for ischemia.
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There is increasing use of vasodilator stress testing; it may be as high as 50% of all stress tests.
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The dosages and mode of administration of the three current vasodilators in clinical use (dipyridamole, adenosine, and regadenoson) are different. Regadenoson is given as a bolus and is not weight-adjusted.
Background
Exercise stress in conjunction with MPI is more commonly used in clinical practice in lieu of TET alone, due to the limitations of TET, such as its low sensitivity, specificity, and accuracy in diagnosing and localizing the extent and severity of ischemia and its inability to provide information on LV function and viability. Half of the patients referred for stress MPI undergo exercise MPI. Exercise is the preferred stress modality in patients who can achieve exercise endpoints such as ≥85% of peak age-adjusted HR and >5 METs. Around 50% of outpatients and 75% of inpatients who undergo exercise stress testing fail to achieve adequate exercise endpoints. Vasodilator stress is reserved for patients who cannot achieve adequate exercise endpoints or who have exercise limitations, LBBB, or pacemakers ( Table 5-1 ). Dobutamine stress is reserved for those who have exercise limitations and contraindications to vasodilator stress.
| Factors That Favor Vasodilator Stress MPI |
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| Factors That Favor Dobutamine Stress MPI When Exercise Is Not Indicated |
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Exercise or pharmacological stress augment MBF; the MBF in coronary beds without significant stenoses increases ~3-fold with exercise, 2.5-fold with dobutamine, and 3- to 5-fold with vasodilator stressors.
The ECG response to stress testing is classified as negative, positive, or nondiagnostic. A positive ECG response is defined by ≥1-mm flat or downsloping ST depression 60 to 80 milliseconds from the J point, ≥1.5-mm upsloping ST depression 80 ms from the J point, or ≥1-mm ST elevation. These changes should be present in three consecutive beats. A nondiagnostic ECG response is seen in the presence of baseline ECG abnormalities that preclude interpretation of ECG changes, such as in the presence of LV hypertrophy, LBBB, WPW syndrome, paced rhythm, digitalis therapy, or ST depression at rest. Failure to achieve a target age-predicted HR in the absence of positive ECG changes is considered a nondiagnostic response during exercise testing. The site of ST depression is not predictive of the location of the coronary stenosis. The severity and extent of ST depressions have a low correlation with the extent of ischemia seen on MPI.
Case 5-1
Normal Exercise ECG, Abnormal Perfusion ( Figure 5-1 )
A 71-year-old white man with HTN, dyslipidemia, remote tobacco abuse, COPD, and erectile dysfunction presented to his primary care physician with a 2-week history of exertional chest pain. He was referred for exercise MPI. The baseline BP was 162/96 mm Hg and HR was 103 bpm. He exercised on the treadmill for 6 minutes 31 seconds according to the Bruce protocol and stopped due to fatigue. He achieved a peak HR of 150 bpm (111% of age-predicted HR) and 7.7 METs (100% of predicted). The exercise ECG was negative for ischemia ( Figure 5-1, A, B ). The SPECT images showed a large area of ischemia in the LAD territory with TID and poststress stunning ( Figure 5-1, C, D ). The rest LVEF was 47%. He had distal anterior and apical wall akinesis after stress. Coronary angiography showed 80% proximal LAD stenosis and 90% mid LAD stenosis. The LCX had minimal disease and the RCA had a 70% proximal stenosis and a 60% mid stenosis ( Figure 5-1, E ). He underwent CABG to the LAD, diagonal, and RCA.
Comments
The exercise ECG showed no ischemia, although the perfusion images showed high-risk features (large perfusion defect, TID, and postexercise stunning).
In a meta-analysis of 147 studies involving around 24,000 patients, the sensitivity and specificity of exercise testing for detection of CAD were 68% and 77%, respectively, with a positive predictive value of 73%. In a meta-analysis of 27 studies involving about 3200 patients, the sensitivity and specificity of exercise MPI were 87% and 64% compared to 54% and 71% with exercise alone, respectively. The yearly rate of major adverse cardiac events in the setting of high-risk perfusion abnormalities is 5.9% (25th percentile 4.6%, 75th percentile 8.5%).
Case 5-2
Abnormal Exercise ECG, Normal Perfusion ( Figure 5-2 )
A 63-year-old African American woman with GERD, osteoporosis, and hypothyroidism was referred for exercise MPI for evaluation of atypical chest pain. Her baseline BP was 131/65 mm Hg and HR was 55 bpm. She exercised on the treadmill for 7 minutes according to the Bruce protocol. She stopped due to fatigue. She achieved a peak HR of 151 bpm (107% of age-predicted HR) and 8.5 METs (127% of predicted). The exercise ECG was positive for ischemia ( Figure 5-2, A, B ). The SPECT images showed normal perfusion ( Figure 5-2, C, D ) and normal LVEF and wall motion/thickening.
Case 5-3
Abnormal Exercise ECG, Abnormal Perfusion ( Figure 5-3 )
A 61-year-old white man with diabetes mellitus, idiopathic ventricular tachycardia (post RV outflow ablation), and dyslipidemia presented with a 1-month history of new-onset exertional chest pain on mild-to-moderate exertion. He was referred for further evaluation with exercise MPI. The baseline BP was 113/79 mm Hg and HR was 69 bpm. He exercised on the treadmill for 7 minutes 15 seconds according to the Bruce protocol. He stopped due to fatigue and chest pain. He achieved a peak HR of 159 bpm (113% of age-predicted HR) and 8.9 METs (91% of predicted). He had a hypotensive BP response. The exercise ECG was positive for ischemia ( Figure 5-3, A, B ). The SPECT images showed a large area of ischemia in the LAD, RCA, and LCX territories with TID and poststress stunning ( Figure 5-3, C, D ). The rest LVEF was 71% and the poststress LVEF was 58%. Coronary angiography showed 90% proximal to mid LAD stenosis, 90% stenosis of the proximal LCX artery, and 90% stenosis of the proximal RCA with left-to-right collaterals. He underwent CABG.
