Assessment of reversible dyssynergic segments after acute myocardial infarction: Dobutamine echocardiography versus thallium-201 single photon emission computed tomography

Assessment of reversible dyssynergic segments after acute myocardial infarction: Dobutamine echocardiography versus thallium-201 single photon emission computed tomography Claude Le Feuvre, FESC, Nicole Baubion, MD, Nicolas Aubry, MD, J e a n Philippe Metzger, FESC, Pierre de Vernejoul, MD, and Andr~ Vacheron, FESC Paris, France

Only a moderate degree of concordance has been reported between stress-redistribution-reinjection thallium-201 single photon emission computed tomography (SPECT) and dobutamine echocardiography for the identification of myocardial viability after acute myocardial infarction. SPECT with rest-reinjection performed 4 hours after exercise testing and digitized two-dimensional (2-D) ultrasound reconstruction of the left ventricle at baseline and after low-dose dobutamine (5 to 10 pg/kg/min) infusion were compared in 50 patients >-8 days (12 ± 7 days) after acute myocardial infarction. Five patients were excluded because of technically inadequate echocardiograms. Both SPECT and dobutamine echocardiography were assessed in a 16-segment model and interpreted in the remaining 45 patients. Digitized 2-D reconstruction of the left ventricle in each wall motion was scored from 1 (normal) to 4 (dyskinesia). Myocardial viability was identified on ultrasound wall-motion improvement of one or more grades from baseline to echocardiography performed ---30 days (60 ± 41 days) after systematic revascularization procedure of the infarct-related artery. Reversible defect under thallium-201 SPECT and wall-motion improvement under dobutamine echocardiography were concordant in 163 (69%) of the 235 baseline dyssynergic segments and in 30 (87%) patients. Myocardial viability was identified after angioplasty (n = 37) or surgery (n = 8) in 29 patients and '109 segments. Positive and negative predictive values per patient in the diagnosis of myocardial viability were 86% and 57%, respectively, for stress thallium-201 SPECT with reinjection, and 100% and 62% for dobutamine echocardiography. Positive and negative predictive values per segment were 80% and 69% for the isotopic method and 91% and 70% for dobutamine echocardiography. We conclude that dobutamine echocardiography and stress thallium-201 SPECT with reinjection have similar accuracies to identify myocardial viability after acute myocardial infarction, with excellent positive but relatively low negative predictive values. (AM HEART J 1996;131:668-75.) From Clinique Cardiologique, Hppital Necker Received for publication May 10, 1995; accepted Sept. 8, 1995. Reprint requests: Claude Le Feuvre, Clinique Cardiologique Hgpital Necker, 149 rue de S~vres, 75015 Paris, France. Copyright © 1996 by Mosby-Year Book, Inc. 0002-8703/96/$5.00 + 0 4/1/70076

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Wall-motion abnormalities after acute myocardial infarction can be fixed or reversible, depending on the timing of reperfusion and collateral blood flow. The ability to identify viable myocardium after myocardial infarction has important prognostic and therapeutic implications because of reversibility after revascularization, which is the most accurate index of potential viability. 1 Low-dose dobutamine echocardiography and thallium-201 myocardial scintigraphy have been used to detect viable myocardium after acute myocardial infarction.2-4 Only a moderate degree of concordance has been reported between stress-redistribution-reinjection thallium201 scintigraphy and dobutamine echocardiography for the identification of myocardial viability after acute myocardial infarction. 5-7 The aim of this study was to compare stress thallium-201 single photon emission computed tomography (SPECT) with reinjection and dobutamine echocardiography in dyssynergic segments ->8 days after acute myocardial infarction and before coronary revascularization to assess their accuracy in estimating postrevascularization recovery. METHODS Study group. The study group consisted of 50 patients

(41 men and 9 women, aged 30 to 79 years [mean 58 years]) with dyssynergic segments in vascular stenotic territories and successful revascularization of this infarct-related artery. Previous myocardial infarction had occurred in all patients >-8 days before the first echocardiographic and scintigraphic studies and was documented in all by electrocardiographic and enzymatic changes. The site of myocardial infarction was anterior in 29 patients and inferior in 21. In the acute phase, 30 patients received thrombolytic treatment 4.6 ± 4.4 hours after the onset of symptoms. Mean peak serum creatine kinase value was 1735 +_ 1226. • Antianginal therapy was discontinued 12 hours before scintigraphic and echocardiographic studies. ~-Blocking

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AmericanHeartJournal medications included propranolol (n = i7) or acebutolol (n = 23). Because ofa contra-indication, 10 patients did not have any B-blocking treatment. Patients were excluded if any of the following were present: unstable angina; history of sustained ventricular tachycardia, atrial flutter, or fibrillation; uncontrolled cardiac failure; valvular heart disease; technically inadequate echocardiogram; failure of revascularization of the infarct-related artery; or ischemic event between the revascularization procedure and the echocardiographic follow-up. The study was approved by an ethical committee on clinical investigation. Written informed consent was obtained from all subjects. Dobutamine echocardiography. Baseline a n d dobutamine two-dimensional echocardiography were performed in the left lateral position with a Vingmed CFM750 (Herren, Norway) instrument with a 2.5-MHz transducer. Parasternal long-axis, midventricular parasternal short-axis, and apical two-cavity and four-cavity images were acquired and transferred to a Mac II Ci (Apple Computer, Cupertino, Calif.). The dynamic series of images was digitized and analyzed by the Echopacs (Vingmed) program. According to the recommendations of the American Society of Echocardiography, segmental wall motion assessed with a 16-segment model was visually graded as normal (1), hypokinetic (2), akinetic (3), or dyskinetic (4).8, 9 Systolic thickening was carefully examined in the central portion of each segment with wall-motion abnormalities. Hypokinesis was defined as reduced endocardial excursion and thickening. Akinesis was defined as absence of endocardial excursion or thickening. Dyskinesis was defined as paradoxic endocardial excursion or systolic wall thinning. The stages of the protocol were baseline, 5 ~g/kg/min, and 10 ~g/kg/min dobutamine infusion rate, with each dose lasting for 5 minutes. Blood pressure, heart rate, and 12-lead electrocardiogram (ECG) were monitored and recorded at the end of each stage. Two investigators blinded to the clinical and study data analyzed the digitized baseline and dobutamine echocardiograms. A patient was defined as a responder to dobutamine when regional wall motion improved by one or more grades compared with the respective baseline value in two or more contiguous infarct zone segments. Intraobserver variability tested in the first 10 patients was 2%. The variability between the two observers was 5% of the total segments analyzed. Interobserver and intraobserver discrepancies were resolved by consensus. Thallium-201 SPECT with reinjection. The interval between dobutamine echocardiography and myocardial scintigraphy was 1 to 4 days. Each patient exercised on a bicycle ergometer with the Bruce protocol. Two millicuries of thallium 201 were injected at 75% of the age-predicted heart rate. This effort was maintained for 1 minute. Scintigraphic imaging was started within 5 minutes of the injection of thallium. Tracer redistribution at the fourth hour was assessed by a second series of scintigraphies 10 minutes after reinjection of I mCi of thallium. Visual assessment of early and 4-hour tracer uptake were compared by two blinded investigators who had no knowledge of the r esults of dobutamine echocardiography and the exercise

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stress test. Regional tracer activity scores ranged from 0 (severe reduction in activity) to 3 (normal activity). A segmental defect was said to be reversible when its abnormal score increased one or more on the delayed images. Interobserver and intraobserver variability for distinguishing fixed from reversible defects was previously tested in our laboratory (coefficient of concordance Kappa, 0.95 and 1, respectively). 1° A consensus was reached in case of discrepancy. SPECT studies were acquired using a rotating gamma camera (Apex, Elscint, Israel) equipped with a low-energy, high-resolution collimator. Thirty projections were acquired over a 180-degree arc, from left posterior oblique to right anterior oblique (30 seconds per step). Oblique-angle myocardial tomograms were reconstructed by using a filtered backprojection algorithm and a Hamming (Elscint) filter. The reconstructed tomographic data were displayed in three planes (short-axis, long-axis, and transverse). The presence of an initial perfusion defect with a phenomenon of redistribution at 4 hours was considered to be indicative of a positive SPECT in the diagnosis of viable myocardium. The left ventricular wall activity was divided into 16 segments to match the echocardiographic segmentation. Coronary angiography. All patients underwent left ventriculography in biplane views and coronary angiography in multiple projections within 1 week of isotopic and echocardiographic studies. Digital computer-assisted calipers (DCI Philips, Eindhoven, Holland) were used to measure stenotic segments of the infarct-related arteries that were quantified as minimal stenosis diameter and minimal luminal diameter. Follow-up. Revascularization of infarct-related artery was successfully performed in all patients, independent of the results of isotopic and echocardiographic studies. Baseline digitized echocardiography was obtained in all patients ->4 weeks (60 _+41 days) after coronary artery bypass surgery (n = 8) or coronary angioplasty (n = 37). No patient had clinical evidence ofrestenosis. Medical therapy was discontinued 12 hours before echocardiographic study. Two investigators blinded to the clinical and study data analyzed the digitized baseline and follow-up echocardiograms. Discrepancies were resolved by consensus. The accuracies of dobutamine echocardiography and thallium201 myocardial scintigraphy for the detection of reversible dysfunction were calculated by using the improvement of dyssynergic segment by one or more echocardiographic grades at follow-up. Myocardial viability per patient was defined as improvement of follow-up echocardiographic grade in two or more contiguous infarct zone segments. Statistics. The following variables were assessed as possible correlates of myocardial viability: clinical characteristics (sex, age, location of the infarction, Q wave, thrombolytic treatment, mean peak serum creatine kinase value), angiographic characteristics (left ventricular ejection fraction, multivessel disease, minimal luminal diameter of the infarct-related artery), dobutamine echocardiography~ and SPECT results. Sensitivity, specificity, and negative and positive predictive values per patient of isotopic and echocardiographic studies in the diagnosis of

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Table h Concordance between T1-201 SPECT and dobutamine echocardiography results in the 45 patients and, in parentheses, in the 235 baseline dyssynergic segments Echocardiography of the left ventricle during dobutamine infusion

T1-201 SPECT Reversible defect Fixed defect

Wall~motion improvement

No wall-motion improvement

13 (33) 6 (31)

9 (41) 17 (130)

myocardial viability were compared by using improvement of follow-up echocardiographic grade in two or more contiguous dyssynergic segments as reference. Univariate analyses were performed by using the chi-square test with the Yates' correction when appropriate for categoric data and variance analysis for continuous variables with twosided statistics testing. Multiple logistic regression analysis and stepwise logistic regression analysis were performed in the standard manner. Continuous data are pre* sented as mean -+ SD. A p value <0.05 was considered significant. RESULTS Concordance between thallium-201 SPECT and dobutamine echocardiography. F i v e p a t i e n t s were excluded because of a technically inadequate echo-

cardiogram. In the 45 remaining patients, 720 myocardial segments were analyzed. At baseline echocardiography, three segments were judged dyskinetic, 151 akinetic, 81 hypokinetic, and 485 normal. Each patient had two or more contiguous dyssynergic segments. Dobutamine echocardiography was carried out 12 _+ 7 days after acute myocardial infarction. Dobutamine infusion was well tolerated in all patients. Regional wall motion improved by one grade or more during dobutamine infusion in 64 segments. Improvement in two or more segments occurred in 19 patients (45%). Thallium-201 SPECT Showed a reversible defect in 74 segments (22 patients) and a fixed defect in 161 segments (23 patients) among the 235 baseline echocardiographic dyssynergic segments. Reversible defect under thallium-201 SPECT and wall-motion improvement under dobutamine echocardiography were concordant in 163 (69%) among the 235 baseline dyssynergic segments and in 30 (67%) patients (Table I). The concordance was lower in the 81 hypokinetic t h a n in the 154 akinetic or dyskinetic segments (60% vs 74%; p < 0.005). Comparison of thallium-201 SPECT with dobutamine echocardiography for detecting myocardial viability. Im-

Table II. Clinical, angiographic, echocardiographic, and

isotopic findings in patients with (group 1) and without (group 2) wall-motion improvement after coronary revascularization Group 1 (n = 29)

Group 2 (n = 16)

58 ± 10 5 (17)

58 ± 13 3 (19)

16 (55) 13 (45) 26 (90) 1702 ± 1188

10 (62) 6 (38) 14 (88) 1810 + 1354

19 (65) 5.0 _+ 4.9

7 (44) 3.3 ± 2.1

19 (65)

9 (56)

8 (28) 2 (7)

4 (25) 3 (19)

16 (55)

9 (56)

3 (10)

2 (13)

10 (35)

5 (38)

Totally occluded vessel, n

5 (17)

5 (31)

Mean stenosis diameter before PTCA (%) Minimal luminal diameter (mm) Dobutamine echocardiography Mean time after myocardial infarction (days) Mean n u m b e r of dyssynegic segments, n Positive test, n (%) T1-201 SPECT Positive test, n (%) Coronary revascularization Surgery, n (%) Angioplasty, n (%) Mean time between revascularization and follow-up echocardiography (days)

71 _+ 19

80 ± 16

0.8 + 0.5

0.5 _+ 0.5*

Mean age (yr) Female gender, n (%) Acute myocardial infarction Location anterior, n (%) inferior, n (%) Q wave, n (%) Peak creatine kinase (IU/

ml) Thrombolysis, n (%) Time to thrombolysis (hr) Coronary angiography Single-vessel disease, n

(%)

Two-vessel disease, n (%) Three-vessel disease, n (%) Left ventricular ejection fraction, % Infarct-related vessel Left anterior descending artery, n (%) Left circumflex artery, n

(%) Right coronary artery, n

(%) (%)

11 ± 5

14 ± 9

5.7 -+ 2.4

4.3 ± 2.2*

19 (66)

0 (0)t

19 (66)

3 (19)$

3 (10) 26 (90) 64 __ 43

5 (31) 11 (69) 54 ± 33

p Value group 1 vs group 2. *p < 0.05. tP < 0.0001. Sp < 0.002.

provement of wall-motion abnomalities 60 +- 41 days after coronary revascularization was obtained in 109 (46%) of the 235 baseline dyssynergic segments. Improvement in two or more contiguous segments was

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Table IH. Prediction of recovery of dyssynergic segments per patient and per segment by using dobutamine

echocardiography and T1-201 SPECT. Baseline dyssynergic segments (n = 235)

Patients (n = 45)

Sensitivity Specificity Positive predictive value Negative predictive value

Dobutamine echocardiography (%)

Tl-201 S P E C T (%)

Dobutamine echocardiography (%)

Tl-201 S P E C T (%)

66 (59-73) 100 100 62 (55-69)

66 (59-73) 81 (75-87) 86 (81-91) 57 (50-64)

53 (50-56) 95 (94-96) 91 (89-93) 70 (67-73)

54 (51-57) 88 (85-91) 80 (78-82) 69 (66-72)

observed in 29 (64%) patients. The 29 patients with myocardial viability (group 1) were compared with the 16 patients without myocardial viability (group 2, Table II). No significant differences were found between the two groups regarding clinical and angiographic characteristics, except a higher minimal luminal diameter of the infarct-related artery in group 1. In univariate analysis, positive echocardiographic and isotopic tests were more frequent in group i than in group 2. The only independent variables associated with myocardial viability per patient in multivariate analysis were a positive dobutamine echocardiography (p < 0.003) and a positive stress thallium-201 SPECT with reinjection (p < 0.04). The number of dyssynergic segments was significantly correlated with the number of Viable segments (r = 0.44; p < 0.003). Dobutamine echocardiography. Echocardiographic score under dobutamine infusion was lower in viable than in nonviable segments (2.07 _+ 0.81 vs 2.62 _+ 0.52;p < 0.0001). Baseline echocardiographic score was not a predictive factor for either a positive dobutamine test (2.61 _+ 0.52 vs 2.69 + 0.49 in negative tests; not significant INS]) or a late wall-motion improvement (2.67 _+ 0.53 vs 2.66 _+ 0.47, NS). Diagnostic value per segment and per patient of dobutamine echocardiography in the diagnosis of myocardial viability is depicted in Table III. A wallmotion improvement after dobutamine infusion was observed in 58 of the 109 viable segments and in 19 patients of group 1. The 10 patients with false-negative dobutamine echocardiography were compared with the 19 patients with true-positive dobutamine echocardiography. There were no predictive factors of false-negative dobutamine echocardiography. The use of ~-blocking medications ->12 hours before the test was similar (8 [80%] patients) with false-negative tests vs 15 patients [79%] with true-positive tests; NS). Minimal luminal diameter of the infarctrelated artery was 0.87 _+ 0.51 mm in true-positive

and 0.73 _+ 0.48 mm in false-negative dobutamine echocardiography (NS). Baseline echocardiographic score was similar in the 51 segments with false-negative and in the 58 segments with true-positive dobutamine echocardiography (2.74 _+ 0.52 vs 2.60 _+ O.53; NS). Thallium-201 SPECT. Baseline echocardiographic score was higher in fLxed than in reversible defects (2.72 _+ 0.48 vs 2.54 _+ 0.50; p < 0.007). Diagnostic value per segment and per patient of thallium-201 SPECT in the diagnosis of myocardial viability is depicted in Table III. A reversible defect was observed in 59 of the 109 viable segments and in 19 patients of group 1. The 10 patients with false-negative thallium-201 SPECT were compared with the 19 patients with true-positive thallium-201 SPECT. There were no predictive factors of false-negative thallium201 SPECT. Baseline echocardiographic score was similar in the 50 segments with false-negative and in the 59 segments with true-positive thallium-201 SPECT (2.76 _+ 0.55 vs 2.59 _+ 0.50; NS). Sensitivities, specificities, and negative and positive predictive values per segments and per patient of dobutamine echocardiography and thallium-201 SPE CT in the diagnosis of myocardial viability are compared in Table III. Results in patients with and without thrombolysis. Residual stenosis of the infarct-related artery was higher in patients without than in patients with thrombolysis (82% _+ 18% vs 68% _+ 17%;p < 0.009), with similar differences in terms of minimal luminal diameter (0.49 _+ 0.52 mm vs 0.89 _+ 0.44 mm; p < 0.01) and of rate of totally occluded vessel (42% vs 8%;p < 0.006). Reversible defects under thallium201 SPECT and wail-motion improvement under dobutamine echocardiography were concordant in 88 (64%) among the 137 baseline dyssynergic segments in patients after thrombolysis and in 75 (76%) among the 98 dyssynergic segments in patients without thrombolysis. Positive predictive values per seg-

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ments of isotopic and echocardiographic testing were 75% and 88%, respectively, in patients after thrombolysis and 85% and 95%, respectively, in patients without thrombolysis. Negative predictive values per segments of isotopic and echocardiographic testing were 65% and 72%, respectively, in patients after thrombolysis and 75% and 67%, respectively, in patients without thrombolysis. DISCUSSION

In this study, the baseline echocardiographic score was higher in fixed than in reversible segments, which suggests that hypokinetic segments contain more viable myocardium than do akinetic or dyskinetic segments. However, the baseline echocardiographic score was similar in segments with and without improvement with dobutamine infusion, as well as in segments with and without late functional recovery. These findings and the lower degree of concordance between isotopic and echocardiographic testing in hypokinetic than in akinetic or dyskinetic segments suggest that the cellular mechanisms responsible for a wall-motion improvement with dobutamine and after revascularization require a higher degree of myocyte functional integrity than do those responsible for thallium uptake. This different approach in the assessment of myocardial viability explains the moderate degree of concordance between thallium-201 SPECT and dobutamine echocardiography for the detection of viable tissue after myocardial infarction. In our study, overall agreement between echocardiographic and isotopic testing was 67% per patient and 69% per segment, similar to those of previous studies, ranging from 61% to 77%.5, 6, 11 In our study, wall-motion improvement after revascularization was unrelated to the location of the myocardial infarction or to the basal echocardiographic score. Although the incidence of use of thrombolytic agent was not statistically different between patients with and without functional recovery, there was a trend toward a higher incidence of thrombolytic agent use (65% vs 44%) and a lower incidence of vessel occlusion (17% vs 31%) among the patients with functional recovery. The lack of statistical significance could reflect the relatively small sample size rather than a true lack of clinical impact of these factors. The significant correlation between the number of dyssynergic and viable segments suggests a higher likelihood of myocardial viability in larger myocardial infarctions. Our data suggest that dobutamine echocardiography and thallium-201 SPECT with reinjection have

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similar accuracies in identification of myocardial viability ->8 days after acute myocardial infarction, with excellent specificities and positive predictive values. In contrast, sensitivities and negative predictive values were low in both tests, with no predictive factors of false-negative results, either for dobutamine echocardiography or for thallium-201 SPECT. A high sensitivity of dobutamine echocardiography in the diagnosis of hibernating and stunned myocardium and in the prediction of recovery of left ventricular function after coronary revascularization has been previously described and ranges from 81% to 86%. 12"15One significant difference between this and previous studies in the postinfarction setting is that not all patients in this series received thrombolytic therapy. It is also interesting to note that the time to reperfusion tends to be longer in group 1 patients who had improvement of wall motion after revascularization. This may distinguish our study from previous studies in which all patients were rapidly reperfused. Because dobutamine echocardiography was carried out in our study 12 _+ 7 days after acute myocardial infarction, the presence of some myocardial stunning in the infarct area cannot be excluded,16 and suggests that significant spontaneous recovery from stunning was present at this time. Any failure to recruit ventricular function at this time would result from the presence of a more significant residual stenosis, limiting the increase in blood flow in response to inotropic stress. The timing of our study and the residual stenosis may explain why patients without wall-motion improvement with dobutamine infusion were still able to recover function after revascularization and could have contributed to the low negative predictive value of dobutamine echocardiography. Recent studies have demonstrated an underestimation of myocardial viability with dobutamine echocardiography in the presence of a flow-limiting residual stenosis inducing persistent myocardial dysfunction (hibernation)S -19 Dobutamine echocardiography seems to be accurate when positive for prediction of myocardial viability but of less value if negative when compared with positron emission tomography (PET)S, is In the study of Hepner et al. 17 114 of 164 segments nonviable by dobutamine echocardiography displayed evidence of myocardial viability by fluorodeoxyglucose, and 80% of these were viable by N13 imaging alone. Elsner et al. is concluded that almost all segments that improve during dobutamine echocardiography are viable by PET, but most of these segments are stunned rather than

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hibernating. In this series, dobutamine echocardiography improvement occurred in only 16% of all hibernating segments. In an experimental study on 15 dogs, Sklenar et al. 19 showed that dobutamine echocardiography can be used to determine the extent of viable myocardium after acute myocardial infarction in the absence of coronary stenosis, whereas the presence of residual coronary stenosis makes this assessment less likely and far less accurate. In our study, the sensitivity of thallium-201 SPECT in the diagnosis of myocardial viability is similar to and the specificity is slightly lower than those of dobutamine echocardiography. However, the confidence limits for these results were widely overlapping, suggesting no statistically significant difference between the two tests. Previous studies demonstrated that thallium-201 reinjection imaging improves detection of viable myocardium in comparison with standard 4-hour redistribution imaging. 2° However, thallium-201 reinjection still underestimates by - 2 5 % to 35% the extent of myocardial viability when compared with PET, 21 tracer uptake, or wall-motion improvement after revascularization.22, 23 Modified thallium-201 imaging protocols have been validated, such as thallium-201 rest injection with delayed redistribution imaging (18 to 24 hours), 23 nitrates and reinjection, 24 and restredistribution studies with quantitative analysis.25, 26 Information from quantitative analysis of rest-redistribution thallium-201 studies has been shown to be concordant with a stress-redistributionreinjection protocol regarding myocardial viability, as identified by PET. 27Rest-redistribution can therefore be proposed in patients with severe ventricular dysfunction in whom viability is a more important issue than stress-induced ischemia. There are several limitations to our study. Patients with angina uncontrolled by medical therapy were not included in this study. Thus our results may not necessarily apply to these patients. The presence of some myocardial stunning in the infarct area cannot be excluded at the time of dobutamine echocardiography, with significant spontaneous recovery from stunning at this time. However, this test was carried out 12 _+ 7 days after acute myocardial infarction, which corresponds to the clinical setting for raising the question of coronary revascularization when the angioplasty has a high success rate, even in an occluded artery. 2s, 29 Although B-blocking medications used in this study have serum half-lives between 6 and 10 hours and were withheld 12 hours before dobutamine echocar-

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diography, they could have still been active to a significant degree at the time of testing and could have contributed to the low predictive value of testing. However, the use of ~-blocking medications was similar in patients with true-positive and false-negative dobutamine echocardiography. The decision to discontinue antianginal therapy only 12 hours before stress testing is, in our experience, a safe clinical practice after myocardial infarction. In our study, the dobutamine stress protocol included only low levels of stress (5 and 10 ]lg/kg/min infusion), which could also have contributed to the low negative predictive value of dobutamine echocardiography. Some more recent studies examining the use of dobutamine stress echocardiography for assessment of viability have described additional diagnostic yield at higher doses of dobutamine infusion, with a biphasic response (improvement at low dose and worsening at high dose).ll, 30, 31 However, in segments with a biphasic response, the dose at which improvement in wall motion was prevalent (84%) was 7.5 pg/kg/min and increased to 94% when the 5 and 7.5 pg/kg/min doses were displayed. 3° Recent studies have shown that the amount of thallium activity in a dyssynergic segments was a good predictor of potential for future recovery. 11, 32 Our study does not quantitate the amount of thallium activity, which could be a limitation of the study in decreasing the accuracy of isotopic testing. Visual and quantitative analysis of thallium myocardial scintigraphy, however, have been reported to be equally valuable in the evaluation of coronary artery disease.33, 34 Thallium uptake has not been assessed after revascularization in segments with baseline wall-motion abnormalities. It is probable that the dyssynergic segments that did not recover function contained the lowest amount of preoperative thallium reinjection activity, consistent with previous studies.11, 32 However, a wall-motion improvement after revascularization is a standard index of myocardial viability. 1, 2, 4, 12-15 It is not certain that echocardiographic segments correspond exactly to the myocardial segments defined by the thallium-201 SPECT studies. The requirement that two contiguous echocardiographic segments be abnormal and have the same change (or lack of improvement) after revascularization would decrease the risk of misleading the analysis with small territories. C o n c l u s i o n s . In patients with technically adequate echocardiograms, the concordance between thallium-201 SPECT with reinjection and dobutamine echocardiography with digitized images is only mod-

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erate in postinfarction myocardium that may or may not have been stunned. Both isotopic and echocardiographic testing have an excellent positive but a poor negative predictive value in the assessment of reversible dyssynergic segments. One third of viable segments cannot be detected with these techniques, which underestimate residual viability and potential benefit of reperfusion strategies. The high rate of viable segment several days after a large acute myocardial infarction and the relatively low negative predictive values of the tests usually used in the diagnosis of myocardial viability raise the question of systematic reopening of the infarct-related artery in these patients. 35 REFERENCES

1. Bach DS, Armstrong WF. Stress echocardiography following thrombolytic therapy and acute myocardial infarction. Am J Cardiac Imag 1992;6:134-40. 2. Barilla F, Gheorghiade M, Alam M, Khaja F, Goldstein S. Low-dose dobutamine in patients with acute myocardial infarction identifies viable but not contractile myocardium and predicts the magnitude of improvement in wall motion abnormalities in response to coronary revascularization. AM HEARTJ 1991;122:1522-31. 3. Bonow RO, Dilsizian V. Assessing viable myocardium with thallium201. Am J Cardiol 1992;70:10E-17E. 4. Salustri A, Elhendy A, Polyxeny G, Ciavatti M, Cornel JH, ten Cate FJ, Boersma E, Gemelli A, Roelandt JRTC, Fioretti PM. Prediction of improvement of ventricular function after first acute myocardial infarction using low-dose dobutamine stress echocardiography. Am J Cardiol 1994;74:853-6. 5. Passoni F, D'Urbano M, Cafiero F, Castelli C, Spaziani D, Cammelli F, Romano S. Comparison of dobutamine echocardiography to thallium reinjection scintigraphy for identification of viable myocardium in patients with acute myocardial infarction [Abstract]. Eur Heart J 1993; 14:446. 6. Athanassopoulos G, Koutelou M, Maginas A, Voudris V, Pontikalds N, Cokkinos P, Cokkinos DV. Wall thickness of akinetic segments at rest correlates with dobutamine stress echocardiography and TI-201 SPECT reinjection for the detection of myocardial viability [Abstract]. Circulation 1994;90:116. 7. Marwick T, Baudhuin T, Willemart B, D'Hondt AM, Wijns W, Detry JM, Melin J. Direct comparison of thallium reinjection scintigraphy and dobutamine stress echocardiography for the diagnosis of viable myocardium in patients late after myocardialinfarction [Abstract]. Eur Heart J 1992;13"44. 8. SchiUer NB, Shah PM, Crawford M, DeMaria A, Devereaux R, Feigenbaum H, GutgeseU H, Reichek N, Sahn D, Schnittger I, Silverman NH, Tajik AJ. Recommendations for quantification of the left ventricle by two-dimensional echocardiography. J Am Soc Echocardiogr 1989;2:35867. 9. Sawada SG, Segr DS, Ryan T, Brown SE, Dohan AM, Willi~ns R, Fineberg NS, Armstrong WF, Feigenbaum H. Echocardiographic detection of coronary artery disease during dobutamine infusion. Circulation 1991;83:1605-14. 10. Le Feuvre C, Vacheron A, Metzger JP, Georges JL, Etienne D, Albarede P, deVernejoul P. Prognostic value of thallium-201 myocardial scintigraphy after transoesophageal pacing in patients with suspected coronary artery disease. Eur Heart J 1993;14:1195-9. 11. Panza JA, Dilsizian V, Laurienzo JM, Curiel RV, Katsiyiannis PT. Relation between thallium uptake and contractile response to dobutamine. Implications regarding myocardial viability in patients with chronic coronary artery disease and left ventricular dysfunction. Circulation 1995;91:990-8. 12. Cigarroa CG, de Filippi CR, Brickner ME, Alvarez LG, Wait MA, Grayburn PA. Dobutamine stress echocardiography identifies hiber-

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30. Afridi I, Kleiman NS, Raizner AE, Zoghbi WA. Dobutamine echocardiography in myocardial hibernation: optimal dose and accuracy in predicting recovery of ventricular function after coronary angioplasty. Circulation 1995;91:663-70. 31. Zhang J, Path G, Chepuri V, Homans DC, Merkle H, Hendrich K, Ugurbil K, Bache RJ. Effects of dobutamine on myocardial blood flow, contractile function, and bioenergetic responses distal to coronary stenosis: implications with regard to dobutamine stress testing. AM HEARTJ 1995;129:330-42. 32. Perrone-Filardi P, Pace L, Prastaro M, Piscione F, Betocchi S, Squame F, Vezzuto P, Soricelli A, Indolfi C, Salvatore M, Chiariello M. Dobutamine echocardiography predicts improvement of hypoperfused dysfunctional myocardium after revascularization in patients with coronary artery disease. Circulation 1995;91:2556-65.

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