Joint Program in Nuclear Medicine

Reverse Redistribution in Resting Tl-201 Myocardial Scintigraphy

Justine Arthur, BMBS, BMedSci, MRCP
Charles Ahn, MD

March 28, 1995

Presentation

A 73 year old man presented with a one month history of intermittent left sided chest pain on exertion radiating to the left shoulder. He had no associated dyspnea or dizziness. Ten years previously he had suffered an anteroseptal myocardial infarction but had not experienced angina since that time. His medical history was significant for insulin dependent diabetes mellitus, hypertension, peripheral vascular disease, atrial fibrillation and mild congestive heart failure.

An exercise stress thallium-201 (27k bytes) study showed hypoperfusion in the medial anterior wall and apex with minimal reperfusion at rest (arrows, 27k bytes). Cardiac catheterisation with angiography revealed a 50%% stenosis of the proximal left anterior descending artery (LAD), 100%% occlusion of the mid-LAD, 80%% stenosis of the distal circumflex and a 70%% lesion in the right posterior descending artery. Resting thallium scintigraphy was performed to further assess the viability of the anterior wall and to delineate whether the LAD required bypass surgery.

Imaging Findings

The resting thallium-201 study with 3 hour delayed imaging showed a fixed defect at the apex, a medium sized defect in the anterior wall which partially redistributed as well as a medium sized area of reverse redistribution in the lateral wall (short axis slices, 45k bytes). The arrows (50k bytes) show the area of reverse redistribution. The redistribution in the anterior wall and apex suggested viability of ischemic myocardium in the LAD territory and so the patient was referred for coronary artery bypass graft surgery. However, the most interesting finding was the reverse redistribution in the lateral wall which was not identified on the exercise thallium imaging despite the presence of an 80%% stenosis of the distal circumflex artery.

Discussion

The poorly understood phenomenon of reverse redistribution has been well documented in exercise thallium myocardial scintigraphy; however, the occurrence of reverse redistribution in the setting of rest and delayed imaging is less well known and reports of such cases in the literature are sparse.

Reverse redistribution appears to occur most frequently following thrombolysis post- myocardial infarction. Langer et al (1) and Weiss et al (2) found reverse redistribution in 40%% of segments at 8 days post-myocardial infarction and 75%% at 10 days post-myocardial infarction respectively, whilst Yamagishi et al (3) recorded reverse redistribution in 48%% at 1-2 months post-myocardial infarction. All three studies demonstrated an association of reverse redistribution with more widely patent infarct-related coronary arteries or collateral circulation, and wall motion that was more nearly normal than segments showing either reversible or fixed perfusion defects. Ohte et al (4), however, recently reported a lower rate of reverse redistribution of 19%% in myocardial segments 4-8 weeks after myocardial infarction. Only mild hypokinesis was observed in regions demonstrating reverse redistribution, although wall motion score was higher in areas of reverse redistribution than regions with moderately decreased thallium-201 activity (or hibernating myocardium). In addition, Ohte et al demonstrated reduced FDG uptake in reverse redistribution segments on PET scanning indicating impaired metabolism of myocardial cells in these regions.

The occurrence of reverse redistribution in patients with chronic coronary artery disease appears to be less frequent than post-myocardial infarction. Between 5 and 9%% of exercise thallium scans demonstrated reverse redistribution in patients with coronary artery disease in studies reported by Hecht et al (5), Pace et al (6) and Silberstein et al (7), whilst Popma et al (8) observed reverse redistribution in 7%% of segments in patients stressed with dipyridamole infusion. A similar rate of 9%% was observed in thallium-201 rest-redistribution studies in a further study by Pace et al (9). Two patterns of reverse redistribution were identified:

Angiography and sestamibi injection demonstrated a significantly higher degree of severe coronary artery stenosis, worse left ventricular wall motion and lower resting sestamibi uptake in RR-A segments when compared to normal segments. Segments with RR-B were comparable to those with reversible or fixed defects in wall motion, sestamibi uptake and the degree of coronary artery disease. Pace's study of exercise thallium-201 scintigraphy in coronary artery disease patients (6) stratified regions of RR-A further into those with positive (>10%%) or negative (<10%%) thallium-201 uptake on reinjection . Those showing enhanced uptake (RR+) showed myocardial and coronary anatomy similar to normal segments whereas those without enhanced uptake after reinjection (RR-) were characterized by lower resting myocardial flow (as evidenced by lower resting sestamibi uptake) and a higher percentage of stenosed coronary arteries. Hecht et al (5) found severely stenosed coronary arteries (of >90%%) in 85%% of the segments with reverse redistribution, nearly half of which were completely occluded and supplied by collateral vessels or grafts. These results were similar to those of Pace et al (9) who found that 46%% of RR-A segments were supplied by completely occluded yet well collateralized (in 58%%) coronary arteries compared with 22%% of normal segments. The studies by Popma et al and Silberstein et al (8,7) on the other hand, failed to demonstrate any relationship between reverse redistribution and the presence and/or severity of coronary artery stenosis.

The mechanism of reverse redistribution remains unclear. In the reperfused myocardium post-myocardial infarction, the association of reverse redistribution with patent infarct-related coronary arteries and near normal wall motion can be explained by the presence of viable stunned myocardial tissue in a region of restored coronary blood flow (10). Initial uptake of thallium-201 is dependent on myocardial blood flow implying post-myocardial infarction that there is either effective recanalisation of the supplying coronary artery or the presence of adequate collaterals. Subsequent thallium-201 washout depends on both the percentage of functioning myocytes in the affected segment that are able to hold onto the delivered thallium-201 and the resting blood flow to the affected area. This theory is supported by Okada's canine transient coronary artery ligation model (11) which demonstrated increased clearance rates of thallium-201 on reperfusion from damaged myocardium compared to normal despite initially normal thallium-201 uptake. In addition, Ohte's finding (4) of reduced FDG uptake in regions of reverse redistribution further supports the association of reverse redistribution with impaired myocyte metabolism.

In chronic coronary artery disease, reverse redistribution regions have been associated with abnormal coronary anatomy, decreased resting flow and abnormal wall motion. Reverse redistribution in these regions can be explained by the presence of viable elements whether normal, stunned or hibernating in a region also containing nonviable "scar". A non-critically stenosed supplying artery or collateral circulation delivers thallium to an area containing a mixture of scar and viable elements with more rapid washout of thallium-201 from the dysfunctional myocytes.

Conclusions:

The presence of normal initial uptake of thallium-201 with reduced uptake on redistribution imaging (RR-A pattern) in rest-redistribution thallium-201 scintigraphy in patients with chronic coronary artery disease has been associated with impaired left ventricular function and the presence of severely stenosed coronary arteries particularly if there is absence of further thallium-201 uptake on reinjection. Pace therefore advises that these scans should not be considered normal. These studies emphasize the importance of performing a redistribution scan even if the initial resting thallium-201 study is normal in order to identify those patients at risk.

References

1. Langer A, Burns RJ, Freeman MR et al. Reverse redistribution on exercise thallium-201scintigraphy: relationship to coronary patency and ventricular patency post-myocardial infarction. Can J Cardiol 1992;8:709-715.

2. Weiss AT, Maddahi J, Lew AS et al. Reverse redistribution of thallium-201: a sign of non-transmural myocardial infarction with patency of the infarct related coronary artery. J Am Coll Cardiol 1986;7:61-67.

3. Yamagishi H, Itagane H, Akioka K et al. Clinical significance of reverse redistribution on thallium-201 single photon emission computed tomography in patients with acute myocardial infarction. Jpn Circ J 1992; 56: 1095-1105.

4. Ohte N, Hashimoto T, Banno T et al. Clinical significance of reverse redistribution on 24-hour delayed imaging of exercise thallium-201 myocardial SPECT: Comparison with myocardial fluorine-18-FDG-PET imaging and left ventricular wall motion. J Nucl Med 1995; 36: 86-92.

5. Hecht HS, Hopkins JM, Rose JG et al. Reverse redistribution: worsening of thallium-201 myocardial images from exercise to redistribution. Radiology 1981;140:177-181.

6. Pace L, Cuocolo A, Nicolai E et al. Reverse redistribution in thallium-201 stress-redistribution myocardial scintigraphy. Effect of rest reinjection. Clin Nucl Med 1994; 19(11):956-961.

7. Silberstein EB, DeVries DF. Reverse redistribution phenomenon in thallium-201 stress tests: angiographic correlation and clinical significance. J Nucl Med 1985;26:707-710.

8. Popma JJ, Smitherman TC, Walker BS et al. Reverse redistribution of thallium-201 detected by SPECT imaging after dipyridamole in angina pectoris. Am J Cardiol 1990; 65:1176-1180.

9. Pace L, Cuocolo A, Maurea S et al. Reverse redistribution in resting thallium-201 myocardial scintigraphy in patients with coronary artery disease: Relation to coronary anatomy and ventricular function. J Nucl Med 1993; 34 (10): 1688-1694.

10. Liu P, Burns RJ. Easy come, easy go: time to pause and put thallium-201 reverse redistribution in perspective. J Nucl Med 1993; 34 (10): 1692-1694.

11. Okada RD, Boucher CA. Differentiation of viable and non-viable myocardium after acute reperfusion using serial thallium-201 imaging. Am Heart J 1987; 113: 241-250.

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J. Anthony Parker, MD PhD, Tony_Parker@bidmc.harvard.edu