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.     

Thallium-201 as a myocardial imaging agent

The field of myocardial perfusion imaging has made many advances but still is in its infancy. The limitations in the technology at this time include limited instrument resolution of 6-9 mm, intrinsic at the energy of the mercury x-ray; significant Rayleigh scatter, which is particularly distrubing because this scatter cannot be removed by pulse-height analysis; and an effective half-life of thallium in the myocardium, which makes repeated imaging over a short period of time very difficult. Although hopes for the development of a technetium-labeled myocardial imaging tracer have burnt brightly, no new agents are presently in sight. Resolution with a technetium-labeled tracer would almost double that of thallium, and the dose that could be administered to the patient would increase by at least a factor of 4. The effective half-life of the tracer in the myocardium would permit multiple images to be obtained at least in the same day. Even with the limitations of the current techniques, however, myocardial perfusion imaging can make a real contribution to the care of the patients with heart disease. Thallium is now produced commercially and reasonably easily obtained. Extraction of thallium by the myocardium is probably somewhat, but not exactly, analogous to potassium. The tracer has major applications in defining shape and size of the heart, thickness of muscle, and especially myocardial ischemia and infarction. This review is aimed at providing a current perspective of these uses.     

Thallium-201 myocardial perfusion imaging in myocarditis

TI-201 myocardial perfusion imaging was performed in six patients with clinically documented myocarditis. Each case manifested electrocardiographic abnormalities with elevation of serum cardiac enzymes and no significant stenosis of the coronary arteries observed on angiogram. Resting TI-201 images were visually assessed by three observers. Focal perfusion defects were observed in three cases (50%), among which two showed multiple perfusion defects. Emission computed tomography using TI-201 clearly delineated multifocal lesions in the first case. On the other hand, no significant perfusion defects were noted in the remaining three cases. Thus, myocarditis should be considered as one of the disease entities that may produce perfusion defects on TI-201 myocardial imaging.     

Persistent chest pain following oral dipyridamole for thallium 201 myocardial imaging

A patient was admitted to the hospital with acute chest pain. After acute myocardial infarction was ruled out, he underwent a stress thallium 201 scintigraphy using oral dipyridamole and developed persistent angina with ST-segment elevation. This complication has not been reported previously. It is recommended that appropriate intervention be available if severe ischemia develops following administration of dipyridamole for diagnostic imaging.     

Worsening of left ventricular ejection fraction induced by dipyridamole on Tl-201 gated myocardial perfusion imaging predicts significant coronary artery disease

BACKGROUND: Vasodilator stress on myocardial perfusion imaging has been found to induce ischemic stunning, which may present as transient worsening of left ventricular ejection fraction (LVEF) or regional wall motion abnormality. This study aimed to evaluate the significance of stress-induced worsening of LVEF in the diagnosis of coronary artery disease (CAD) on dipyridamole thallium 201 gated single photon emission computed tomography (SPECT). METHODS AND RESULTS: The study included 126 patients who underwent dipyridamole Tl-201 gated SPECT and coronary angiography within 3 months. Poststress and 4-hour rest images were obtained, and LVEF was calculated by use of automated software (QGS 3.0). A decrease in LVEF of 6% or greater from rest to poststress was considered significant, and this threshold was determined by the serial reproducibility assessment of Tl-201 gated SPECT. If worsening of LVEF was used as the criterion for detecting significant CAD (> or = 70% coronary stenoses in > or = 1 vessel), the sensitivity, specificity, positive predictive value, and negative predictive value were 35%, 93%, 90%, and 44%, respectively. CONCLUSION: Dipyridamole-induced worsening of LVEF, as shown by Tl-201 gated SPECT, is a valuable nonperfusion marker of significant CAD. Although the sensitivity of LVEF worsening in detecting significant CAD is only 35%, the specificity is as high as 93%.     

I-123 labeled hexadecenoic acid in comparison with Thallium-201 for myocardial imaging in coronary heart disease

The imaging properties of ¹²³I-16-iodo-9-hexadecenoic acid (¹²³I-HA), a terminally iodinated 17-carbon atom fatty acid analogue, were compared with Thallium-201 (²⁰¹Tl). Because of its shorter half-life, favourable photon-energy and rapid myocardial turnover rate, ¹²³I-HA possesses potential advantages in the study of regional myocardial perfusion and metabolism. Twelve patients with documented coronary artery disease (CAD) were studied; eight patients sustained an acute myocardial infarction, four patients suffered from unstable angina. Visually assessed, a similar distribution pattern and comparable imaging quality was demonstrated with both radionuclides. The scintigraphic results were also correlated with coronary arteriographic findings. A good relationship was found between the perfusion defects and the location of the coronary artery lesions in the patients with acute myocardial infarction.We conclude that ¹²³I-HA is comparable to ²⁰¹Tl in detecting areas of reduced myocardial perfusion in patients with CAD with the advantage of studying myocardial metabolism.     

Effect of aminophylline on thallium-201 washout rate during myocardial perfusion imaging with dipyridamole

Thallium-201 myocardial perfusion imaging with dipyridamole was performed on 78 patients (pts) with suspected coronary artery disease (CAD). Twenty eight pts had normal coronary arteries (control group), and 50 pts had 50% or greater stenosis in one or more major coronary arteries (CAD group). In control group, aminophylline (Am) was infused intravenously on 12 pts during dipyridamole testing. Mean washout rate (WR) of these 12 pts was greater than that of 16 pts without Am (42% vs 35%, p less than 0.01). Then normal limit of WR was defined separately from the pts of control group with and without Am. The sensitivity for detecting the pts with CAD by WR analysis which normal limit was calculated separately with and without Am was 92% (46/50). When normal limit of WR was determined from all pts in control group, the sensitivity decreased to 84% (42/50). Am significantly affected thallium-201 washout during dipyridamole testing. WR of CAD pts should be estimated by specific set of normal limit with and without Am.     

Thallium-201 for myocardial imaging: appearance of the normal heart.

Thallium-201 myocardial perfusion images were obtained from 13 healthy adults after tracer administration both at rest and at maximal stress. On the rest-injected scan, tracer was seen in left ventricular myocardium, liver, and spleen. In two subjects with resting tachycardia, the right ventricular myocardium was slightly visualized after tracer injection at rest. When tracer was administered at stress, the left ventricular activity was more nearly homogeneous and the left ventricle was better defined on the scan. The left-ventricle-to-lung-background activity ratio increased from 2.4 at rest to 3.4 at stress. The right ventricular myocardium was seen on the stress-injected scan. Phantom studies, performed to define the optimum position for visualization of lesions, showed that small lesions were best defined when seen either en face or in tangent. Scans should be performed at stress whenever possible and multiple views are essential.     

Thallium-201 imaging in anomalous left coronary artery originating from pulmonary trunk

A 3-month-old infant with anomalous origin of the left main coronary artery (LMCA) from the pulmonary trunk was evaluated using resting thallium imaging. The imaging findings were consistent with myocardial scar and ischemia of the anterolateral and posterolateral walls in the distribution of the LMCA.     

冠状动脉痉挛患者心电图及201Tl心肌灌注显像负荷试验的特征

目的探讨冠状动脉痉挛患者心电图运动试验和201Tl心肌灌注显像双嘧达莫(潘生丁)试验的特征及非创伤性检测冠状动脉痉挛的理想方法.方法以临床上52例具有胸痛、冠状动脉造影无显著狭窄而接受乙酰胆碱试验的患者为研究对象,进行心电图活动平板运动试验和201Tl心肌灌注显像双嘧达莫试验,探讨其试验结果与冠状动脉痉挛的关系.结果52例受检者中阳性即冠状动脉痉挛患者42例,多以静息性胸闷为主,不同于冠状动脉狭窄所引起的劳累性胸痛;10例阴性患者多以与活动和休息无关的刺痛为主.心电图运动试验阳性3例.52例患者中48例201Tl心肌灌注显像呈反向再分布.单纯反向再分布预测冠状动脉痉挛的灵敏度和特异性分别为100%和40%;而以同时具备静息性胸闷、运动试验阴性和反向再分布3个特征预测冠状动脉痉挛的灵敏度和特异性分别为98%和90%.结论反向再分布可能是冠状动脉痉挛的特征之一;同时具备静息性胸闷、运动试验阴性和反向再分布是预测冠状动脉痉挛较理想的非创伤性方法.     

Thallium-201 myocardial imaging: a comparison of the redistribution and rest images

Forty-one patients with chest pain and suspected coronary artery disease underwent thallium-201 myocardial imaging, performed immediately following maximal treadmill exercise, also at "redistribution" 4--5 hr after exercise, and at rest 1 wk later. All had coronary angiography. All images in seven patients without coronary artery disease were normal. Twenty-seven of the 34 (79%) patients with coronary artery disease had new, exercise-induced image defects. The redistribution and rest images were identical in 15/27 (56%) patients (complete redistribution). In 10/27 (37%) patients with exercise-induced defects, some redistribution occurred but defect size on the redistribution image was larger than that on the rest images (incomplete redistribution). In 2/27 (7%) of patients with exercise-induced defects, redistribution was absent. The presence of prior myocardial infarction, regional abnormalities of left-ventricular contraction or the severity of coronary stenoses did not correlate with the presence or absence of redistribution. Overall image quality between the two studies was similar, although image collection times for the redistribution study were prolonged. We conclude that some redistribution (complete or incomplete) occurs in most patients with exercise-induced image defects. When both fixed and reversible perfusion defects are present, defect size was often larger in the redistribution image and may thus overestimate the extent of prior myocardial infarction.     

Inadequate exercise leads to suboptimal imaging. Thallium-201 myocardial perfusion imaging after dipyridamole combined with low-level exercise unmasks ischemia in symptomatic patients with non-diagnostic thallium-201 scans who exercise submaximally

This study was undertaken to establish the additional value of 201TI imaging after dipyridamole in combination with low-level exercise in 15 symptomatic patients with non-diagnostic 201TI scans, who exercised submaximally. Most patients had angina, ST-segment depression and even exertional hypotension and were referred for stress 201TI testing for determining the functional significance of known coronary artery disease. Six patients with a normal exercise 201TI test and one patient with an apical defect only were found to have 37 segments (of 105 segments) with reversible perfusion defects after dipyridamole infusion. One patient showing two reversible defects after exercise had five reversible segments after dipyridamole. Seven patients with fixed defects in 28 segments after exercise and two with small areas of border zone ischemia in seven additional (sub)segments, demonstrated fixed in defects in only nine segments but reversible defects in 40 segments after dipyridamole. Quantitative analysis resulted in 24.8 +/- 28.5 (mean value) sample points below -2 s.d. of the mean normal uptake after exercise, which increased to 72 +/- 26.5 after dipyridamole infusion (p less than 0.005). The washout analysis resulted in a mean value of 5.5 +/- 8.1 sample points below -2 s.d. after exercise, increasing to 33.3 +/- 22.1 after dipyridamole (p less than 0.005). Thallium-201 myocardial perfusion imaging after dipyridamole combined with low-level upright bicycle exercise may unmask scintigraphic evidence for ischemia in symptomatic patients who would otherwise have non-diagnostic imaging studies during submaximal exercise.     

The significance of the abnormal rest Thallium-201 myocardial image in coronary artery disease

Rest Thallium-201 myocardial images were abnormal in 20 out of 40 patients with arteriographically proven coronary artery disease. The myocardial image appearances did not accurately reflect the extent of coronary artery disease present. However, in 35 of the 40 patients (88%) the presence or absence of abnormalities on the rest myocardial image correleted respectively with the presence or absence of abnormal wall motion at left ventriculography. Most rest image abnormalities could be attributed to previous myocardial infarction, but in six patients myocardial ischaemia was possibly the cause. These results suggest that though myocardial fibrosis is usually the cause of rest myocardial image abnormalities in coronary artery disease, this is not invariably so. The possible therapeutic implications are discussed.     

冠状动脉痉挛致心肌血流灌注降低：反向再分布的机制研究

目的 探讨冠状动脉痉挛患者核素心肌灌注显像反向再分布（RR）的机制.方法 选择双嘧达莫负荷201TI心肌灌注显像表现为RR且诊断为冠状动脉痉挛的患者26例（RR组）、无冠状动脉狭窄及RR者16例（对照组）,在冠状动脉造影术中重复双嘧达莫试验,测量并比较注射双嘧达莫前后RR相关、非RR相关血管和对照组相应血管的校正心肌梗死溶栓疗法（TIMI）血流帧计数（CTFC）和心肌血流灌注积分（TMPG）.统计学处理采用t检验、χ2检验及相关分析.结果 冠状动脉造影见RR相关血管僵硬,血流速度和心肌灌注明显低于非RR相关血管,且RR区域静态心肌灌注缺损与冠状动脉造影血流速度缓慢高度相关（r=0.79,t=10.18,P＜0.001） 而对照组的各支冠状动脉血流速度和心肌灌注无明显差异.RR相关血管注射双嘧达莫前后CTFC分别为（36±6）帧及（26±7）帧（t=4.15,P＜0.01） TMPG分别为（2.02±0.39）级和（2.92±0.12）级（t=2.25,P＜0.05） 非RR相关血管注射前后CTFC分别为（29±7）帧及（25±5）帧（t=2.31,P＜0.05） TMPG分别为（2.56±0.31）级和（2.96±0.06）级（t=2.17,P＜0.05） 而对照组注射双嘧达莫前后TCFC及TMPG均无明显变化（t=0.932及0.867,P均＞0.05）.结论 冠状动脉痉挛患者静息状态下RR相关血管及微血管处于轻度痉挛状态,导致血流速度及心肌灌注缓慢 而负荷状态下血管扩张,使血流速度和心肌灌注加快,因而呈现RR.