Clinical value of delayed thallium-201 myocardial imaging in suspected acute myocardial infarction.

Fifty patients with acute chest pain had thallium-201 myocardial imaging performed three to six days after emergency admission to hospital. The image was abnormal in 20 out of 22 patients with acute transmural myocardial infarcts but in only 1 of 5 with acute subendocardial infarcts. Indistinguishable scan abnormalities caused by old infarcts were seen in 7 patients, and caused by myocardial ischaemia in 1 patient. A single thallium-201 myocardial scan some days after the onset of symptoms appears to be of little value in the clinical assessment of patients with suspected acute myocardial infarction.     

Spontaneous changes in thallium-201 myocardial perfusion imaging after myocardial infarction

To examine regional myocardial perfusion after myocardial infarction, 26 patients underwent exercise electrocardiographic testing with thallium-201 myocardial perfusion imaging 3 weeks and 3 months after infarction. At 3 weeks, 9 of 26 patients (35%) had myocardial ischemia by exercise electrocardiographic testing, whereas 18 of 26 (69%) had ischemia by thallium-201 imaging. The thallium-201 scintigrams were scored by dividing each image, in 3 views, into 5 segments, using a 5-point scoring scheme. The exercise thallium-201 score was 44.3 ± 1.2 and increased to 47.3 ± 1.2 in the redistribution study (p < 0.001). Three months after infarction, although there was a significantly greater rate-pressure product which would predict a larger ischemic defect and a decrease in the stress thallium-201 score, the stress score was improved (48.3 ± 1.1, p < 0.001). The redistribution score was similar, that is, 48.9 ± 1.0. The improvement in thallium-201 myocardial perfusion was associated with a loss of stress-induced ischemia in 8 patients (30%). These results indicate that spontaneous improvements in thallium-201 myocardial perfusion imaging may occur after myocardial infarction.     

Clinical significance of the technetium-99m/thallium-201 overlap in acute myocardial infarction

The region of overlap of thallium-201 (Tl) and technetium-99m pyrophosphate (Tc) was evaluated as a scintigraphic prognosticator of future necrosis. Serial time courses of myocardial perfusion according to Tl and left ventricular wall motion evaluated by two-dimensional echocardiography (2D echo) were used in 22 patients. In all, dual energy emission computed tomography (dual-SPECT) showed the Tl/Tc overlap on identical slices on the third post-infarction day. According to the results of dual-SPECT, the patients were categorized in three groups: nine with large Tl/Tc overlap (group A); five with small Tc accumulation and small Tl/Tc overlap (group B); and eight with large Tl defect and Tc accumulation, which are concordant with each other (group C). Tl-201 SPECT and 2D echo were attempted serially on the 1st and 2nd days, the 7th-10th days and the 28th-30th days. To estimate infarct size with Tl-201 SPECT, we measured pixel counts of eight short-axis images with the 40% cut-off level and computed "% defect". To evaluate the viability of the myocardium, "% Tl uptake" was computed from the ROIs both in the centers of the infarct areas and their border zones. 2D echoes of the left ventricular short axis at the chordae tendineae level were recorded to identify the time course of percent fractional area change (% FAC) of the ischemic left ventricular wall. The scintigraphic results were compared with the serial changes of regional ejection fraction in the areas of infarcts and ischemic lesions. The % defect remained unchanged in group C (29.2 +/- 11.5----25.7 +/- 8.3%); whereas those of groups A and B decreased significantly (21.2 +/- 11.3----9.9 +/- 6.3%, 13.8 +/- 2.6----5.4 +/- 2.9%, respectively). In groups A and B, % FAC improved significantly in the centers of the infarct areas and the border zones, but not in group C. Exercise-induced ischemia determined by redistribution of Tl at the chronic phase was observed more frequently in groups A and B than in group C. These findings indicated that more myocardium can be saved from necrosis in group A than in group C. In conclusion, it is suggested that there is considerable viable myocardium in patients with large Tl/Tc overlap on dual-SPECT.     

Evaluation of myocardial infarction by radioisotope myocardial imaging with special reference on thallium-201 myocardial perfusion imaging

One hundred and three patients with myocardial infarctions were studied with 201-thallium chloride and/or 99m-technetium pyrophosphate myocardial imaging and were followed-up for an average of 23 months. There were 24 false negative cases with 201-thallium chloride, but no deaths or serious complications occurred during the follow-up period in these false negative cases. There were six patients with widened QRS complexes (more than 0.12 seconds) without bundle branch blocks and in three of them myocardial infarction was not identified by electrocardiography. However, there were large myocardial perfusion defects in the anterior-inferior wall of the left ventricle. All of this group of patients died suddenly during the follow-up period. The incidence of complications and mortality rose sharply in patients whose myocardial perfusion defects detected by thallium-201 were larger than 40% of the entire left ventricle. The myocardial infarction areas measured by 99m-technetium pyrophosphate were 28.5 +/- 9.8 cm2 in non-survivors and 16.5 +/- 1.7 cm2 in survivors. In addition, ten patients with acute myocardial infarction were studied by double scan methods with thallium-201; myocardial perfusion defect areas were reduced from 29 +/- 3% of the entire left ventricle to 19 +/- 4% by nitrate administration, indicating that there were reversibly ischemic areas in acute myocardial infarction which could be transiently reduced by nitrate. Thus, the study suggests the possibility of decreasing myocardial perfusion defects in the early phase of acute myocardial infarction, leading to a better long term prognosis for the patients.     

Clinical value of immediate thallium-201 reinjection imaging for the detection of ischaemic heart disease

Immediate reinjection of thallium-201 after acquisition of thestress images followed by imaging 60 min later has been proposedas a novel time-saving and patient-convenient approach for theevaluation of myocardial ischaemia and viability. The objectiveof this study was to establish the clinical value of thallium-201stress immediate reinjection imaging in the evaluation of patientswith suspected and known coronary artery disease. Quantitative planar thallium-201 stress immediate reinjectionimaging was performed in 138 patients with undiagnosed chestpain, of whom 114 underwent cardiac catheterization and 24 hada <5% likelihood for coronary artery disease; 56 patientshad previously suffered a myocardial infarction. Sensitivitiesand accuracies were determined for coronary artery disease,reversible myocardial ischaemia, and myocardial viability. Of the 138 patients studied for coronary artery disease, thalliumstress scintigraphy identified 85 of 93 patients with angiographicallyproven coronary artery lesions (overall sensitivity 91%). Thenormalcy rate in the low-likelihood patients was 88% (21 of24 patients) and the overall diagnostic accuracy was 83%. Inthe 56 patients who had suffered a previous myocardial infarction,and in whom the suitability for reversible ischaemia was sought,the overall patient-related sensitivity and accuracy were 93%and 92% respectively. In the 56 patients with a previous myocardialinfarction a total of 168 vessel regions were studied to detectviability. Of the 142 normal or hypokinetic regions, 127 regionswere scintigraphically identified as viable (sensitivity 89%). The thallium stress immediate reinjection imaging protocol isan appropriate clinical approach in patients with undiagnosedchest pain. The combined identification of stress-induced ischaemiaand viability by thallium stress immediate reinjection imagingprovides adequate algorithms allowing optimal management andrisk assessment in the individual cardiac patient.     

Comparison of low-dose dobutamine echocardiography and thallium-201 reinjection for the determination of myocardial viability in the early post myocardial infarction period

OBJECTIVE: Determination of viability in the infarction zone in the early post Ml period is an important parameter in clinical decision making. METHODS: In an attempt to compare the places of low-dose dobutamine echocardiography (LDDE) and thallium-201 reinjection SPECT (TI-SPECT) in the determination of viability in dyssynergic myocardial segments, 17 patients (mean age: 54.6 +/- 12.8 years, 16 male, 1 female) with a recent myocardial infarction and an uneventful early clinical course underwent both tests within 5-13 days of infarction. The 16-segment model was utilised to evaluate the left ventricular wall motion and each segment was graded as 1) normokinetic, 2) hypokinetic, 3) akinetic and 4) dyskinetic or aneurysmal on a 4-scale basis. A dyssynergic segment of myocardium was considered to be viable by LDDE if it showed an improvement in wall motion of at least one grade with low-dose dobutamine infusion (10 microg/kg/min). On the other hand, mild to moderate (< 50%) fixed perfusion defects and reversible (at least a 10% improvement in perfusion on either redistribution or reinjection images) severe (50% or more) perfusion defects were considered positive for viability by TI-SPECT. RESULTS: Of the 76 segments with resting dyssynergy (10 dyskinetic/aneurysmal, 33 akinetic, 33 hypokinetic), 51 (67%) were shown to be viable by LDDE and 61 (80%) by TI-SPECT. There was an agreement of 76% (p = 0.03, K = 0.63) between the two methods. CONCLUSION: This study disclosed a moderate degree of agreement between LDDE and TI-SPECT for the determination of viability in dyssynergic myocardial segments in the early post-myocardial infarction period.     

201Tl静息-再分布显像后行再注射心肌断层显像检测存活心肌的价值

为评价２０１Ｔｌ静息－再分布显像后行再注射显像检测存活心肌的价值,对２４例心肌梗死患者行２０１Ｔｌ静息－再分布－再注射显像。８例经皮穿刺腔内冠状动脉成形术（ＰＴＣＡ）的患者术前及术后２周～４周随访了超声心动图。结果显示２０１Ｔｌ静息显像有９７个心肌节段放射性摄取异常,其中４ｈ再分布显像有可逆性灌注缺损３１个节段,再注射显像均为可逆性缺损;再分布显像为不可逆性灌注缺损的６６个节段,其中９个节段（１３．６４％）再注射显像表现为再充填。２０１Ｔｌ静息－再分布显像和２０１Ｔｌ静息－再分布－再注射显像预测ＰＴＣＡ术后心肌灌注改善的阳性预测值分别为７７．７８％和８０．９５％,阴性预测值分别为７７．７８％和９３．３３％。２０１Ｔｌ静息－再分布显像和２０１Ｔｌ静息－再分布－再注射显像预测存活心肌的准确性分别为７７．７８％和８６．１１％。因此２０１Ｔｌ静息－再分布显像后行再注射显像可提高对部分存活心肌的检出。这种显像方案尤其适合于伴严重左室功能障碍和运动试验有禁忌证的患者的存活心肌的评价。     

Correlation between non-reversible thallium-201 myocardial perfusion defect and ECG criteria in the diagnosis of apical myocardial infarction

BACKGROUND: ECG identification of apical myocardial infarction (MI) is controversial and lacks of accuracy. Our aim was to investigate the sensitivity of different proposed ECG criteria in the presence of apical perfusion defects assessed with SPECT analysis. METHODS: One hundred twenty-four (98 M, 26 F) out of 1500 patients with suspected coronary artery disease, showed apical perfusion defect not reversible at rest and after reinjection at tomographic SPECT analysis during thallium-201 scintigraphy. RESULTS: In the group of 29 patients presenting wide isolated apical perfusion defect (wAPD) Q waves in anterior segments with definition of antero-septal MI was prevalent (51.7%), while few patients (41.3%) presented the ECG criteria of apical MI as proposed in the literature. In 19 of the 25 patients with partial isolated apical perfusion defect (pAPD), the absence of Q wave was clearly prevalent. Fifty patients had a wAPD partially extended in surrounding regions, as anterior or septal, inferior or lateral myocardial segments, in these patients, the site of Q wave location was more variable, with prevalent Q wave in anterior leads, but with more incidence of Q waves in leads II III aVF, especially in patients with associated perfusion defect in inferior segments. Substantially, the same finding resulted in the 20 patients showing a pAPD extended in surrounding myocardial segments. CONCLUSION: In conclusion, the low diagnostic sensitivity of the ECG criteria of identification of apical MI is clearly demonstrated by our analysis carried out using SPECT perfusion scintigraphy, with ECG findings of anterior/anterior-septal myocardial necrosis in the patients with wAPD.     

Coronary artery reperfusion in acute myocardial infarction: assessment by pre- and postintervention thallium-201 myocardial perfusion imaging

In a randomized trial of intracoronary streptokinase (STK) therapy in acute myocardial infarction, 44 patients (21 control subjects and 23 patients treated with STK) underwent sequential thallium-201 planar imaging before angiography and after 4 hours (redistribution), 4 days and 6 weeks. Patients were classified according to the presence or absence of angiographic reperfusion of the infarct-related artery. The semiquantitative score of myocardial thallium uptake was expressed as percent of maximal defect score. Both in control and in STK-treated groups, thallium defect scores decreased over time, but this decrease was smaller in the control group (before angiography, 33 +/- 4%; redistribution, 29 +/- 4%; 4 days, 25 +/- 4%; and 6 weeks, 22 +/- 4%) than in the STK group (44 +/- 4%, 38 +/- 4%, 26 +/- 4% and 21 +/- 3%, respectively). In patients in whom reperfusion was achieved (20 STK-treated, 6 control subjects), a marked decrease in thallium score was observed (before angiography, 40 +/- 4%; redistribution, 32 +/- 4%; 4 days, 20 +/- 5%; and 6 weeks, 14 +/- 22%) compared with patients in whom reperfusion was not achieved (37 +/- 4%, 36 +/- 5%, 33 +/- 5% and 33 +/- 4%, respectively). These results indicate that serial thallium imaging is an accurate method of assessing changes in myocardial perfusion after acute myocardial infarction. Restoration of thallium uptake was observed after reperfusion of the infarct-related artery whether this recanalization was seen spontaneously or after successful thrombolysis.     

Gated cardiac blood pool imaging and thallium-201 myocardial scintigraphy for detection of remote myocardial infarction

The primary goal of this study was to assess the frequency of persistent regional wall motion abnormalities and myocardial perfusion defects detectable late after myocardial infarction with radionuclide ventriculography and thallium-201 imaging, respectively. The study was performed prospectively in 32 patients in whom infarct size was estimated enzymatically at the time of the acute episode and in 10 patients without infarction. Thallium-201 imaging and radionuclide ventriculography were performed with the patient at rest an average of 11 months after infarction (range 6 to 20 months) and analyzed independently by two observers who were unaware of results of other clinical and laboratory data. Perfusion defects were detected in 94 percent (30 of 32) by observer I and in 91 percent (29 of 32) by observer II. Wall motion abnormalities were detected in 78 percent (25 of 32) and 75 percent (24 of 32) by observers I and II, respectively, but in 10 of the patients with an infarct size less than 20 creatine kinase-gram-equivalents (CK-g-eq), wall motion abnormalities were found in only 50 and 40 percent, respectively, by these observers (p <0.04). Electrocardiographic changes of infarction (Q waves) were present in only 56 percent (18 of 32) of patients. Sixty-eight percent of patients with an infarct size greater than 20 CK-g-eq had persistent Q waves but these were present in only 30 percent with an infarct size less than 20 CK-g-eq (p <0.04). The sites of perfusion defects and of wall motion abnormalities corresponded closely and were concordant with electrocardiographic localization. Thus, thallium-201 imaging and radionuclide ventriculography are sensitive noninvasive techniques for identifying prior myocardial infarction, and are particularly helpful in patients with conduction abnormalities or equivocal electrocardiographic findings.     

Clinical significance of reverse redistribution on thallium-201 single-photon emission computed tomography in patients with acute myocardial infarction.

To determine the clinical significance of reverse redistribution (RR), resting thallium-201 myocardial single-photon emission computed tomography was performed once or twice in 80 patients in subacute phase (1 week to 2 months) of myocardial infarction. Thirty eight patients demonstrated RR on at least one study (group RR) and 32 a fixed defect only (group FD). Group RR had significantly smaller defects than group FD. Standardizing the relation of the severity of wall motion abnormality of left ventricle on echocardiogram with that of perfusion defect, in group RR wall motion abnormality in the acute and subacute phase reflected the defect of delayed image, while that in chronic phase, which was thought to reflect the viability of myocardium in the infarct region, reflected the defect of initial image. In serial thallium-201 studies, only the defect of delayed image of group RR improved on the second study, while the defect of initial image of group RR and defect of group FD did not improve. Wall motion of group RR improved with the disappearance of RR, and when RR remained, wall motion did not improve so much. We concluded that RR was thought to be demonstrated in viable myocardium with severe wall motion abnormality.     

Exercise training following myocardial infarction improves myocardial perfusion assessed by thallium-201 scintigraphy

AIM: We assessed the effects of a 6-week exercise programme on the thallium-201 myocardial perfusion characteristics of patients following myocardial infarction. METHODS: Twenty-five patients presenting with a first acute myocardial infarction were randomised into two groups: (i) those undergoing a supervised exercise training programme over 6 weeks (n=15) and (ii) a control group who did not attend the exercise programme (n=10). All underwent three sequential stress thallium myocardial perfusion scans at 10 days, 6 weeks and 3 months after infarction. The stress conditions were identical on each occasion. The images were analysed using a polar plot with a computer assisted algorithm comparing stress and redistribution data. Values for extent, severity and percentage redistribution of the thallium images were generated. RESULTS: A total of 29 perfusion defects were identified, 18 in the exercise group and 11 in the control group. Over 3 months in the exercise group the mean extent of the stress image defect fell from 109+/-64 to 95+/-51 pixels (P<0.05) while in the control group there was an increase from 133+/-57 to 144+/-57 pixels (P=ns). Stress defect severity fell in the exercise group from 581+/-417 to 494+/-346 S.D. (P<0.05) but increased in the control group from 765+/-494 to 877+/-543 S.D. (P=ns). On redistribution imaging in the exercise group a significant decrease was observed in both extent (94+/-56 to 76+/-43 pixels (P<0.05)) and severity (541+/-387 to 438+/-291 S.D. (P<0.05)) of the defects. However in the control group no significant change was observed for extent (125+/-54 to 125+/-52 pixels) or severity (745+/-485 to 820+/-503 S.D.) of the redistribution defects (P=ns). Reversibility of the defects increased slightly in both the exercise group (from 14.6+/-17 to 17.5+/-20%) and the control group (5.2+/-5 to 9.6+10%) (P=ns). CONCLUSION: Following myocardial infarction a 6-week exercise programme improves myocardial perfusion characteristics. An exercise programme should be integrated into cardiac rehabilitation protocols for patients after infarction.     

Quantification of thallium-201 scintigrams in acute myocardial infarction.

A method has been developed for measurement of myocardial infarct size from thallium-201 scintigrams that depends on computer measurement of levels of radioactivity in the myocardium. In 16 dogs, thallium-201 scintigrams were obtained in the left lateral and left anterior oblique projections 48 hours after ligation of the left anterior descending coronary artery. Scintigraphic results were obtained by two independent observers and were compared with tissue measurements of infarct volume calculated from thallium autoradiograms and nitro-blue tetrazolium (NBT)-stained tissue slices. Infarct volumes derived from tissue measurements were used to develop criteria for the computer scintigraphic technique. There was no significant difference in the scintigraphic measurements made by the two observers. Scintigraphic infarct size in the left lateral and left anterior oblique projections correlated with tissue infarct size with r values of 0.88 and 0.75, respectively, for thallium autoradiography and 0.71 and 0.70, respectively, for NBT tissue staining. The range of infarct volume was 3.3 to 14.8 percent of the left ventricular mass. Results of this study suggest that scintigraphic quantitation of infarct size is feasible in this dog model.     

Evaluation of thallium-201 imaging in nontransmural ischemia and infarction

To assess the validity of thallium-201 myocardial imaging in the diagnosis of non-transmural ischemia and infarction, the proximal left anterior descending coronary artery was partially occluded for 60 minutes with a balloon-tip catheter in intact anesthetized dogs in a basal state or during atrial pacing. In vivo sclntigrams of myocardium were compared with those obtained in the isolated heart and in the incised ventricle spread flat. None of the animals with partial occlusion wtth or without pacing demonstrated abnormal scintiscans in vivo. Removal of background by isolating the heart increased positive images to 30%; positive images were associated wtth an isotope count ratio between ischemlc and normal muscle of less than 0.67. Removal of superimposed nonischemic muscle in the heart enface increased image detection after pacing to 11 of 15. Since animals with subendocardlal scar failed to demonstrate a “cold area” in vivo, unfavorable geometry as well as extent and degree of ischemia appear to be important Thus, thallium radioactivity in superimposed and adjacent myocardium, as well as background, may limit the detection of nontransmural ischemia and scar.     

Clinical assessment of myocardial perfusion with thallium-201

Assessment of myocardial perfusion and coronary blood flow in man can be performed reliably and successfully using thallium-201 imaging. The extent of exercise myocardial perfusion abnormalities reflects the functional significance of coronary artery stenosis. Accordingly, myocardial perfusion imaging is not only useful for the detection of coronary artery disease, but it also provides unique functional information which should be helpful in the management of patients with known coronary artery disease. The unfavorable physical properties of thallium-201 have limited to a certain extent full utilization of the clinical potential of the methodology. Now technetium-99m-labeled myocardial perfusion imaging agents promise to further enhance the clinical usefulness of myocardial perfusion imaging in patients.     

Comparison of the predischarge exercise thallium-201 perfusion defect after myocardial infarction with myocardium at risk measured during acute infarction with technetium-99m sestamibi imaging

Background Exercise thallium-201 imaging provides a noninvasive estimate of the amount of myocardium presumed to be at risk of infarcting should a complete occlusion of the coronary stenosis occur. The relationship between the size of the exercise thallium perfusion defect and the extent of myocardium supplied by a diseased coronary artery has not been established. This study evaluates that presumed correlation. Methods Patients were injected intravenously with technetium-99m sestamibi during acute myocardial infarction before thrombolysis or conventional therapy to quantify the myocardium at risk. Twenty-six patients who underwent risk-area assessment subsequently underwent clinically driven, predischarge, submaximal exercise imaging with thallium-201. The exercise testing was performed on day 7 ± 2 days. A conventional polar map display was used to quantify the perfusion defect. Results The myocardium at risk determined by technetium-99m sestamibi at the time of infarction was 30% ± 20% of the left ventricle. The mean exercise thallium-201 defect was 34% ± 22% of the left ventricle. The exercise defect tended to be slightly larger than the myocardium at risk (4% ± 10% of the left ventricle, P = .05). There was a close correlation between the 2 measurements (r = 0.89, SE = 9.4, P < .0001). Conclusions This study shows a close correlation between the myocardium “at risk” assessed acutely by technetium-99m sestamibi and the “presumed at-risk area” determined by thallium-201 imaging on predischarge exercise testing. This finding supports the concept that the size of the exercise thallium defect caused by coronary stenosis indicates the likely size of a myocardial infarction resulting from occlusion of that stenosis. (Am Heart J 2003;145:357-63.)     

Determination of perioperative cardiac risk by adenosine thallium-201 myocardial imaging.

To determine the predictive value of adenosine thallium-201 myocardial imaging for perioperative cardiac events, 60 consecutive patients referred for preoperative cardiac evaluation were studied before vascular (n = 25), orthopedic (n = 14), or general (n = 21) surgery. Tomographic (n = 52) and planar (n = 8) thallium-201 imaging was performed after adenosine infusion at a rate of 140 micrograms/kg/min for 6 minutes. Two blinded expert observers graded results of adenosine thallium-201 studies as normal (33%), fixed defect only (2%), reversible defect only (48%), and combined (fixed and reversible) defects (17%). After 6 +/- 3 months of follow-up, 81% proceeded to surgery and 43% underwent preoperative coronary angiography. Clinical variables that correlated with perioperative cardiac events were a history of diabetes mellitus (p = 0.05), left bundle branch block (p = 0.02), and left ventricular hypertrophy (p = 0.06) on the resting ECG. This clinically "high-risk" group had an event rate of 22% as compared with no cardiac events in patients in the "low-risk" group without these clinical characteristics (p = 0.005). Stepwise logistic regression analysis revealed that the presence of a combined (fixed and reversible) adenosine thallium-201 defect (p = 0.0007), three-vessel coronary artery disease (p = 0.001), and left bundle branch block (p = 0.02) was predictive of subsequent cardiac events with relative risk ratios of 4.9, 2.9, and 2.2, respectively. Therefore the presence of an adenosine thallium-201 perfusion defect is correlated with and predictive of an increased risk of perioperative cardiac events in patients referred for preoperative risk evaluation.