Normal Thallium Uptake Research Articles

Prediction of Post-revascularization Ejection Fraction in Patients with Coronory Artery Disease Using Cavity-to-Myocardial Ratio of Thallium Reinjection Image (Multicenter Trial)

Background: We reported the high correlation between cavity-to-myocardial (C/M) count ratio at stress and rest thallium SPECT, and stress-rest EF calculated by MUGA test, this was confirmed by others. This correlation was explained partially by the functional mass. On the other hand, two important prognostic parameters should be considered before any revascularization technique: (1) Identification of viable myocardium and its amount, (2) Prediction of EF improvement post revascularization. Aim of the study: Correlating EF (C/M) on RD and RI image (EFRD & EFRI) image to actual EF (prevascularization EF1) and 1 year post revascularization EF2. Patients and methods: 78 patients with CAD (68 males and 10 females with mean age of 54.2+9 years) had been subjected to: (1) St-RD-RI thallium SPECT with assessment of reversible or fixed perfusion defects and calculation of C/M and consequently the EFC/M at the three settings. (2) Assessment of EF by MUGA at rest pre and 1 year post revascularization EF1 & EF2 respectively. These patients had been subjected to revascularization either by PTCA and stent (23/78 i.e., 29.5%) or by CABG (55/78, i.e., 70.5%). Results: Out of the 1560 myocardial segments (20 segments × 78 patients), 780 (50%) segments had abnormal resting wall motion. 441/780 (56.5%) of these segments were either of normal thallium uptake or with reversible perfusion defects while the rest (43.5%) showed fixed defects. 233/441 (52.8%) of those normal uptake or reversible segments showed recovery of wall motion post revascularization (PRV) while only 29/339 (15.1%) showed similar improvements. EFRI was found higher than EFRD in 44/78 of patients, no change in 23/78 patients and worsened in 11/78 patients with total agreements of 63/78 (80.8%) with EF2. On the other hand, EFRD was matched with EF1 in 64/78 of patients. 30/64 (46.9%) showed higher EF2, 23/64 (35.9%) showed similar EF2 while 11/64 (17.2%) showed lower EF2. The rest of cases 14/78 showed mismatch between EFRD and EF1 with higher values of EFRD. These patients still had higher values of EFRI and EF2 than EFRD. Conclusion: (1) Mismatch between EFRD and EF1 is an indication of presence of stunning myocardium and of good prognosis. (2) EFRI can be used to predict EF2 and so helps on selecting patients who can benefit from revascularization.

Comparison of dobutamine echocardiography, dobutamine sestamibi, and rest-redistribution thallium-201 single-photon emission computed tomography for determining contractile reserve and myocardial ischemia in ischemic cardiomyopathy

Both dobutamine stress echocardiography (DSE) and myocardial perfusion scintigraphy are used to assess myocardial viability. Few studies have compared the data on myocardial viability and ischemia by low and peak dose DSE and myocardial perfusion imaging in the same patients. Fifty-four patients (45 men and 9 women aged 65 ± 9 years) with ischemic cardiomyopathy (mean ejection fraction 24 ± 9%) underwent rest 4-hour redistribution thallium-201 single-photon emission computed tomography (SPECT), low and peak dose DSE, and dobutamine sestamibi SPECT. A total of 864 segments were analyzed (16 segments/patient). Wall motion abnormality was present in 796 segments (92%), and contractile reserve during dobutamine infusion was seen in 400 of these segments (50%). Contractile reserve was seen in 331 of 509 hypokinetic segments (65%) and 69 of 287 akinetic/dyskinetic segments (24%) (p <0.001). Contractile reserve was more frequent in segments with normal thallium uptake (64%), reversible thallium defects (42%), or mild to moderate fixed thallium defects (48%) than severely fixed defects (22%) (p <0.05 each). Concordant information about viability by thallium imaging and DSE was obtained in 62% of segments. Dobutamine sestamibi ischemia was seen in 518 of 796 segments (65%) compared with 265 segments (33%) by DSE (p <0.001). Scintigraphic ischemia was noted in 126 of 195 segments (65%) demonstrating biphasic response, 129 of 205 segments (63%) showing sustained improvement, 42 of 70 segments (60%) deteriorating during dobutamine infusion, and 221 of 326 (68%) demonstrating no change (p = NS). Thus, in patients with ischemic cardiomyopathy, contractile reserve is more frequent in hypokinetic segments than akinetic/dyskinetic segments. The number of segments with normal or near-normal thallium uptake or with scintigraphic ischemia is significantly greater than the number of those capable of increasing contractile function or demonstrating an ischemic response during dobutamine echocardiography.

Diagnostic accuracy and prognostic value of combined dipyridamole-exercise thallium imaging in hemodialysis patients

Non-invasive detection of coronary artery disease in dialysis patients, a major cause of mortality, often remains difficult. The aim of the study was to test the diagnostic and prognostic accuracies of combined dipyridamole-exercise thallium imaging in dialysis patients. Dipyridamole-exercise thallium imaging and coronary angiography were both performed prospectively in 60 asymptomatic hemodialysis patients who were followed up, long term, by recording any major coronary event. Coronary angiography was abnormal in 13 patients (21%), and there was abnormal thallium uptake in 17 patients. Sensitivity, specificity, positive and negative predictive values, and overall accuracy of thallium to detect a coronary artery disease were 92, 89, 71, 98 and 90%, respectively. After a median follow-up of 2.8 years, 12 patients experienced at least one major coronary event (4 cardiac deaths, 5 myocardial infarctions and 3 revascularizations). Eight of the 17 patients with abnormal thallium uptake (47%) suffered a coronary event, compared to only 4 of the 43 patients (9%) with a normal thallium uptake (P < 0.001). The positive prognostic predictive value of thallium imaging was 47% and its negative predictive value was 91%. The probability of survival free of coronary events was significantly higher in patients with normal thallium uptake than in those with abnormal thallium uptake (crude risk ratio 7.6; P < 0.001) even after adjustment for several risk factors for cardiovascular disease (adjusted risk ratio 9.2; P < 0.005). In dialysis patients, combined dipyridamole-exercise thallium imaging is an accurate method for detecting coronary stenosis and for predicting future coronary events.

Resting technetium-99m methoxyisobutylisonitrile cardiac imaging in chronic coronary artery disease: comparison with rest-redistribution thallium-201 scintigraphy

We studied 19 patients with angiographically proven coronary artery disease and left ventricular dysfunction (ejection fraction 33% +/- 8%) by resting technetium-99m methoxyisobutylisonitrile (99mTc-MIBI) and rest-redistribution thallium-201 cardiac imaging. Thallium and 99mTc-MIBI studies were visually analysed. Of 285 segments, 203 (71%) had normal thallium uptake, 48 (17%) showed reversible thallium defects and 34 (12%) showed irreversible thallium defects. Of these 34 irreversible thallium defects, 19 (56%) were moderate and 15 (44%) were severe. Of the corresponding 285 segments, 200 (70%) had normal 99mTc-MIBI uptake, while 37 (13%) showed moderate and 48 (17%) showed severe reduction of 99mTc-MIBI uptake. Myocardial segmental agreement for regional uptake score between initial thallium and resting 99mTc-MIBI images was 90% (kappa = 0.78). Segmental agreement between delayed thallium and resting 99mTc-MIBI images was 77% (kappa = 0.44). In particular, in 26 (9%) segments 99mTc-MIBI uptake was severely reduced while delayed thallium uptake was normal or only moderately reduced. These data suggest that although rest-redistribution thallium and resting 99mTc-MIBI cardiac imaging provide concordant results in the majority of myocardial segments, some segments with severely reduced resting 99mTc-MIBI uptake may contain viable but hypoperfused myocardium. Thus, conclusions on myocardial viability based on 99mTc-MIBI uptake should be made with caution in chronic coronary artery disease.

The noninvasive assessment of myocardial viability

The major objective of noninvasive imaging for detection of myocardial viability is to assist in the improved selection of patients with coronary artery disease and severe left ventricular dysfunction who would benefit most from revascularization. The techniques most commonly used to identify viable myocardium are thallium-201 (201Tl) scintigraphy, positron emission tomography (PET) using a flow tracer in combination with a metabolic tracer, technetium-99m (99mTc) sestamibi imaging, and dobutamine echocardiography. On stress 201Tl scintigraphy, asynergic regions showing normal thallium uptake, an initial defect with delayed redistribution at 3-4 h, late redistribution at 24 h, or defect reversibility after reinjection of a second dose of 201Tl at rest all suggest preserved viability. The greater the final uptake of 201Tl in areas of regional myocardial dysfunction preoperatively, the greater the improvement in ejection fraction after coronary revascularization. Demonstration of uptake of fluoro-18 deoxyglucose (FDG) in regions of diminished blood flow on PET imaging also correlates well with improved systolic function after revascularization. 99mTc sestamibi may also be useful for assessment of myocardial viability, particularly after thrombolytic therapy for acute myocardial infarction. Dobutamine echocardiography has good positive predictive value for viability determination, but absence of systolic thickening in an akinetic zone in response to intravenous infusion of the drug may still be associated with viable myocardium in 25-50% of segments. Of all the techniques cited above, quantitative resting 201Tl scintigraphy may be the best approach for distinguishing between viable and irreversibly injured myocardium.

Scintigraphic assessment of sympathetic innervation after transmural versus nontransmural myocardial infarction

To evaluate the feasibility of detecting denervated myocardium in the infarcted canine heart, the distribution of sympathetic nerve endings using I-123 metaiodobenzylguanidine (MIBG) was compared with the distribution of perfusion using thallium-201, with the aid of color-coded computer functional map in 16 dogs. Twelve dogs underwent myocardial infarction by injection of vinyl latex into the left anterior descending coronary artery (transmural myocardial infarction, n = 6), or ligation of the left anterior descending coronary artery (nontransmural myocardial infarction, n = 6). Four dogs served as sham-operated controls. Image patterns were compared with tissue norepinephrine content and with histofluorescence microscopic findings in biopsy specimens. Hearts with transmural infarction showed zones of absent MIBG and thallium, indicating scar. Adjacent and distal regions showed reduced MIBG but normal thallium uptake, indicating viable but denervated myocardium. Denervation distal to infarction was confirmed by reduced norepinephrine content and absence of nerve fluorescence. Nontransmural myocardial infarction showed zones of wall thinning with decreased thallium uptake and a greater reduction or absence of MIBG localized to the region of the infarct, with minimal extension of denervation beyond the infarct. Norepinephrine content was significantly reduced in the infarct zone, and nerve fluorescence was absent. These findings suggest that 1) MIBG imaging can detect viable and perfused but denervated myocardium after infarction; and 2) as opposed to the distal denervation produced by transmural infarction, nontransmural infarction may lead to regional ischemic damage of sympathetic nerves, but may spare subepicardial nerve trunks that course through the region of infarction to provide a source of innervation to distal areas of myocardium.

Enhanced Detection of Ischemic but Viable Myocardium by the Reinjection of Thallium after Stress-Redistribution Imaging

The identification of ischemic but viable myocardium by thallium exercise scintigraphy is often imprecise, since many of the perfusion defects that develop in ischemic myocardium during exercise do not "fill in" on subsequent redistribution images. We hypothesized that a second injection of thallium given after the redistribution images were taken might improve the detection of ischemic but viable myocardium. We studied 100 patients with coronary artery disease, using thallium exercise tomographic imaging and radionuclide angiography. Patients received 2 mCi of thallium intravenously during exercise, redistribution imaging was performed three to four hours later, and a second dose of 1 mCi of thallium was injected at rest immediately thereafter. The three sets of images (stress, redistribution, and reinjection) were then analyzed. Ninety-two of the 100 patients had exercise-induced perfusion defects. Of the 260 abnormal myocardial regions identified by stress imaging, 85 (33 percent) appeared to be irreversible on redistribution imaging three to four hours later. However, 42 of these apparently irreversible defects (49 percent) demonstrated improved or normal thallium uptake after the second injection of thallium, with an increase in mean regional uptake from 56 +/- 12 percent on redistribution studies to 64 +/- 10 percent on reinjection imaging (P less than 0.001). Twenty patients were restudied three to six months after coronary angioplasty. Of the 15 myocardial regions with defects on redistribution studies that were identified as viable by reinjection studies before angioplasty, 13 (87 percent) had normal thallium uptake and improved regional wall motion after angioplasty. In contrast, all eight regions with persistent defects on reinjection imaging before angioplasty had abnormal thallium uptake and abnormal regional wall motion after angioplasty. These data indicate that the reinjection of thallium improves the detection of ischemic myocardium and that myocardial regions with improved thallium uptake on reinjection imaging represent viable but jeopardized myocardium.

Myocardial stunning in hypertrophic cardiomyopathy: Recovery predicted by single photon emission computed tomographic thallium-201 scintigraphy

A young woman with hypertrophic cardiomyopathy confirmed by echocardiography and cardiac catheterization presented with chest pain and features of a large left ventricular aneurysm. The initial diagnosis was myocardial ischemia with either an evolving or an ancient myocardial infarction. Subsequently, verapamil therapy was associated with complete resolution of the extensive left ventricular wall motion abnormalities, normalization of left ventricular ejection fraction and a minimal myocardial infarction. Normal thallium uptake on single photon emission computed tomographic scintigraphy early in the hospital course predicted myocardial viability in the region of the aneurysm. Thus, orally administered verapamil may reverse spontaneous extensive myocardial ischemia in hypertrophic cardiomyopathy and possibly limit the extent of myocardial infarction in such circumstances.

Value of magnetic resonance imaging in patients with a recent myocardial infarction: Comparison with planar thallium-201 scintigraphy

The diagnostic accuracy of spin-echo Magnetic Resonance (MR) imaging in the detection and localization of a recent myocardial infarction (mean 4 days old) was compared to planar thallium-201 scintigraphy in 20 patients with a documented myocardial infarction. A control group of 10 subjects underwent a similar MR imaging procedure without thallium-201 scintigraphy. T1-weighted MR images (TE 30 msec) showed abnormal thinning of the infarcted left ventricular wall during systole (less than 50% of the opposite wall) in 11 patients (55%). On T2-weighted multi-echo MR images, (TE 30-60-90-120 msec) abnormally increased signal intensity was found in 17 patients and coincided with the location of the infarction. Thallium-201 scintigraphy detected the infarction in 18 patients. Comparison of T2-MR imaging and thallium-201 scintigraphy showed concordant findings in 82% of the left ventricular segments. In 9% of segments, thallium uptake was reduced with normal T2-MR and in 9% we found a normal thallium uptake with abnormal T2-MR findings. In all subjects of the control group, T1-MR images were normal, and only one subject showed increased signal intensity on T2-MR images. We conclude that the diagnostic accuracy of MR imaging in detecting a myocardial infarction is similar to that of T1-201 scintigraphy.

Evaluation of response to dopamine in idiopathic dilated cardiomyopathy by echocardiography and thallium-201 myocardial scintigraphy.

Twenty-six patients with idiopathic dilated cardiomyopathy (DCM) underwent thallium-201 myocardial scintigraphy. Nine patients (group A) showed a perfusion defect in the interventricular septum (IVS) and 7 patients (group B) showed a defect in the left ventricular posterior wall (LVPW). Hemodynamic responses and catecholamine levels were compared between 16 patients (DCM group) and 6 control subjects (control group) following dopamine infusion (6 micrograms/Kg/min). The end-diastolic thickness of the IVS and LVPW, and the percentage wall thickening were assessed by echocardiography. Plasma dopamine and norepinephrine concentrations in the DCM group were not different from those of the control group at rest. During the dopamine infusion, however, norepinephrine increased only in the control group. There were significant differences in the thickness of the IVS among the 3 groups [7.3 +/- 1.4 mm for group A (p less than 0.001 vs control and p less than 0.05 vs group B), 8.9 +/- 1.5 mm for group B (p less than 0.01 vs control), 10.2 +/- 1.5 mm for the control group]. The percentage thickening of the IVS increased during the dopamine infusion in group B only and the thickening of the LVPW increased in group A only. Thus, in the myocardium of DCM patients with thallium perfusion defects, the degree of thickening did not change during dopamine infusion, but in the myocardium of DCM patients with normal thallium uptake the percentage thickening increased more than in the control group.

Value and limitations of myocardial thallium washout rate in the noninvasive diagnosis of patients with triple-vessel coronary artery disease

This study tested the hypothesis that recognition of delayed washout of thallium from myocardial scan zones with apparently normal thallium uptake is useful for identifying patients with triple-vessel coronary artery disease (CAD). Exercise thallium stress tests were performed in 21 patients with angiographically proven triple-vessel CAD (≥50% stenosis of all three major vessels). Anterior and left anterior oblique thallium images were obtained 5 to 10 minutes after stress and 2 hours later. Background corrected scans (bilinear interpolative method) were analyzed by computer (radial analysis program) for the presence of initial uptake defects as well as delayed thallium washout. Twenty-five patients with single or double-vessel CAD and 14 patients with normal coronary arteries also were studied to obtain specificity data regarding the diagnosis of triple-vessel coronary disease. In patients with triple-vessel CAD, 50 of 63 (79%) stenosed vessels were detected by combined use of uptake and washout criteria. However, only 8 of 63 (13%) diseased vessels were detected by washout criteria alone. Nevertheless, use of washout criteria did increase the number of patients correctly identified as having triple-vessel disease from seven (identified on the basis of uptake defects alone) to 10. Accordingly, sensitivity using both uptake and washout criteria was 48% (10 of 21 patients). Specificity for the diagnosis of triple-vessel disease using combined uptake and washout criteria was 76% for patients with single- or double-vessel CAD and 95% for normals, and was little different from values obtained based on uptake criteria alone (80% and 100%, respectively). Thus even though relatively few stenosed vessels in patients with triple-vessel CAD are associated with isolated thallium wahout abnormalities, use of washout criteria does increase the sensitivity of the thallium stress test for the detection of such patients and therefore is a worthwhile addition to routine uptake analysis of thallium images of the myocardium.

Prospective assessment of regional myocardial perfusion before and after coronary revascularization surgery by Quantitative Thallium-201 scintigraphy

Because thallium-201 uptake relates directly to the amount of viable myocardium and nutrient blood flow, the potential for exercise scintigraphy to predict response to coronary revascularization surgery was investigated in 47 consecutive patients. All patients underwent thallium-201 scintigraphy and coronary angiography at a mean (+/- standard deviation) of 4.3 +/- 3.1 weeks before and 7.5 +/- 1.6 weeks after surgery. Thallium uptake and washout were computer-quantified and each of six segments was defined as normal, showing total or partial redistribution or a persistent defect. Persistent defects were further classified according to the percent reduction in regional thallium activity; PD25-50 denoted a 25 to 50% constant reduction in relative thallium activity and PD greater than 50 denoted a greater than 50% reduction. Of 82 segments with total redistribution before surgery, 76 (93%) showed normal thallium uptake and washout postoperatively, versus only 16 (73%) of 22 with partial redistribution (probability [p] = 0.01). Preoperative ventriculography revealed that 95% of the segments with total redistribution had preserved wall motion, versus only 74% of those with partial redistribution (p = 0.01). Of 42 persistent defects thought to represent myocardial scar before surgery, 19 (45%) demonstrated normal perfusion postoperatively. Of the persistent defects that showed improved thallium perfusion postoperatively, 75% had normal or hypokinetic wall motion before surgery, versus only 14% of those without improvement (p less than 0.001). Whereas 57% of the persistent defects that showed a 25 to 50% decrease in myocardial activity demonstrated normal thallium uptake and washout postoperatively, only 21% of the persistent defects with a decrease in myocardial activity greater than 50% demonstrated improved perfusion after surgery (p = 0.02). Thus, preoperative quantitative thallium-201 scintigraphy appears useful in predicting response to revascularization surgery, and some persistent defects may revert to normal thallium uptake after surgery. Importantly, the preoperative distinction between viable and nonviable myocardium can be reasonably established by quantitating the amount of persistent reduction in thallium uptake and correlating this with preoperative wall motion.

Effect of coronary collateral circulation on regional myocardial perfusion assessed with quantitative thallium-201 scintigraphy

The functional role of the coronary collateral circulation in patients with coronary artery disease has yet to be clarified. Because the distribution of thallium in the myocardium after its intravenous injection is proportional to regional blood flow, quantitative thallium scintigraphy was employed to assess noninvasively the effect of collateral vessels on regional myocardial perfusion at rest and after exercise stress. Sixty-two patients with significant (greater than 50 percent stenosis of luminal diameter) coronary artery disease had after exercise thallium imaging and 35 patients underwent imaging at rest. Delayed redistribution images were obtained after exercise and at rest. Images were divided into six segments for analysis and interpreted using computer-assisted quantitative techniques. In patients undergoing exercise stress, collateral vessels did not significantly influence thallium uptake patterns in segments associated with electrocardiographic Q waves. In segments without Q waves, thallium uptake was more frequently abnormal (p <0.001) in segments with than in segments without collateral vessels whether or not such vessels were jeopardized. The presence or absence of collateral channels did not affect the frequency of occurrence of thallium redistribution. In patients undergoing serial imaging at rest, the prevalence of segments with normal thallium uptake was greater in segments with nonjeopardized than in those with jeopardized collateral vessels (p <0.05). It is concluded that (1) coronary collateral vessels are an indicator of severe coronary arterial obstruction and do not protect against exercise-induced hypoperfusion or affect the occurrence of redistribution, and (2) non-jeopardized collateral vessels appear to augment perfusion at rest in some segments to the degree that normal thallium uptake at rest is observed.