Assessment of non-reperfused and reperfused myocardial infarction using diffusible or deposited radiolabelled perfusion imaging agents.

PURPOSE: Incomplete microvascular reperfusion is often observed in patients undergoing thrombolytic therapy or angioplasty for acute myocardial infarction and has important prognostic implications. We compared the myocardial uptake of diffusible ((201)Tl) and deposited ((99m)TcN-NOET) perfusion imaging agents in the setting of experimental infarction. METHODS: Rats were subjected to permanent coronary occlusion (OCC, n=10) or to 45-min occlusion and reperfusion (REP, n=17). Seven days later, the tracers were co-injected and the animals were euthanised 15 min (all ten rats in the OCC group and 12 rats in the REP group) or 120 min (five rats from the REP group, euthanised at this time point to evaluate any redistribution of the tracers: REP-RED group) afterwards. Infarct size determination and (99m)TcN-NOET/(201)Tl ex vivo imaging were performed. Regional flow and tissue oedema were quantified using radioactive microspheres and (99m)Tc-DTPA, respectively. RESULTS: (99m)TcN-NOET and (201)Tl defect magnitudes were similar in OCC animals (0.11+/-0.01 vs 0.13+/-0.01). In REP animals, (201)Tl defect magnitude (0.25+/-0.02) was significantly lower than the magnitude of (99m)TcN-NOET and flow defects (0.14+/-0.03 and 0.17+/-0.01, respectively; p<0.05), despite the lack of (201)Tl redistribution (REP-RED animals). (99m)Tc-DTPA indicated the presence of oedema in the reperfused area. Blood distribution studies showed that, unlike (99m)TcN-NOET, (201)Tl plasma activity was mostly unbound to plasma proteins. CONCLUSION: (99m)TcN-NOET and (201)Tl delineated the non-viable area in chronic non-reperfused and reperfused myocardial infarction. The significantly decreased (201)Tl defect in reperfused infarction was likely due to partial diffusion of the tracer from the plasma into the oedema present in the infarcted area. Deposited perfusion tracers might be better suited than diffusible agents for the assessment of regional flow following reperfusion of myocardial infarction.

Assessment of insulin sensitivity in vivo in control and diabetic mice with a radioactive tracer of glucose transport: [125I]-6-deoxy-6-iodo-D-glucose.

BACKGROUND: Impairment of insulin-stimulated glucose transport is a characteristic of type 2 diabetes. A radioactive glucose analogue has been synthesized: [(125)I]-6-deoxy-6-iodo-D-glucose. Its biological behaviour in vitro is similar to that of 3-O-methyl-D-glucose, the reference tracer of glucose transport. The aim of the present study was to determine the ability of [(125)I]-6-deoxy-6-iodo-D-glucose to evaluate variations in glucose transport in vivo. METHODS: Biodistributions of [(125)I]-6-deoxy-6-iodo-D-glucose were performed with or without exogenous insulin (iv injection of 1.5 IU/kg) in db/+ non-diabetic control mice and in db/db type 2 diabetic mice, exhibiting a severe insulin resistance characterized by a lack of increase in glucose uptake in response to insulin. RESULTS: In db/+ mice, insulin increased [(125)I]-6-deoxy-6-iodo-D-glucose transport by 30% in most insulin-sensitive tissues (heart, diaphragm and skeletal muscle, p < 0.05) and had no effect in other organs. In db/db mice, [(125)I]-6-deoxy-6-iodo-D-glucose transport in these organs was not modified by insulin. CONCLUSION: [(125)I]-6-deoxy-6-iodo-D-glucose is able to trace in vivo an increase in glucose transport with insulin in non-diabetic mice and a defect of glucose transport in type 2 diabetic mice. It is the first time that an iodinated analogue of glucose has shown such promising results after in vivo injection. The use of this tracer to assess glucose transport in vivo in humans via nuclear imaging warrants further investigation.

Assessment of myocardial viability in patients with previous myocardial infarction by using single-photon emission computed tomography with a new metabolic tracer: [123I]-16-iodo-3-methylhexadecanoic acid (MIHA). Comparison with the rest-reinjection thallium-201 technique.

OBJECTIVES: We compared the ability of rest single-photon emission computed tomography (SPECT) with [123I]-16-iodo-3-methylhexadecanoic acid (MIHA) and the thallium-201 (Tl-201) rest-reinjection technique to detect myocardial viability after infarction. BACKGROUND: After myocardial infarction, MIHA frequently shows increased uptake in the areas with exercise Tl-201 defects (mismatch), even in patients with an irreversible Tl-201 reinjection defect. Whether such increased uptake is indicative of ischemic but viable myocardium is not known. METHODS: We studied 38 patients who 1) underwent exercise SPECT Tl-201 with rest-reinjection and rest SPECT with MIHA before undergoing percutaneous transluminal coronary angioplasty (PTCA) of an infarct-related coronary artery, and 2) were found to have successful revascularization at follow-up angiography. The relation between SPECT results before PTCA and subsequent improvement in left ventricular wall motion was assessed. RESULTS: A mismatch was evident before PTCA in 51 of 76 infarct-related segments and correlated with subsequent improvement in wall motion (overall accuracy 71%), even for the 27 segments whose exercise defects remained irreversible after Tl-201 reinjection (overall accuracy 81%). The finding of a mismatch clearly enhanced the results provided by the finding of > or = 50% Tl-201 uptake as determined at redistribution (p < 0.05), but not as determined at reinjection, although there was a trend toward a better specificity for the findings of a mismatch. CONCLUSIONS: MIHA is an efficient marker of viability inside exercise-underperfused areas after infarction, even in patients with irreversible Tl-201 reinjection defects. Assessment by conventional SPECT of a mismatch between results obtained with a metabolic tracer (MIHA) and a flow tracer analyzed at exercise (Tl-201) as a marker of myocardial viability is a promising area of research.

Metabolic myocardial viability assessment with iodine 123-16-iodo-3-methylhexadecanoic acid in recent myocardial infarction: comparison with thallium-201 and fluorine-18 fluorodeoxyglucose.

The best test presently available to ascertain residual viability within an infarct-related area involves the use of fluorine-18 fluorodeoxyglucose (FDG) to detect the persistence of some cellular metabolism. Rest reinjection of thallium-201 is a less accurate alternative but is easy to perform. Iodinated fatty acids, which are used with standard gamma cameras, are proposed as markers of cellular metabolism. This study was performed to assess the value of 16-iodo-3-methylhexadecanoic acid (MIHA) as a marker of the residual cellular metabolism by comparison with FDG in patients with a recent myocardial infarction, and to evaluate its contribution compared with the 201Tl stress-redistribution-reinjection technique. Stress-redistribution-reinjection 201Tl imaging, rest MIHA imaging and glucose-loaded FDG imaging were performed in 22 patients with recent myocardial infarction. Out of the 628 myocardial segments obtained from the left ventricular analysis, 400 were hypoperfused (relative uptake <0.75 of maximum uptake on stress 201Tl imaging), 177 of which were severely hypoperfused (relative uptake <0.50). Receiver operating characteristic (ROC) curves for predicting metabolic myocardial viability with FDG were derived from the results in respect of (a) 201Tl activity during exercise, redistribution and reinjection and (b) MIHA uptake, using the two FDG thresholds most commonly considered to define metabolic viability (0.50 and 0.60). Analysis of the 400 hypoperfused segments demonstrated that 201Tl reinjection was the most accurate test in predicting the presence of myocardial viability (area under the ROI curves=0.85 and 0.86 at the 0.50 and 0.60 FDG thresholds, respectively; P<0.05 vs other tests). The global predictive values of MIHA and 201Tl reinjection were, respectively, 0.87 and 0.89 at the 0.50 FDG threshold (NS), and 0.82 and 0.87 at the 0.60 FDG threshold (NS). When only the 177 severely hypoperfused segments were considered, 201Tl reinjection remained the most accurate test (accuracy 0.84 at the 0.50 FDG threshold and 0.82 at the 0.60 FDG threshold), while the accuracy of MIHA decreased significantly (0.78 at the 0.50 FDG threshold and 0.73 at the 0.60 FDG threshold, P<0.05 vs 201Tl reinjection). In all circumstances, MIHA was less specific than 201Tl reinjection for the detection of metabolic viability. In conclusion, in patients with recent myocardial infarction, MIHA accurately detects the persistence of metabolic viability, but is not superior to 201Tl.

[Cost/efficacy ratio in the diagnosis of coronary disease. Bayes' analysis by computer: respective role of the exercise test, isotopic methods and coronarography]. / Rapport efficacité/coût du diagnostic de la maladie coronarienne. Analyse bayesienne sur ordinateur: place respective de l'épreuve d'effort, des méthodes isotopiques et de la coronarographie.

UNLABELLED: Between January 1983 and May 1984, 104 patients with no known cardiac pathology were referred by their cardiologist for diagnosis of chest pain. They all underwent coronary angiography which was used as the reference investigation and the following sequential Bayes' analysis was performed. The percentage probability of coronary artery disease was estimated from clinical date (age, sex, characteristics of the chest pain subdivided into 3 groups); an exercise ECG was performed in all cases (classified as positive, negative or non diagnostic); if the probability of coronary artery disease was greater than 95% (or less than 5%) after exercise stress testing the patients was diagnosed as having (or not having) coronary artery disease. If the probability was between 6 and 94% the patient underwent Thallium myocardial scintigraphy (Thallium dipyridamole; analysis on a colour television screen); the coronary risk probability before Thallium was that calculated after exercise stress testing. If after myocardial scintigraphy the coronary risk remained between 6 and 94%, an exercise angioscintigraphy was performed and interpreted in the same way. The clinical and complementary date was analysed on a mini-computer, the values of the sensitivity and specificity of the tests used for the calculation of the probability of coronary artery disease were those previously published by our group. RESULTS: 31/88 (35%) of patients were classified in the 5% risk groups after exercise stress testing (24 coronary artery disease; 7 normals: no errors of classification). Fifty six out of the 88 patients (65%) were classified in the 5% risk group after myocardial scintigraphy (42 patients with coronary artery disease with 41 abnormal coronary angiographies and 14 normal patients, all of whom had normal coronary angiographies; this represents a 1.8% divergence of classification compared with coronary angiography). Angioscintigraphy only classified 3 of the remaining patients, one wrongly, and did not seem to be useful diagnostically as a third-line investigation after Thallium scintigraphy or as a second-line investigation instead of Thallium scintigraphy. This strategy is less costly than carrying out coronary angiography systematically in these patients: if diagnostic coronary angiography is performed alone in patients with a risk of 6 to 94% the cost is 4 800 FF vs 10 400 FF per patient; if coronary angiography is performed in all patients in whom coronary artery disease is possible or certain (all patients with a risk of over 5%), the cost is 8 400 FF vs 10 400 FF per patient, a saving of 20%.(ABSTRACT TRUNCATED AT 400 WORDS)