- Email: [email protected]
Exercise thallium-201 single photon emission computed tomography for evaluation of coronary artery bypass graft patency
Exercise Thallium-20 1 Single Photon Emission Computed Tomography for Evaluation of Coronary Artery Bypass Graft Patency Nasser
M. Lakkis, MD, John J. Mahmarian,
Thallium-201 single photon emission computed tomography (SPECT) is superior to planar imaging for localizing native coronary stenoses, but has not yet been studied for assessing graft patency late after coronary artery bypass graft surgery (CABG). Accordingly, we studied 50 patients (40 males), aged 58 2 9 years (mean + SD), who presented for evaluation of angina (30 patients), atypical chest ain (20 patients), and other symptoms (9 patients), Pate after CABG (51 f 47 months). Patients with prior myocardial infarction were excluded. The mean ejection fraction was 58 + 17%. All patients underwent coronary angiography within 3 weeks of symptom-limited exercise thallium-201 SPECT. There were 119 rafts, of which 48 had ~50% stenoSPECT detected 40 sis by angiograp i! y. Thallium-201
MD, and Mario
S. Verani,
MD
of these 48 (83%) stenosed grafts. The sensitivity of thallium-201 SPECT for detecting any graft stenosis was higher than that of the exercise electrocardiogram in patients with typical recurrent an ina (84% vs 24%, p
7
gram) or progression of coronary disease in non-bypassedvessels were excluded becauseof the possibility of a confounding effecton the interpretation of the SPECT emission computed tomography (SPECT), performed images. The ejection fraction of this patient population was either during exercise or pharmacologic stress, has become a standarddiagnostic technique, largely because 58 f 17% (mean + SD). The slightly depressedejection of its high sensitivity and specificity for detecting native fraction in a few of the patients was possibly due to precoronary artery disease.1,2 The value of this test for vious non-Q-wave myocardial infarction, stunning, or assessmentof stenosisafter coronary artery bypass graft hibernation. Exercise testing: Patients performed a symptom-limsurgery (CABG) has not yet been established. Previous studies have evaluated planar thallium imaging as a ited exercise treadmill test using the standardBruce promeansto document improved myocardial perfusion after tocol. The electrocardiogram was monitored continuCABG or to detect early graft stenosis.3-5Since SPECT ously and a 1Zlead tracing was recorded at rest, at the is superior to planar imaging for identifying individual end of each exercise stage,and after 2,4, and 6 minutes coronary artery stenosis,one would anticipate that it can of recovery. Electrocardiographic ischemia was defined also accurately detect graft stenosis after CABG. as 1 mm horizontal or downsloping ST-segmentdepresAccordingly, the purpose of this study was to assessthe sion or 1 mm ST-segment elevation measured 80 ms utility of thallium-201 SPECT (compared with the exer- after the J point. cise electrocardiogram alone) in detecting graft stenosis Thallium-201 single photon emission computed tomoglate after CABG in patients presenting with or without raphy: Thallium imaging was performed according to typical angina pectoris. the standardprotocol in our laboratory. One minute before terminating exercise, 3.0 mCi of thallium-201 was METHODS injected intravenously. SPECT imaging began 10 minPatient population: The study cohort comprised50 con- utes after completion of exercise and was repeated 4 secutive patients with prior CABG who had graft con- hours later. Thirty-two imageswere acquired over a 180” trast angiography within 3 weeks of exercise thallium anterior arc, using a high-resolution collimator. Oblique SPECK Patients who had prior myocardial infarction (by reconstruction was performed with reorientation into history and pathological Q waves on the electrocardio- short, horizontal, and vertical long axes.Myocardial segments were visually interpreted in all 3 standardplanes. From the Section of Cardiology, Department of Medicine, Baylor ColThallium-201 activity in each myocardial segment was lege of Medicine, The Methodist Hospital, Houston, Texas. Manuscored as normal, decreased,or absent.Myocardial perscript received February 22, 1995; revised manuscript received and fusion defects were quantified using methods from our accepted May 15, 1995. laboratory aspreviously described.l Thallium-201 SPECT Address for reprints: Mario S. Verani, MD, Director, Nuclear Carwas performed before coronary angiography in 37 padiology, Baylor College of Medicine, The Methodist Hospital, 6535 Fannin, F-905, Houston, Texas 77030. tients and after angiography in 13 patients. In the latter uring the last decade, radionuclide approachesfor D evaluating myocardial perfusion and function have improved considerably. Thallium-201 single photon
CORONARY
ARTERY DISEASE/THALLIUM-201
TOMOGRAPHY
AFTER CORONARY
BYPASS GRAFT SURGERY
107
TABLE I Patient Characteristics No. Sex [M/F) Mean age (years, f SD) Angina (no. patients) Atypical chest pain (no. patients) Time from CABG (mo) Ejection fraction (%) No. of stenosed native arteries/patient Total no. of grafts Internal mammary graft Total no. of stenosed grafts Stenosed internal mammary graft Total no. of patent grofts with distal disease Medications (%) B-blockers Calcium antagonists Digitalis Aspirin Abnormal baseline electrocardiogram (%)
58 iz 30 20 52 * 58* 2.3 zt 119
9
47 17 1.6
ii 4 10 17 (34) 27 (54)
Exercise treadmill test: With exercise, 25 patients reached 85% of their target heart rate and 25 patients had a submaximal test. The average exercise time was 6.4 rt 3.6 minutes. The mean maximal heart rate attained was 133 r+ 31 beats/min and the mean double product was 20,700 f 5,400 mm Hg.min-l. There was no significant difference in exercise time, maximal heart rate, or double product in patients with patent (n = 15) or stenotic grafts (n = 35). Only 12 patients developed ischemic ST-segment depression during exercise. An additional 6 patients had nondiagnostic electrocardiographic changessecondary to left bundle branch block, left ventricular hypertrophy, or digitalis therapy. Exercise electrocardiogram and thallium-201 SPECTin patients with sfenofic and patent grafts: Thirty-five of 50
patients had at least 1 stenotic coronary bypassgraft. As shown in Figure 1, the sensitivity, specificity, and predictive accuracy of thallium-201 SPECT to detect graft Results expressed as mecln f SD or number of patients u&s otherwise noted. stenosislate after CABG were all high (SO%,87%, 82%, respectively). Conversely,the exerciseelectrocardiogram subjects, SPECT was carried out to assessthe function- had a sensitivity of only 31%, with a specificity of 93% al significance of stenosesobserved in the native vessels and predictive accuracy of 50%. Of the 119coronary bypass grafts placed at surgery, or grafts. Coronary angiography: All patients underwent diag- 48 had significant luminal diameter narrowing (>50%) nostic coronary angiographv within 3 weeks of SPECT. by angiography. Thallium-201 SPECT detected40 of 48 Coronary angibgramswere visually interpreted by cardi- (83%) stenosedgrafts with the perfusion defects correologists not involved with the radionuclide test. A >50% sponding to the proper vascular territory. Eighty-five perstenosisin the grafts or in the native arteries distal to the cent of the defects were either totally or predominantly anastomosis site was considered significant. Left ven- reversible, whereas 15% were fixed. The mean perfusion tricular wall motion was analyzed by contrast left ven- defect size was 17 + 8% of the left ventricle. Of the 10 triculography and/or 2-dimensional echocardiography. patent grafts with a corresponding SPECT defect in their Statistical analysis: Results are reported as mean + vascular territory, half were in patients with distal native SD. Student’s t test for paired samples and chi-square vessel diseasein the bypassedvessels; the remaining 5 test for categorical variables were used to compare re- occurred in patients with either left bundle branch block sults of SPECT and electrocardiography.A p value ~0.05 (n = 2) or left ventricular hypertrophy (n = 3). Thallium-201 SPECTfor location of graft stenosis: The was considered significant. ability of thallium-201 SPECT to localize stenosedgrafts is summarizedin Table II. Of 28 patients with a stenosed RESULTS The clinical characteristics of the study cohort are left anterior descendingartery graft, 23 (82%) had a persummarized in Table I. Stenotic grafts were observed in fusion defect involving the anteroseptal, anterolateral, 25 of 30 patients who had typical exertional angina pec- and/or apical regions. Eleven of 12 patients with a stetoris and 10 of 20 patients who had atypical chest pain nosed graft to the right coronary artery had a defect in the inferoposterior or apical segments,whereas 6 of 8 patterns (p
P<0.0001
80 @
FIGURE 1. Sensitivity, specificity, and predictive accuracy of exercise thallium-20 1 sin le photon emission computed tomograpll y (SPECT) and exercise elecirocardiography (ECG) in the total study cohort.
60
Percentage 40
I
Sensitivity
108
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OF CARDIOLOGY@
Accuracy
VOL. 76
JULY 15,
1995
TABLE II Diagnostic Stenosed Grafts
Ability
of Thallium-201
Graft to: Left anterior descending Right coronary artery Circumflex artery
Single Photon Emission Computed
Stenosed Grafts
Matching Thallium Defects
Sensitivity
(No.1
(No.)
PI
28 12
23 11
82 92
8
6
75
artery
patients with a stenosedgraft to the circutiex artery or its branches had perfusion defects in the lateral or posterolateral walls. Figure 2 illustrates a patient with stenosedgrafts late after CABG. The vascular locations of the perfusion defects in this patient closely matched those of the stenosedgrafts. The sensitivity, specificity, and positive and negative predictive values of thallium201 SPECT to localize all graft stenoseswere 83%, 85%, 77%, and 90%, respectively. Thallium-201 To SYMPTOMS:
SPECT versus graft patency:
RELATION
Patients presenting with typical angina
Tomography
to localize
Positive Predictive Value
Negative Predictive Value
(“V
WI
(“4
90 91
85 85
88 95
75
60
86
Specificiv
were more likely to have stenotic grafts (83%) than those with atypical symptoms (50%) (p
FIGURE 2. Example of a patient with an ischemic anterior, septal, apical, and mixed inferoposterior defect. This patient had a high-grade stenosis in the left anterior descending and right coronary grafts. HL = horizontal long axis; VL = vertical long axis; ZgJg FC= polar map depictivg completeness of redjstribution (amber depicts 60% filling; qren flepick r30 but <60% filling); lar map deplctmg the overall defect size (dark green deplck areas with redlstrlbuhon and black depicts regions with a fixed de =lz t); SDCOMP SS = polar ma de icting severity of hypoperfusion (amber depick a ~60% tracer activity, green depicts a tracer activity r30 but <60% and b Pcf ue epick a tracer activity <30%).
CORONARY
ARTERY DISEASE/THALIIUM-201
TOMOGRAPHY
AFTER CORONARY
BYPASS GRAFT SURGERY
109
TABLE III Diagnosis Computed
of Graft Stenosis by Single Photon Emission Tomography (SPECT) and Electrocardiography (ECG)
Sensitivity
Specificity
Wd
(“V Typical
SPECT ECG
84 24
SPECT ECG
70 50
Positive Predictive Value (%)
Negative Predictive Value (%)
Chest Pain 80 80
Atypical
95 86
50 17
87 100
75 67
Chest Pain 90 100
dictive value of thallium-201 SPECT was higher than that of exercise electrocardiogram in patients with typical angina (p
DISCUSSION Significance of chest pain after coronary bypass graft surgery: Recurrent chest pain or the appearanceof other
symptoms after CABG may be multifactorial in origin. Myocardial ischemia,due either to graft occlusion or progression of diseasein both grafted and ungrafted vessels, is the major concern. Alternatively, the symptoms may be noncardiac and related to patient fear or anxiety. Previous studies have concluded that symptoms are not reliable predictors of graft patency or stenosis.c8 For example, Di Luzio et al7 reported relief of angina in 5 previously symptomatic patients, despite the occurrence of a perioperative infarction and occluded coronary bypass grafts. Similarly, Benchimol et al* reported on 12 patients with occluded grafts, of whom 4 were minimally symptomatic and the remainder asymptomatic. In our cohort, 83% of patients presenting with typical angina had stenotic grafts, whereas50% of those with atypical chest pain syndrome also had graft stenoses. Importantly, in our study, we deliberately focused on patients who had undergone CABG several years earlier becauseit is well known that graft patency is high in the fist years after CABG, but precipitously decreases 5 or more years following surgery.9Because the focus of our investigation was late detection of graft stenosis, we excluded patients with progression of diseasein nongrafted vessels.Inclusion of such patients would further hamper our ability to ascribe perfusion defects to specific grafts. It is also important to acknowledge that SPECT perfusion imaging cannot differentiate between graft stenosis and stenosis in the native coronary artery distal to the graft insertion site. Exercise testing for assessing graft patency: The exercise electrocardiogram alone provides only limited information regarding graft patency or occlusion,10in part becausepatients often have either decreasedexercisetolerance or are being treated with multiple antiischemic medications. Other patients have nonspecific postopera110
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tive electrocardiographic changes and/or left bundle branch block, which may preclude analysis of ST-segment changes.Furthermore, Bartel et ali0 reported that 57% of patients with occluded grafts following CABG had improved exercise tolerance, 39% had no exerciseinduced angina, and 36% had normalization of previous exercise-induced ST-segment changes. In our study cohort, in which 35 patients (70%) had at least 1 stenosed graft, only 11 (31%) had ischemic changeson the exercise electrocardiogram. Thus, the development of angina and/or electrocardiographic ischemia during exercise testing are both inaccurate predictors of graft patency status. Thallium-201 scintigraphy for assessing coronary bypass graft surgery: Most previous studies assessingthe use of
myocardial perfusion scintigraphy after CABG were performed relatively early after surgery and were designed to demonstrateimproved myocardial perfusion.“J* Pfisterer et all3 evaluated the patency status of saphenous venous grafts in 55 patients who presented 2 weeks to 1 year after CABG. Planar thallium-201 imaging had an 80% sensitivity and 88% specificity for detecting grafts found to be occluded at angiography. However, the vascular territory of the occluded grafts could only be accurately localized in 61% of the cases,in keeping with the poor ability of planar imaging to localize stenosesto specific coronary arteries. Rasmussenet all4 studied 41 patients 6 months after CABG and concluded that planar thallium-201 scintigraphy had 71% sensitivity and 94% specificity to detect occluded grafts. The positive predictive value of the test was 79% and the negative predictive value was 91%. Our sensitivity using SPECT imaging was somewhat higher (83%). To our knowledge, the present study is the first to evaluate SPECT imaging for detection and localization of stenosedvenous grafts late after CABG. This method is shown to be far superior to symptom assessmentalone or electrocardiography exercise testing for this purpose. Moreover, when compared with previous reports, SPECT achieved a higher sensitivity than planar scintigraphy for detecting14 or localizing13 stenosed grafts. Interestingly, in our study thallium-201 SPECT had a high accuracy for predicting graft stenosis even in the difficult group of patients who presented with atypical symptoms. In these patients, a thallium defect was a good indicator of graft stenosis; conversely, when the thallium-201 SPECT was normal, the grafts were patent in the majority of patients. Unfortunately, we did not evaluate the impact of a positive thallium-201 SPECT study on patient managementand outcome. However, a recent report by Palmaset all5 showed that routine thallium SPECT testing (compared with exercise testing alone) provided incremental prognostic information in patients late after CABG. Future studies are warranted to determine whether the identification of patients with occluded grafts by thallium-201 SPECT would have an impact on clinical outcome. 1. Mabmarian JJ, Boyce TM, Goldberg RK, Cocanougher MK, Roberts R, Verani MS. Quantitative exercise thallium-201 single photon emission tomography for the enhanced diagnosis of ischemic heart disease. JAm Co/l Car&A 1990;15:318-329.
JULY 15,
1995
2. Kiat H, Berman DS, Maddahi J. Comparison of planar and tomographic exercise thallium-201 imaging methods for the evaluation of coronary artery disease. J Am Co11 Cardiol 1989;13:613616. 3. Zaret BL, Martin ND, McGowan RL, Strauss HW, Wells HP Jr, Flamm MD Jr. Rest and exercise potassium-43 myocardial perfusion imaging for the noninvasive evaluation or aortocoronary bypass surgery. Circulation 1974;49:688-695. 4. Verani MS, Marcus ML, Spot0 G, Rossi NP, Ehrhardt JC, Razzak MA. Thallium-201 myocardial perfusion scintigrams in the evaluation of aorta-coronary saphenous bypass surgery. J Nucl Med 1978;19:765-772. 5. Iskandrian AS, Haaz W, Segal BL, Kane SA. Exercise thallium-201 scintigraphy in evaluating aorta-coronary bypass surgery. Chest 1981;80:11-15. 6. Hirzel HO, Sailer G, Hurst W, Kmyenbuebl HP. Thallium-201 exercise myocardial imaging to evaluate myocardial perfusion after coronary artery bypass surgery. Br Hear? .I 1980;43:426435. 7. Di Luzio V, Roy PR, Sowton E. Angina in patients with occluded aorto-coronary vein grafts. Br Hean J 197436:139-147. 8. Benchimol A, dos Santos A, Desser KB. Relief of angina pectoris in patients with occluded coronary bypass grafts. Am J Med 1976;60:338-343. 9. Campeau L, Lesperance .I, Hermann .I, Corbam F, Grondin CM, Bourassa MG. Loss of the improvement of angina between 1 and 7 years after aottocoronary bypass surgery. Circulation 1979;6O(Suppl 1):1-l-I- 13.
CORONARY
ARTERY DISEASE/THALLIUM-201
10. Bartel AG, Behar VS, Peter RH, Orgain ES, Kong Y. Exercise stress testing in evaluation of aottocoronary bypass surgery: report of 123 patients. Circulation 1973;48:141-148. 11. Ritchie JL, Narahara KA, Trobaugb GB, Williams DL, Hamilton GW. Thallium-201 myocardial imaging before and after coronary revascularization assessment of regional myocardial blood flow and graft patency. Circulation 1977;56:83&836. 12. Gibson RS, Watson DD, Taylor Gl, Crosby IK, Wellons HL, Holt ND, Belier GA. Prospective assessment of regional myocardial perfasion before and after mvascularization surgery by quantitative thallium-201 scintigraphy. J Am Co11 Cardiol 1983;1:8&815. 13. Pfisterer M, Emmenegger H, Schmitt HE, Moller-Brand J, Hasse J, Grade1 E, Laver MB, Borckhardt D, Bmkart F. Accuracy of serial myocardird perfusion scintigraphy with thallium-201 for prediction of gmft patency early and late after coromuy may bypass surgery: a contmlled prospective study. Circulaiion 198266: 1017-1024. 14. Rasmussen SL, Nielsen SL, Amtorp 0, Folke K, Fritz-Hansen P. 201 thallium imaging as an indicator of graft patency after coronary artery bypass surgery. Eur Hemi J 1984;5:494499. 15. Palmas W, Bingham S, Diamond GA, Deaton TA, Kiat H, Friedman JD, Scarlata D, Maddabi J, Cohen I, Berman DS. Incremental prognostic value of exercise thallium-201 myocardial single-photon emission computed tomography late after coronary artery bypass surgery. J Am Coil Cardiol 1995;25:403409.
TOMOGRAPHY
AFTER CORONARY
BYPASS GRAFT SURGERY
111
M. Lakkis, MD, John J. Mahmarian,
Thallium-201 single photon emission computed tomography (SPECT) is superior to planar imaging for localizing native coronary stenoses, but has not yet been studied for assessing graft patency late after coronary artery bypass graft surgery (CABG). Accordingly, we studied 50 patients (40 males), aged 58 2 9 years (mean + SD), who presented for evaluation of angina (30 patients), atypical chest ain (20 patients), and other symptoms (9 patients), Pate after CABG (51 f 47 months). Patients with prior myocardial infarction were excluded. The mean ejection fraction was 58 + 17%. All patients underwent coronary angiography within 3 weeks of symptom-limited exercise thallium-201 SPECT. There were 119 rafts, of which 48 had ~50% stenoSPECT detected 40 sis by angiograp i! y. Thallium-201
MD, and Mario
S. Verani,
MD
of these 48 (83%) stenosed grafts. The sensitivity of thallium-201 SPECT for detecting any graft stenosis was higher than that of the exercise electrocardiogram in patients with typical recurrent an ina (84% vs 24%, p
7
gram) or progression of coronary disease in non-bypassedvessels were excluded becauseof the possibility of a confounding effecton the interpretation of the SPECT emission computed tomography (SPECT), performed images. The ejection fraction of this patient population was either during exercise or pharmacologic stress, has become a standarddiagnostic technique, largely because 58 f 17% (mean + SD). The slightly depressedejection of its high sensitivity and specificity for detecting native fraction in a few of the patients was possibly due to precoronary artery disease.1,2 The value of this test for vious non-Q-wave myocardial infarction, stunning, or assessmentof stenosisafter coronary artery bypass graft hibernation. Exercise testing: Patients performed a symptom-limsurgery (CABG) has not yet been established. Previous studies have evaluated planar thallium imaging as a ited exercise treadmill test using the standardBruce promeansto document improved myocardial perfusion after tocol. The electrocardiogram was monitored continuCABG or to detect early graft stenosis.3-5Since SPECT ously and a 1Zlead tracing was recorded at rest, at the is superior to planar imaging for identifying individual end of each exercise stage,and after 2,4, and 6 minutes coronary artery stenosis,one would anticipate that it can of recovery. Electrocardiographic ischemia was defined also accurately detect graft stenosis after CABG. as 1 mm horizontal or downsloping ST-segmentdepresAccordingly, the purpose of this study was to assessthe sion or 1 mm ST-segment elevation measured 80 ms utility of thallium-201 SPECT (compared with the exer- after the J point. cise electrocardiogram alone) in detecting graft stenosis Thallium-201 single photon emission computed tomoglate after CABG in patients presenting with or without raphy: Thallium imaging was performed according to typical angina pectoris. the standardprotocol in our laboratory. One minute before terminating exercise, 3.0 mCi of thallium-201 was METHODS injected intravenously. SPECT imaging began 10 minPatient population: The study cohort comprised50 con- utes after completion of exercise and was repeated 4 secutive patients with prior CABG who had graft con- hours later. Thirty-two imageswere acquired over a 180” trast angiography within 3 weeks of exercise thallium anterior arc, using a high-resolution collimator. Oblique SPECK Patients who had prior myocardial infarction (by reconstruction was performed with reorientation into history and pathological Q waves on the electrocardio- short, horizontal, and vertical long axes.Myocardial segments were visually interpreted in all 3 standardplanes. From the Section of Cardiology, Department of Medicine, Baylor ColThallium-201 activity in each myocardial segment was lege of Medicine, The Methodist Hospital, Houston, Texas. Manuscored as normal, decreased,or absent.Myocardial perscript received February 22, 1995; revised manuscript received and fusion defects were quantified using methods from our accepted May 15, 1995. laboratory aspreviously described.l Thallium-201 SPECT Address for reprints: Mario S. Verani, MD, Director, Nuclear Carwas performed before coronary angiography in 37 padiology, Baylor College of Medicine, The Methodist Hospital, 6535 Fannin, F-905, Houston, Texas 77030. tients and after angiography in 13 patients. In the latter uring the last decade, radionuclide approachesfor D evaluating myocardial perfusion and function have improved considerably. Thallium-201 single photon
CORONARY
ARTERY DISEASE/THALLIUM-201
TOMOGRAPHY
AFTER CORONARY
BYPASS GRAFT SURGERY
107
TABLE I Patient Characteristics No. Sex [M/F) Mean age (years, f SD) Angina (no. patients) Atypical chest pain (no. patients) Time from CABG (mo) Ejection fraction (%) No. of stenosed native arteries/patient Total no. of grafts Internal mammary graft Total no. of stenosed grafts Stenosed internal mammary graft Total no. of patent grofts with distal disease Medications (%) B-blockers Calcium antagonists Digitalis Aspirin Abnormal baseline electrocardiogram (%)
58 iz 30 20 52 * 58* 2.3 zt 119
9
47 17 1.6
ii 4 10 17 (34) 27 (54)
Exercise treadmill test: With exercise, 25 patients reached 85% of their target heart rate and 25 patients had a submaximal test. The average exercise time was 6.4 rt 3.6 minutes. The mean maximal heart rate attained was 133 r+ 31 beats/min and the mean double product was 20,700 f 5,400 mm Hg.min-l. There was no significant difference in exercise time, maximal heart rate, or double product in patients with patent (n = 15) or stenotic grafts (n = 35). Only 12 patients developed ischemic ST-segment depression during exercise. An additional 6 patients had nondiagnostic electrocardiographic changessecondary to left bundle branch block, left ventricular hypertrophy, or digitalis therapy. Exercise electrocardiogram and thallium-201 SPECTin patients with sfenofic and patent grafts: Thirty-five of 50
patients had at least 1 stenotic coronary bypassgraft. As shown in Figure 1, the sensitivity, specificity, and predictive accuracy of thallium-201 SPECT to detect graft Results expressed as mecln f SD or number of patients u&s otherwise noted. stenosislate after CABG were all high (SO%,87%, 82%, respectively). Conversely,the exerciseelectrocardiogram subjects, SPECT was carried out to assessthe function- had a sensitivity of only 31%, with a specificity of 93% al significance of stenosesobserved in the native vessels and predictive accuracy of 50%. Of the 119coronary bypass grafts placed at surgery, or grafts. Coronary angiography: All patients underwent diag- 48 had significant luminal diameter narrowing (>50%) nostic coronary angiographv within 3 weeks of SPECT. by angiography. Thallium-201 SPECT detected40 of 48 Coronary angibgramswere visually interpreted by cardi- (83%) stenosedgrafts with the perfusion defects correologists not involved with the radionuclide test. A >50% sponding to the proper vascular territory. Eighty-five perstenosisin the grafts or in the native arteries distal to the cent of the defects were either totally or predominantly anastomosis site was considered significant. Left ven- reversible, whereas 15% were fixed. The mean perfusion tricular wall motion was analyzed by contrast left ven- defect size was 17 + 8% of the left ventricle. Of the 10 triculography and/or 2-dimensional echocardiography. patent grafts with a corresponding SPECT defect in their Statistical analysis: Results are reported as mean + vascular territory, half were in patients with distal native SD. Student’s t test for paired samples and chi-square vessel diseasein the bypassedvessels; the remaining 5 test for categorical variables were used to compare re- occurred in patients with either left bundle branch block sults of SPECT and electrocardiography.A p value ~0.05 (n = 2) or left ventricular hypertrophy (n = 3). Thallium-201 SPECTfor location of graft stenosis: The was considered significant. ability of thallium-201 SPECT to localize stenosedgrafts is summarizedin Table II. Of 28 patients with a stenosed RESULTS The clinical characteristics of the study cohort are left anterior descendingartery graft, 23 (82%) had a persummarized in Table I. Stenotic grafts were observed in fusion defect involving the anteroseptal, anterolateral, 25 of 30 patients who had typical exertional angina pec- and/or apical regions. Eleven of 12 patients with a stetoris and 10 of 20 patients who had atypical chest pain nosed graft to the right coronary artery had a defect in the inferoposterior or apical segments,whereas 6 of 8 patterns (p
P<0.0001
80 @
FIGURE 1. Sensitivity, specificity, and predictive accuracy of exercise thallium-20 1 sin le photon emission computed tomograpll y (SPECT) and exercise elecirocardiography (ECG) in the total study cohort.
60
Percentage 40
I
Sensitivity
108
THE AMERICAN
JOURNAL
Specificity
OF CARDIOLOGY@
Accuracy
VOL. 76
JULY 15,
1995
TABLE II Diagnostic Stenosed Grafts
Ability
of Thallium-201
Graft to: Left anterior descending Right coronary artery Circumflex artery
Single Photon Emission Computed
Stenosed Grafts
Matching Thallium Defects
Sensitivity
(No.1
(No.)
PI
28 12
23 11
82 92
8
6
75
artery
patients with a stenosedgraft to the circutiex artery or its branches had perfusion defects in the lateral or posterolateral walls. Figure 2 illustrates a patient with stenosedgrafts late after CABG. The vascular locations of the perfusion defects in this patient closely matched those of the stenosedgrafts. The sensitivity, specificity, and positive and negative predictive values of thallium201 SPECT to localize all graft stenoseswere 83%, 85%, 77%, and 90%, respectively. Thallium-201 To SYMPTOMS:
SPECT versus graft patency:
RELATION
Patients presenting with typical angina
Tomography
to localize
Positive Predictive Value
Negative Predictive Value
(“V
WI
(“4
90 91
85 85
88 95
75
60
86
Specificiv
were more likely to have stenotic grafts (83%) than those with atypical symptoms (50%) (p
FIGURE 2. Example of a patient with an ischemic anterior, septal, apical, and mixed inferoposterior defect. This patient had a high-grade stenosis in the left anterior descending and right coronary grafts. HL = horizontal long axis; VL = vertical long axis; ZgJg FC= polar map depictivg completeness of redjstribution (amber depicts 60% filling; qren flepick r30 but <60% filling); lar map deplctmg the overall defect size (dark green deplck areas with redlstrlbuhon and black depicts regions with a fixed de =lz t); SDCOMP SS = polar ma de icting severity of hypoperfusion (amber depick a ~60% tracer activity, green depicts a tracer activity r30 but <60% and b Pcf ue epick a tracer activity <30%).
CORONARY
ARTERY DISEASE/THALIIUM-201
TOMOGRAPHY
AFTER CORONARY
BYPASS GRAFT SURGERY
109
TABLE III Diagnosis Computed
of Graft Stenosis by Single Photon Emission Tomography (SPECT) and Electrocardiography (ECG)
Sensitivity
Specificity
Wd
(“V Typical
SPECT ECG
84 24
SPECT ECG
70 50
Positive Predictive Value (%)
Negative Predictive Value (%)
Chest Pain 80 80
Atypical
95 86
50 17
87 100
75 67
Chest Pain 90 100
dictive value of thallium-201 SPECT was higher than that of exercise electrocardiogram in patients with typical angina (p
DISCUSSION Significance of chest pain after coronary bypass graft surgery: Recurrent chest pain or the appearanceof other
symptoms after CABG may be multifactorial in origin. Myocardial ischemia,due either to graft occlusion or progression of diseasein both grafted and ungrafted vessels, is the major concern. Alternatively, the symptoms may be noncardiac and related to patient fear or anxiety. Previous studies have concluded that symptoms are not reliable predictors of graft patency or stenosis.c8 For example, Di Luzio et al7 reported relief of angina in 5 previously symptomatic patients, despite the occurrence of a perioperative infarction and occluded coronary bypass grafts. Similarly, Benchimol et al* reported on 12 patients with occluded grafts, of whom 4 were minimally symptomatic and the remainder asymptomatic. In our cohort, 83% of patients presenting with typical angina had stenotic grafts, whereas50% of those with atypical chest pain syndrome also had graft stenoses. Importantly, in our study, we deliberately focused on patients who had undergone CABG several years earlier becauseit is well known that graft patency is high in the fist years after CABG, but precipitously decreases 5 or more years following surgery.9Because the focus of our investigation was late detection of graft stenosis, we excluded patients with progression of diseasein nongrafted vessels.Inclusion of such patients would further hamper our ability to ascribe perfusion defects to specific grafts. It is also important to acknowledge that SPECT perfusion imaging cannot differentiate between graft stenosis and stenosis in the native coronary artery distal to the graft insertion site. Exercise testing for assessing graft patency: The exercise electrocardiogram alone provides only limited information regarding graft patency or occlusion,10in part becausepatients often have either decreasedexercisetolerance or are being treated with multiple antiischemic medications. Other patients have nonspecific postopera110
THE AMERICAN
JOURNAL
OF CARDIOLOGYa
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tive electrocardiographic changes and/or left bundle branch block, which may preclude analysis of ST-segment changes.Furthermore, Bartel et ali0 reported that 57% of patients with occluded grafts following CABG had improved exercise tolerance, 39% had no exerciseinduced angina, and 36% had normalization of previous exercise-induced ST-segment changes. In our study cohort, in which 35 patients (70%) had at least 1 stenosed graft, only 11 (31%) had ischemic changeson the exercise electrocardiogram. Thus, the development of angina and/or electrocardiographic ischemia during exercise testing are both inaccurate predictors of graft patency status. Thallium-201 scintigraphy for assessing coronary bypass graft surgery: Most previous studies assessingthe use of
myocardial perfusion scintigraphy after CABG were performed relatively early after surgery and were designed to demonstrateimproved myocardial perfusion.“J* Pfisterer et all3 evaluated the patency status of saphenous venous grafts in 55 patients who presented 2 weeks to 1 year after CABG. Planar thallium-201 imaging had an 80% sensitivity and 88% specificity for detecting grafts found to be occluded at angiography. However, the vascular territory of the occluded grafts could only be accurately localized in 61% of the cases,in keeping with the poor ability of planar imaging to localize stenosesto specific coronary arteries. Rasmussenet all4 studied 41 patients 6 months after CABG and concluded that planar thallium-201 scintigraphy had 71% sensitivity and 94% specificity to detect occluded grafts. The positive predictive value of the test was 79% and the negative predictive value was 91%. Our sensitivity using SPECT imaging was somewhat higher (83%). To our knowledge, the present study is the first to evaluate SPECT imaging for detection and localization of stenosedvenous grafts late after CABG. This method is shown to be far superior to symptom assessmentalone or electrocardiography exercise testing for this purpose. Moreover, when compared with previous reports, SPECT achieved a higher sensitivity than planar scintigraphy for detecting14 or localizing13 stenosed grafts. Interestingly, in our study thallium-201 SPECT had a high accuracy for predicting graft stenosis even in the difficult group of patients who presented with atypical symptoms. In these patients, a thallium defect was a good indicator of graft stenosis; conversely, when the thallium-201 SPECT was normal, the grafts were patent in the majority of patients. Unfortunately, we did not evaluate the impact of a positive thallium-201 SPECT study on patient managementand outcome. However, a recent report by Palmaset all5 showed that routine thallium SPECT testing (compared with exercise testing alone) provided incremental prognostic information in patients late after CABG. Future studies are warranted to determine whether the identification of patients with occluded grafts by thallium-201 SPECT would have an impact on clinical outcome. 1. Mabmarian JJ, Boyce TM, Goldberg RK, Cocanougher MK, Roberts R, Verani MS. Quantitative exercise thallium-201 single photon emission tomography for the enhanced diagnosis of ischemic heart disease. JAm Co/l Car&A 1990;15:318-329.
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2. Kiat H, Berman DS, Maddahi J. Comparison of planar and tomographic exercise thallium-201 imaging methods for the evaluation of coronary artery disease. J Am Co11 Cardiol 1989;13:613616. 3. Zaret BL, Martin ND, McGowan RL, Strauss HW, Wells HP Jr, Flamm MD Jr. Rest and exercise potassium-43 myocardial perfusion imaging for the noninvasive evaluation or aortocoronary bypass surgery. Circulation 1974;49:688-695. 4. Verani MS, Marcus ML, Spot0 G, Rossi NP, Ehrhardt JC, Razzak MA. Thallium-201 myocardial perfusion scintigrams in the evaluation of aorta-coronary saphenous bypass surgery. J Nucl Med 1978;19:765-772. 5. Iskandrian AS, Haaz W, Segal BL, Kane SA. Exercise thallium-201 scintigraphy in evaluating aorta-coronary bypass surgery. Chest 1981;80:11-15. 6. Hirzel HO, Sailer G, Hurst W, Kmyenbuebl HP. Thallium-201 exercise myocardial imaging to evaluate myocardial perfusion after coronary artery bypass surgery. Br Hear? .I 1980;43:426435. 7. Di Luzio V, Roy PR, Sowton E. Angina in patients with occluded aorto-coronary vein grafts. Br Hean J 197436:139-147. 8. Benchimol A, dos Santos A, Desser KB. Relief of angina pectoris in patients with occluded coronary bypass grafts. Am J Med 1976;60:338-343. 9. Campeau L, Lesperance .I, Hermann .I, Corbam F, Grondin CM, Bourassa MG. Loss of the improvement of angina between 1 and 7 years after aottocoronary bypass surgery. Circulation 1979;6O(Suppl 1):1-l-I- 13.
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10. Bartel AG, Behar VS, Peter RH, Orgain ES, Kong Y. Exercise stress testing in evaluation of aottocoronary bypass surgery: report of 123 patients. Circulation 1973;48:141-148. 11. Ritchie JL, Narahara KA, Trobaugb GB, Williams DL, Hamilton GW. Thallium-201 myocardial imaging before and after coronary revascularization assessment of regional myocardial blood flow and graft patency. Circulation 1977;56:83&836. 12. Gibson RS, Watson DD, Taylor Gl, Crosby IK, Wellons HL, Holt ND, Belier GA. Prospective assessment of regional myocardial perfasion before and after mvascularization surgery by quantitative thallium-201 scintigraphy. J Am Co11 Cardiol 1983;1:8&815. 13. Pfisterer M, Emmenegger H, Schmitt HE, Moller-Brand J, Hasse J, Grade1 E, Laver MB, Borckhardt D, Bmkart F. Accuracy of serial myocardird perfusion scintigraphy with thallium-201 for prediction of gmft patency early and late after coromuy may bypass surgery: a contmlled prospective study. Circulaiion 198266: 1017-1024. 14. Rasmussen SL, Nielsen SL, Amtorp 0, Folke K, Fritz-Hansen P. 201 thallium imaging as an indicator of graft patency after coronary artery bypass surgery. Eur Hemi J 1984;5:494499. 15. Palmas W, Bingham S, Diamond GA, Deaton TA, Kiat H, Friedman JD, Scarlata D, Maddabi J, Cohen I, Berman DS. Incremental prognostic value of exercise thallium-201 myocardial single-photon emission computed tomography late after coronary artery bypass surgery. J Am Coil Cardiol 1995;25:403409.
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