Author + information
- Received February 1, 1995
- Revision received March 26, 1996
- Accepted May 14, 1996
- Published online October 1, 1996.
- JUERGEN vom DAHL*,
- CARSTEN ALTEHOEFER,
- PETRA BUECHIN,
- RAINER UEBIS,
- BRUNO J MESSMER,
- UDALRICH BUELL and
- PETER HANRATH
- ↵*Address for correspondence: Dr. Juergen vom Dahl, Department of Internal Medicine I (Cardiology), University Hospital, Rheinisch-Westfälische-Technische Hochschule Aachen, Pauwelsstrasse 30, 52057 Aachen, Germany.
- FLORENCE H SHEEHANa
Objectives. This study sought to evaluate an imaging approach using technetium-99m sestamibi scintigraphy and positron emission tomography with fluorine-18 fluorodeoxyglucose for assessment of myocardial viability proved by serial quantitative left ventricular angiography. Furthermore, the influence of successful long-term revascularization on functional recovery was studied.
Background. Previous studies using positron emission tomography of myocardial perfusion and metabolism have demonstrated accurate identification of myocardial viability. However, most of these studies used a qualitative or semiquantitative wall motion analysis approach.
Methods. Nuclear imaging with semiquantitative analysis of tracer uptake was performed in 193 patients with regional wall motion abnormalities. Regions were categorized as normal, viable with perfusion/metabolism mismatch, viable without mismatch (intermediate) and scar. Seventy-two of 103 patients with subsequent revascularization underwent follow-up angiography. In 52 of 72 patients, changes in regional wall motion were measured by the centerline method from serial angiography.
Results. Wall motion improved in mismatch regions from −2.2 ± 1.0 to −1.1 ± 1.4 SD (p < 0.001). In contrast, regions with an intermediate pattern and those with scar did not improve. Restenosis or graft occlusion influenced functional outcome because regions with preoperative mismatch and successful long-term revascularization improved at follow-up (from −2.3 ± 1.0 to −0.8 ± 1.4 SD, p < 0.001), whereas wall motion did not change with recurrent hypoperfusion. Metabolic imaging added diagnostic information, particularly in regions with mild and moderate perfusion defects.
Conclusions. This imaging approach allows detection of viability in regions with myocardial dysfunction. Wall motion benefits most in myocardium with perfusion/metabolism mismatch and successful long-term revascularization.
Regional dysfunction due to coronary artery disease in viable myocardium may be either temporary and spontaneously reversible after early reperfusion [1, 2]or sustained in the presence of chronic hypoperfusion with reversibility after revascularization [3, 4]. Clinical benefit as well as recovery of global and regional left ventricular dysfunction has been documented in patients with depressed ventricular function undergoing surgical revascularization and in patients with previously stable angina pectoris after angioplasty [5–15].
The need for techniques to identify dysfunctioning but viable myocardium is well appreciated because angiographic evaluation of regional perfusion and contractility does not distinguish between viable and irreversibly damaged tissue. Positron emission tomography using fluorine-18 fluorodeoxyglucose allows detection of metabolic changes at the cellular level that occur with either reversible ischemia or irreversible necrosis [16–20]. By measuring functional recovery after revascularization, it has been shown that myocardium with concordant reduction of perfusion and glucose metabolism (“match”) is necrotic, whereas tissue with reduced perfusion but preserved metabolism (“mismatch”) improves after revascularization [21–29]. However, most studies used a semiquantitative visual analysis of regional function and did not always consider the long-term success of revascularization.
The aim of the present study was to evaluate myocardial scintigraphy for measurement of regional perfusion and metabolic imaging by positron emission tomography to assess viability. Regional left ventricular function was analyzed quantitatively from serial contrast angiograms serving as the reference standard of myocardial viability. Furthermore, the influence of vessel patency or recurrent stenosis after revascularization on functional outcome was assessed.
Patient selection. Nuclear imaging for assessment of myocardial viability was sought in patients with angiographically proved coronary artery disease and ischemic wall motion abnormalities considered for coronary revascularization. Patients were included in this prospective angiographic study if they fulfilled the following inclusion criteria: 1) significant stenosis (>70% diameter reduction) or occlusion in one or more major coronary artery; and 2) reduced ventricular contractility by visual analysis (severe hypokinetic wall motion or akinesia) in the region perfused by a stenosed or occluded vessel considered for revascularization. Baseline exclusion criteria were 1) recent myocardial infarction (<6 weeks) or unstable angina pectoris; 2) evidence for a cardiac event (new onset of unstable angina, myocardial infarction, emergency revascularization, cardiopulmonary resuscitation) between baseline studies and revascularization; 3) concomitant heart disease (cardiomyopathy, valve disease); and 4) permanent atrial fibrillation, left bundle branch block and ventricular pacemaker.
Baseline nuclear and clinical data for 111 patients without clinical or angiographic follow-up have been reported previously from our laboratory [30, 31]. The protocol was approved by the local institutional ethical board, and patients gave informed consent.
Single-photon emission computed tomography. Perfusion imaging was performed according to standard protocols [30, 31]. Patients were studied at rest 2 h after injection of 10 mCi of technetium (Tc)-99m sestamibi (Cardiolite, DuPont), with a light meal after tracer application. Data were acquired using a Gammasonics ROTA double-head camera (Siemens, Erlangen) equipped with a low energy all-purpose collimator allowing a simultaneous 360° rotation (180° for each camera head) with 2 × 30 steps of 6° each. Transaxial slices (6.25-mm thickness) were reconstructed using a Butterworth filter third order and a cutoff frequency of 0.5 on a MaxDelta computer system (Siemens, Erlangen).
Positron emission tomography. After 50 g of oral dextrose, 6 to 8 mCi of fluorine (F)18 fluorodeoxyglucose (Nuclear Research Center, Juelich) was injected. Attenuation-corrected static images were acquired 30 to 45 min after tracer injection using an ECAT 953/15 scanner (Siemens/CTI). Because of the one-ring configuration of the scanner, providing 15 transaxial slices over a 5-cm field of view, at least two adjacent bed positions were imaged to cover the entire heart. Transaxial images were reconstructed with a Hanning filter (cutoff frequency 0.4) on a 64 × 64 matrix using a defined zoom factor to obtain the same in-plane pixel size as that for the scintigraphic images. Consecutive pairs of positron emission tomographic slices were then combined to achieve an identical axial pixel size.
Coronary and left ventricular angiography. Cardiac catheterization was performed using the Judkins technique and recorded on cinefilm with 50 frames/s. Left ventricular angiography in the 30° right anterior oblique and 60° left anterior oblique view always preceded coronary angiography . Coronary angiography was performed after intracoronary administration of 0.2 mg of nitroglycerin with documentation in two or more identical orthogonal projections at baseline and at follow-up.
Coronary revascularization. Physicians were not restricted from assessing the nuclear data if the need for revascularization was equivocal. Angioplasty was attempted predominantly in patients with single-vessel disease. The indication was based on clinical or viability imaging information, or both. Thus, if a patient had typical angina or a positive stress test result, or both, he or she underwent angioplasty regardless of nuclear imaging results.
In patients with several viable or ischemic regions, or both, supplied by two or more stenosed vessels, the majority had surgical revascularization. Bypass surgery was performed using standard techniques with complete revascularization if technically feasible. Thus, in case of multivessel disease, regions with evidence for maintained tissue viability as well as those identified as scar were revascularized.
Data analysis.Ventriculograms. Quantitative analysis of ventriculograms was performed in random order without knowledge of clinical, angiographic or nuclear data. Left ventricular ejection fraction was calculated by the area length method . Regional wall motion was analyzed by the centerline method in the distribution territories of the three major coronary arteries (Fig. 1) and expressed in units of standard deviations (SD) of the normal mean, with negative values indicating reduced contractility [33, 34]. Within each vessel territory, wall motion as computed as mean motion of chords in the most abnormally contracting region (Fig. 2) whose length was restricted to 50% of the territory . This “worst case” approach was taken to avoid regression toward the mean value .
Improvement of wall motion ≥1 SD was considered significant [35, 37]. The septum was excluded because of the effects of bypass surgery on septal motion [38, 39]and the indistinguishable influence of either the left anterior descending or right coronary artery in multivessel disease.
Coronary angiography. Angioplasty was considered successful if it reduced diameter stenosis >20%, with a residual stenosis <50% in the absence of in-hospital complications. Restenosis was defined as diameter stenosis >50%. Surgery was considered successful if the venous graft or mammary artery did not reveal a diameter stenosis >50% or a stenosis >50% at the coronary anastomosis.
Analysis of nuclear data. Short- and long-axis cuts of the isotropic transaxial slices of both image sets were rearranged to achieve corresponding tomograms. A previously published method was adapted for semiquantitative analysis [30, 40, 41]. The short-axis slices were divided in 25 regions that were combined into 13 segments (Fig. 3). Sestamibi and fluorodeoxyglucose uptake in each segment was expressed as percent of the region with the maximal sestamibi uptake.
In regions with reduced perfusion (sestamibi ≤70%), sestamibi and fluorodeoxyglucose uptake values for this perfusion defect were used for tissue viability characterization: normal = sestamibi uptake >70% of the reference region; mismatch sestamibi uptake ≤70%, fluorodeoxyglucose minus sestamibi uptake >20% and fluorodeoxyglucose uptake >50%; intermediate = mild reduction of sestamibi uptake of 51% to 70% without evidence for mismatch (fluorodeoxyglucose minus sestamibi uptake ≤20%); and scar = marked reduction of sestamibi ≤50% without evidence for a mismatch (fluorodeoxyglucose minus sestamibi uptake ≤20%). If there was a mixture of different tissue types within one artery territory, the tissue type for most of the corresponding segments was chosen.
Statistical analysis. Results are presented as mean value ± SD. Comparisons between two data sets were made by the Student t test for paired or unpaired data using the analysis software StatView 4.02 (Abacus Concepts, Inc.). Comparisons between more than two groups were performed by analysis of variance combined with Bonferroni/Dunn post hoc testing; p < 0.05 was considered significant.
Patients and clinical follow-up. One hundred ninety-three consecutive patients underwent both cardiac catheterization and nuclear imaging. Baseline characteristics and angiographic data are summarized in Table 1. Sixty-five patients (34%) had single-vessel disease; 54 (28%) had two significant stenoses; and 74 (38%) had multivessel disease.
Eighty-eight patients (46%) were subsequently treated conservatively, and two underwent cardiac transplantation. One hundred three patients (53%) had coronary revascularization (56 bypass surgery, 47 angioplasty). In these 103 patients, the rates of single-, double- and multivessel disease was 27%, 29% and 44%, respectively. Overall, the left anterior descending coronary artery was revascularized in 76 patients (74%), the left circumflex coronary artery in 60 (58%) and the right coronary artery in 67 (65%), with 2.4 ± 1.4 revascularized vessels/patient. Nineteen patients undergoing single- (n = 16) or double-vessel (n = 3) angioplasty had limited revascularization without evidence for ischemia or residual viability in nonrevascularized territories. Demographic and clinical details for patients with and without revascularization are presented in Table 1.
The first interval between angiography and nuclear imaging was 3 ± 2 weeks, and the second was 4 ± 3 weeks until coronary revascularization. Seventeen of 103 patients who underwent revascularization were excluded from angiographic follow-up: in four patients, percutaneous recanalization of an occluded artery was unsuccessful; they were treated medically. Four patients had valve replacement or aneurysmectomy, and three patients died between revascularization and repeat angiography. In six patients, repeat angiography seemed not indicated because of a complicated outcome after revascularization or new, noncardiac diseases without clinical evidence for bypass or angioplasty failure. In another 14 patients, follow-up angiography was refused. These patients were asymptomatic and had no evidence of recurrent ischemia.
Thus, 72 of 103 patients underwent follow-up angiography with an interval of 5 ± 2 months (2 to 20). In 20 of the 72 patients, at least one film was unsuitable for centerline analysis because of insufficient contrast of the ventricular contour or arrhythmias during angiography. The 52 patients with analyzable paired angiograms were the final source for angiographic analysis (Table 1). Sixteen patients (31%) had single-vessel disease; 17 (33%) had double-vessel disease; and 19 (36%) had multivessel disease. Twenty-eight patients underwent angioplasty, of whom 11 had limited revascularization, and 24 underwent bypass surgery.
During the two catheterization procedures, heart rate (70 ± 14 beats/min at baseline, 68 ± 11 beats/min at follow-up), blood pressure (systolic: 135 ± 23 mm Hg at baseline, 131 ± 21 mm Hg at follow-up; diastolic: 73 ± 13 mm Hg at baseline, 72 ± 14 mm Hg at follow-up) and end-diastolic left ventricular pressure (14 ± 5 mm Hg at baseline, 12 ± 6 mm Hg at follow-up) were not significantly different. Cardiac medication, which could influence left ventricular performance, did not differ between both studies.
Nuclear tissue characterization and functional changes at follow-up. One hundred fifty-six coronary territories (52 patients with three territories each) were analyzed. Of these 156 regions, 95 (61%) were revascularized and 61 (39%) were not revascularized. Baseline tracer uptake values are presented in Table 2. Fluorodeoxyglucose uptake of hypoperfused regions differed (by definition) significantly between intermediate, mismatch and scar regions. Nonrevascularized regions displayed normal uptake, indicating no critical stenoses and no evidence of previous infarction.
The results of serial wall motion measurements are presented in Table 2. Wall motion improved in all revascularized regions, from −1.8 ± 1.1 to −1.3 ± 1.3 SD (p < 0.01). This improvement was mainly the effect of changes in mismatch regions, which improved from −2.2 ± 1.0 to −1.1 ± 1.4 SD (p < 0.001) and differed significantly from all other groups (p < 0.01). Typical nuclear and angiographic images of a patient with this mismatch pattern are illustrated in Fig. 4.
In regions with a mismatch, the magnitude of functional improvement did not depend on the baseline discrepancy between perfusion and metabolism. Mismatch regions with a mild perfusion defect (sestamibi uptake 61 ± 6%) but preserved glucose metabolism (97 ± 18%) improved from −2.1 ± 0.9 to −0.9 ± 1.5 SD (n = 22, p < 0.001). Similarly, regions with moderate or severe perfusion defects (sestamibi uptake 44 ± 6%) but preserved fluorodeoxyglucose uptake (90 ± 11%) improved from −2.3 ± 1.1 to −1.6 ± 1.1 SD (n = 16, p < 0.001). Categorizing the mismatch regions by severity of preoperative dysfunction (better or worse than −2 SD) in addition to viability characterization did not reveal significant differences with regard to functional recovery. In contrast, regions with an intermediate pattern (−2.5 ± 0.7 and −2.5 ± 0.7 SD, respectively) and those with scar (−1.9 ± 1.1 and −2.1 ± .8 SD, respectively) did not improve.
Influence of successful long-term revascularization. Follow-up angiography revealed no diameter stenosis >50% in 72 of 95 revascularized vessels. In these 72 regions, wall motion improved from −2.0 ± 1.1 to −1.1 ± 1.4 SD (p < 0.01). In contrast, 23 regions with restenosis or graft occlusion did not improve (−1.1 ± 1.1 and −1.8 ± 1.0 SD, respectively, p = 0.42).
In 28 successfully revascularized regions displaying a perfusion/mismatch pattern (sestamibi uptake 56 ± 10%, fluorodeoxyglucose uptake 92 ± 11%), wall motion improved from −2.3 ± 1.0 to −0.8 ± 1.5 SD (p < 0.001), whereas 10 regions with a mismatch (sestamibi uptake 56 ± 8%, fluorodeoxyglucose uptake 105 ± 30%) but evidence for recurrent hypoperfusion did not change (−2.0 ± .6 and −2.0 ± .4 SD, respectively).
Predictive accuracy of viability assessment. To evaluate whether the chosen viability categorizations and the predictive value would be influenced by different thresholds for the definition of functional improvement, several thresholds from 0.5 to 2 SD were tested in those regions with reduced perfusion (≤70%), dysfunction of at least −1 SD and successful revascularization (Table 3). According to these results and previous reports [35, 37], the threshold of 1 SD was chosen for the following analysis of the different tissue categorizations and the separate analysis of sestamibi and fluorodeoxyglucose.
Of all 38 mismatch regions, 52% recovered at follow-up angiography. The predictive accuracy of a mismatch pattern increased to 68% in 28 regions with successful revascularization, whereas 90% of mismatch regions with evidence for restenosis or graft failure did not recover. In contrast, tissue categorization as scar resulted in the accurate prediction of nonrecovery in 93% of 14 revascularized regions. Similarly, 12 (92%) of 13 viable regions with an intermediate nuclear pattern did not improve. The effect of the presence or absence of a mismatch pattern in regions with reduced perfusion and successful revascularization on the prediction of functional outcome is presented in Table 4.
Prediction of functional recovery by sestamibi and fluorodeoxyglucose. To evaluate the predictive value for functional changes of both imaging techniques separately, regions were classified by baseline sestamibi and fluorodeoxyglucose uptake. Sensitivity, specificity and, perhaps more important, positive and negative predictive values are presented in Table 5. Severe sestamibi defects were associated with lack of functional improvement in 75% of segments, whereas in regions with moderate or mild defects, a substantial number of segments recovered (Fig. 5). Fig. 5 also illustrates that the positive predictive value significantly decreases for sestamibi uptake >70% because these regions had normal rest perfusion at baseline and did not show further functional improvement after revascularization.
In contrast, fluorodeoxyglucose uptake had the highest positive predictive value in segments with uptake values >100% (Fig. 5), indicating relative elevated glucose uptake compared with sestamibi uptake, which was 58 ± 18% in these regions. Reduced fluorodeoxyglucose uptake was associated with lack of functional improvement in 75% of segments.
Changes in global function. Overall, global ejection fraction improved from 46.8 ± 10.3% to 51.5 ± 10.8% (p < 0.01). Left ventricular improvement was similar in patients undergoing angioplasty (47.2 ± 11% and 52.5 ± 9.9%, respectively, p < 0.05) and in those receiving surgical treatment (46.1 ± 9.5% and 50.3 ± 11.9%, respectively, p < 0.05). Ejection fraction improved in 23 patients with revascularization of one or more mismatch territory and no restenosis (from 46.7 ± 10.1% to 54.4 ± 10.2%, p < 0.01). In patients without revascularization of a mismatch region, ejection fraction did not change (46.9 ± 11.1% and 41.6 ± 12.7%, respectively, p = 0.26).
To our knowledge, the present study is the first to use serial left ventricular angiography with quantitative regional wall motion analysis to validate the diagnostic information achieved from single-photon emission computed tomography with Tc-99m sestamibi and positron emission tomography with F-18 fluorodeoxyglucose. Furthermore, the study evaluates the influence of sustained vessel patency after coronary revascularization on functional recovery. The results confirm and validate, using quantitative angiographic data, previous publications reporting the influence of tissue viability on functional outcome.
Regional tissue viability and functional outcome. Our study agrees with previous publications [21–29, 42]reporting functional recovery of myocardium with evidence for maintained viability. In the present study, recovery of viable myocardium was more pronounced in regions displaying a perfusion/metabolism mismatch compared with those showing maintained metabolism but no evidence of severe rest hypoperfusion (the intermediate group). This finding supports the hypothesis that preserved or elevated fluorodeoxyglucose uptake in the presence of reduced perfusion reflects “hibernating” myocardium [3, 4]. This assumption is supported by the low sestamibi uptake in these regions, indicating decreased rest perfusion. However, we can not completely rule out that the low sestamibi signal indicates to some extent additional subendocardial necrosis and that repetitive stunning episodes, as recently proposed , might have influenced ventricular function.
In contrast to mismatch regions, dysfunctioning regions with only mildly reduced perfusion but without a mismatch did not recover. This phenomenon most probably reflects myocardium with nontransmural necrosis and islets of viable myocardium, resulting in an imaging signal of a “mild match.” In these regions, the amount of hibernating myocardium may be too small to result in angiographically measurable improvement, but revascularization may prevent further ventricular enlargement and functional deterioration resulting from repetitive episodes of stress-induced ischemia. Furthermore, the functional reserve may be improved after revascularization. Preliminary long-term follow-up data indicate, that revascularization of patients displaying these intermediate pattern resulted in subjective functional improvement .
The finding that the severity of the perfusion/metabolism mismatch did not affect the magnitude of improvement was an observation for which there is no obvious explanation because one would expect that the more severe the flow reduction at baseline the higher the functional improvement after restoration of perfusion. However, the baseline wall motion abnormality in the present study did not correlate with severity of flow reduction, which might explain the missing difference in functional outcome.
Severity of baseline wall motion abnormality did not distinguish between viable and potentially salvageable regions and those with irreversible damage. This finding supports the baseline hypothesis that coronary angiography in combination with left ventricular angiography does not allow differentiation of myocadial viability.
Influence of revascularization success. In addition to preoperative tissue characterization by nuclear imaging, the second factor influencing postoperative outcome was revascularization success. In regions with a preoperative mismatch pattern, restenosis or graft occlusion prevented functional improvement, a finding in agreement with reports without viability imaging [7, 15, 44, 45]. Because there are no serial angiograms of individual patients at several time points, we do not know whether wall motion recovered initially after revascularization and deteriorated again with graft occlusion or recurrent stenosis. Furthermore, a fixed cut point of 50% diameter stenosis has inherent limitations because it does not assess functional consequences of stenoses. Studies in patients undergoing perfusion scintigraphy after revascularization support our findings [46–48]. Thus, the results indicate that restenosis or graft failure should be considered if dysfunctioning regions with a preoperative mismatch do not recover.
Incremental diagnostic value of metabolic imaging. Metabolic imaging using fluorodeoxyglucose with evidence for a perfusion/metabolism mismatch added diagnostic information, particularly in regions with mild or moderate sestamibi defects. Severely depressed sestamibi uptake had a high predictive value for irreversibility of functional damage. Thus, in regions with severely reduced sestamibi uptake, metabolic imaging is unlikely to affect substantially therapeutic consequences and should therefore be restricted to patients with moderate or mild defects. This finding is supported by previous observations, [31, 49, 50]demonstrating metabolic activity in only few regions with severely reduced sestamibi uptake but a significant underestimation of viability in regions with moderately reduced perfusion.
Limitations and technical considerations. Despite the baseline analysis of nuclear data from 13 left ventricular segments, we chose large angiographic territories to assess functional changes. This approach limits the sensitivity to detect small regions with rest hypoperfusion, maintained viability and recovery of function because they are averaged by the centerline method. Furthermore, the threshold of 1 SD to define improvement may also explain the lower positive predictive value compared with previous reports [21, 22, 24, 26–29]. This threshold has been found to be most meaningful in previous studies [35, 37]. In the present study, the specificity was rather low, which was mainly due to several regions with a mismatch but functional improvement <1 SD.
A challenging problem in combining tomographic studies with two-dimensional angiographic images is the exact localization and alignment of regions. The large angiographic territories and subsequent adaptation of tomographic segments limit this problem because minor regional misalignments are averaged . Furthermore, comparison of data acquired by different nuclear imaging techniques inherits other intrinsic technical aspects that have been discussed in detail previously [30, 31, 41, 51, 52]. These differences include the problem of missing attenuation correction for single-photon imaging, the partial volume effect and the different spatial resolution of the tomographs. Specifically, in regions with reduced systolic thickening, positron emissions tomography is superior to scintigraphy for detecting the counts in these regions because of the higher spatial resolution capacity. Furthermore, besides the presence of “true” perfusion/metabolism mismatches, missing attenuation correction with scintigraphy seems to be an important reason for discordancies between uptake of sestamibi and fluorodeoxyglucose, resulting in “false” mismatches, particularly in inferior regions [49, 51, 52]. In the present study we found no significant differences in functional outcome between different regions.
Sestamibi at rest-4-h redistribution-stress imaging, as recently used , may improve the viability imaging capacity of sestamibi and reduce the rate of discordant results between the dual-imaging modality technique. More studies with assessment of functional changes after revascularization, as recently published , need to elucidate further the ability of sestamibi to trace myocardial viability.
In our study, regional sestamibi and fluorodeoxyglucose uptake were normalized to the region with maximal sestamibi uptake . This approach implies that the region with highest sestamibi signal reflects “normal” perfusion. In patients with multivessel disease, this assumption might result in overestimation of sestamibi uptake in hypoperfused myocardium.
It would have been ideal to perform complete revascularization in all patients without knowledge of scintigraphic data. In the present study, surgeons or interventional cardiologists were not blinded to the results of viability assessment. Thus, the proportion of patients with nonviable myocardium after revascularization may be underestimated because those without refractory symptoms would have been relegated to medical therapy. However, this should not alter the results because wall motion in these patients has been previously shown [21, 22, 29]not to benefit from revascularization. Furthermore, recent reports [43, 54–57]indicate that revascularization of patients without evidence for jeopardized myocardium does not alter the functional status or the rate of future cardiac events. This conceptional limitation of our study is inherent in all previously published data; to our knowledge, there is no study with prospective revascularization of all patients in which investigators were blinded to the results of viability imaging.
Finally, our study and follow-up results from other groups [28, 52, 58]provide evidence that the combination of scintigraphic perfusion imaging and metabolic imaging by positron emission tomography allows clinically useful diagnostic identification of myocardial viability. Thus, the availability of an on-site cyclotron is not mandatory for assessment of viability using positron emission tomography with F-18 fluorodeoxyglucose. This should be considered if cost aspects of viability imaging are discussed.
Conclusions. A combined nuclear imaging approach using resting Tc-99m sestamibi single-photon emission computed tomography for assessment of myocardial perfusion and positron emission tomography with F-18 fluorodeoxyglucose for detection of preserved metabolism allows identification of viability in regions with myocardial dysfunction. Metabolic imaging added most diagnostic information in regions with mild or moderate perfusion defects, whereas severely reduced sestamibi uptake was associated with a high probability of irreversible dysfunction. Improvement of regional wall motion was greatest in myocardial regions with evidence for a preoperative perfusion/metabolism mismatch and successful longterm revascularization, whereas restenosis or graft occlusion prevented functional changes even in myocardial regions with preoperative evidence for a perfusion/metabolism mismatch.
The production and delivery of fluorine-18 fluorodeoxyglucose from the Department of Radiochemistry (Prof. Dr. G. Stoecklin, Director) at the Nuclear Research Center in Juelich, Germany is gratefully appreciated.
↵1 This study was supported by Collaborative Research Grant 910576 from the North Atlantic Treaty Organization. It was presented in part at the 43rd Annual Scientific Session of the American College of Cardiology, Atlanta, Georgia, March 1994.
- Received February 1, 1995.
- Revision received March 26, 1996.
- Accepted May 14, 1996.
- THE AMERICAN COLLEGE OF CARDIOLOGY
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