Routine exercise testing or thallium-201 scintigraphy for prediction of cardiac events post-myocardial infarction?

The efficacy of 12 lead exercise testing and rest/exercise ²⁰¹Tl scintigraphy as indicators of coronary anatomy and prognosis was compared in 46 low risk survivors of acute myocardial infarction. The non invasive procedures were performed at discharge, and cardiac catheterization was performed six weeks post discharge. On exercise testing, ST depression in leads remote from the site of infarction was considered to indicate multivessel disease and reversible ischaemia. On ²⁰¹Tl scintigraphy, a perfusion defect remote from the site of infarction indicated multivessel disease, while a defect which reperfused at rest indicated reversible ischaemia. During the mean follow-up of 13±3 months, 14(30%) patients experienced cardiac events. Thallium scintigraphy was a more sensitive, but less specific, indicator of multivessel disease than exercise testing. Both exercise testing and ²⁰¹Tl scintigraphy had a similar sensitivity (79% vs 79%), specificity (78% vs 88%) and predictive accuracy (78% vs 85%) for predicting subsequent cardiac events. Thus, in our patient population, ²⁰¹Tl scintigraphy could not be demonstrated to be superior to routine exercise testing in low risk patients post myocardial infarction.     

Routine exercise testing or thallium-201 scintigraphy for prediction of cardiac events post-myocardial infarction?

The efficacy of 12 lead exercise testing and rest/exercise 201Tl scintigraphy as indicators of coronary anatomy and prognosis was compared in 46 low risk survivors of acute myocardial infarction. The non invasive procedures were performed at discharge, and cardiac catheterization was performed six weeks post discharge. On exercise testing, ST depression in leads remote from the site of infarction was considered to indicate multivessel disease and reversible ischaemia. On 201Tl scintigraphy, a perfusion defect remote from the site of infarction indicated multivessel disease, while a defect which reperfused at rest indicated reversible ischaemia. During the mean follow-up of 13 +/- 3 months, 14(30%) patients experienced cardiac events. Thallium scintigraphy was a more sensitive, but less specific, indicator of multivessel disease than exercise testing. Both exercise testing and 201Tl scintigraphy had a similar sensitivity (79% vs 79%), specificity (78% vs 88%) and predictive accuracy (78% vs 85%) for predicting subsequent cardiac events. Thus, in our patient population, 201Tl scintigraphy could not be demonstrated to be superior to routine exercise testing in low risk patients post myocardial infarction.     

The VANQWISH Trial: Support for the nonivasive strategy for risk stratification after acute myocardial infarction

Conclusions  The data from the VANQWISH trial coupled with the results of published studies in the literature during the past 15 years clearly show no advantage of an initial routine invasive strategy for risk stratification and management of uncomplicated postinfarction patients. This conclusion has been derived from observational studies, from randomized studies and from epidemiologic studies looking at variation in practice patterns within regions of the United States and between the United States and Canada. The variables derived from exercise or pharmacologic stress myocardial perfusion imaging can separate the high- and low-risk subgroups perhaps even better than achieved by identification of the extent and severity of coronary anatomic stenoses alone by coronary angiography. Currently the noninvasive risk stratification approach can be undertaken very early (2 to 4 days) using vasodilator stress during hospitalization for patients judged to have an uncomplicated course. Alternatively, submaximal treadmill testing can safely be performed at 4 to 6 days after admission with information obtained relevant to both exercise tolerance and the extent of inducible ischemia. Finally, gated ^99mTc SPECT imaging not only permits the assessment of infarct size and the extent of inducible ischemia but also can be used to quantify the resting left ventricular ejection fraction and determine the extent of regional systolic thickening abnormalities that also have prognostic value. The VANQWISH trial was the first large randomized trial to use stress myocardial perfusion imaging in the noninvasive strategy for risk stratification and was highly effective in identifying a low-risk group, even though planar ²⁰¹Tl imaging was used rather than the more sensitive SPECT imaging approach. Hopefully, clinicians will now be convinced that routine coronary angiography after uncomplicated non-Q-wave or Q-wave infarction with a view toward revascularization of all stenotic vessels is not the desirable approach for achieving optimal cost-effective patient care.     

Fast washout of thallium-201 from area of myocardial infarction: possible artifact of background subtraction

A recent report described a pattern of "reverse redistribution" on poststreptokinase 201Tl studies which was believed to be due to rapid washout of 201Tl from the infarct area related to reperfusion of the infarct vessel. We have also observed the phenomenon of rapid washout of 201Tl from the area of infarction in the absence of thrombolytic therapy. This study was undertaken to test the hypothesis that rapid washout of 201Tl from an area of infarction is an artifact of background subtraction usually employed in analysis of washout. A total of 61 patients with previous myocardial infarction who underwent cardiac catheterization and exercise 201Tl imaging were examined. Thallium-201 images were analyzed using a validated quantitative method employing interpolative background correction. Abnormally increased 201Tl washout was noted in 11 infarct segments in 10 (18%) patients. Infarct segments with rapid washout had significantly less initial uptake, and more severe associated wall motion abnormalities than infarct segments with normal washout. When quantitative analysis was repeated without background subtraction, no segments with rapid washout were observed. A phantom model was constructed to further test our hypothesis. The frequency of observed rapid washout was directly related to the severity of the initial defect and was entirely dependent upon utilizing background correction during the quantitative analysis. Our study suggests that rapid washout of 201Tl in an area of previous infarction reflects an artifact of background subtraction involved with standard quantitative analysis.     

Exercise myocardial perfusion scintigraphy is useful for evaluating myocardial ischemia even in the elderly

Pharmacologic stress testing is recommended to elderly patients as a valuable alternative to exercise testing. We examined whether exercise testing is as useful for evaluating myocardial ischemia in the elderly as in the young. The consecutive 1,508 patients who underwent exercise 201Tl single-photon emission computed tomography (SPECT) were divided into six age groups: 6-29 years (n = 56), 30-44 (n = 143), 45-54 (n = 311), 55-64 (n = 498), 65-74 (n = 402), and 75-88 (n = 98). Both heart rate and rate-pressure product at peak exercise were significantly lower in patients aged 75-88 than in the other five groups. The frequency of ischemic ST depression was higher in patients aged 75-88 than in those aged 6-74, although the difference was not significant. Moreover, the frequency of 201Tl transient defect was significantly higher in patients aged 75-88 than in those aged 6-74. On the other hand, the sensitivity of ischemic ST depression for 201Tl transient defect was similar among the six groups, but the specificity was significantly lower in patients aged 75-88 than in those aged 6-74. In conclusion, exercise 201Tl SPECT is useful for evaluating myocardial ischemia even in the elderly, but exercise electrocardiography has limitations such as lower specificity in the elderly than 201Tl SPECT.     

Quantification of myocardial ischemia and infarction with single photon emission computed tomography

To evaluate the feasibility of ²⁰¹Tl single photon emission computed tomography (SPECT) for quantitative detection of myocardial infarction and ischemia, scintigraphic studies were related to angiographic findings. In study A infarct sizes with SPECT were compared with the angiographic infarct sizes of 30 patients. A linear correlation was found for the % infarct of the left ventricular circumference between both methods (r=0.73; P< 0.001; mean infarct size 20.7%±10.5% (angio) vs 19.8%±12.9% (SPECT), mean±SD). Furthermore, a significant inverse correlation between scintigraphic infarct size and left ventricular ejection fraction (r=-0.87, P< 0.001) was obtained. In study B exercise/rest ²⁰¹Tl SPECT was used for quantification of myocardial ischemia. Forty-three patients underwent both stress ²⁰¹Tl SPECT and biplane exercise left ventriculography. Ischemia was expressed as % defect size of the left ventricular circumference. Sensitivity and specificity for detection of ischemia were 96% and 100% respectively with stress SPECT. Extent of myocardial ischemia correlated significantly with both methods (r=0.63; SPECT defect=1.0 angiographic ischemia +2%; P< 0.001). The regression followed the line of identity and the mean sizes of ischemia were identical (SPECT 12.2±7.6% vs 14.6±12.4% ventriculography, mean±SD) demonstrating the agreement of both methods. However, there was some intraindividual variance between the scintigraphic and the angiographic study. The sensitivity and specificity in single regions with SPECT were lower compared to the global test results. The correlation between the non invasive SPECT and the ventriculography in detection of myocardial infarction and ischemia indicates the clinical value of ²⁰¹Tl SPECT for diagnosis of coronary heart disease.Parts of the results were presented at the 58th sessions of the American Heart Association at Washington, DC (1985)     

Comparison of myocardial perfusion imaging by thallium-201 single-photon emission computed tomography with SUNY4001 (adenosine) and exercise--crossover clinical trial at multi-center

We compared the ischemic diagnosis ability and adverse events of 201Tl myocardial perfusion imaging with SUNY4001 (adenosine) stress to that with exercise (ergometer) stress both on random crossover trial. Thirty one known or suspected chronic stable angina patients who are able to exercise and 10 healthy volunteers were enrolled for the trial. The early and delayed images were obtained by SPECT imaging. The concordance of diagnoses [ischemia vs. no ischemia] between the two types of stresses was 97.3% (36/37) [Kappa: 0.9068]. The sensitivity and specificity based on the exercise test were 100% (6/6) and 96.8% (30/31) respectively. The incidence of adverse events caused by SUNY4001 and the exercise were 44.7% (17/38) and 52.6% (20/38), respectively. Major adverse events caused by SUNY4001 were BP decrease, flushing and headache. And those by exercise were ST decrease, dyspnea and chest pain. None of the adverse events required the intervention or caused life-threatening complication in the trial. The trial showed that the ischemic diagnosis ability and safety of 201Tl scintigraphy with SUNY4001 stress are almost equal to those of the exercise stress that is considered as the standard stress method. We concluded that 201Tl imaging with SUNY4001 is safe and useful for detecting ischemic heart disease, especially for patients unable to exercise adequately.     

Reverse redistribution of thallium-201 represents a low-risk finding in thrombolysed patients following myocardial infarction

The aim of the study was to evaluate the prevalence and clinical significance of reverse redistribution on thallium-201 imaging in post-myocardial infarction patients who have undergone thrombolytic therapy. Sixty-two patients aged 35–79 (mean 60) years with proven myocardial infarction who had undergone thrombolysis were studied 6 weeks post infarction. Standard stress and 4-h redistribution imaging was performed with ²⁰¹Tl following treadmill exercise. Separate day rest injection of ²⁰¹T1 was given after sublingual nitroglycerine; imaging was performed at 1 h. Planar images were acquired in three standard views and semiquantitative segmental analysis of the images was performed from the unprocessed images. All patients had radionuclide ventriculography for the assessment of left ventricular ejection fraction and wall motion abnormality. Thirty-three patients also had coronary angiography. ²⁰¹T1 scintigraphy revealed fixed defects in 19 patients, reversible defects in 22, and reverse redistribution in 21. Those with reverse redistribution had a significantly higher exercise capacity (P < 0.01). Mean (SD) left ventricular ejection fraction was 46 (12)% for those with fixed defects, 47 (9)% for those with reversible defects and 45 (15)% for patients with reverse redistribution (P = NS). The regional wall motion abnormality score was 8 (5), 11.8 (2.2) and 14.2 (6) respectively in patients with reverse redistribution, redistribution alone and fixed defects. Regions with reverse redistribution revealed less regional wall motion abnormality compared to the other two groups (P < 0.01). Fifteen patients demonstrated significant ²⁰¹Tl uptake in the region showing reverse redistribution, with rest injection of ²⁰¹Tl following sublingual nitroglycerine, suggesting viable myocardium in that region. Patients with reverse redistribution had less residual stenosis of the infarct-related artery than those with fixed or reversible defects. Reverse redistribution on ²⁰¹T1 scintigraphy is a common phenomenon, even at 6 weeks, in patients with myocardial infarction who have received thrombolytic therapy. Areas with reverse redistribution demonstrate ²⁰¹T1 uptake following rest injection, less regional wall motion abnormality and a more patent infarct-related artery. Thus, reverse redistribution in these patients represents a low risk finding which suggests retained myocardial viability and successful thrombolytic therapy.     

ECG gated thallium 201 myocardial images: value in detecting multivessel disease in patients on anti anginal therapy 1-3 months after myocardial infarction

ECG gated 201Tl scintigraphy was compared to non gated images for detecting 2-3 vessel disease 1-3 months after a first uncomplicated myocardial infarction. In all, 111 patients on anti anginal treatment underwent coronary arteriography and stress thallium imaging; 39 showed single vessel disease (SVD), and 72 multivessel disease (MVD). Sensitivity of black and white analog images was 82% for SVD and 8% for MVD. Sensitivity of computerized colored static images was 87% for SVD and 33% for MVD. For gated images, sensitivity was 100% and 92% in patients with SVD and MVD respectively. Specificity for detecting MVD was 95% for black and white images, 77% for computerized colored static images, and 69% for ECG gated images. Thus, ECG gated exercise 201TL scintigraphy is useful for predicting the extent of coronary artery disease 1-3 months after myocardial infarction in patients on anti anginal therapy.     

Assessment of myocardial viability with SPECT and PET imaging

The use of thrombolytic therapy for the treatment of acute myocardial infarction has increased the number of patients presenting for assessment of myocardial viability. Stress SPECT 201Tl perfusion imaging performed in the conventional manner with delayed imaging at 4 hr can identify a large percentage of patients with ischemic but viable areas of myocardium. In some patients, delayed imaging up to as long as 24-48 hr after exercise may be required to show 201Tl redistribution indicative of viability. Thus, in most patients, stress 201Tl scintigraphy will correctly identify the presence of viable myocardium. PET imaging, with its ability to assess blood flow and metabolism separately, offers the ability to identify myocardial areas with diminished blood flow but preserved metabolism. Areas with such a blood flow-metabolism mismatch may benefit from revascularization, even in the absence of 201Tl redistribution. The exact role PET will play in the initial evaluation of patients presenting for assessment of myocardial viability remains to be established as more clinical data are accumulated.     

Quantification of myocardial ischemia and infarction with single photon emission computed tomography

To evaluate the feasibility of 201Tl single photon emission computed tomography (SPECT) for quantitative detection of myocardial infarction and ischemia, scintigraphic studies were related to angiographic findings. In study A infarct sizes with SPECT were compared with the angiographic infarct sizes of 30 patients. A linear correlation was found for the % infarct of the left ventricular circumference between both methods (r = 0.73; P less than 0.001; mean infarct size 20.7% +/- 10.5% (angio) vs 19.8% +/- 12.9% (SPECT), mean +/- SD). Furthermore, a significant inverse correlation between scintigraphic infarct size and left ventricular ejection fraction (r = -0.87, P less than 0.001) was obtained. In study B exercise/rest 201Tl SPECT was used for quantification of myocardial ischemia. Forty-three patients underwent both stress 201Tl SPECT and biplane exercise left ventriculography. Ischemia was expressed as % defect size of the left ventricular circumference. Sensitivity and specificity for detection of ischemia were 96% and 100% respectively with stress SPECT. Extent of myocardial ischemia correlated significantly with both methods (r = 0.63; SPECT defect = 1.0 angiographic ischemia +2%; P less than 0.001). The regression followed the line of identity and the mean sizes of ischemia were identical (SPECT 12.2 +/- 7.6% vs 14.6 +/- 12.4% ventriculography, mean +/- SD) demonstrating the agreement of both methods. However, there was some intraindividual variance between the scintigraphic and the angiographic study. The sensitivity and specificity in single regions with SPECT were lower compared to the global test results.(ABSTRACT TRUNCATED AT 250 WORDS)     

Incremental value of left ventricular ejection fraction for detection of multivessel coronary artery disease in exercise (201)Tl gated myocardial perfusion imaging.

Assessment of reversible defects in exercise (201)Tl perfusion SPECT has low sensitivity and high specificity for detection of multivessel coronary artery disease (CAD). The goal of this study was to evaluate whether the left ventricular ejection fraction (LVEF) in exercise (201)Tl gated SPECT had incremental diagnostic value over perfusion data for detection of multivessel CAD. METHODS: One hundred eighty-two patients underwent exercise (201)Tl gated SPECT. Automated LV function analysis software was used for calculation of the postexercise and the rest LVEF. The best threshold between 0- to 1-vessel CAD and 2- to 3-vessel CAD was determined as the cutoff that on receiver-operating-characteristic analysis resulted in the best sensitivity for detection of multivessel CAD with an associated specificity of >90%. RESULTS: Only 18 (26.9%) of 67 patients with multivessel CAD had reversible defects in multiple territories. Sensitivities of the postexercise and the rest LVEF and the worsening of the LVEF by exercise did not differ from those of perfusion data alone. Sensitivities of the combination of perfusion data and the postexercise and rest LVEF did not differ from those of perfusion data alone, whereas the sensitivity of the combination of perfusion data and worsening of the LVEF (i.e., reversible defects in multiple territories or worsening of the LVEF >5.6% [or both]) was significantly greater than that of perfusion data alone (43.3% vs. 26.9%; P < 0.05), with an acceptable level of specificity (90.4%). CONCLUSION: The worsening of the LVEF by exercise has the potential to detect patients with multivessel CAD among those without multivessel patterns of reversible defects.     

Effects of diltiazem on myocardial perfusion abnormalities during exercise in patients with hypertrophic cardiomyopathy

The effect of diltiazem on myocardial ischemia in patients with hypertrophic cardiomyopathy (HCM) was evaluated by exercise myocardial²⁰¹Tl single photon emission computed tomography (SPECT). Exercise myocardial SPECT was performed before and 8 weeks after oral administration of diltiazem (180 mg/day) in 20 patients with HCM who showed transient perfusion defects on exercise myocardial²⁰¹Tl SPECT under control conditions. SPECT images were divided into 17 segments. The²⁰¹Tl perfusion defects were visually scored and evaluated as the defect score. The transient dilation index was calculated as an index of subendocardial ischemia. Improvement of the defect score was demonstrated in 15 patients after the administration of diltiazem. The mean defect score decreased significantly from 9.90± 5.17 to 5.50±4.89 (p < 0.0001). Although 16 of 20 patients showed an abnormal transient dilation index before diltiazem treatment, 16 showed improvement and 13 of these normalized after diltiazem therapy. The mean transient dilation index decreased from 1.16 + 0.10 to 1.02 ± 0.09 (p < 0.0001). In conclusion, diltiazem prevents or diminishes myocardial ischemia in patients with HCM.     

Stress-induced myocardial ischemia is associated with early post-stress left ventricular mechanical dyssynchrony as assessed by phase analysis of 201Tl gated SPECT myocardial perfusion imaging

Purpose

In ²⁰¹Tl SPECT myocardial perfusion imaging (MPI) data are acquired shortly after the stress injection to assess early post-stress left ventricle (LV) function. The purpose of this study was to use ²⁰¹Tl SPECT MPI to investigate whether stress-induced myocardial ischemia is associated with LV mechanical dyssynchrony.

Methods

Enrolled in the study were 75 patients who were referred for dipyridamole stress and rest ²⁰¹Tl gated SPECT MPI. The early post-stress scan was started 5?min after injection, and followed by the rest scan 4?h later. The patients were divided into three groups: ischemia group (N?=?25, summed stress score, SSS, ≥5, summed rest score, SRS, <5), infarct group (N?=?16, SSS ≥5, SRS ≥5) and normal group (N?=?34, SSS <5, SRS <5). LV dyssynchrony parameters were calculated by phase analysis, and compared between the stress and rest images.

Results

In the ischemia group, LV dyssynchrony was significantly larger during stress than during rest. On the contrary, LV dyssynchrony during stress was significantly smaller than during rest in the normal and infarct groups. LV dyssynchrony during rest was significantly larger in the infarct group than in the normal and ischemia groups. There were no significant differences in LV dyssynchrony during rest between the normal and ischemia groups.

Conclusion

Stress-induced myocardial ischemia caused dyssynchronous contraction in the ischemic region, leading to a deterioration in LV synchrony. Normal myocardium had more synchronous contraction during stress. The different dyssynchrony pattern between ischemic and normal myocardium early post-stress may aid the diagnosis of coronary artery disease using ²⁰¹Tl gated SPECT MPI.     

201Tl-redistribution analysis in early and delayed myocordial scintigrams of patients with coronary heart disease (CHD)

Scans were performed on 8 healthy subjects and 25 with coronary heart disease proven by angiography and ventriculography including 6 with previous myocardial infarction at rest, exercise, and 1 and 2 h after exercise. Data were collected by a gamma camera interfaced to a data collection system. In healthy subjects ²⁰¹Tl distribution was homogeneous at rest and after exercise, the count rate ranging between 100%—as set in the region of maximum—and 80% over other regions of myocardium. In 19 patients with coronary heart disease it was uniform only at rest; 6 patients with previous myocardial infarction had locally diminished ²⁰¹Tl uptake even at rest. In patients with coronary heart disease without previous myocardial infarction, scans made immediately after exercise showed significant ²⁰¹Tl hypofixation in region of minimum, the count rate of which was less than 80% of the count rate as determined over region of maximum, ²⁰¹Tl uptake. Scans made 1 and 2 h after exercise had filling-in of ²⁰¹Tl within the region of minimum the count rate of which returned to the normal range of at least 80% of the count rate measured over region of maximum uptake. This return to resting distribution was called ²⁰¹Tl redistribution. Six patients with coronary heart disease and previous myocardial infarction had ²⁰¹Tl defects larger after exercise than at rest, without redistribution being observed. Redistribution in late postexercise scans is a sign of reversible ischemia in coronary heart disease. Scans at rest may be omitted in coronary heart disease, because transient ischemia is undetectable, unless spontaneous angina occurs during scan procedure.     

Incremental value of assessment of regional wall motion for detection of multivessel coronary artery disease in exercise (201)Tl gated myocardial perfusion imaging.

Assessment of reversible perfusion defects in exercise (201)Tl perfusion SPECT has low sensitivity and high specificity for detection of multivessel coronary artery disease (CAD). The goal of this study was to evaluate whether worsening of left ventricular regional wall motion assessed by an automated algorithm in exercise (201)Tl electrocardiography-gated SPECT had incremental diagnostic value over perfusion data for detection of multivessel CAD. METHODS: Two hundred one patients underwent exercise (201)Tl gated SPECT. Software that automatically analyzes left ventricular function was used to assess exercise and rest regional wall motion. Regional wall motion on initial images was compared with that on rest images, that is, delayed images for patients without reinjection images and reinjection images for patients with reinjection images. The left ventricle was divided into 9 segments, with individual segments assigned to 3 coronary territories. Worsening of wall motion was defined as worsening in any segment on initial images compared with rest images. RESULTS: Of 73 patients with multivessel CAD, 20 (27.4%) had reversible perfusion defects in multiple coronary territories, 26 (35.6%) exhibited worsening of regional wall motion in multiple territories, and 37 (50.7%) had reversible perfusion defects or worsening of regional wall motion in multiple territories. The sensitivity of the combination of reversible perfusion defect and worsening of regional wall motion was significantly higher than that of reversible perfusion defect alone for detection of multivessel CAD (50.7% vs. 27.4%, P < 0.05). The specificity of the combination of reversible perfusion defect and worsening of regional wall motion for detecting multivessel CAD did not differ from that of reversible perfusion defect alone and that of worsening of regional wall motion alone (94.5% vs. 99.2% and 97.7%, respectively, P = not statistically significant). CONCLUSION: Combined assessment of worsening of left ventricular regional wall motion by exercise and perfusion data in exercise (201)Tl gated myocardial SPECT was more sensitive, with acceptable specificity, than was assessment with perfusion data alone for detection of multivessel CAD.     

Clinical comparison of technetium-99m-teboroxime and thallium-201 utilizing a continuous SPECT imaging protocol.

To examine the advantages of a 99mTc-labeled cardiac perfusion agent, teboroxime or SQ30,217 (Squibb Diagnostics), a prospective study was undertaken comparing it to 201Tl stress testing in 17 patients suspected or known of having coronary artery disease (CAD). All patients were studied utilizing a single-detector SPECT camera with a continuous acquisition imaging protocol. Testing was performed on a treadmill to comparable levels with both agents within a 2-wk period. Concordance between the two studies on a patient by patient basis was seen in 16/17 (94%) patients, and discordance was seen in 1/17 (6%) patients. Comparison of findings between 201Tl and 99mTc-teboroxime on a segment by segment basis showed concordance in 107/119 (90%) segments, and 12/119 (10%) were discordant. Both examinations independently detected an equal number of normal (77) and abnormal (42) segments. There was no significant difference between the two agents in classifying lesions as ischemic, although there were significant differences between thallium and teboroxime in classifying infarct and infarct/ischemia. Technetium-99m-teboroxime SPECT imaging is a clinically useful method for detecting CAD, with a major advantage being the shorter examination time per individual patient study. The mean total examination time for completion of the 99mTc-teboroxime study was 2.5 hr versus 4.0 hr for 201Tl.     

Comparison of reinjection thallium 201 and resting technetium 99m sestamibi tomographic images for the quantification of infarct size after acute myocardial infarction

Background

Both thallium 201 and technetium 99m sestamibi have been used to quantitate infarct size at rest. Exercise²⁰¹Tl scintigraphy has been shown to have powerful prognostic information after myocardial infarction. A single study using these agents that could provide data on infarct size and prognosis would be of value. The purpose of this study was to compare estimates of infarct size by use of²⁰¹Tl and^99mTc sestamibi and to correlate these measurements with left ventricular ejection fraction in patients after acute myocardial infarction.

Methods and Results

The study group consisted of 20 patients who underwent low-level²⁰¹Tl stress studies with reinjection and^99mTc sestamibi resting studies within 4 days. Acute reperfusion was attempted in 18 of 20 patients. For^99mTc sestamibi tomographic imaging, infarct size was quantitated with 60% of maximal counts per slice for five short-axis slices as described in multiple previous studies. The postreinjection delayed²⁰¹Tl images acquired 4 hours after stress were quantitated according to the same threshold method.²⁰¹Tl patient images were also quantitated with a commercially available polar map program and compared with sex-matched control subjects. Ejection fraction was determined for each patient by radionuclide ventriculography 6 weeks later. Ejection fraction was well preserved for the group: mean 0.53±0.10. Infarct size with^99mTc sestamibi was 12%±13% of the left ventricle, which was significantly smaller than either method with²⁰¹Tl: threshold method, 29%±18% of left ventricle; polar map method, 25%±17% of left ventricle (both²⁰¹Tl estimates,p<0.0001 vs^99mTc sestamibi;²⁰¹Tl, 70% threshold vs²⁰¹Tl polar map,p=0.04). There was a significant correlation between infarct size with^99mTc sestamibi and that with²⁰¹Tl (r=0.72 to 0.73;p<0.001). Infarct size with^99mTc sestamibi, however, provided the closest correlation with ejection fraction (r=0.81;p<0.001), with the two²⁰¹Tl quantitative methods providing very similar correlations (r=0.69;p<0.001).

Conclusions

Infarct size with reinjection²⁰¹Tl imaging correlates significantly with resting infarct size with^99mTc sestamibi, although it provides significantly larger estimates. Although both approaches can be combined with a same-day exercise protocol, the closer correlation of infarct size with ejection fraction at 6 weeks suggests that resting infarct size with^99mTc sestamibi may be slightly more accurate.     

Comparative accuracy of various Tl-201 reinjection imaging protocols to detect myocardial viability

The conventional exercise-3 hours-redistribution thallium-201 [²⁰¹Tl] imaging protocol has been recognized to be suboptimal for reliable detection of myocardial viability. Although²⁰¹Tl restreinjection after exercise has improved detection of viable myocardium, it is still underestimated in some patients. The present study was designed to compare detection of viable myocardium in five separate imaging steps: step 1: initial-exercise imaging, step 2: delayed-exercise imaging, step 3: Tl-201 reinjection imaging after delayed-exercise imaging, step 4: separate day rest-reinjection imaging, and step 5: separate day delayed-rest imaging. The study group consisted of 22 patients scheduled for coronary revascularization (either percutaneous transluminal coronary angioplasty or coronary bypass surgery). Pre- and postintervention echocardiographic wall motion and thickness served as independent markers of myocardial viability. Results: Accuracy in identifying myocardial viability gradually improved incrementally from²⁰¹Tl imaging step 1 to step 5. The positive predictive value, negative predictive value and overall accuracy were best for the separate day delayed-rest study (step 5) at 90%, 33% and 78%, respectively. Myocardial segments had fixed defects on separate day delayed-rest²⁰¹Tl imaging (step 5), but nevertheless echocardiographic evidence of myocardial viability indicated less severe defects than segments judged non viable by echocardiography (p = 0.021). The overall accuracy of separate day delayed-rest imaging (step 5) in predicting viability improved to 88% when segments with moderate or mild defects were considered viable. In conclusion, the most reliable predictor of myocardial viability with²⁰¹Tl imaging is defect severity on separate day delayed-rest images.     

Prediction of functional recovery and prognosis in patients with acute myocardial infarction by123I-BMIPP and201Tl myocardial single photon emission computed tomography: A multicenter trial

¹²³I-BMIPP [15-(p-iodophenyl)-3-(R,S)-methylpentadecanoic acid] was developed for metabolic imaging with SPECT. A multicenter collaborative study was conducted on a large patient series to determine whether¹²³I-BMIPP and²⁰¹Tl myocardial SPECT are of use in predicting the prognosis and ventricular function after acute myocardial infarction (AMI). Patients with uncomplicated first AMI underwent resting¹²³I-BMIPP and²⁰¹Tl myocardial SPECT in the subacute phase after the onset of AMI. Of these, 167 patients who had been followed up for an average of 22 months were retrospectively reviewed to predict serious cardiac events and recurrent ischemia. In addition, the association between changes in radionuclide parameters and recurrent ischemia was investigated in Subgroup A (58 patients) who had repeated SPECT in the chronic phase. Furthermore, prediction of the ejection fraction (EF) was investigated in Subgroup B (94 patients) and Subgroup C (76 patients) in whom left ventriculography was performed at the time of discharge and 90 days or more after the onset, respectively. The prognosis was generally favorable, with 4 cases of cardiac death (2%), 3 of heart failure (2%), 4 of nonfatal reMI (2%), and 25 of recurrent ischemia (15%). The results of Cox multivariate regression analysis revealed a high probability of serious cardiac events in patients who were elderly (p = 0.04), who had 90% or more residual stenosis of the infarct-related artery (p = 0.09), and who had a high BMIPP defect score (p = 0.17). There was a high probability of recurrent ischemia in elderly patients (p = 0.10) who had multi-vessel disease (p = 0.03), but no association was found with radionuclide parameters in the subacute phase. In Subgroup A, however, the probability of recurrent ischemia tended to be high in patients with a large mismatch score between¹²³I-BMIPP and²⁰¹Tl in the subacute to chronic phase. An important observation was that the extent of BMIPP defect was more strongly correlated with EF at the time of discharge and 90 days or more after the onset than the extent of Tl defect (r = ?0.60 vs. r = ?0.47, and r = ?0.53 vs. r = ?0.43, respectively). In addition, multiple regression analysis showed that parameters related to the BMIPP defect were also better predictive factors of EF both at the time of discharge and 90 days or more after the onset. In conclusion, resting¹²³I-BMIPP and²⁰¹Tl myocardial SPECT performed in the subacute phase of AMI were shown to be useful in predicting prognosis and ventricular function for patient management.