670 JACC Vol. 17, No.3 March I, 1991:670-7

Silent Ischemia After Coronary Angioplasty: Evaluation of Restenosis and Extent of Ischemia in Asymptomatic Patients by Tomographic Thallium-20l Exercise Imaging and Comparison With Symptomatic Patients

HARVEY s. HECHT, MD, FACC, RICHARD E. SHAW, PHD, HENRY L. CHIN, MD, COLMAN RYAN, MD, FACC, SIMON H. STERTZER, MD, FACC, RICHARD K. MYLER, MD, FACC Daly City, California

One hundred sixteen patients were evaluated to determine the ability of single photon emission computed tomographic (SPECT) thallium-201 exercise and redistribution imaging to detect silent ischemia secondary to restenosis in asymptomatic patients after single and multiple vessel percutaneous transluminal coronary angioplasty and the findings were compared with SPECT imaging detection of restenosis in symptomatic patients. The value of exercise electrocardiography (ECG) and the amount of ischemic myocardium in symptomatic and asymptomatic patients were determined. Forty-one patients were asymptomatic after angio­plasty; 77% of these had chest pain before angioplasty. Seventy­five patients had chest pain after angioplasty; 99% of these had chest pain before angioplasty.

Restenosis occurred in 61 % of asymptomatic and 59% of symptomatic patients and in 46 % of the vessels in both asympto­matic and symptomatic patients. Sensitivity, specificity and accu­racy for detection of restenosis by SPECT in individual patients were 96%, 75% and 88% versus 91 %, 77% and 85%, respec­tively, in the asymptomatic versus symptomatic groups (p = NS).

After coronary angioplasty, 19% to 33% of patients with restenosis are asymptomatic (1-3). These patients are at high risk for the consequences of silent ischemia. The purpose of this study was to determine the role of single photon emission computed tomographic (SPECT) thallium-201 ex­ercise and redistribution imaging in the evaluation of silent ischemia secondary to restenosis in asymptomatic patients after coronary angioplasty and to compare it with the eval­uation of symptomatic patients with respect to detection of restenosis and amount of ischemic myocardium and compar­ison with exercise electrocardiography (ECG).

From the San Francisco Heart Institute, Seton Medical Center, Daly City, California.

Manuscript received April 27, 1991; revised manuscript received Septem­ber 19, 1990, accepted September 26, 1990.

Address for reprints: Harvey S. Hecht, MD, San Francisco Heart Institute, Seton Medical Center, 1900 Sullivan Avenue, Daly City, California 94015.

©1991 by the American College of Cardiology

Sensitivity, specificity and accuracy for restenosis detection in individual vessels were 90%,89% and 89% versus 84%,77% and 84%, respectively, in the asymptomatic and symptomatic groups (p = NS), with similar results for the three major arteries. Sensitivity and accuracy of exercise ECG were significantly less than those ofSPECT imaging for the patients with silent (40% and 44%) and symptomatic (59% and 64%) ischemia (p < 0.001). Restenosis of vessels in the patients with silent and symptomatic ischemia was associated with an equal amount and degree of severity of ischemic myocardium in the two groups.

It is concluded that 1) restenosis may occur without angina despite the presence of angina before coronary angioplasty. 2) Exercise ECG is inaccurate in detecting silent ischemia result­ing from restenosis. 3) SPECT accurately identifies restenosis in both asymptomatic and symptomatic patients. 4) The amount of ischemic myocardium does not differ in silent and symptomatic restenosis.

(J Am Coll CardioI1991;17:670-7)

Methods Study patients. The study group consisted of 116 consec­

utive patients referred for evaluation of possible restenosis after angioplasty. These patients underwent SPECT thallium imaging within 1 week before coronary angiography. The mean time of referral was 6 months after angioplasty. Forty-one patients were entirely asymptomatic after angio­pia sty and constitute the silent ischemia study group. Twelve of these patients (29%), because they had no chest pain or anginal equivalent before angioplasty and conse­quently could not be expected to have symptoms with restenosis, were scheduled for SPECT imaging and angiog­raphy no later than 6 months after angioplasty. Twenty-nine patients (71%) had angina before angioplasty but were asymptomatic afterward. Seventeen of these patients had unusually complex angioplasty and were scheduled for angiographic and SPECT reevaluation from the time of the

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initial intervention, irrespective of development of symp­toms. The other 12 asymptomatic patients were referred for reevaluation by their primary physicians, who, as part of their practice pattern, had ordered an exercise test with (eight patients) or without (four patients) thallium-20l imag­ing, that was abnormal. Seventy-five patients had chest pain after angioplasty and constitute the symptomatic ischemia group. All patients in this group had recurrent chest pain after an initial symptom-free period. All patients gave in­formed consent before evaluation.

Exercise protocol and thallium imaging procedure. All patients underwent standard Bruce protocol exercise testing to a symptom-limited maximum (4). The standard 12 lead ECG during exercise was considered positive if there was ;::: 1 mm of horizontal or downs loping ST depression for at least 0.08 s after the J point compared with the tracing recorded at rest. Five patients, three in the symptomatic and two in the silent ischemia group, had baseline ST depression > 1 mm that precluded accurate analysis of further ST­segment changes with exercise and were excluded from analysis of ECG restenosis detection. One minute before the termination of exercise, 3 mCi of thallium-20 1 was injected. SPECT images were obtained 10 min after isotope injection and 3 to 5 h later and, when indicated, 24 h later. A Siemens Orbiter large-field-of-view tomographic camera interfaced with a Medical Data Systems A3 computer was used. The camera was equipped with 75 photomultiplier tubes, a 0.25 in. (0.64 cm) thick NaI crystal and an all-purpose, parallel-hole collimator. A 20% energy window was posi­tioned on the 80 keY photopeak and a second 15% energy window was centered on the high energy peak of thallium-201. Thirty-two equidistant projections were obtained for 40 s each for the exercise and 4 h images and for I min for the 24 h images over a 1800 rotation from the 45" right anterior oblique to the 450 left posterior oblique position. Data were stored on magnetic disc with use of a 64 x 64, 16 bit matrix. Each of the 32 projections was corrected for nonuniformity with a cobalt-57 source, collecting 30 million counts. The mechanical center of rotation was determined to align the detector data with respect to the reconstruction matrix and to monitor gantry stability. The raw data were smoothed with use of a nine-point weighted averaging system. Filtered back projection was performed with use of a Butterworth filter with a cutoff frequency of 0.2 cycles/pixel and order 5.

Tomograms were reoriented in the short-axis, vertical long-axis and horizontal long-axis planes, reconstructed at 1 pixel/slice, representing approximately 6.2 mm thickness, and normalized and displayed with the maximal pixel value set at 100%. The short-axis slices were separated into six equal segments (anterior, anteroseptal, inferoseptal, infe­rior, inferolateral and anterolateral) at apical, mid and basal ventricular levels. The vertical long-axis slices were divided into anterior, apical and inferior segments from septal to lateral surfaces and the horizontal long-axis slices were divided into the superior septal, inferoseptal, apical, super-

HECHT ET AL. SILENT ISCHEMIA AFTER CORONARY ANGIOPLASTY

APICAL MIO­VENTRICULAR

BASAL

671

Figure 1. Separation of SPEer thallium myocardial images into 20 myocardial segments. Anterior = 1,7,13; anteroseptal = 2,8,14; inferoseptal = 3,9,15; inferior = 4,10,16; inferolateral = 5,11,17; anterolateral = 6,12,18; anteroapical = 19; inferoapical = 20. Reprinted from Hecht et al (9).

olateral and inferolateral segments from the superior to the inferior portions of the heart.

Qualitative analysis of each segment of the exercise and redistribution views was performed on a 0 to 4 scale (0 =

normal, 1 = equivocally reduced thallium uptake, 2 = mildly reduced uptake, 3 = moderately reduced uptake, 4 = severely reduced uptake) by two independent observers. Scores ;:::2 were considered abnormal and differences of opinion were resolved by consensus. Polar maps were generated (5) and used for confirmation of visual analysis.

Ischemia was categorized as either total or partial nor­malization of a segment from exercise to redistribution imaging with a minimal improvement of one point on the visual scale.

Coronary arteriography. All patients underwent selec­tive coronary arteriography within a week after SPECT exercise imaging. Selective left and right coronary arterio­grams were obtained by either the Judkins or the Sones approach. Restenosis was defined as return of a previously dilated vessel to ;:::50% diameter reduction, determined by magnified electronic caliper measurements (6).

SPECT image-vascular territory correlations. The SPECT image regions were assigned to the distribution of individual vessels guided by the coronary anatomy obtained from the angiogram performed before the angioplasty, as follows: anteroseptal, anterolateral, superolateral and anterior to the left anterior descending coronary artery; inferolateral to the left circumflex coronary artery; inferior and inferoseptal to the right coronary or left circumflex coronary artery, de­pending on the right or left dominance of the circulation. The apex was assigned to whichever vessel supplied this area as determined from the pre-angioplasty angiogram. Absence or presence of restenosis was predicted before angiographic reevaluation on the basis of presence or absence of ischemic redistribution in the territory of the individual vessels.

To evaluate the extent of the myocardial ischemia asso­ciated with restenosis, only 20 segments were used (Fig. I) to avoid duplication of the same anatomic area on different projections. The number of segments, score of each segment and sum of the scores from each segment demonstrating ischemic redistribution assigned to the individual vessels (severity score) were determined and used as a measure of the geographic extent and severity of ischemia.

672 HECHT ET AL. SILENT ISCHEMIA AFTER CORONARY ANGIOPLASTY

Table 1. Characteristics of 116 Patients

Silent Symptomatic Ischemia Ischemia (n = 41) (n = 75)

Age (yr) 62.1 ± 9.8 56.4 ± 8.1 * Gender (male) 90% 75%t Prior myocardial infarction 41% 43% Diabetes mellitus 15% 4%t Antianginal drugs 95% 89%

Calcium channel blockers 88% 84% Nitrates 43% 55% Beta-adrenergic blockers 3% 8%

Chest pain before 71% 99%* angioplasty

Months after angioplasty 6.6 ± 3.2 6.0 ± 2.9 (mean ± SO)

*p < 0.01; tp < 0.05.

Statistical analysis. Continuous variables are expressed as mean values ± SD. Student's t tests were performed to determine significant differences between mean values for the continuous variables. Chi-square analyses or Fisher's exact tests were used to compare categorical variables. In situations (primarily in comparing sensitivity, specificity and accuracy by vessel) where multiple comparisons were per­formed, the Bonferroni method was used to adjust signifi­cancelevel.

Results Patient characteristics and exercise performance (Tables 1

and 2). Patients with silent ischemia were significantly older and were more likely to be male. A significantly larger proportion of patients with silent ischemia had diabetes mellitus (15% versus 4%, p < 0.05). Similar high proportions of patients were taking antianginal medications. Seventy-one percent of the patients with silent ischemia had chest pain before coronary angioplasty, compared with 99% of the patients with symptomatic ischemia (p < 0.01). None of the patients with silent ischemia and 41% with symptomatic ischemia had chest pain during the treadmill test (p < 0.001). The patients in both groups were studied at similar time intervals after angioplasty. Exercise performance in both groups was virtually identical, with similar exercise dura-

Table 2. Exercise Performance in 116 Patients

Exercise duration (min) Metabolic equivalents (METs) Maximal heart rate (beats/min) Maximal blood pressure (mm Hg) Chest pain during exercise test

*p < 0.001.

Silent Ischemia (n = 41)

7.8 ± 3.1 10.1 ± 2.9 141 ± 13 173 ± 21

0%

Symptomatic Ischemia (n = 75)

7.4 ± 2.9 9.7 ± 3.2 139 ± 12 168 ± 18

41%*

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Table 3. Coronary Arteriography in 116 Patients

Silent Painful Ischemia Ischemia (n = 41) (n = 75)

Single vessel angioplasty 54% 52% Multivessel angioplasty 46% 48% Total vessels dilated 65 120

Left anterior descending 32 51 Right coronary 19 43 Left circumflex 14 26

Patients with restenosis 61% 59% Vessels with restenosis

Total vessels 46% 46% Left anterior descending 44% 59% Right coronary 53% 33% Left circumflex 43% 42%

Diameter reduction Immediately before angioplasty 80 ± 14% 77 ± 13% Immediately after angioplasty 22 ± 12% 23 ± 14% At time of restudy 76 ± 17% 81 ± 14%

tion, metabolic equivalents, maximal heart rate and maximal blood pressure.

Coronary arteriography (Table 3). The coronary arterio­graphic characteristics of patients with silent and sympto­matic ischemia were remarkably similar both before and after angioplasty. Approximately half of the patients in both groups underwent single vessel and multiple vessel angio­plasty. The left anterior descending artery, right coronary artery and left circumflex coronary artery were represented in equal proportions in both groups. Sixty-one percent of patients with silent ischemia and 59% with symptomatic ischemia had restenosis in at least one vessel. Among those with silent ischemia, restenosis occurred in 67% with angina before angioplasty and 70% of those without angina (p = NS). Fifteen percent of the asymptomatic patients with restenosis had diabetes mellitus, compared with 4% of symptomatic patients (p < 0.05). In both groups 46% of vessels had restenosis. There were no significant differences in the proportion of the individual vessels undergoing re­stenosis, Similarly, percent diameter reduction immediately before and immediately after angioplasty and at the time of restudy were almost identical in both groups.

SPECT imaging versus exercise ECG (Table 4). SPECT thallium imaging was significantly more sensitive in patients with silent ischemia (96% versus 40%, p < 0,001) and accurate (88% versus 44%, p < 0,001) than was exercise ECG in detecting ischemia with similar specificity. In pa­tients with symptomatic ischemia, SPECT was also more sensitive (91% versus 59%, p < 0.001) and accurate (85% versus 64%, p < 0.001) than was exercise ECG, and speci­ficity was again similar. SPECT imaging was equally sensi­tive, specific and accurate in patients with silent or sympto­matic ischemia. Exercise ECG was significantly more accurate in patients with symptomatic than with silent ische­mia (64% versus 44%, p < 0.05).

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Table 4. Detection of Restenosis After Angioplasty by SPECT Thallium Imaging and Exercise ECG: Silent Versus Symptomatic Ischemia

Sensitivity Specificity Accuracy (%) (%) (%)

Silent Ischemia SPECr 96* 75 88* Exercise ECG 40 50 44t

Symptomatic Ischemia SPECr 91* 77 85* Exercise ECG 59 71 64

*p < 0.001 vs exercise ECG; t p < 0.05 vs symptomatic ischemia.

Detection of restenosis in individual vessels (Table 5). There were no differences in detection of individual vessel restenosis by SPECT imaging between patients with silent and symptomatic ischemia (sensitivity 90% and 84%. speci­ficity 89% and 77% and accuracy 89% and 84%, respectively. for all vessels). Detection of restenosis in specific arteries was also similar.

Severity of ischemia (Table 6). The number of ischemic segments and severity score of ischemia were similar in patients with silent and symptomatic restenosis for each of the coronary arteries. Examples of silent ischemia on SPECT imaging are shown in Figures 2 and 3.

Discussion This study shows that SPECT thallium imaging is useful

for evaluating restenosis in asymptomatic and symptomatic patients after angioplasty and that restenosis jeopardizes equivalent amounts of myocardium, irrespective of presence or lack of symptoms.

Clinical and arteriographic patterns. The group of pa­tients with silent ischemia had a larger proportion of men and patients with diabetes and a mean older age. The higher incidence of diabetes among asymptomatic patients with restenosis is consistent with a prior report (7) of a higher incidence in exercise-induced silent ischemia and is at odds with others (8-10). The discrepancy might be the result of

HECHT ET AL. 673 SILENT ISCHEMIA AFTER CORONARY ANGIOPLASTY

Table 5. Detection of Restenosis in Individual Vessels by SPECT Thallium Imagining: Silent Versus Symptomatic Ischemia

Silent ischemia All vessels

Left anterior descending Right coronary Left circumflex

Symptomatic ischemia All vessels

Left anterior descending Right coronary Left circumflex

Sensitivity (%)

90 93 90 83

84 87 86 83

Specificity (%)

89 89

100 75

77 100 72 75

Accuracy (%)

89 91 95 79

84 92 77 81

varying definitions of silent ischemia. Although the inci­dence of chest pain before angioplasty was significantly lower among patients with silent ischemia, 71% did have angina before angioplasty. Moreover, 76% of the patients with asymptomatic restenosis had chest pain before angio­plasty. Thus. the presence of angina before angioplasty does not mean that restenosis will be accompanied by angina. Coronary patency should not be assumed simply because symptoms are absent.

Our study group was not a consecutive series of patients who had undergone angioplasty, but rather a consecutive series in whom SPECT imaging and arteriography were obtained within a I-week period. It. is therefore subject to numerous sources of selection bias. which are more promi­nent in the asymptomatic group. The 60% incidence of restenosis in the symptomatic patients is consistent with prior reports of 50% to 56% in nonselected series (1,2) and is very likely more representative of the group of patients with symptoms after angioplasty who are referred because of the common denominator of recurrent chest pain. On the other hand, asymptomatic patients are not routinely evaluated and the 59% restenosis rate in this group cannot be construed as the frequency of restenosis in the general population of asymptomatic patients, which has been reported as 14% to 16% (1.2.11). Selection was used in the decision to restudy

Table 6. Severity of Ischemia by SPECT Thallium Imaging: Silent Versus Symptomatic Restenosis LAD RCA LCx

Silent restenosis No. of vessels 14 10 6 Ischemic segments/vessel 7.8 ± 4.3 4.3 ± 1.4 3.5 ± 1.7 Score/segment 2.4 ± 0.7 2.7 ± 0.7 2.3 ± 0.4 Severity score/vessel 19.8 ± 15.4 12.0 ± 7.1 8.3 ± 4.8

Symptomatic restenosis No. of vessels 30 14 II Ischemic segments/vessel 7.6 ± 3.9 3.7 ± 1.2 2.3 ± 0.9 Score/segment 2.6 ± 0.6 2.4 ± 0.5 2.6 ± 0.7 Severity score/vessel 21.1 ± 14.0 9.1 ± 4.0 5.9 ± 3.3

LAD = left anterior descending coronary artery; RCA = right coronary artery; LCx = left circumflex coronary artery.

674 HECHT ET AL. SILENT ISCHEMIA AFTER CORONARY ANGIOPLASTY

Figure 2. SPECr thallium images in a 55 year old asymptomatic man with prior inferior myocardial infarction and total right coro­nary artery obstruction, 4 months after left anterior descending and obtuse marginal angioplasty. A, Short axis from apex to base (I to 8) shows anterior, anteroseptal, inferoseptal and inferior ischemia and inferior myocardial infarction. B, Horizontal long axis from superior to inferior (I to 6) shows anteroseptal and inferoseptal ischemia. C, Vertical long axis from septal to lateral (I to 3) shows inferoapical ischemia and myocardial infarction. Prediction: Restenosis of left anterior descending artery, patency of obtuse marginal artery. Angiography: 95% left anterior descending stenosis, patency of obtuse marginal artery. srR = immediate postexercise images; 4HR = images 4 hours postexercise.

asymptomatic patients who had undergone unusually com­plex angioplasty and who might be expected to have a higher restenosis rate. Similarly, the asymptomatic patients with angina before angioplasty who were referred by their physi-

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Figure 3. SPECr thallium images in a 65 year old asymptomatic man 6 months after left circumflex and right coronary artery angioplasty. A, Short axis from apex to base (1 to 7) shows inferolateral and inferior ischemia. B, Horizontal long axis from superior to inferior (I to 7) shows inferolateral ischemia. C, Vertical long axis from septal to lateral (I to 4) shows inferior ischemia. Prediction: Restenosis of both left circumflex and right coronary arteries. Angiography: 85% left circumflex and 80% right coronary artery stenoses.

cians after abnormal exercise testing are not a random sample. The asymptomatic patients who were free of symp­toms before angioplasty as well have not been previously described in published reports and are clearly a selected group.

However, the purpose of this study was not to define the frequency of restenosis in asymptomatic patients but rather to assess the ability of SPECT thallium imaging to detect

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restenosis in asymptomatic and symptomatic patients. The arteriographic characteristics, incidence of restenosis, per­cent diameter reductions (Table 3) and exercise performance (Table 2) were remarkably similar in both the symptomatic and asymptomatic patients; therefore, these patients can be defined as populations with similar disease prevalence and exercise variables on which to base valid comparisons of the utility of a diagnostic tool.

SPECT thallium imaging and exercise ECG. Although prediction of future restenosis by exercise ECG (12) and thallium-201 imaging (13,14) within the 1st week of coronary angioplasty has been studied, there are no data regarding the detection of restenosis by thallium-201 imaging and compar­ison with exercise ECG in either symptomatic or asympto­matic patients, evaluation of individual vessel restenosis or comparison of the amount of ischemia associated with silent and symptomatic restenosis.

Exercise ECG. The relatively low sensitivity and accu­racy of exercise ECG for detecting restenosis is consistent with prior reports in symptomatic (11,15) and asymptomatic (16) patients, as is the 40% sensitivity for exercise ECG in silent ischemia, independent of restenosis (9,17,18). The value of exercise ECG is further limited by the lack of applicability to patients with noninterpretable tracings (left bundle branch block, digoxin, marked baseline ST and T wave abnormalities) and the absence of vascular localizing information, which may be crucial to patient management.

SPECT thallium imaging. Our study demonstrates that SPECT thallium imaging is an excellent tool for detecting both silent and symptomatic restenosis (Tables 4 and 5), with significantly higher sensitivity and accuracy than exercise ECG (Table 4). Our results for restenosis detection, which rely on visually interpreted SPECT imaging, are similar or slightly superior to those in prior reports (19-22) using SPECT imaging with or without quantitative analysis to detect coronary artery disease and individual vessel stenosis not related to coronary angioplasty.

We (9) have previously shown that patients with chronic coronary artery disease with silent or symptomatic ischemia during exercise have similar amounts of ischemic myocar­dium by SPECr imaging; almost all of the patients presented with angina but 75% underwent exercise testing without chest pain. The present study extends the comparison to a group that is entirely asymptomatic after angioplasty and demonstrates, on a vessel by vessel basis, that the amount and degree of ischemia associated with restenosis are similar in patients with silent or symptomatic ischemia (Table 6).

The accurate identification of the restenotic vessel and the ability to assess the amount of ischemic myocardium have an important role in decision making. Figure 2 shows a SPECT thallium image from a patient in whom a finding of left anterior descending artery restenosis with associated massive ischemia supported early intervention. If obtuse marginal artery restenosis with a smaller amount of ischemia had been the only finding, a less aggressive approach might be considered.

HECHT ET AL. 675 SILENT ISCHEMIA AFTER CORONARY ANGIOPLASTY

Clinical implications. Many reports document that in patients who have silent ischemia by ECG criteria the degree of coronary artery disease is similar (10,17,23-25) and the prognosis is similar or worse (10,17,23-28) than that of patients who have angina. More recently, prognostic studies using either thallium-201 perfusion criteria (29-31) or exer­cise radio nuclide ventriculography (18) to define silent ische­mia have confirmed that patients with silent and sympto­matic ischemia have comparable risks. The previous study from our laboratory (9), a planar thallium-201 study (32) in a general coronary artery disease population and the present study in patients with restenosis after angioplasty reveal the physiologic basis for the similar prognosis by showing that equal amounts of ischemic myocardium are present in silent and symptomatic ischemia.

Although there are no prognostic studies of silent ische­mia after angioplasty in asymptomatic patients, there is no reason to assume that the outcome would be different from prior studies in such patients without angioplasty, especially since the degree of restenosis and amount of ischemic myocardium are similar to those in patients with sympto­matic restenosis. Although no published data are available with regard to angioplasty performed for silent restenosis, recent reports (33-35) demonstrate comparable outcomes for angioplasty in the settings of silent and symptomatic ische­mia.

Thus, a wealth of data are accumulating to support the recent comment of Chatterjee (36) that "the time has ar­rived . . . to direct therapeutic objectives for the detection and treatment of ischemia whether or not it manifests clinically or remains silent." The present study shows that SPECT thallium-201 imaging has excellent and comparable results for detection and localization of ischemia secondary to restenosis in both asymptomatic and symptomatic pa­tients after coronary angioplasty.

In the earlier days of angioplasty, the reported restenosis rates were 20% to 35% (1,2,37,38). Now that this procedure is performed for multiple vessel stenoses (39,40), total oc­clusion (41) and unstable angina (42), the restenosis rates may rise to 40% to 50%. The previously reported restenosis rates of 14% to 16% (1,2,11) in asymptomatic patients were in populations in which 85% of patients underwent only single vessel angioplasty, 75% of whom underwent the procedure before 1984, when cases were less complex. Therefore, one may assume that the present restenosis rate in asymptomatic patients is very likely higher than 14% to 16%. Moreover, a recent study (3) demonstrated that 33% of restenoses were associated with an asymptomatic state. Thus, the prevalence of restenosis in both symptomatic and asymptomatic patients after angioplasty is in the range that, according to Bayes' theorem (43), greatly enhances the value of the accurate diagnostic examination.

We recommend that SPECT thallium-201 imaging be performed after coronary angioplasty in all symptomatic patients. Only 50% to 60% of symptomatic patients have restenosis, which can be accurately identified by the SPECT

676 HECHT ET AL. SILENT ISCHEMIA AFTER CORONARY ANGIOPLASTY

evaluation. In asymptomatic patients who undergo complex angioplasty, in whom a high restenosis rate is anticipated (39-42), SPECT imaging should be performed no later than 6 months after angioplasty, the period during which almost all restenoses occur (44,45). In asymptomatic patients who undergo simple angioplasty, in whom a lower restenosis rate is expected, SPECT imaging should be considered; the lower prevalence of restenosis in this subset requires a highly accurate SPECT evaluation for an enhanced diagnostic yield.

We acknowledge the help of Steve Lugon in typing this manuscript.

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