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Jaume Candell Riera, MD; Josep Rodés,
Santiago Aguadé, MD; Joan Castell, MD
Cardiology Department, Hospital Universitari Vall d'Hebron, Barcelona, Spain
MYOCARDIAL PERFUSION SPECT POST-ANGIOPLASTY AND POST-STENT
The incidence of restenosis after percutaneous transluminal coronary angioplasty (PTCA) is high: 30-40% at 3 months, 45% at 6 months, and near 50% at 12 months. This makes it mandatory to establish which is the correct follow-up of these patients in order to diagnose that complication. Twenty-five percent of patients with restenosis do not have symptoms and 40% of patients without restenosis have thoracic discomfort. It is well established that catheterization must be indicated to the patients with angina, but the diagnosis of restenosis in the asymptomatic patients arises some questions: Is it correct to perform a conventional electrocardiographic exercise test or a myocardial SPECT in order to achieve a higher diagnostic accuracy?, When to perform the noninvasive diagnostic test?
Conventional exercise test is a good technique evaluating functional capacity, angina threshold and ST segment depression post-PTCA but its sensitivity (60%) and positive predictive value (50%) are low for the diagnosis of restenosis (1). In our experience, after PTCA or stent implantation we recommend conventional exercise test 4 weeks after PTCA and thereafter every year. After 4 years follow-up we observed that 50% of patients had a negative test, 20% a positive test and 15% a non-diagnostic ECG test. In the remaining 15% of patients exercise test could not be performed due to physical problems of the patient. In these two instances we indicate a myocardial perfusion SPECT: with exercise only in case of nondiagnostic ECG , with exercise + dipyridamole if exercise is insufficient (2,3), dipyridamole only if a nonasmathic patient cannot perform exercise, and with dobutamine in asthmatic patients that do cannot exercise.
We evaluated the diagnostic performance of exercise (± dipyridamole) myocardial SPECT with technetium compounds in order to diagnose restenosis post-PTCA in 71 patients with angiographic verification (35 with multivessel disease, 78 PTCA) (4). All patients had myocardial SPECT with technetium compounds indicated for clinical purposes between 1 month and 4 years after PTCA. Sensitivity, specificity and positive and negative predictive values were significantly higher than those of the conventional exercise test (), mainly in patients with multivessel disease ( ).
Higher diagnostic accuracy for thallium-201 scintigraphy (5-8), radionuclide ventriculography (10,11) and stress echocardiography (12) have also been reported as compared to conventional exercise ECG test. However, a reversible or "ischemic" pattern greater 30% in the region of the successfully dilated coronary artery has been reported in >30% of cases when thallium SPECT was performed during the first month after PTCA. More than 25% of these early defects normalized during the subsequent 6 months (13), but patients with that pattern had a high risk of restenosis during follow-up. Various mechanisms have been proposed to explain this early myocardial ischemia with a good angiographic result of PTCA: disturbances in small coronary vessels (14), "recoil" phenomena after PTCA (15), suboptimal functional result in spite of a good angiographic result (16).
Angiographic results have improved after stent introduction and, consequently, the rate of restenosis has decreased. Coronary reserve evaluated by intracoronary Doppler is abnormal after PTCA in a large number of cases and improves after stent implantation (17). Until now there are no reports evaluating whether this improvement in coronary reserve reduces the number of early reversible defects after stent implantation and if their presence predicts restenosis during the follow-up.
Exercise myocardial perfusion SPECT (± dipyridamole) with technetium compounds during the first week after stent implantation has shown a low incidence of reversible or "ischemic" patterns as compared to those previously reported with thallium, and a high incidence of restenosis and ischemic complications in patients with such defects. We studied 30 patients without previous myocardial infarction in whom a coronary stent was successfully implanted < 8 days previously. The rate of stenosis was reduced from 68 ± 13% to 9 ± 8% and the mean luminal diameter increased from 0,9 ± 0,4 mm. to 2,8 ± 0,5 mm. Reversible defects were observed in only 5 cases (16,6%). During a mean clinical (100% of cases) and angiographic (77% of cases) follow-up of 8 ± 3 months, 4 patients (2 with reversible defects) needed revascularization. Three out of 4 patients with reversible defects and 3 out of 19 patients without reversible defects (75% vs. 16%, p < 0,05) angiographic restenosis has been observed. These preliminary results permit to suggest that the rate of early reversible defects with technetium compounds after stent implantation is lower than previously described after PTCA with thallium, and that patients with these defects have an increased rate of restenosis during follow-up (18).
Accuracy of exercise myocardial 99mTc-tetrofosmin SPECT for the diagnosis of restenosis after stent implantation has been evaluated by Galassi et al.(19) in 97 patients, and a sensitivity of 82% and a specificity of 84% have been observed. These values are higher than those previously reported with exercise ECG conventional test (20).
MYOCARDIAL PERFUSION SPECT AFTER SURGICAL REVASCULARIZATION
Patients with coronary artery by-pass graft are an important group among patients with coronary artery disease. New ischemic events and evolution towards occlusion, basically in patients with venous grafts, can be observed after successful surgical coronary revascularization, even in asymptomatic patients. More than 50% of saphenous aortocoronary by-pass grafts are occluded after 10 years in contrast with only 10% of mammary artery by-pass (21-24). Thus, the role of myocardial SPECT in the clinical follow-up of these patients can be important.
In order to evaluate the accuracy of exercise myocardial SPECT with technetium compounds in the diagnosis of stenosis >70% of aortocoronary by-pass grafts we analyzed 67 coronary grafts (31 of mammary artery and 36 of saphenous vein). The mean interval between surgery and SPECT was 9,7 years. Sensitivity, specificity, positive and negative predictive value of SPECT were significantly higher than those obtained with conventional exercise ECG test (), mainly in grafts to the left anterior descending and right coronary arteries ( ) (25).Other authors have reported similar diagnostic accuracy of myocardial SPECT in these patients (26-28). Rasmussen et al. (26) reported a sensitivity of 71% for the diagnosis of occlusion of coronary by-pass grafts in 41 symptomatic patients and Pfisterer et al. (27) reported a sensitivity of 80% in a series of 154 grafts in asymptomatic patients. In these series, patients with significant stenosis of native coronary tree distal to by-pass were excluded, even though the grafts were patent, and, therefore, the number of false positive results could be decreased. The lack of discrimination the cause of ischemia, either in the native coronary circulation or in by-pass grafts, is one of the main limitations of the SPECT.
A high predictive power of mortality
and ischemic events has been reported recently in studies using myocardial perfusion
scintigraphy in surgical revascularized patients (30,31). Reversible defects
in more than one coronary region and high pulmonary uptake has been associated
with a bad prognosis during follow-up. Zellweger et al.(32), analyzing a series
of more than 1500 consecutive surgical revascularized patients, observed that
myocardial perfusion SPECT was predictive of mortality, with significant incremental
value as compared to that of exercise ECG test. These authors concluded that
in symptomatic patients less than 5 years after surgery and in all patients
longer than 5 years after revascularization, a benefit in their clinical management
can be obtained through the performance of myocardial perfusion SPECT study.
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