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Myocardial Perfusion SPECT in
Revascularized Patients

Jaume Candell Riera, MD; Josep Rodés, MD;
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 (Table 1), mainly in patients with multivessel disease (Table 2).

   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 (Table 3), mainly in grafts to the left anterior descending and right coronary arteries (Table 4) (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.

REFERENCES

1. Gibbsons RJ, Balady GJ, Beasley JW, et al. ACC/AHA Guidelines for Exercise Testing. A report of the American College of Cardiology/American Heart Association. Task force on practice guidelines (Committee on Exercise Testing). J Am Coll Cardiol 1997; 30: 260-315.

2. Candell-Riera J, Santana-Boado C, Castell-Conesa, et al. Simultaneous dipyridamole/maximal subjective exercise with 99mTc-MIBI SPECT : improved diagnostic yield in coronary artery disease. J Am Coll Cardiol 1997 ; 29 : 531-536.

3. Candell-Riera J, Santana-Boado C, Bermejo B, et al. Dipyridamole administration at the end of an insufficient exercise 99mTc-MIBI SPECT improves detection of multivessel coronary artery disease in patients with previous myocardial infarction. Am J Cardiol 2000; 85: 532-535.

4. Candell-Riera J, de la Hera JM, Santana-Boado C, et al. Eficacia diagnóstica de la tomogammagrafía miocárdica en la detección de reestenosis coronaria postangioplastia. Rev Esp Cardiol 1998; 51: 648-654.

5. Hecht HS, Shaw RE, Chin HL, et al. RK. Silent ischemia after coronray angioplasty: Evaluation of restenosis and extent of ischemia in asymptomatic patients by tomographic thallium-201 exercise imaging and comparison with symptomatic patients. J Am Coll Cardiol 1991; 17: 670-677.

6. Hardoff R, Shefer A, Gips S, et al. Predicting late restenosis after coronary angioplasty by very early (12-24 h) thalium-201 scintigraphy: implications with regard to mechanisms of late coronary restenosis. J Am Coll Cardiol 1990; 15: 1486-1492.

7. Breisblatt WM, Weiland FL, Spaccaventop LJ. Stress thallium-201 imaging after coronary angioplasty predicts restenosis and recurrent symptoms. J Am Coll Cardiol 1988; 12: 1199-1204.

8. El-Tamimi H, Davies GJ, Hackett D, et al. Very early prediction of restenosis after successful coronary angioplasty: anatomic and functional assessment. J Am Coll Cardiol 1990; 15: 259-264.

9. Jain A, Mahmarian JJ, Borges-Neto S, et al. Clinical significance of perfusion defects by thalium-201 single photon emission tomography following oral dipyridamole early after coronary angioplasty. J Am Coll Cardiol 1988; 11: 970-976.

10. De Puey EG, Leatherman LL, Leachman RD, et al. Restenosis after transluminal coronary angioplasty detected with exercise-gated radionuclide ventriculography. J Am Coll Cardiol 1984; 4: 1103-1113.

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12. Dagianti A, Rosanio S, Penco M, et al. Clinical and prognostic usefulness of supine bycycle exercise echocardiography in the functional evaluation of patients undergoing elective percutaneous transluminal coronary angioplasty. Circulation 1997; 95: 1176-1184.

13. Manyari DE, Knudtson M, Kloiber R, et al. Sequential thallium-201 myocardial perfusion studies after successful percutaneous transluminal coronary artery angioplasty: delayed resolution of exercise-induced scintigraphic abnormalities. Circulation 1988; 77: 86-95.

14. El-Tamimi H, Davies GJ, Sritara P, et al. Inappropriate constriction of small coronary vessels as a posible cause of a positive exercise test early after successful coronary angioplasty. Circulation 1991; 84: 2307-2312.

15. Foley DP, Deckers J, van den Bos AA, et al. Usefulness of repeat coronary angiography 24 hours after successfull balloon angioplasty to evaluate early luminal deterioration and facilitate quantitative analysis. Am J Cardiol 1993; 72: 1341-1347.

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17. Kern MJ, Puri S, Bach RG, et al. Abnormal coronary flow velocity reserve after coronary stenting in patients. Role of relative coronary reserve to assess potential mechanisms. Circulation 1999; 100: 2491-2498.

18. Rodés J, Domingo E, Candell J, et al. Specificity of exercise-dipyridamole Tc-99m-tetrofosmin myocardial tomography early after successful coronary stent implantation. Eur Heart J 1999; 20 Abstr. Suppl: 617.

19. Galassi AR, Foti R, Azzarelli S, et al. Usefulness of exercise tomographic myocardial perfusion imaging for detection of restenosis after coronary stent implantation. Am J Cardiol 2000; 85: 1362-1364.

20. Legrand V, Raskinet B, Laarman G, et al. Diagnostic value of exercise electrocardiography and angina after coronary artery stenting. Am Heart J 1997; 133: 240-248.

21. Grondin CM, Campeau L, Thornton JC, Emgle JC, Cross FS, Schreiber H. Coronary artery bypass grafting with saphenous vein. Circulation 1989; 79 (suppl 1): 24-9.

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25. Carballo J, Candell-Riera J, Aguadé-Bruix S, et al. Eficacia de la tomogammagrafía miocçardica en la valoración de la permeabilidad de los injertos aortocoronarios. Rev Esp Cardiol 2000; 53: 611-616.

26. Rasmussen SL, Nielsen SL, Amtorp O, Folke K, Fritz-Hansen P. 201-Thallium imaging as an indicator of graft patency after coronary artery bypass surgery . Eur Heart J 1984; 5: 494-499.

27. Pfisterer M, Emmenegger H, Schmitt HE, et al. Accurary of serial myocardial perfusion scintigraphy with thallium 201 for prediction of graft patency early and late after coronary artery bypass surgery. Circulation 1982; 66: 1017-1024.

28. Iskandrian AS, Haaz W, Segal BL, Kane SA. Exercise thallium-201 scintigraphy in evaluating aortocoronary bypass surgery. Chest 1981; 80: 11-15.

29. Lakkis NM ML, Mahmarian J, Verani MS. Exercise thallium-201 single photon emission computed tomography for evaluation of coronary artery bypass graft patency. Am J Cardiol 1995; 76: 107-111.

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31. Palmas W, Bingham S, Diamond GA, et al. Incremental prognostic value of exercise thallium-201 myocardial single photon emission computed tomography late after coronary artery bypass surgery. J Am Coll Cardiol 1995; 25: 403-409.

32. Zellweger MJ, Lewin HC, Lai S, et al. When to stress patients after coronary artery bypass surgery? Risk stratification in patients early and late post-CABG using stress myocardial perfusion SPECT: Implications of appropriate clinical strategies. J Am Coll Cardiol 2001; 37: 144-152.

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2nd Virtual Congress of Cardiology

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