Myocardial 201Tl washout after combined dipyridamole submaximal exercise stress: reference values from different patient groups

Dipyridamole stress is favorable in patients unable to exercise maximally for 201Tl myocardial scintigraphy. Aside from an analysis of uptake defects, proper washout analysis can be limited by heart rate variations when isolated dipyridamole stress is used. Heart rate standardized 201Tl washout kinetics after a combined dipyridamole and submaximal exercise stress protocol (CDSE), feasible in elderly patients as well as in patients with peripheral artery disease, were therefore studied to investigate the 201Tl washout after CDSE in differently defined patient groups: Group I comprised 19 patients with documented heart disease and angiographically excluded coronary artery disease (CAD); group II contained 17 patients with a very low likelihood of CAD determined by both normal exercise radionuclide ventriculography and normal 201Tl uptake. Group III comprised 56 patients with a 50% pretest likelihood of CAD but normal 201Tl uptake. Mean washout values were nearly identical in all groups. Despite similar uptake patterns, however, washout standardized by CDSE was significantly lower than the normal washout values after maximal treadmill exercise. Thus an obviously lower 201Tl washout after CDSE than after maximal treadmill exercise must be considered if washout analysis criteria after dipyridamole are applied to evaluate ischemic heart disease. Nevertheless, heart rate elevation achieved by additional submaximal exercise stress seems necessary, adequate and clinically safe for standardisation of washout analysis in dipyridamole 201Tl scintigraphy.     

Quantitative thallium-201 scintigraphy after dipyridamole infusion combined with low level exercise in healthy volunteers

To establish test specific normal limits for quantitative analysis of uptake and washout of ²⁰¹Tl after dipyridamole infusion combined with low level exercise, 20 healthy volunteers were studied with low likelihood of coronary artery disease (CAD) assessed by a stepwise probability analysis based on age, sex, symptoms, resting electrocardiogram, and exercise electrocardiography. Likelihood of CAD in these volunteers was calculated as 1%. After dipyridamole infusion combined with low level exercise, one volunteer complained of headache; no other side effects were observed. There were no chest pain complaints. Maximal hemodynamic changes were achieved during the 6th and 7th min of the test. No ST segment depression was recorded. Visual analysis of the ²⁰¹Tl scintigrams was normal in all volunteers. Mean regional washout at 4 h was 44.37%±2.11%. The regional washout in the 70° LAO view (46.65%±1.10%) was significantly higher than in the anterior and 30° LAO views (43.44%±1.50% and 43.02%±1.45%, respectively). Profiles of uptake and washout of ²⁰¹Tl were different after dipyridamole infusion combined with low level exercise as compared to maximal exercise. Thus, in quantitative analysis of ²⁰¹Tl scintigraphy after dipyridamole infusion in conjunction with low level exercise as applied in the present study, it is mandatory to use normal limits of uptake and washout of ²⁰¹Tl derived from healthy volunteers who underwent the same combined protocol.     

Quantitative thallium-201 scintigraphy after dipyridamole infusion combined with low level exercise in healthy volunteers

To establish test specific normal limits for quantitative analysis of uptake and washout of 201Tl after dipyridamole infusion combined with low level exercise, 20 healthy volunteers were studied with low likelihood of coronary artery disease (CAD) assessed by a stepwise probability analysis based on age, sex, symptoms, resting electrocardiogram, and exercise electrocardiography. Likelihood of CAD in these volunteers was calculated as less than or equal to 1%. After dipyridamole infusion combined with low level exercise, one volunteer complained of headache; no other side effects were observed. There were no chest pain complaints. Maximal hemodynamic changes were achieved during the 6th and 7th min of the test. No ST segment depression was recorded. Visual analysis of the 201Tl scintigrams was normal in all volunteers. Mean regional washout at 4 h was 44.37% +/- 2.11%. The regional washout in the 70 degrees LAO view (46.65% +/- 1.10%) was significantly higher than in the anterior and 30 degrees LAO views (43.44% +/- 1.50% and 43.02% +/- 1.45%, respectively). Profiles of uptake and washout of 201Tl were different after dipyridamole infusion combined with low level exercise as compared to maximal exercise. Thus, in quantitative analysis of 201Tl scintigraphy after dipyridamole infusion in conjunction with low level exercise as applied in the present study, it is mandatory to use normal limits of uptake and washout of 201Tl derived from healthy volunteers who underwent the same combined protocol.     

The (F)utility of the thallium-201 quantitative lung/myocardial ratio in the detection of coronary artery disease

Exercise-induced increases in pulmonary uptake of thallium-201 (²⁰¹Tl) have been associated with exercise-induced myocardial dysfunction. To evaluate this phenomenon more replicably, a quantitative semi-automated computer program was used to generate, from anterior exercise and delayed views, lung-myocardial ratios (LMR) of²⁰¹Tl uptake in 78 patients [40 normal, 38 with coronary artery disease (CAD)]. Patients with CAD had a significantly higher mean exercise lung myocardial ratio (EXLMR) than normals (30.8 vs. 27.3;P < 0.003). In patients with adequate exercise (85% of an age-adjusted maximal heart rate), the EXLMRs of CAD patients were significantly higher than those of normals (29.7 vs. 25.5;P=0.003). However, this difference between CAD and normal patients was not apparent in a patient subgroup with submaximal exercise levels (< 85% of an age-adjusted maximal heart rate). In both normal and CAD patients, EXLMR decreased with increasing exercise levels (r=-0.555;P=0.007). In patients with²⁰¹Tl scans lacking visually defined perfusion defects (visually normal), an elevated LMR detected 60% of CAD cases with 81% specificity. A considerably elevated EXLMR in patients achieving adequate exercise should suggest the presence of CAD, even if there are no visually apparent cardiac perfusion defects. With submaximal exercise, however, the EXLMR is not a useful discriminator between CAD patients and normals.     

Quantitative thallium-201 myocardial exercise scintigraphy in normal subjects and patients with normal coronary arteries

Quantitative thallium-201 myocardial exercise scintigraphy was tested in two patient populations representing alternative standards for cardiac normality: group I comprised 18 male uncatheterized patients with a low likelihood of coronary artery disease (CAD); group II contained 41 patients with normal coronary arteriograms. Group I patients were younger, they achieved a higher rate-pressure product than group II patients; all had normal findings by physical examination and electrocardiography at rest and exercise. Group II patients comprised 21 females, 11 patients showed abnormal electrocardiography at rest, and five patients showed ischemic ST depression during exercise. Twelve patients had signs of minimal CAD. Twelve patients revealed abnormal visual and quantitative thallium findings, three of these patients had minimal CAD. Profiles of uptake and washout of thallium-201 were derived from both patient groups, and compared with normal limits developed by Maddahi et al. Furthermore, low likelihood and angiographically normal patients may differ substantially, and both sets of normal patients should be considered when establishing criteria for abnormality in exercise thallium imaging. When commercial software containing normal limits for quantitative analysis of exercise thallium-201 imaging is used in clinical practice, it is mandatory to compare these with normal limits of uptake and washout of thallium-201, derived from the less heterogeneous group of low-likelihood subjects, which should be used in selecting a normal population to define normality.     

Usefulness of resting thallium-201 delayed imaging for detecting myocardial viability in patients with previous myocardial infarction

To test the feasibility of resting thallium-201 (²⁰¹Tl) initial and delayed scintigraphy for detecting the area of viable myocardium, we performed single photon emission computed tomography (SPECT) in 57 patients with previous myocardial infarction (MI). All had received coronary arteriography (CAG) and left ventriculography (LVG). Initial and delayed myocardial imagings were carried out 10 min and 2 hours, respectively, after the injection of²⁰¹Tl at rest. Redistribution was judged by visual interpretation and/or the circumferential profile curve, and found in the infarcted or its adjacent area in 40 of the 57 cases (70.2%). A negative washout (net increase of²⁰¹Tl uptake in delayed image) was detected in 17 of these 40 cases. In 10 of the 57 patients, both exercise and rest-injected²⁰¹Tl myocardial images were obtained at exercise and rest, and compared visually. The areas of abnormal perfusion were smaller in the resting delayed images than those seen after exercise in 9 of the 10 cases, and were equal in one case. Thus, resting²⁰¹Tl delayed myocardial scintigraphy appears to reduce the underestimation of the size of the viable myocardium by the usual²⁰¹Tl images obtained after exercise or by single initial images obtained at rest in patients with previous MI.     

The (F)utility of the thallium-201 quantitative lung/myocardial ratio in the detection of coronary artery disease

Exercise-induced increases in pulmonary uptake of thallium-201 (201Tl) have been associated with exercise-induced myocardial dysfunction. To evaluate this phenomenon more replicably, a quantitative semi-automated computer program was used to generate, from anterior exercise and delayed views, lung-myocardial ratios (LMR) of 201Tl uptake in 78 patients [40 normal, 38 with coronary artery disease (CAD)]. Patients with CAD had a significantly higher mean exercise lung myocardial ratio (EXLMR) than normals (30.8 vs. 27.3; P less than 0.003). In patients with adequate exercise (greater than or equal to 85% of an age-adjusted maximal heart rate), the EXLMRs of CAD patients were significantly higher than those of normals (29.7 vs. 25.5; P = 0.003). However, this difference between CAD and normal patients was not apparent in a patient subgroup with submaximal exercise levels (less than 85% of an age-adjusted maximal heart rate). In both normal and CAD patients, EXLMR decreased with increasing exercise levels (r = -0.555; P = 0.007). In patients with 201Tl scans lacking visually defined perfusion defects (visually normal), an elevated LMR detected 60% of CAD cases with 81% specificity. A considerably elevated EXLMR in patients achieving adequate exercise should suggest the presence of CAD, even if there are no visually apparent cardiac perfusion defects. With submaximal exercise, however, the EXLMR is not a useful discriminator between CAD patients and normals.     

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.     

Identification of advanced coronary artery disease with exercise myocardial perfusion imaging: the clinical value of a novel approach for assessing lung thallium-201 uptake

Introduction The precise clinical utility of lung ²⁰¹Tl uptake in exercise SPECT myocardial perfusion imaging remains open to research. This study validates an optimal index for lung ²⁰¹Tl uptake measurement and assesses its value in the prediction of higher-risk coronary artery disease (CAD). Method Three hundred and ninety-eight patients underwent exercise SPECT myocardial perfusion imaging. They were separated into derivation (n = 217) and validation (n = 186) groups, both including sub-populations of lower- and higher-risk CAD, according to coronary angiography. Another 56 individuals with a low probability of CAD comprised the control group. From a planar, anterior, post-exercise acquisition, the lung (L) to heart (H) maximal (L/H_max), total (L/H_mean) and background-subtracted total (L/H_net) ratios were calculated. These were also adjusted for confounding variables, as assessed from the control group. ROC analysis was used to compare the L/H ratios and define thresholds of abnormality. The performance of the optimal index was assessed in the derivation group and was then tested in the validation population. Subsequently, it was compared with other scintigraphic, exercise electrocardiography and clinical variables. Results In the derivation group L/H_net was a better discriminator for higher-risk CAD than both L/H_max and L/H_mean. Similarly, the adjusted L/H_net was a better discriminator than both the adjusted L/H_max and the adjusted L/H_mean. No significant difference was attained between L/H_net and the adjusted L/H_net. At the upper defined threshold of abnormality, sensitivity and specificity of L/H_net in the detection of higher-risk CAD in the derivation and the validation cohorts were 52% and 92% versus 47% and 94%, respectively (p =  ns). The results were similar at other defined thresholds. Moreover, L/H_net was found to be a significant predictor of higher-risk CAD, superior to myocardial perfusion images, transient ventricular dilation measurements, and clinical and exercise testing variables (ROC analysis and logistic regression). By raising the threshold of abnormality of L/H_net, specificity and positive predictive value increased, whereas sensitivity and negative predictive value decreased. Conclusion Lung ²⁰¹Tl assessment assists substantially in the identification of higher-risk CAD in exercise SPECT myocardial perfusion imaging and this is best achieved by L/H_net. This index is a significant predictor of higher-risk CAD, superior to myocardial perfusion images, and its value is associated with the probability of a disease state.     

Effects of physical stress and pharmacologically induced coronary dilation on myocardial and non-myocardial 201Thallium-uptake

After subtraction of the ²⁰¹Tl background radioactivity which was obtained from the paracardiac region, left ventricular (LV)-²⁰¹Tl net uptake at rest correlated with (1) the LV-muscle mass and therefore with (2) the LV-oxygen consumption. In normal LV, after maximum coronary dilation with dipyridamole, LV-²⁰¹Tl net uptake increased little more than LV-oxygen consumption but by factor of 2.27 less than was coronary vascular reserve. In coronary heart disease (c.h.d.), dipyridamole caused a significantly smaller increase of LV-²⁰¹Tl uptake (factor 1.16) than in normal LV myocardium (factor 1.76). This correlated well with the severity of the disease. Therefore, in maximum coronary dilation passive transport mechanisms may be responsible for augmented uptake and changed LV distribution of ²⁰¹Tl which depends on the perfusion pattern. In exercise, the ²⁰¹Tl-background radioactivity decreased from 54% (at rest) to 35% in normal patients and to 44% in c.h.d. Stressed thigh muscles accumulated ²⁰¹Tl 4.72-fold more than at rest. Therefore, it is still questionable if the myocardium during exercise receives enough ²⁰¹Tl to be labelled maximum. Since the LV-²⁰¹Tl count rates in c.h.d., measured over the maximum uptake area were increased to the same amount as in normal myocardium neither in coronary dilation nor during exercise, the validity of using the maximum LV-²⁰¹Tl uptake as a reference for the minimum one under these conditions is problematic.     

Clinical significance of thallium-201 and gallium-67 scintigraphy in pulmonary tuberculosis

One hundred and thirty-nine patients with pulmonary tuberculosis were evaluated by means of gallium-67 and thallium-201 scintigraphy. The disease was clinically active in 83 and inactive in 56. The uptake ratio between the lesion and the contralateral normal lung field was calculated. The ratio determined by⁶⁷Ga scintigraphy was expressed as GR, and that determined by²⁰¹Tl scintigraphy (early or delayed) as ER or DR. The²⁰¹Tl retention index (RI) was calculated using the following equation: RI=DR—ER/ER×100. The sensitivity, specificity and accuracy of²⁰¹Tl scintigraphy with respect to the activity of pulmonary tuberculosis were better than those of⁶⁷Ga scintigraphy (the figures for²⁰¹Tl scintigraphy were 88.0%, 82.1% and 85.6%, respectively, and those for⁶⁷Ga scintigraphy, 83.1%, 60.7% and 74.1%).We found a significant correlation between GR and ER, but there was no significant correlation between RI and ER. When the relationships between ER, C-reactive protein and 1-h erythrocyte sedimentation rate were examined among patients with abnormal uptake, no significant relationships were noted. In the 27 patients who could be followed up, GR and ER decreased with duration of the therapy, indicating a decrease in disease activity which was consistent with clinical findings. The RI was significantly higher in the early stages of therapy than in the later stages (P<0.01), suggesting a temporary delay in²⁰¹Tl washout in the early stages. The washout seemed to be promoted by the effects of the therapy. Overall, it is concluded that²⁰¹Tl scintigraphy is more useful and more suitable than⁶⁷Ga scintigraphy for the evaluation of disease activity and therapeutic effects in patients with pulmonary tuberculosis.     

Incremental diagnostic value of dipyridamole echocardiography and exercise thallium 201 scintigraphy in the assessment of presence and extent of coronary artery disease

Background  

The incremental diagnostic information of two noninvasive tests for the detection of coronary artery disease (CAD), dipyridamole echocardiography, and exercise²⁰¹Tl myocardial scintigraphy was assessed in a series of 102 patients with ordered logistic regression and receiver-operating characteristic curves.     

双嘧达莫负荷心肌201Tl SPECT显像诊断冠状动脉微循环障碍的价值

目的 探讨双嘧达莫负荷心肌201Tl SPECT显像在诊断冠状动脉微循环障碍中的价值.方法 选取临床符合心脏X综合征诊断标准的患者共48例,按患者体质量0.56mg/kg予双嘧达莫针剂静脉注射(4min),在心脏负荷达高峰后注入201Tl 111 MBq,10min及240min后分别进行心肌201Tl SPECT显像,原始图像经三维重建后由2位以上有经验的核医学科医师进行分析.对出现“反向再分布”现象的患者采用山莨菪碱(654-2)治疗2周后,再次进行双嘧达莫负荷心肌201TlSPECT显像,同时比较患者治疗前后临床症状和平板运动试验结果.结果 48例患者中有42例延迟(240min)显像时均显示部分心肌节段反向放射性分布稀疏或缺损,即“反向再分布”,检出阳性率为87.50％(42/48).在42例出现“反向再分布”现象的患者中,治疗后临床症状及平板运动试验结果均有改善的36例患者再次进行延迟(240min)显像时原受累的49个节段中有45个节段放射性分布有不同程度改善,检出阳性率达91.84％(45/49).两者有1项未改善或2项均未改善的6例患者延迟(240min)显像时原受累的7个节段放射性分布无改善.结论 双嘧达莫负荷心肌201Tl SPECT显像对诊断以心脏X综合征为代表的冠状动脉微循环障碍疾病有一定的价值.     

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.     

Myocardial imaging with dipyridamole: Comparison of the sensitivity and specificity of 201Tl versus MUGA

Myocardial imaging was performed at rest and after dipyridamole infusion using ²⁰¹Tl and ⁹⁹Tc^m-gated blood pool studies (MUGA). Of 38 patients studied, 21 had coronary artery disease (CAD) and 17 were normal. With ²⁰¹Tl imaging, 19 of 21 patients with CAD (sensitivity 88%) showed perfusion defects during dipyridamole. Of 17 normals 6 (specificity 65%) showed clear perfusion defects during dipyridamole. With MUGA, 2 of 15 patients with CAD (sensitivity 13%) developed abnormal wall motion during dipyridamole; both patients developed ST depression >1 mm. Of 10 normals none developed abnormal wall motion. Twenty six of 38 patients developed angina during dipyridamole, which was reversed by aminophylline in 24 of 26. We suggest that dipyridamole infusion is effective for ²⁰¹Tl-perfusion imaging, and easily performed, but is not suitable for MUGA studies where ischaemia is the required end-point.     

The optimum time for tumour imaging with thallium-201

Following the intravenous injection of 75 MBq ²⁰¹Tl-chloride we have assessed the uptake kinetics in the myocardium and in the primary tumour in 56 patients with lung cancer, 26 with breast cancer and 13 with mediastinal lymphoma. The time of maximal tumour uptake ranged from 8–20 min post-injection and did not differ significantly between lung cancer (mean±SD=11.9±3.34 min), breast cancer (11.21±1.88 min) and lymphoma (11.76±3.25 min). The time of maximum cardiac uptake of ²⁰¹Tl was 11.61±3.25 min. There was no significant washout of ²⁰¹Tl from the tumours in the first hour after injection in the various malignant lesions studied. The time of maximal tumour to background activity was 18.3±0.59 min for lung cancer, 13.0±1.16 min for breast cancer and 16.7±1.04 min for lymphoma.The time course of ²⁰¹Tl uptake in the tumours suggests that the mechanism of uptake is similar to that in the myocardium. The optimal time of ²⁰¹Tl tumour imaging is from 20–60 min following injection and did not differ in various tumours studied.     

Prognostic investigations after myocardial infarction: A comparison of radionuclide angiography and 201Tl scintigraphy

The ability of pre-discharge thallium Tl201 scintigraphy and radionuclide angiography (RNA) to predict subseqeunt cardiac events was investigated in 46 apparently low-risk survivors of a first acute myocardial infarction. All patients underwent selective coronary arteriography at 3 months post-discharge. At the time of the initial investigation, half were beta-blocked, and thereafter, all patients were given prophylactic beta-blockade. During a mean follow-up period of 12±4 months, 14 patients (30%) experienced cardiac events, i.e. recurrent myocardial infarction (3 patients), angina pectoris (13 patients) and coronary surgery (8 patients). No patient died during the follow-up period. Of the 14 with subsequent cardiac events, 11 were identified by the presence of a reversible perfusion defect at ²⁰¹Tl scintigraphy, while 7 exhibited abnormal left ventricular exercise reserve on RNA. The predictive accuracy of ²⁰¹Tl (85%) for subsequent cardiac events exceeded that of RNA (56%; P<0.01) and of arteriographic multi-vessel disease (65%; P<0.05). The sensitivity of the non-invasive techniques was not influenced by beta-blockade at the time of investigation. Thus, ²⁰¹Tl scintigraphy appears to be the more accurate technique for the assessment of the prognosis of apparently low-risk patients following myocardial infarction. The accuracy of the technique was not reduced by beta-adrenergic blockade.     

Exercise supplementation of dipyridamole for myocardial perfusion imaging

The substitution of intravenous dipyridamole for symptom-limited treadmill exercise has provided a non-invasive means to diagnose coronary artery disease with 201Tl scintigraphy in patients unable to adequately exercise. Limitations of dipyridamole/thallium imaging are primarily due to suboptimal image quality secondary to hepatic tracer concentration and decreased test sensitivity in patients who are dipyridamole "non-responders." Low-level treadmill exercise supplementation improves image quality, whereas handgrip has little, if any, benefit. The effect of low-level exercise in augmenting coronary blood flow is unknown and reports regarding the effect of handgrip are conflicting. The diagnostic benefit of these maneuvers in improving test sensitivity and decreasing the number of "non-responders" has not been documented. The combination of maximal, symptom-limited treadmill exercise and intravenous dipyridamole is a theoretically attractive option to improve overall test sensitivity, but the physiologic consequences and potential side effects should be more thoroughly investigated.     

Whole-body (201)Tl scintigraphy can detect exercise lower limb perfusion abnormalities in asymptomatic diabetic patients with normal Doppler pressure indices

Significant lower limb arterial obstruction is usually detected by Doppler ankle-brachial pressure index (ABPI) measurement. However, ABPI is non-contributory in cases of diabetic medial sclerosis or calcifications and is unsuitable for the detection of small vessel involvement. Thallium-201, a perfusion agent, is frequently used for the investigation of coronary artery disease, and whole-body (201)Tl scintigraphy (WBS) has also been reported to be useful in the assessment of peripheral artery disease (PAD). Thus, we evaluated the clinical feasibility of simultaneous myocardial and lower limb perfusion assessment. WBS was performed after treadmill exercise and myocardial scintigraphy, and again 4 h later. Calf (201)Tl fractional activities (percentage of whole-body (201)Tl uptake) were calculated. We determined a threshold value of normal post-exercise calf (201)Tl uptake (mean of the (201)Tl fractional uptakes minus 2 SD) in a control group of nine healthy volunteers. We checked its accuracy in a pilot group of 25 diabetic patients with proven PAD. This method permitted the detection of lower limb perfusion abnormalities in 38% of 47 asymptomatic diabetic patients with no evidence of PAD. In conclusion, for asymptomatic diabetic patients, whole-body (201)Tl scintigraphy after a treadmill test seems an efficient method of showing lower limb perfusion abnormalities not detected by ABPI measurement. It allows the evaluation of vascular status with no additional inconvenience for patients when performed after myocardial scintigraphy.     

Dipyridamole and exercise SPET provide different estimates of myocardial ischaemic areas: role of the severity of coronary stenoses and of the increase in heart rate during exercise

In patients unable to perform a maximal exercise test, dipyridamole single-photon emission tomography (SPET) has a higher capacity than exercise SPET to detect coronary artery disease (CAD). However, in patients with myocardial ischaemia who are able to perform a maximal exercise test, it is not known whether these two tests may be equally used to assess the areas of myocardial ischaemia. This study was aimed at comparing the results provided by dipyridamole and exercise SPET in CAD patients with documented exercise myocardial ischaemia. Forty CAD patients who had undergone exercise thallium-201 SPET and who had myocardial ischaemia documented by an unequivocally positive exercise test underwent an additional ²⁰¹Tl SPET study after dipyridamole infusion and low-level (40 W) exercise. The extent of defects was compared between the two tests and predictors of discrepant results were sought among data from exercise testing and coronary angiography. The extent of SPET defects was equivalent between the two tests in only 11 patients (28%), larger defects being observed with exercise in 18 [average difference: 12%±5% of left ventricle (LV)] and with dipyridamole in 11 (average difference: 15%±11% of LV). The best independent predictors of discrepancies between the two tests were: (1) increase in heart rate at exercise SPET, with defects being smaller at exercise than after dipyridamole in none of the patients with an increase >60 bpm (0/14), but in 42% of the others (11/26; P=0.004); and (2) an ischaemic territory related to a <70% coronary stenosis, for which SPET defects were always induced at exercise (10/10) but in only 30% (3/10) with dipyridamole (P=0.0004). Exercise and dipyridamole SPET provide different estimates of myocardial ischaemic areas. Dipyridamole allows the unmasking of perfusion abnormalities in patients who have low increases in heart rate at exercise SPET. However, dipyridamole is also much less efficient at inducing perfusion abnormalities in the ischaemic areas supplied by coronary stenoses of intermediate severity at rest angiography. Received 20 January 2000 and in revised form 18 March 2000