The effect of glucose-insulin-potassium on thallium-201 myocardial redistribution

Intravenous infusion of glucose-insulin-potassium (GIK) has been shown to alter the net rate of clearance of ²⁰¹Tl from transiently ischemic and normally perfused canine myocardium. This study was performed to determine if GIK would also decrease the extent of thallium redistribution after transient myocardial ischemia. Six anesthetized, open-chest dogs underwent two studies, one with GIK and another with saline infusion. The left anterior descending coronary artery was occluded, ²⁰¹Tl injected, and the occlusion released 5-min later. An i.v. infusion of either GIK (4 dogs) or saline (2 dogs) was then begun and continued for the 120-min duration of serial myocardial imaging using a standard scintillation camera. The experiment was then repeated with an infusion of saline (4 dogs) or GIK (2 dogs). The dose of ²⁰¹Tl for the second study was at least 5 times more than was used for the first study.The serial 2-min images were then displayed on computer and regions of interest were drawn over the areas of transient ischemia (TI) and normal perfusion (NP). The ratio of average counts per picture element for the area of TI compared to NP was calculated. One hundred and twenty minutes after ²⁰¹Tl administration, the change in the TI/NP ratio (% fill-in) was significantly less for the GIK infusion compared to saline infusion (control) 15.4 ± 4.0% vs 26.2 ± 6.0% (mean ± SE) (P < 0.01), respectively. Therefore, GIK infusion appeared to decrease the extent of thallium redistribution compared to saline control.     

Ribose facilitates thallium-201 redistribution in patients with coronary artery disease

To investigate whether i.v. infusion of ribose, an adenine nucleotide precursor, postischemia facilitates thallium-201 (201Tl) redistribution and improves identification of ischemic myocardium in patients with coronary artery disease (CAD), 17 patients underwent two exercise 201Tl stress tests, performed 1-2 wk apart. After immediate postexercise planar imaging, patients received either i.v. ribose (3.3 mg/kg/min x 30 min) or saline as a control. Additional imaging was performed 1 and 4 hr postexercise. Reversible defects were identified by count-profile analysis. Significantly more (nearly twice as many) reversible 201Tl defects were identified on the post-ribose images compared to the post-saline (control) images at both 1 and 4 hr postexercise (p less than 0.001). Quantitative analyses of the coronary arteriogram was available in 13 patients and confirmed that the additional reversible defects were in myocardial regions supplied by stenosed arteries. We conclude that ribose appears to facilitate 201Tl redistribution in patients with CAD and enhances identification of ischemic myocardium.     

Relationship between exercise-induced myocardial ischemia and reduced left ventricular distensibility in patients with nonobstructive hypertrophic cardiomyopathy.

Many studies have demonstrated that reduced left ventricular (LV) diastolic distensibility plays a key role in the pathophysiology of hypertrophic cardiomyopathy (HCM). However, the relationship between myocardial ischemia and reduced LV distensibility in HCM remains unclear. We aimed to clarify the relationship between exercise-induced ischemia and reduced LV distensibility in patients with HCM. METHODS: Twenty patients with HCM and 5 age-matched control subjects underwent stress-redistribution (201)Tl myocardial scintigraphy and biventricular cardiac catheterization and echocardiography at rest and during exercise. Scintigraphic defect analysis was interpreted using Berman's 20-segment model. The summed stress score (SSS) was calculated as the sum of scores of the 20 LV segments and the summed difference score (SDS) was calculated as the sum of differences between each of the 20 LV segments on stress and rest images. RESULTS: Patients were divided into 2 groups according to the (201)Tl defect as follows: 9 patients with an SSS on (201)Tl of >or=10 and an SDS on (201)Tl of >or=5 (ischemic group) and 11 patients with an SSS of <10 or an SDS of <5 (nonischemic group). The absolute increases from rest to peak exercise in LV end-diastolic pressure (LVEDP) and pulmonary artery wedge pressure were significantly greater (15.5 +/- 5.2 vs. 7.6 +/- 5.5 mm Hg and 17.3 +/- 5.0 vs. 8.9 +/- 5.0 mm Hg, P < 0.01, respectively), and the percentage changes from rest to peak exercise in the maximum first derivative of LV pressure and LV pressure half-time were significantly smaller in the ischemic HCM group compared with the nonischemic HCM group (70% +/- 24% vs. 123% +/- 43% and -32% +/- 6.4% vs. -44% +/- 9.4%, P < 0.01, respectively). However, the end-diastolic dimensions did not differ between the 2 HCM groups. One of the 9 patients in the ischemic group, as revealed by fill-in on (201)Tl scintigraphy, showed increased (18)F-FDG uptake in the anteroseptal wall. CONCLUSION: Some HCM patients show a significant increase in LVEDP without chamber dilatation, indicating reduced LV diastolic distensibility. Myocardial ischemia may at least in part contribute to this condition.     

Evaluation of I-123-BMIPP myocardial SPECT on the detection of ischemic heart disease by comparing with stress thallium-201 myocardial SPECT]

To evaluate the usefulness of I-123-BMIPP as a tracer of fatty acid metabolism in ischemic heart disease, we performed both rest BMIPP myocardial SPECT and stress thallium-201 (Tl) SPECT in 15 patients with prior myocardial infarction, and compared the segmental findings each other. The abnormality of BMIPP images was more intense than that of Tl redistribution images (Tl-RD) in more than 60% of the abnormal segments. The degree of myocardial uptake of BMIPP was more concordant with that of Tl stress scan (Tl-EX) than with that of Tl-RD. This agreement of the findings between BMIPP and Tl-EX was found more remarkably in the regions of incomplete Tl redistribution or in the collateralized regions. These results revealed that ischemia in the jeopardized regions was able to be detected even by rest BMIPP scan. Abnormal findings in BMIPP were observed in more than 95% of segments with persistent defects or incomplete redistribution in Tl, but observed in only 41 or 45% of segments with complete redistribution. Normal findings in BMIPP were observed in 94% of normal segments in Tl. From these results, we can speculate that abnormal regions in BMIPP may have necrotic or ischemic myocardial tissue and normal regions in BMIPP may not have necrotic tissue. These results suggest that I-123-BMIPP may be available to detect myocardial ischemia or infarction in the clinical study. Additionally, the difference in findings between the early images and the delayed images in rest BMIPP scan was observed with relatively high incidence (14% of regions and 73% of patients). More detailed analysis will be required to reveal the importance of this difference.     

Exercise myocardial perfusion scintigraphy is useful for evaluating myocardial ischemia even in the elderly

Pharmacologic stress testing is recommended to elderly patients as a valuable alternative to exercise testing. We examined whether exercise testing is as useful for evaluating myocardial ischemia in the elderly as in the young. The consecutive 1,508 patients who underwent exercise 201Tl single-photon emission computed tomography (SPECT) were divided into six age groups: 6-29 years (n = 56), 30-44 (n = 143), 45-54 (n = 311), 55-64 (n = 498), 65-74 (n = 402), and 75-88 (n = 98). Both heart rate and rate-pressure product at peak exercise were significantly lower in patients aged 75-88 than in the other five groups. The frequency of ischemic ST depression was higher in patients aged 75-88 than in those aged 6-74, although the difference was not significant. Moreover, the frequency of 201Tl transient defect was significantly higher in patients aged 75-88 than in those aged 6-74. On the other hand, the sensitivity of ischemic ST depression for 201Tl transient defect was similar among the six groups, but the specificity was significantly lower in patients aged 75-88 than in those aged 6-74. In conclusion, exercise 201Tl SPECT is useful for evaluating myocardial ischemia even in the elderly, but exercise electrocardiography has limitations such as lower specificity in the elderly than 201Tl SPECT.     

Gd(ABE-DTTA)-enhanced cardiac MRI for the diagnosis of ischemic events in the heart

PURPOSE: To demonstrate that contrast-enhanced MRI (ceMRI) with the aid of Gd(ABE-DTTA) is able to detect ischemic events in the heart in a canine ischemia/reperfusion (30/40 minutes) model. MATERIALS AND METHODS: ECG-gated, T1-weighted MR image sets (four to five slices each) with three-minute time resolution were collected in transiently LAD-occluded dogs. Following the acquisition of control image sets, ischemia was started by occluding the LAD. Either Gd(ABE-DTTA) (N = 6) or Gd(DTPA) (N = 6) was injected, and imaging was continued for 30 minutes of ischemia and 40 minutes of reperfusion. The contrast agent (CA)-induced MRI signal intensity enhancement (SIE) and contrast were monitored. Microspheres measured myocardial perfusion (MP) to verify areas of ischemia and reperfusion. RESULTS: SIEs of 86% +/- 3% and 97% +/- 3% in nonischemic, and 25% +/- 5% and 29% +/- 8% in ischemic regions were found within three minutes of onset of ischemia with Gd(ABE-DTTA) and Gd(DTPA), respectively. For the rest of the 30 minutes of ischemia, with Gd(ABE-DTTA) SIE of 60% +/- 3% and 25% +/- 5% persisted in the nonischemic and ischemic regions, respectively. With Gd(DTPA), however, SIE in the nonischemic areas decreased rapidly after the first three minutes of ischemia, while SIE in the ischemic areas increased, abolishing contrast. Thus, there was a persistent contrast with Gd(ABE-DTTA) and a short-lived contrast with Gd(DTPA) during ischemia. Furthermore, with Gd(ABE-DTTA) some contrast was still visible in the early reperfusion period. CONCLUSION: Gd(ABE-DTTA) in an ischemia/reperfusion model induces a persistent MRI contrast between regions of normal and ischemic myocardium, and verifies reperfusion. Therefore, it can be used to detect myocardial ischemic events.     

双核素心肌显像检测存活心肌的对比研究

目的 对比多巴酚丁胺负荷201Tl/静息99Tcm-甲氧基异丁基异腈(MIBI)双核素同步心肌断层显像及多巴酚丁胺负荷-再分布/再注射201Tl心肌断层显像法检测存活心肌的作用.方法 对160例临床怀疑有冠心病的患者予静息状态下静脉注射740 MBq99Tcm-MIBI,休息15 min后进行多巴酚丁胺负荷试验,在达到终止指标时静脉注射111 MSq201TICI.注射后观察5-lO min,分别行早期(10 min)、延迟(3 h)99Tcm-MIBI和201Tl双核素同步心肌断层显像.对早期负荷201Tl图像发现放射性缺损,延迟再分布201Tl和静息99Tcm-MIBI图像未见放射性填充的患者再注射37 MBq201TICI,30min后行再注射心肌灌注显像.负荷枷201Tl图像示放射性缺损,静息99Tcm-MIBI、再分布201Tl及再注射201Tl图像中发现任何一种放射性填充者均为存活心肌.断层显像后2周内全部患者进行了冠状动脉造影.采用SAS 6.12软件进行x2检验.结果 (1) 160例患者冠状动脉造影均发现冠状动脉狭窄.其中单支病变76例、双支病变5l例、三支病变33例.(2)152例多巴酚丁胺负荷201Tl图像发现放射性缺损的患者中,63例201Tl再分布和静息99Tcm-MIBI图像均发现放射性填充,5例201Tl再分布发现放射性填充而静息99Tcm-MIBI图像未见放射性填充,9例静息99Tcm-MIBI图像发现放射性填充而2001Tl再分布未见放射性填允,75例201Tl再分布和静息99Tcm-MIBI图像均未发现放射性填充,负荷201Tl-延迟再分布显像(66.0%,68/103)和负荷201Tl/静息99Tcm-MIBI显像(69.9%,72/103)鉴别存活心肌的灵敏度差异无统计学意义(x2=O.36,P>0.05).(3)75例201Tl再分布和静息99Tcm-MIBI图像均未发现放射性填充患者中,再注射201Tl显像后有26例放射性填充,再注射201Tl显像较单纯201Tl再分布或静息99Tcm-MIBI显像多检测出34.7%(26/75)患者有存活心肌.(4)8例多巴酚丁胺负荷201Tl、201Tl再分布图像和静息99Tcm-MIBI图像均未发现放射性稀疏,为假阴性,其中3例为三支冠状动脉病变,1例为双支冠状动脉病变(狭窄分别为90%及60%),3例为单支冠状动脉病变(狭窄<75%2例,85%1例),1例冠状动脉闭塞后有充分的侧枝循环.结论 多巴酚丁胺负荷-再分布/再注射201Tl心肌断层显像鉴别存活心肌优于多巴酚丁胺负荷201Tl/静息99Tcm-MIBI双核素同步心肌断层显像,是一种有效、无创的鉴别存活心肌的方法.     

The effect of nitroglycerin on myocardial blood flow in various segments characterized by rest-redistribution thallium SPECT.

The use of nitrates is reported to be effective in viability detection in scintigraphic perfusion imaging. The purpose of the study was to evaluate the effect of nitroglycerin (NTG) on myocardial blood flow (MBF) and coronary vascular resistance (CVR) in various segments characterized by rest-redistribution (201)Tl SPECT. METHODS: Twenty-three patients with coronary artery disease underwent rest-redistribution (201)Tl SPECT and (15)O-labeled water PET at rest and after NTG spray (0.3 mg). In addition, 11 healthy volunteers were also studied using PET. RESULTS: NTG did not change global MBF in the volunteers or in the patients. In segments with normal (201)Tl uptake and in those with a severe irreversible (201)Tl defect, NTG significantly reduced MBF without changing CVR. NTG reduced CVR in segments with a reversible (201)Tl defect (141 +/- 50 to 114 +/- 29 mm Hg/[mL/min/g], P = 0.004) and in those with a mild-to-moderate irreversible (201)Tl defect (165 +/- 64 to 149 +/- 60 mm Hg/[mL/min/g], P = 0.003), while maintaining MBF. CONCLUSION: NTG preferentially reduces CVR in the viable myocardium with ischemia. After NTG, tracer uptake in the ischemic myocardium will be relatively increased compared with that in the nonviable and nonischemic myocardium, leading to improvements in viability detection.     

Acute ischemic dysfunction alters coronary flow reserve in remote nonischemic regions: Potential mechanical etiology identified in an acute canine model

BACKGROUND: Impaired coronary flow reserve (CFR) has been observed in remote nonischemic regions in patients after myocardial infarction. The mechanism for this impairment in remote nonischemic CFR remains undefined. This study evaluates the effect of progressive regional ischemic dysfunction on function in remote nonischemic regions, and the effect of the extent of dysfunction on remote nonischemic coronary flow and CFR. METHODS: In an anesthetized open-chest canine model (n = 7) of acute progressive distal and proximal left anterior descending (LAD) coronary artery occlusion, regional myocardial thickening fraction and coronary flow and CFR were measured with Doppler probes. CFR was assessed by an intracoronary injection of 36 microg of adenosine. Changes in thickening fraction and CFR were evaluated for isovolumic, ejection, and diastolic phases. Changes in resting regional flow were also assessed using radiolabeled microspheres. The extent of the ischemic area was defined as regions of myocardium with endocardial microsphere blood flow less than 0.3 mL/min/g. RESULTS: The ischemic area increased from 12% +/- 1% of left ventricle with distal occlusion to 30% +/- 2% of left ventricle with proximal occlusion (P < .001). The LAD thickening fraction decreased significantly from baseline (18% +/- 1%) to distal (-8% +/- 1%,) and proximal (-4% +/- 1%) occlusion (P < .001 for distal and proximal vs baseline). Isovolumic bulging in the LAD region was associated with a progressive increase in thickening fraction in the remote nonischemic left circumflex (LCX) artery region (baseline 12% +/- 1%; distal occlusion 15% +/- 2%, P = .014 vs baseline; proximal occlusion 17% +/- 2%, P = .02 vs baseline). Most of the increase in remote thickening fraction occurred during the isovolumic phase. There was no significant change in resting flow in remote nonischemic LCX regions or global hemodynamic parameters. However, there was a progressive decrease in remote nonischemic CFR (baseline 2.44 +/- 0.3), distal occlusion (2.19 +/- 0.31; P = .055 vs baseline), and proximal occlusion (1.79 +/- 0.22; P = 0.004 vs baseline, and P = .012 vs distal occlusion). A progressive decrease in CFR was noted in each phase of the cardiac cycle. CONCLUSION: In a canine model of acute progressive distal and proximal coronary occlusion, we observed a progressive decrease in CFR in remote nonischemic regions concurrent with an increase in the extent of ischemia. The decrease in remote nonischemic CFR was associated with ischemia-induced isovolumic bulging, which placed the remote regions at a mechanical disadvantage. These observations suggest a potential mechanical etiology for the observed impairment in remote CFR. Alterations in remote nonischemic CFR during acute ischemia may have important clinical implications for perfusion scintigraphy.     

Comparison of myocardial imaging with iodine-123-iodophenyl-9-methyl pentadecanoic acid and thallium-201-chloride for assessment of patients with exercise-induced myocardial ischemia

Iodine-123-iodophenyl-9-methyl-pentadecanoic acid [( 123I]MPDA) and thallium-201 (201Tl) were sequentially injected in 11 patients during exercise-induced myocardial ischemia. Simultaneous dual-energy planar images were obtained at 5 min, 3 and 5 hr. All studies were concordantly either positive (8/11) or negative (3/11) by both radionuclides. Exact agreement for segmental uptake was 93%, 94% and 94% for 5-min, 3- and 5-hr images, respectively. Exact agreement for defect reversibility by 3 and 5 hr were 95% and 92%. The initial defect contrasts and myocardial-to-lung ratios were similar by both agents but myocardial-to-liver ratio was lower by [123I]MPDA at 5 min, which became similar to 201Tl at 5 hr. Normal percent myocardial clearances of both agents were comparable and significantly higher than those in defect zones. Thus [123I]MPDA is suitable for myocardial imaging and correlates closely with 201Tl for initial postexercise myocardial uptake and defect reversibility. Defect reversibility appears to result from differential myocardial clearance from normal and ischemic regions.     

Quantification of myocardial ischemia and infarction with single photon emission computed tomography

To evaluate the feasibility of 201Tl single photon emission computed tomography (SPECT) for quantitative detection of myocardial infarction and ischemia, scintigraphic studies were related to angiographic findings. In study A infarct sizes with SPECT were compared with the angiographic infarct sizes of 30 patients. A linear correlation was found for the % infarct of the left ventricular circumference between both methods (r = 0.73; P less than 0.001; mean infarct size 20.7% +/- 10.5% (angio) vs 19.8% +/- 12.9% (SPECT), mean +/- SD). Furthermore, a significant inverse correlation between scintigraphic infarct size and left ventricular ejection fraction (r = -0.87, P less than 0.001) was obtained. In study B exercise/rest 201Tl SPECT was used for quantification of myocardial ischemia. Forty-three patients underwent both stress 201Tl SPECT and biplane exercise left ventriculography. Ischemia was expressed as % defect size of the left ventricular circumference. Sensitivity and specificity for detection of ischemia were 96% and 100% respectively with stress SPECT. Extent of myocardial ischemia correlated significantly with both methods (r = 0.63; SPECT defect = 1.0 angiographic ischemia +2%; P less than 0.001). The regression followed the line of identity and the mean sizes of ischemia were identical (SPECT 12.2 +/- 7.6% vs 14.6 +/- 12.4% ventriculography, mean +/- SD) demonstrating the agreement of both methods. However, there was some intraindividual variance between the scintigraphic and the angiographic study. The sensitivity and specificity in single regions with SPECT were lower compared to the global test results.(ABSTRACT TRUNCATED AT 250 WORDS)     

Thallium-201 myocardial perfusion imaging during adenosine-induced coronary vasodilation in patients with ischemic heart disease]

201Tl myocardial perfusion imaging during adenosine infusion was performed in consecutive 55 patients with suspected coronary artery disease. Adenosine was infused intravenously at a rate of 0.14 mg/kg/min for 6 minutes and a dose of 111 MBq of 201Tl was administered in a separate vein at the end of third minute of infusion. Myocardial SPECT imaging was begun 5 minutes and 3 hours after the end of adenosine infusion. For evaluating the presence of perfusion defects, 2 short axis images at the basal and apical levels and a vertical long axis image at the mid left ventricle were used. The regions with decreased 201Tl uptake were assessed semi-quantitatively. Adenosine infusion caused a slight reduction in systolic blood pressure and an increase in heart rate. The rate pressure products increased slightly (9314 +/- 2377 vs. 10360 +/- 2148, p < 0.001). Chest pain (24%) and headache (13%) were the frequent side effects. The second-degree atrioventricular block was developed in 11 of 55 (20%) patients. All symptoms and hemodynamic changes were well tolerated and disappeared within 1 or 2 minutes after discontinuing adenosine infusion. The sensitivity and specificity for the detection of patients with coronary artery disease were 100% (31/31) and 88% (7/8), respectively. 201Tl myocardial imaging during adenosine infusion was considered to be safe and useful for evaluating the patients with ischemic heart disease.     

Dual isotope myocardial scintigraphy (201thallium at rest/99 M technetium tetrofosmin with exercise) in the detection of reversible hypoperfusion

The dual-isotope technique (rest 201Tl and stress 99mTc-sestamibi) is useful to assess myocardial perfusion in coronary disease patients. 99mTc-labeled tetrofosmin is a radiopharmaceutical whose characteristics are similar to sestamibi. Thus, we decided to use it to detect reversible myocardial hypoperfusion in patients with a background of myocardial infarction and ischemia. A sequential dual-isotope scintigraphy (3 mCi rest 201Tl and 25 mCi stress 99mTc-tetrofosmin) with 24-hour 201Tl redistribution (RD) was performed in 20 patients with previously confirmed myocardial infarction and clinical and ergometric signs of ischemia. Each patient also underwent a stress-redistribution protocol with redistribution at 4 and 24 hours post injection with 201Tl scintigraphy within two weeks of the first study. The qualitative uptake analysis showed no significant differences in the number of myocardial segments with severe reduction of tracer uptake on stress that improved at rest or in RD images, even if 24-hour RD images were considered. The quantitative global uptake analysis showed a similar defect reversibility with both protocols; however if 24-hour RD images were considered the uptake improvement was significant only when compared with the rest 201Tl images in dual-isotope scintigraphy protocol (75+/-8% vs. 81+/-9% of peak activity, rest vs. 24-hour RD; p<0.01) and not when compared with the 4-hour RD in the 201Tl scintigraphy. On the other hand, when only the segments with severely reduced uptake (<50% of peak activity) were analyzed, the 24-hour RD improved myocardial uptake significantly (p<0.001 vs. rest and vs 4-hour RD) in both protocols. We conclude that a sequential dual-isotope rest 201Tl/stress 99mTc-tetrofosmin scintigraphy is comparable with stress-redistribution 201Tl scintigraphy to detect reversible myocardial hypoperfusion; however in both cases, the addition of 24-hour images increases its usefulness in severely hypoperfused segments, if the uptake of the radiopharmaceutic is quantified.     

The comparison of 2-18F-2-deoxyglucose and 15-(ortho-123I-phenyl)-pentadecanoic acid uptake in persisting defects on thallium-201 tomography in myocardial infarction

The myocardial uptake of glucose and fatty acids into 201Tl redistribution defects were studied in 32 patients with myocardial infarction by tomography using 2-18F-2-deoxyglucose (FDG) and 15-(ortho-123I-phenyl)-pentadecanoic acid (oPPA). A total of 1153 segments were analyzed, 408 (35%) of which showed a persistent thallium-defect in stress-redistribution images. Of the segments with a decreased 201Tl uptake in these redistribution tomograms, 50.5% had a decreased uptake of both FDG and oPPA; in 21.8% FDG as well as oPPA uptake was within normal range. Normal FDG uptake but decreased oPPA uptake was detected in 17.4%, whereas 10.3% of the segments had normal oPPA uptake but decreased FDG uptake (chi-square test, p less than 0.001). A significant correlation of FDG and oPPA uptake (r = 0.51) was found in the segments with persistent 201Tl defect. Thus, a substantial fraction of persistent thallium-defects after healed myocardial infarction exhibit FDG as well as oPPA uptake, probably due to residual fatty acid metabolism in partially ischemic regions.     

(201)Tl and (99m)Tc-MIBI retention in an isolated heart model of low-flow ischemia and stunning: evidence of negligible impact of myocyte metabolism on tracer kinetics.

It is not known whether cellular metabolic disorders play a role in the decreased tracer uptake that is documented by conventional SPECT during low-flow ischemia or stunning. This study sought to determine the impact of low-flow ischemia and stunning on the kinetics of (201)Tl and MIBI across the plasma membrane of myocytes. METHODS: The global myocardial retention (Rf) of (201)Tl and MIBI was determined in isolated working hearts from rabbits, perfused with red blood cell-enhanced solution. Experiments were performed in normoxia, with physiological values of coronary flow (N; n = 16); in low-flow ischemia, with a >50% reduction of coronary flow and a > or =20-mm Hg fall in systolic left ventricle pressure (L; n = 15); and in stunning, with 15 min of acute ischemia followed by reperfusion (S; n = 15). Concentration ratios across the plasma membrane of myocytes were also determined for both tracers and expressed as Ci/Cc, where Ci is interstitial activity determined with microdialysis, and Cc is activity from cellular space determined from Rf and Ci values. RESULTS: There was a slight increase in average values of Ci/Cc in ischemia, but not in stunning, for (201)Tl (L, 0.011 +/- 0.006 vs. N, 0.006 +/- 0.004 [P < 0.05]; S, 0.007 +/- 0.004 vs. N [not significant]) and for MIBI (L, 0.011 +/- 0.008 vs. N, 0.005 +/- 0.004 [P < 0.05]; S, 0.005 +/- 0.003 vs. N [not significant]). Moreover, ischemia and stunning had no deleterious effects on the average values of global myocardial retention for (201)Tl (L, 0.63 +/- 0.09 vs. N, 0.50 +/- 0.14 [P < 0.05]; S, 0.59 +/- 0.10 vs. N [P < 0.05]) or for MIBI (L, 0.45 +/- 0.10 vs. N, 0.31 +/- 0.09 [P < 0.05]; S, 0.41 +/- 0.12 vs. N [P < 0.05]). In fact, these values were significantly enhanced in the 2 situations. CONCLUSION: The kinetics of (201)Tl and MIBI across the plasma membrane of myocytes were affected only poorly by low-flow ischemia and not at all by stunning, without any deleterious effects on myocardial retention of both tracers. During low-flow ischemia or stunning, therefore, the information provided by (201)Tl or MIBI SPECT is expected to depend on myocardial perfusion but not on cellular metabolic disorders.     

201Tl-redistribution analysis in early and delayed myocordial scintigrams of patients with coronary heart disease (CHD)

Scans were performed on 8 healthy subjects and 25 with coronary heart disease proven by angiography and ventriculography including 6 with previous myocardial infarction at rest, exercise, and 1 and 2 h after exercise. Data were collected by a gamma camera interfaced to a data collection system. In healthy subjects ²⁰¹Tl distribution was homogeneous at rest and after exercise, the count rate ranging between 100%—as set in the region of maximum—and 80% over other regions of myocardium. In 19 patients with coronary heart disease it was uniform only at rest; 6 patients with previous myocardial infarction had locally diminished ²⁰¹Tl uptake even at rest. In patients with coronary heart disease without previous myocardial infarction, scans made immediately after exercise showed significant ²⁰¹Tl hypofixation in region of minimum, the count rate of which was less than 80% of the count rate as determined over region of maximum, ²⁰¹Tl uptake. Scans made 1 and 2 h after exercise had filling-in of ²⁰¹Tl within the region of minimum the count rate of which returned to the normal range of at least 80% of the count rate measured over region of maximum uptake. This return to resting distribution was called ²⁰¹Tl redistribution. Six patients with coronary heart disease and previous myocardial infarction had ²⁰¹Tl defects larger after exercise than at rest, without redistribution being observed. Redistribution in late postexercise scans is a sign of reversible ischemia in coronary heart disease. Scans at rest may be omitted in coronary heart disease, because transient ischemia is undetectable, unless spontaneous angina occurs during scan procedure.     

Technetium-99m-sestamibi myocardial perfusion imaging in detection of coronary artery disease: comparison between initial (1-hour) and delayed (3-hour) postexercise images.

Technetium-99m-sestamibi, a new myocardial perfusion imaging agent, does not show significant or rapid myocardial redistribution following its intravenous injection at stress. The purpose of this study was to evaluate the myocardial clearance of 99mTc-sestamibi and ischemic/normal wall ratios at 1 hr and at 3 hr after injection at stress in patients with significant coronary artery disease. Twenty-five patients with ischemic defects on 201Tl scans (n = 15) and/or significant disease on coronary angiogram (n = 18) were prospectively studied. Planar images were obtained at 65 and at 190 min after an injection at stress of 20-25 mCi of 99mTc-sestamibi. A rest study was performed 1-6 days later. Ischemic/normal wall ratios were 0.73 +/- 0.10 and 0.83 +/- 0.12 (p less than 0.05) at 1 and 3 hr, respectively (0.98 +/- 0.15 at rest). Myocardial washout was 26% +/- 12% for normal walls and 15% +/- 8% for ischemic walls (p less than 0.001). Segmental analysis showed 48 and 46 ischemic segments at 1 and 3 hr, respectively. In conclusion, although only a few ischemic segments were missed at 3 hr, significantly lower ischemic/normal wall ratios were found at 1 hr. Faster myocardial washout from normal walls is responsible for the partial reduction of this ratio.     

An assessment of wall motion, perfusion and glucose metabolism in recent myocardial infarction: a comparison in patients with and without revascularization

The aim of this study was to compare the extent and severity of wall motion abnormalities, perfusion and glucose metabolism, in recent myocardial infarction in patients with and without revascularization. Forty-nine patients were studied (82% men; mean age 58 years) by using echocardiography, 201Tl single photon emission computed tomography (SPECT) rest and redistribution, and 2-[18F]fluoro-2-deoxy-D-glucose (18F-FDG) SPECT at a mean of 9.2 days (range, 1-24 days) after myocardial infarction. Twenty-seven of the 49 patients underwent revascularization while the other 22 received medical therapy before echocardiography and studies using radionuclides. A contrast angiogram was obtained for each patient. A follow-up echocardiogram at 3 months was obtained for 44 patients. Images were read blindly, using a 17 segment model, with semi-quantitative analysis. In the whole group, the extent of hypokinesia was 15%+/-14 (mean+/-SD); the extent of mild defects was determined as 5%+/-6 by using 201Tl at rest, 6%+/-9 by using 201Tl redistribution, and 4%+/-6 by using 18F-FDG (P<0.0005, echocardiogram/radionuclides). Echocardiography showed that the extent of akinesia-dyskinesia was 16%+/-18 in revascularized patients and 28%+/-18 in non-revascularized patients (P=0.017). With regard to moderate and severe defects, 201Tl rest showed 19%+/-16 and 28%+/-17, respectively (P=0.047); 201Tl redistribution 17%+/-15 and 26%+/-15, respectively (P=0.043); and 18F-FDG 17%+/-13 and 24%+/-15, respectively (NS). In echocardiography, the extent of hypokinetic segments decreased from 16%+/-15 at baseline to 10%+/-11 at 3 months (P=0.045), in revascularized patients. It is concluded that, in recent myocardial infarction, hypokinesia extent on echocardiogram is greater than mild perfusion or metabolic defect extent, reflecting stunning and so the use of radionuclide techniques appear more accurate for defining the extent of myocardial infarction. Non-revascularized patients showed a significantly greater extent of akinesia-dyskinesia and moderate-severe perfusion defects than did revascularized patients, which can be considered a result of therapy. It is suggested that 201Tl rest perfusion be used for the assessment of myocardial infarction soon after revascularization.     

Tl-201 myocardial SPECT in differentiation of ischemic from nonischemic dilated cardiomyopathy in patients with left ventricular dysfunction

BACKGROUND: The differentiation between ischemic and nonischemic cardiomyopathy by noninvasive modalities is of clinical importance. Whether thallium 201 single photon emission computed tomography (SPECT) could accurately distinguish the two groups remains unclear. METHODS AND RESULTS: Twenty-nine patients with chronic heart failure (left ventricular ejection fraction < or =40%), including fourteen patients with ischemic cardiomyopathy and fifteen patients with nonischemic dilated cardiomyopathy, underwent Tl-201 SPECT. The stress protocols included treadmill exercise in 8 patients, dipyridamole in 6 patients, and dobutamine infusion in 15 patients. Myocardial SPECT was interpreted with the use of a 17-segment model and 0- to 4-point scale system. Patients with ischemic cardiomyopathy had higher summed stress defect scores (27.9 +/- 9.4 vs 20.6 +/- 8.9, P =.04), more fixed defect segments (5.9 +/- 2.9 vs 3.8 +/- 2.9, P =.05), and more moderate or severe perfusion defect segments on stress scan (7.2 +/- 2.0 vs 4.5 +/- 2.6, P =.004) than did those with nonischemic dilated cardiomyopathy. However, considerable overlap of the scan patterns between the two groups existed. Moderate or severe perfusion defects on stress scan in at least 7 segments were noted in 71% of patients (10/14) with ischemic cardiomyopathy, as compared with 20% of patients (3/15) with nonischemic cardiomyopathy (P =.016). CONCLUSIONS: Assessment of Tl-201 myocardial SPECT yields only modest value to distinguish nonischemic dilated cardiomyopathy from ischemic cardiomyopathy in patients with chronic heart failure. This technique cannot clearly differentiate individual patients.     

Inability of seven-pinhole myocardial tomography to obtain accurate 201Tl kinetic data

Seven-pinhole myocardial tomography has been reported to enhance the accuracy of thallium-201 (²⁰¹Tl) studies in detecting patients with coronary artery disease. To determine if this approach can accurately assess regional ²⁰¹Tl kinetics, 12 dogs with temporary occlusion (mean 15 min) of either the left anterior descending (LAD) (n=6) or left circumflex (LCX) (n=6) coronary artery were studied. Thallium-201 was injected and serial 7-pinhole images were acquired during occlusion and following reflow (mean duration 175 min). Time-activity analysis was obtained from normal and ischemic regions of interest in the central pinhole image and the reconstructed, tomographic images (TOMO-ROI). Time-activity data from corresponding normal and ischemic regions were also obtained using a circumferential graph program (TOMO-MAX). In addition, regional myocardial ²⁰¹Tl activity was recorded continuously with a cadmium telluride radiation probe sutured directly to the posterior myocardial wall. Defects in ²⁰¹Tl distribution with subsequent partial or complete redistribution were present in 11 of 12 central pinhole images and tomographic studies. In the normal and ischemic anterior myocardial segments the percentage change in ²⁰¹Tl activity in the central pinhole image from occlusion to the end of reflow correlated well with the percentage change in activity for both TOMO-ROI (r=0.93) and TOMO-MAX (r=0.85). In the normal posterior segments the percentage change in ²⁰¹Tl activity in the central pinhole image correlated well with TOMO-ROI (r=0.98) and TOMO-MAX (r=0.87). However, the correlation fell when the ischemic posterior segments were included: TOMO-ROI (r=0.62); TOMO-MAX (r=0.43). The percentage change in ²⁰¹ Tl activity from the direct myocardial probe counting of the posterior wall had a poor correlation with both TOMO-ROI (r=0.11) and TOMO-MAX (r=0.31). Despite the poor correlation with ²⁰¹Tl kinetics, 7-pinhole tomography remains a sensitive technique for the detection of myocardial ischemia.