Identification of viable myocardium in patients with chronic coronary artery disease and left ventricular dysfunction. Comparison of thallium scintigraphy with reinjection and PET imaging with 18F-fluorodeoxyglucose.

Abstract

In patients with chronic coronary artery disease and left ventricular dysfunction, the distinction between ventricular dysfunction arising from myocardial fibrosis and ischemic, but viable, myocardium has important clinical implications. By positron emission tomography (PET), enhanced fluorine-18-labeled fluorodeoxyglucose (FDG) uptake in myocardial segments with impaired function and reduced blood flow is evidence of myocardial viability. Reinjection of thallium-201 at rest immediately after stress-redistribution imaging may also provide evidence of myocardial viability by demonstrating thallium uptake in regions with apparently "irreversible" defects. To compare these two methods, we studied 16 patients with chronic coronary artery disease and left ventricular dysfunction (ejection fraction, 27 +/- 9%), all of whom had irreversible defects on standard exercise-redistribution thallium single-photon emission computed tomography (SPECT) imaging. Thallium was reinjected immediately after the redistribution study, and SPECT images were reacquired. The patients also underwent PET imaging with FDG and oxygen-15-labeled water. A total of 432 myocardial segments were analyzed from comparable transaxial tomograms, of which 166 (38%) had irreversible thallium defects on redistribution images before reinjection. FDG uptake was demonstrated in 121 (73%) of these irreversible defects. Irreversible defects were then subgrouped according to the degree of thallium activity, relative to peak activity in normal regions. Irreversible defects with only mild (60-85% of peak activity) or moderate (50-59% of peak) reduction in thallium activity were considered viable on the basis of FDG uptake in 91% and 84% of these segments, respectively. In contrast, in irreversible defects with severe reduction in thallium activity (less than 50% of peak), FDG uptake was present in 51% of segments. In such severe defects, an identical number of segments (51%) demonstrated enhanced uptake of thallium after reinjection. In these severe "irreversible" defects, data on myocardial viability were concordant by the two techniques in 88% of segments, with 45% identified as viable and 43% identified as scar on both PET and thallium reinjection studies. These observations suggest that thallium imaging can be used to identify viable myocardium in patients with chronic coronary artery disease and left ventricular dysfunction. Most irreversible defects with only mild or moderate reduction in thallium activity represent viable myocardium as confirmed by FDG uptake.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of Dysfunctional Myocardium by Positron Emission Tomography and Magnetic Resonance

“…Revascularization was performed 31Ϯ21 and 30Ϯ27 days after the MR and PET studies, respectively, and follow-up MR was performed 11Ϯ2 months after intervention (without clinical evidence of myocardial infarction during follow-up). One patient with medical treatment died during the follow-up period, and 1 (Figure 1) demonstrates that the threshold value of 50% FDG uptake often used to predict functional recovery 22,23,25 corresponds to a rim thickness of Ϸ4.5 mm. Application of these PET and MR criteria for predicting functional recovery (Ն50% FDG uptake relative to the reference segment and rim thickness Ͼ4.5 mm on ce-MR, respectively) yielded 4 classes of myocardial segments, as follows: (1) thick metabolically viable segments (PET/MRϩ/ ϩ); (2) thin metabolically nonviable segments (PET/MRϪ/ Ϫ); (3) thin but metabolically viable segments (PET/MRϩ/ Ϫ); and (4) thick metabolically nonviable segments (PET/ MRϪ/ϩ).…”

“…These findings are in keeping with histological data of hibernating tissue that demonstrated severe ultrastructural changes of myocytes with intact cell membranes. 12,13 Conversely, in approximately half of segments with an impaired FDG uptake (predicting lack of functional recovery 22,23,25 ), the thickness of viable tissue on MR exceeded 4.5 mm. Despite this thick rim of viable tissue, 77% of these segments did not improve postoperative function.…”

“…Mismatch segments explain partly the scatter observed in this relationship, which indicates that viable tissue as defined by ce-MR may differ with respect to flow-metabolism balance. The PET threshold of Ն50% FDG uptake (predicting functional recovery 22,23,25 ) corresponds to a viable rim thickness on MR of Ϸ4.5 mm. These findings allow the subdivision of dysfunctional myocardial segments into various classes meeting both MR and PET criteria for recovery of function, only 1 criterion (intermediate segments), or none of these criteria.…”

“…11,12,14 A 50% FDG uptake (a cut off value often used to predict functional recovery 22,23,25 ) corresponded to a viable rim thickness on MR of Ϸ4.5 mm. Although segments above and below these thresholds are expected to recover function with high and low probability, the fate of intermediate segments (fulfilling only 1 criterion for functional recovery) is of particular interest.…”

Myocardial viability in patients with Q wave myocardial infarction and no residual ischemia.

“…Most infarct areas contain both dead and viable myocytes, and positron emission tomography demonstrated a concordant reduction in regional perfusion and glucose usage in only 32% of Q wave regions; the majority of chronic Q wave regions had persistent metabolic activity.37 Stable 201T1 defects frequently manifest '8F-2-fluoro-deoxyglucose uptake, which confirms that permanent defects contain viable myocardium.3839 Nevertheless, 201T1 imaging with reinjection and interpretation of the level of 201T1 activity within persistent defects identifies the same viable regions as does positron emission tomography with 18F-2-fluoro-deoxyglucose. 34 Reliable evaluation of viability by 201T1 SPECT is important to prospectively identify patients in whom it is probable that wall motion will improve after revascularization. We believe that some`1Tl defects in our patients would have been reversible after 201T1 reinjection or after late redistribution imaging.…”