Key points
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PCI and CABG are commonly used modalities for revascularization in patients with stable and unstable CAD.
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Ideally, stress testing (in conjunction with imaging) should be used to guide the need for coronary angiography, PCI, or CABG in patients with stable symptoms.
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Stress MPI is helpful in patients with recurrent symptoms after PCI or CABG to assess for in-stent stenosis, bypass graft disease, progression of disease in native vessels, or incomplete revascularization.
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Stress MPI is helpful for risk stratification of patients after PCI or CABG.
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Stress MPI is acceptable for routine evaluation of high-risk asymptomatic patients who are more than 5 years post-CABG, especially those who had no angina before CABG.
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After successful PCI, new fixed perfusion defects might indicate periprocedural MI, while reversible defects might be due to jailed branches, such as diagonal or septal branches in the case of LAD stenting.
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After CABG, new fixed defects might be due to periprocedural MI, while reversible defects at the basal septum and anterior wall could be due to jeopardized branches prior to left internal mammary artery (LIMA) anastomosis. These abnormalities should not be confused with LIMA or downstream disease, where the reversible defects almost always involve the distal septum, anterior wall, and the apex.
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After CABG, septal wall motion, but not thickening, is abnormal despite a normal perfusion pattern and normal EF. The presence of a thickening abnormality suggests necrosis.
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Contrary to popular belief, normalization of the perfusion pattern in patients with stable angina after PCI is immediate and any residual abnormality should not be ascribed to the technique but to the results of the intervention.
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Unlike patients with stable CAD mentioned earlier, residual defects might persist immediately after PCI in patients with acute MI and resolve gradually after 1 to 2 weeks.
Coronary artery revascularization with either PCI or CABG is commonly performed in patients with stable angina and severe CAD for the alleviation of symptoms and for improved survival in a subset of patients with high-risk anatomy. PCI and CABG remain the mainstays of therapy in patients with unstable angina or MI. Stress testing is valuable before and after revascularization to evaluate recurrent symptoms or in asymptomatic high-risk patients. Stress MPI can identify restenosis after PCI, significant stenosis in bypass grafts, progression of native CAD, or assess the significance of disease in territories that were not completely revascularized.
Current guidelines recommend the use of imaging in conjunction with stress testing when evaluating patients with prior revascularization. Imaging can localize the site and extent of ischemia and improves the sensitivity of ischemia detection, compared to exercise testing alone. In a pooled analysis of studies that assessed restenosis after balloon angioplasty, the sensitivity of exercise ECG alone was 54% compared to 83% with stress MPI, with comparable specificities of 77% and 78%, respectively. Exercise is the preferred stress modality in patients who can exercise and achieve adequate exercise end points, while vasodilator stress is reserved for patients who cannot exercise or for those who have an underlying LBBB or a ventricular paced rhythm. Dobutamine stress is reserved for patients who have contraindications to vasodilator stress. Appropriateness guidelines have been published to assist in the proper selection of patients with prior revascularization who are referred for stress MPI ( Table 8-1 ).
| Score | |
|---|---|
| Appropriate Indications | |
| Symptomatic patients evaluated for ischemic symptoms | 8 |
| Asymptomatic patients evaluated for incomplete revascularization when additional revascularization is feasible | 7 |
| Asymptomatic patients ≥ 5 years after CABG | 7 |
| Uncertain Indications | |
| Asymptomatic patients ≥ 2 years after PCI | 6 |
| Asymptomatic patients < 5 years after CABG | 5 |
| Inappropriate Indications | |
| Asymptomatic patients < 2 years after PCI | 3 |
| Before participation in cardiac rehabilitation | 3 |
Earlier stress MPI studies that evaluated restenosis post-PCI were done in the era of balloon angioplasty and bare metal stenting, where the restenosis rates approached 30% to 50% and 20% to 30%, respectively. The use of drug eluting stents has decreased the restenosis rate by up to 50%. One should also keep in mind that the incidence of clinical restenosis is significantly lower than angiographic restenosis. In one large study of bare metal stents, the incidence of clinical in-stent restenosis was 50% lower than the angiographic in-stent restenosis (defined as > 50% diameter stenosis). In-stent restenosis of greater than 70% was more commonly associated with symptoms. Additionally, aggressive medical therapy and risk factor modification have further improved the outcomes of patients with CAD by decreasing the rate of CAD progression and decreasing the rate of cardiac events.
Ischemic symptoms that occur within 48 hours of PCI are usually related to periprocedural events, such as acute closure, distal embolization, coronary vasospasm, no reflow, jailing of side branches, or acute stent thrombosis. Stress MPI is not helpful in this situation. Ischemic symptoms within 1 month of PCI are more commonly related to sub-acute stent thrombosis and less likely from in-stent restenosis. Patients presenting with typical symptoms within 6 months after PCI are usually evaluated with coronary angiography. Stress MPI is performed in patients with PCI who present with atypical symptoms or with typical symptoms beyond 6 to 9 months after PCI. Routine evaluation of asymptomatic patients after PCI is not endorsed by the various guidelines. Routine stress MPI of asymptomatic patients after PCI should be reserved for high risk patients such as those with multivessel PCI, suboptimal PCI, incomplete revascularization, previous sudden cardiac death, proximal LAD PCI, prior silent ischemia, and hazardous occupation.
Graft disease, or failure after CABG, remains an important reason of symptom recurrence or other adverse cardiac events. Although internal mammary artery (IMA) grafts have a 10-year patency rate that approaches 90%, saphenous vein grafts have patency rates of around 75% and 40% at 5 and 10 years, respectively. As with PCI, stress testing in patients with prior CABG should be performed in conjunction with imaging. In a study that assessed graft stenosis after CABG, the sensitivity of the exercise ECG alone for detecting any graft stenosis was 31% compared to 80% with exercise MPI, with comparable specificities of 93% and 87%, respectively. The relationship between graft patency and perfusion pattern is far more complicated than in patients with native vessel disease. The presence of a patent graft does not guarantee a normal perfusion pattern and neither does the presence of graft disease guarantee an abnormal perfusion pattern. The size of the vessel and the status of other branches in the same territory are important factors that affect this relationship. This, most likely, explains the lower sensitivity of the test in such patients. It is imperative to review both the coronary angiogram and the MPI and not to rely on reports that often are not very helpful. Stress MPI is indicated in patients with CABG with recurrent symptoms during the 5-year window following CABG. Routine and periodic testing in patients 5 years following CABG is appropriate except in a select group of high-risk patients.
Case 8-1
Stress Testing Before and After PCI ( Figure 8-1 )
A 52-year-old African American man with HTN, obesity, GERD, and CAD underwent exercise MPI in 2008 for evaluation of chest pain. The images showed a large area of ischemia in the territory of the LCX artery with normal LVEF ( Figure 8-1, A, B ). Coronary angiography showed mild to moderate disease in the LAD and RCA and severe stenoses in the LCX artery ( Figure 8-1, C ). He underwent PCI of the LCX with two drug-eluting stents. He had recurrent atypical chest pains in 2010 and was evaluated with a regadenoson MPI. He had no ECG changes and the perfusion pattern and EF were normal (not shown). He was continued on medical therapy and did not undergo repeat coronary angiography.
Case 8-2
Stress Testing After PCI for Acute MI ( Figure 8-2 )
A 31-year-old white man with type 1 DM and dyslipidemia sustained an anterior ST elevation MI in October 2009. Coronary angiography showed thrombotic occlusion of the mid LAD and mild disease in the RCA and LCX ( Figure 8-2, A ). He underwent PCI of the LAD with deployment of a drug-eluting stent ( Figure 8-2, B ). Two-dimensional echocardiography showed moderate LV dysfunction. In July 2010, he underwent an exercise MPI for evaluation of atypical chest pains. He exercised on the treadmill for 14 minutes and 30 seconds and stopped due to fatigue. The exercise ECG showed no ischemia. The perfusion images showed a large LAD scar ( Figure 8-2, C ). He had septal and apical dyskinesis and a mildly depressed rest LVEF of 46% ( Figure 8-2, D, and Video 8-1). He was continued on medical therapy.
Case 8-3
Stress Testing After Multiple PCIs for Recurrent Symptoms ( Figure 8-3 )
An 83-year-old white man with HTN, dyslipidemia, chronic kidney disease, peptic ulcer disease, and CAD with a history of MI and multiple PCIs of the LAD, RCA, and LCX underwent regadenoson MPI for evaluation of recurrent chest pain. The stress ECG was negative for ischemia. The SPECT images showed a large area of ischemia in the LAD and LCX territories ( Figure 8-3, A ). The wall motion and EF were normal. Coronary angiography showed a patent RCA stent with minimal RCA disease, severe stenosis of the proximal LAD, and an occluded second diagonal (in-stent) with left to left collaterals. The LCX had severe stenoses of the first and second obtuse marginal branches ( Figure 8-3, B ). The patient underwent successful CABG.
