Thallium-201 myocardial perfusion scintigraphy for the clinical clarification of normal,abnormal and equivocal electrocardiographic stress tests

Sixty-five patients were studied with stress electrocardiography and thallium-201 relative myocardial perfusion scintigraphy. Results were correlated with selective coronary angiography. Scintigraphy was more sensitive (85 versus 67 percent), more specific (89 versus 63 percent) and significantly more accurate (87 versus 65 percent) than stress electrocardiography for the diagnosis of significant coronary arterial lesions in patients with isoelectric S-T segments at rest. Stress scintigraphy helped clarify the equivocal stress test due to left bundle branch block, left ventricular hypertrophy, drugs, hyperventilation and other conditions and was more accurate than the stress electrocardiogram (89 versus 53 percent) even in the presence of a depressed S-T segment at rest. Thallium-201 scintigraphy is a safe and simple noninvasive method for identifying abnormal myocardial perfusion, stress-induced ischemia and, indirectly, significant coronary arterial lesions.     

Spectrum of exercise thallium-201 myocardial perfusion imaging in patients with chest pain and normal coronary angiograms.

Twenty-seven consecutive patients with chest pain and no significant obstructive coronary lesions on arteriography were studied with thallium-201 myocardial imaging during exercise and at rest. Fifteen of the patients had typical and 12 atypical angina pectoris. All underwent treadmill exercise electrocardiographic testing; the results were abnormal in 10 patients (37 percent), normal in 14 (52 percent) and uninterpretable in 3 (11 percent). The exercise and resting thallium-201 myocardial images were normal in 23 patients (85 percent); the results of exercise testing were normal in 12 of these patients, abnormal in 8 and uninterpretable in 3. Four patients had a perfusion defect on exercise thallium-201 myocardial imaging; the defect filled in by 4 hours in two patients but persisted in the other two. In contrast, when thallium-201 myocardial imaging was performed in 28 consecutive patients with angiographic coronary artery disease, only 5 patients (16 percent) had normal exercise and resting thallium-201 myocardial images. Therefore, thallium-201 myocardial imaging offers a more effective means of identifying patients with chest pain and no obstructive coronary artery disease than the clinical history or the exercise electrocardiographic test, or both. However, 15 percent of these patients will have abnormal exercise thallium-201 myocardial images because of factors that have not yet been identified.     

Idiopathic hypertrophic subaortic stenosis: evaluation of anginal symptoms with thallium-201 myocardial imaging.

The evaluation of angina pectoris in patients with idiopathic hypertrophic subaortic stenosis is difficult in those in the age group prone to coronary artery disease. Ten patients with angina pectoris, normal coronary angiograms and idiopathic hypertrophic subaortic stenosis were studied with thallium-201 myocardial imaging performed in conjunction with submaximal treadmill exercise testing. The resting electrocardiogram demonstrated left ventricular hypertrophy with S-T segment abnormalities in seven patients, thereby vitiating the further increase in S-T segment abnormalities that developed in these patients during exercise or in the postexercise period. Of the three patients with a normal resting electrocardiogram, one had significant exercise-induced S-T segment depression. Thallium-201 myocardial imaging revealed no significant perfusion defects in 9 of the 10 patients (90 percent). In one patient with severe left ventricular hypertrophy significant perfusion defects developed after exercise that were not present at rest. Stress thallium-201 myocardial perfusion imaging is a useful noninvasive technique that assists in ruling out the presence of significant coronary artery disease in patients with idiopathic hypertrophic subaortic stenosis.     

Assessment of single vessel coronary artery disease: results of exercise electrocardiography, thallium-201 myocardial perfusion imaging and radionuclide angiography

The sensitivity of the commonly used stress tests for the diagnosis of coronary artery disease was analyzed in 46 patients with significant occlusion (greater than or equal to 70% luminal diameter obstruction) of only one major coronary artery and no prior myocardial infarction. In all patients, thallium-201 perfusion imaging (both planar and seven-pinhole tomographic) and 12 lead electrocardiography were performed during the same graded treadmill exercise test and radionuclide angiography was performed during upright bicycle exercise. Exercise rate-pressure (double) product was 22,307 +/- 6,750 on the treadmill compared with 22,995 +/- 5,622 on the bicycle (p = NS). Exercise electrocardiograms were unequivocally abnormal in 24 patients (52%). Qualitative planar thallium images were abnormal in 42 patients (91%). Quantitative analysis of the tomographic thallium images were abnormal in 41 patients (89%). An exercise ejection fraction of less than 0.56 or a new wall motion abnormality was seen in 30 patients (65%). Results were similar for the right (n = 11) and left anterior descending (n = 28) coronary arteries while all tests but the planar thallium imaging showed a lower sensitivity for isolated circumflex artery disease (n = 7). The specificity of the tests was 72, 83, 89 and 72% for electrocardiography, planar thallium imaging, tomographic thallium imaging and radionuclide angiography, respectively. The results suggest that exercise thallium-201 perfusion imaging is the most sensitive noninvasive stress test for the diagnosis of single vessel coronary artery disease.     

Myocardial perfusion imaging and gated cardiac blood pool scanning: clinical application.

Myocardial perfusion imaging with thallium-201 and gated cardiac blood pool scanning are finding increasing use in clinical cardiology. These noninvasive techniques have been found useful in detecting myocardial infarction independent of the electrocardiogram and determining the site and extent of the infarct as well as its effect on left ventricular function. These studies provide important prognostic data and are proving to be of value in evaluating patients with cardiogenic shock. Neither the thallium-201 myocardial perfusion image nor the gated cardiac blood pool scan can distinguish between acute and chronic myocardial damage. In clinical situations where this is important, infarct avid imaging with technetium-99m pyrophosphate allows determination of whether a given perfusion defect or wall motion abnormality is acute. Myocardial perfusion imaging with thallium-201 at rest and after exercise is also proving to be of value in evaluating patients with suspected ischemic heart disease. Initial studies suggest that the technique may be more sensitive than exercise electrocardiography and is of special value in minimizing the occurrence of false positive exercise tests for the diagnosis of ischemic heart disease. The combined tracers technique is also of value in the evaluation of patients undergoing coronary bypass graft surgery and those with cardiomyopathy.     

Merits of stress thallium-201 myocardial perfusion imaging in patients with inconclusive exercise electrocardiograms: Correlation with coronary arteriograms

Stress thallium-201 myocardial perfusion images were obtained in 65 patients with an inconclusive exercise electrocardiogram. All 65 patients underwent coronary angiographic studies. The exercise electrocardiogram was judged inconclusive in 35 patients (54 percent) because submaximal exercise had been performed and in 30 patients (46 percent) who manifested ST-T segment abnormalities at rest. Exercise thallium-201 myocardial perfusion images were abnormal in 20 patients and normal in 45. Nineteen (95 percent) of the 20 patients with abnormal exercise images had severe disease of one or more major coronary arteries. Thirty-seven (82 percent) of the 45 patients with normal exercise images had no significant coronary artery disease; the remaining 8 patients had coronary artery disease. Therefore, 19 of 27 patients with coronary artery disease had abnormal exercise images (sensitivity 70 percent), and 37 of 38 patients without coronary artery disease had normal exercise images (specificity 97 percent). Thallium-201 imaging predicted the correct diagnosis in 56 patients (86 percent). Thus, exercise myocardial imaging with thallium-201 appears to be a useful diagnostic aid in patients with an inconclusive exercise electrocardiogram.     

Can exercise electrocardiography and thallium-201 myocardial imaging exclude the diagnosis of coronary artery disease?: Bayesian analysis of the clinical limits of exclusion and indications for coronary angiography

The objective of this study was to determine whether exercise electrocardiography can be combined with thallium-201 myocardial imaging and the clinical history to exclude the diagnosis of coronary artery disease. All 96 patients in this study were referred for coronary angiography because of chest pain but did not have prior myocardial infarction; 52 percent had coronary artery disease. Each patient's chest pain was classified as either typical or not typical of angina pectoris. Negative tests with inadequate exercise stress (less than 85 percent of the age-predicted maximal heart rate) and combined tests with discordant results (either exercise electrocardiography or thallium imaging positive and the other test negative) were judged nondiagnostic. Nondiagnostic tests that contributed most to the uncertainty of results were classified separately: exercise electrocardiogram, 35 patients; thallium imaging, 9 patients; and combined exercise electrocardiogram and thallium imaging, 50 patients. The ability of each test to rule out coronary artery disease was defined by its predictive error (probability of coronary disease despite a negative test): history of chest pain not typical of angina, 26 percent (11 of 42); exercise electrocardiogram, 22 percent (5 of 23); thallium imaging, 27 percent (6 of 35); and negative findings on both exercise electrocardiogram and thallium imaging, 6 percent (1 of 17). Finally, when only the patients with atypical chest pain were considered, there was zero (0 of 15) predictive error if both tests were negative.Negative exercise electrocardiography and thallium imaging during adequate stress ruled out any coronary artery disease in these patients with considerable reliability (94 percent) and excluded multivessel disease with even greater reliability. These exclusion tests for coronary artery disease were most reliable in patients in whom the clinical diagnosis of coronary artery disease was least likely, as defined by Bayes' theorem. It is concluded that there is no perfect noninvasive test to exclude coronary disease in all patient populations; however, coronary angiography is not necessary to rule out the diagnosis of coronary artery disease in patients who'have (1) no clinical indicators of a very high probability of coronary disease, such as typical angina, (2) adequate exercise stress, (3) negative exercise electrocardiogram and (4) negative exercise thallium images.     

Discriminant function analysis using thallium-201 scintiscans and exercise stress test variables to predict the presence and extent of coronary artery disease

The ability to predict the presence and extent (number of affected vessels) of coronary artery disease objectively from an exercise treadmill test and thallium-201 myocardial perfusion scintiscans was evaluated using linear discriminant function analysis. Exercise and redistribution scans in the 30 ° left anterior oblique view were characterized by their two dimensional Fourier transforms. The analysis was performed in 141 persons, including 110 patients with coronary artery disease (70 percent or greater stenosis of luminal diameter) and 31 control subjects. There were 43 patients with single vessel and 67 patients with multivessel disease.

Input to the discriminant analysis included age, sex, 18 variables from the exercise treadmill test and 36 Fourier frequency coefficients from each scan (exercise and redistribution). Two analyses were performed. In the first, a discriminant function was constructed to detect the presence of coronary artery disease. Seven input variables were chosen: maximal exercise pressure-rate product, sex, anginal pain, change in S-T segment slope with exercise, two Fourier coefficients from the exercise scan and one Fourier coefficient from the redistribution scan. The function correctly classified 103 of 110 patients with coronary artery disease and 27 of 31 control subjects; the estimated sensitivity of the technique is 94 percent, with 87 percent specificity and an overall accuracy of 92 percent for the detection of coronary artery disease. The discriminant function was significantly more sensitive and accurate than qualitative scan interpretation (p < 0.05).

In the second analysis, two discriminant functions were developed to predict the extent of disease. In addition to the preceding variables, the duration of exercise, change in systolic blood pressure during the last two stages of exercise, and another Fourier coefficient from the exercise scan were chosen. Using two functions, the method detected the presence of coronary artery disease in 104 of 110 patients (95 percent sensitivity) and correctly classified 28 of 31 control subjects (90 percent specificity). Multivessel disease was correctly predicted in 53 of 67 patients (79 percent accuracy); another 11 patients with multivessel disease were predicted to have single vessel disease. Twenty-nine (67 percent) of 43 patients with single vessel disease were correctly classified; of the remaining 14 patients, 12 were predicted to have multivessel disease and 2 were judged to have normal vessels.

The data demonstrate that numerical functions derived from the exercise treadmill test variables and Fourier coefficients of thallium-201 scans can be used to detect the presence of coronary artery disease with 92 percent accuracy. The predictive accuracy for the number of diseased vessels was 78 percent (110 of 141 patients classified correctly).     

Serial Exercise Thallium Myocardial Perfusion Scanning and Exercise Electrocardiography in the Diagnosis of Coronary Artery Disease*

Summary: Serial exercise thallium-201 myocardial perfusion scanning (exercise and 4-hour redistribution) was compared to rest and exercise electrocardiography (ECG) for the detection of coronary artery disease in 125 patients with known or suspected coronary artery disease. All patients underwent coronary arteriography and 108 were found to have significant coronary artery lesions. The serial exercise thallium scan was significantly more sensitive than rest and exercise ECG in detecting coronary artery disease (94% v. 83% P <0.01). The sensitivity of a reversible thallium perfusion scan abnormality and a positive exercise ECG for detecting exercise induced myocardial ischaemia in coronary artery disease was similar (69% v. 63%). The exercise thallium scan complemented the exercise EGG, and the sensitivity of the combined test was significantly greater than the exercise ECG alone (84% v. 63% P<0.001). The specificity for coronary artery disease of the exercise ECG was 65% and that of the exercise thallium-201 myocardial perfusion scan was 82% (P = NS). Thallium-201 myocardial perfusion scanning complements the rest and exercise ECG in the non-invasive detection of coronary artery disease.     

Importance of coronary collateral circulation in interpreting exercise test results

The Importance of the coronary collateral circulation as a cause of false negative exercise tests was studied in 37 patients who had a 90 percent or greater isolated stenosis of the luminal diameter in one major coronary artery. Sixteen patients had large collateral vessels and 21 patients had either minimal or no collateral circulation. Myocardial scintigraphy was performed in 22 of the 37 patients. The final treadmill time was similar in both groups (521 ± 192 versus 554 ± 144 seconds [mean ± standard error of the mean]). The presence and depth of S-T segment depression was not influenced by the degree of collateralization. The sensitivity of the exercise electrocardiogram was greater for patients with disease in the left anterior descending than in the right or left circumflex coronary arteries (95 versus 60 percent, p <0.03). Among the 22 patients with thallium-201 scintigrams, myocardial perfusion defects were more common in patients without collateral circulation (100 versus 40 percent, p <0.01) and Involved more myocardial segments (p <0.005). The overall sensitivity of exercise electrocardiography for the detection of single vessel stenosis 90 percent or greater was similar to that of myocardial scintigraphy (81 versus 73 percent). In conclusion, large intercoronary collateral vessels are not a cause of false negative exercise electrocardiograms in patients with single vessel disease but are a common cause of false negative scintigrams. Large collateral vessels may limit the quantity and location of myocardial ischemia, but exercise etectrocardtography and thallium-201 scintigraphy may detect different aspects of ischemia.     

Comparison of exercise electrocardiography and quantitative thallium imaging for one-vessel coronary artery disease

The relative value of exercise electrocardiography and computer analyzed thallium-201 imaging was compared in 124 patients with 1-vessel coronary artery disease (CAD). Of these, 78 had left anterior descending (LAD), 32 right and 14 left circumflex (LC) CAD. In patients with no previous myocardial infarction (MI), thallium imaging was more sensitive than the electrocardiogram (78% vs 64%, p less than 0.01), but in patients with previous MI, sensitivity was similar. Further, thallium imaging was more sensitive only in LAD and LC disease. Redistribution was compared with ST-segment depression as a marker of ischemia. Only in patients with prior MI (76% vs 44%, p less than 0.01) and only in LC and right CAD did redistribution occur more often than ST depression. Thallium imaging was more accurate in localizing stenoses than the electrocardiogram (p less than 0.001), but did not always correctly predict coronary anatomy. Septal thallium defects were associated with LAD disease in 84%, inferior defects with right CAD in 40% and posterolateral lesion defects with LC CAD in 22%. The results indicate the overall superiority of thallium imaging in 1-vessel CAD compared with exercise electrocardiography; however, there is a wide spectrum of extent and location of perfusion defects associated with each coronary artery. Thallium imaging complements coronary angiography by demonstrating the functional impact of CAD on myocardial perfusion.     

Noninvasive assessment of coronary stenoses by myocardial imaging during pharmacologic coronary vasodilatation. III. Clinical trial

Thallium-201 myocardial imaging was performed at rest, after maximal treadmill exercise and during coronary vasodilatation induced by the intravenous administration of dipyridamole in 62 patients undergoing coronary angiography. Myocardial images after dipyridamole infusion were compared with rest and exercise thallium-201 images to determine the utility of pharmacologic stress for detecting coronary artery disease. Dipyridamole, 0.142 mg/min, was infused for 4 minutes with electrocardiographic and blood pressure monitoring, and thallium-201 was injected intravenously 4 minutes after infusion.Myocardial/background count ratios of 2.3 ± 0.5 (mean ± 1 standard deviation) after the administration of dipyridamole were higher than similar ratios for exercise images (2.1 ± 0.5; P < 0.001). The sensitivity of thallium-201 imaging for detecting significant coronary artery disease was equal for dipyridamole and exercise stress. In 51 patients with a 50 percent or greater stenosis of one or more coronary arteries, image defects were identified in 34 of 51 (67 percent) exercise and dipyridamole images. Twenty of 51 patients (39 percent) had abnormal rest images; in 17 of 20 patients, new or increased image defects were present after exercise and the infusion of dipyridamole. One of 11 patients (9 percent) with no stenosis of 50 percent or greater had a defect on exercise and dipyridamole images. Six of seven patients with new or enlarged image defects after the intravenous administration of dipyridamole also had new or enlarged defects after the oral administration of dipyridamole.After the infusion of dipyridamole, the heart rate increased from 64 ±10 beats/min supine to 88 ± 13 beats/min standing (P < 0.001), and blood pressure decreased from $\text{129 ±}\text{16}\text{80}\text{± 9}\text{to}\text{120 ±}\text{17}\text{75}\text{± 9}\text{mm Hg}\text{(P < 0.001)}$. Angina and S-T depression occurred more frequently with exercise than with dipyridamole. S-T depression occurred in only two patients (3 percent) with dipyridamole, suggesting that diagnostic images were often obtained without significant ischemia. This study demonstrates that pharmacologic coronary vasodilatation is as effective as maximal treadmill exercise in creating myocardial perfusion abnormalities detectable with thallium-201 imaging in man.     

Dipyridamole thallium-201 myocardial scintigraphy in coronary diagnosis; a comparison of methods with thallium-201 myocardial scintigraphy after ergometer stress

Two scintigraphic methods, resting dipyridamole and exercise thallium-201 myocardial perfusion imaging, to detect and localize coronary artery stenosis were compared in 32 patients suffering from coronary artery disease. The sensitivity of detecting a greater than 50% coronary stenosis was 94% for exercise thallium-201 perfusion imaging and 88% for dipyridamole thallium-201 perfusion imaging. The overall sensitivity and specificity of localizing a greater than 50% coronary stenosis by the two methods were also not significantly different. The results of the two scintigraphic methods were independent of the severity of coronary artery disease. Dipyridamole thallium-201 myocardial perfusion imaging provides a useful and safe alternative test for detecting and localizing coronary artery stenosis in patients unable to perform maximal exercise.     

Septal myocardial perfusion imaging with thallium-201 in the diagnosis of proximal left anterior descending coronary artery disease

The use of myocardial perfusion imaging (MPI) to identify obstructive coronary disease of the left anterior descending coronary artery proximal to the first septal perforator (prox LAD) was studied in 60 patients. Perfusion of the septum and anteroapical areas with thallium-201 injected during exercise was compared to results of coronary arteriography. Septal MPI defect was found in 92.3% of patients with obstruction of the proximal LAD, 27.7% of patients with obstruction of LAD distal to first septal perforator, 0% in patients with obstructions involving right or circumflex arteries, and in 10.5% of patients without coronary disease. Anteroapical MPI defects were found with similar frequency in the three groups with obstructive coronary disease. Septal MPI defect had a sensitivity of 92.3% and specificity of 85.4% in the diagnosis of proximal LAD disease. Normal septal perfusion with thallium-201 virtually excluded proximal LAD disease.     

Localization of coronary artery disease with exercise electrocardiography: correlation with thallium-201 myocardial perfusion scanning

In 61 patients with single vessel coronary artery disease (70 percent or greater obstruction of luminal diameter in only one vessel) and no previous myocardial infarction, the sites of ischemic changes on 12 lead exercise electrocardiography and on thallium-201 myocardial perfusion scanning were related to the obstructed coronary artery. The site of exercise-induced S-T segment depression did not identify which coronary artery was obstructed. In the 37 patients with left anterior descending coronary artery disease S-T depression was most often seen in the inferior leads and leads V₄ to V₆, and in the 18 patients with right coronary artery disease and in the 6 patients with left circumflex artery disease S-T depression was most often seen in leads V₅ and V₆. Although S-T segment elevation was uncommon in most leads, it occurred in lead V₁ or aVL, or both, in 51 percent of the patients with left anterior descending coronary artery disease. A reversible anterior defect on exercise thallium scanning correlated with left anterior descending coronary artery disease (probability [p] < 0.0001) and a reversible inferior thallium defect correlated with right coronary or left circumflex artery disease (p < 0.0001).In patients with single vessel disease, the site of S-T segment depression does not identify the obstructed coronary artery; S-T segment elevation in lead V₁ or aVL, or both, identifies left anterior descending coronary artery disease; and the site of reversible perfusion defect on thallium scanning identifies the site of myocardial ischemia and the obstructed coronary artery.     

Predicting the extent and location of coronary artery disease during the early postinfarction period by quantitative thallium-201 scintigraphy

The ability of quantitative thallium-201 scintigraphy to predict the extent and location of coronary artery disease before hospital discharge after acute myocardial infarction was evaluated in 52 patients. All patients underwent coronary angiography and serial thallium-201 imaging either at rest (10 patients) or after submaximal exercise stress (42 patients; target heart rate 120 beats/min). Two or three vessel disease was designated if abnormal thallium-201 uptake or washout patterns, or both, were seen in two or three vascular segments, respectively. Of 156 vessels analyzed in the 52 patients, 91 stenoses of 70 percent or greater were found by angiography. Seventy-four (81 percent) of these were predicted by scintigraphy. The specificity of scintigraphy for identifying vessel stenoses was 92 percent. Sensitivity for detecting and localizing stenoses supplying an infarct zone was 96 percent compared with 62 percent for stenoses supplying myocardium remote from the acute infarct. Perfusion abnormalities were more frequently seen in the distribution of vessels with severe (90 percent or greater) stenoses than in those with moderate (70 to 90 percent) stenoses (87 versus 53 percent, p <0.01). Scintigraphy detected a greater proportion of left anterior descending and right coronary arterial stenoses than circumflex stenoses (91 and 87 versus 63 percent, respectively, p <0.006).In the 42 patients who underwent submaximal exercise testing, multivariate analysis of 23 clinical and laboratory variables identified multiple thallium-201 defects as the best predictor of multivessel disease. The predictive accuracy of exercise-induced S-T segment depression was only 45 percent compared with 88 percent (p <0.05) for thallium-201 scintigraphy. Thus, 2 weeks after myocardial infarction, exercise thallium-201 scintigraphy is useful for predicting the extent and location of coronary artery disease, particularly stenoses in the left anterior descending and right coronary arteries. Moreover, thallium-201 imaging at rest is reliable in assessing the extent of coronary disease in hospitalized patients who cannot undergo exercise testing because of unstable angina, uncompensated heart failure, poorly controlled arrhythmias or physical limitations.     

Specificity of the stress electrocardiogram during adenosine myocardial perfusion imaging in patients taking digoxin

BACKGROUND: In patients taking digoxin, the exercise electrocardiogram has a lower specificity for detecting coronary artery disease. However, the effect of digoxin on adenosine-induced ST-segment depression is unknown. The purpose of this study was to evaluate the specificity of the electrocardiogram during adenosine myocardial perfusion imaging in patients taking digoxin. METHODS: Between May 1991 and September 1997, patients (n = 99) taking digoxin who underwent adenosine stress imaging with thallium-201 or technetium-99m sestamibi and coronary angiography within 3 months were retrospectively identified. Exclusion criteria included prior myocardial infarction, coronary artery angioplasty or bypass surgery, left bundle branch block, paced ventricular rhythm, or significant valvular disease. Twelve-lead electrocardiograms were visually interpreted at baseline, during adenosine infusion, and during the recovery period. The stress electrocardiogram was considered positive if there was > or =1 mm additional horizontal or downsloping ST-segment depression or elevation 0.08 seconds after the J-point compared with the baseline tracing. RESULTS: ST-segment depression and/or elevation occurred in 24 of 99 patients. There were only 2 false-positive stress electrocardiograms, yielding a specificity of 87% and positive predictive value of 92%. All 8 patients with > or =2 mm ST segment depression had multivessel disease by coronary angiography. CONCLUSIONS: ST-segment depression or elevation during adenosine myocardial perfusion imaging in patients taking digoxin is highly specific for coronary artery disease. Marked (> or =2 mm) ST-segment depression and/or ST-segment elevation is associated with a high likelihood of multivessel disease.     

Safety and feasibility of two-dimensional echocardiography and myocardial perfusion imaging in patients with chest pain

The accurate identification of patients at high risk for acute coronary syndromes among those seen in the emergency department with possible myocardial ischemia and nonischernic electrocardiograms is a problem. Two-dimensional echocardiography and myocardial perfusion imaging with 99m-technetium sestamibi can identify patients at low and high risk; however, comparative studies are lacking. The authors studied 555 patients considered at low or moderate risk for myocardial ischemia in our emergency department on the basis of the presenting history, and results of physical examination and electrocardiography. These patients underwent echocardiography and myocardial perfusion imaging within 4 hours of presentation. Endpoints included myocardial infarction, percutaneous transluminal coronary angioplasty, and positive results on stress perfusion imaging. Both imaging procedures were performed in the emergency department on 370 patients. Overall agreement between the two techniques was high (concordance, 89%) in the patients who had myocardial infarction or underwent coronary angiography. Agreement between the two techniques is high when used in patients with possible myocardial ischemia. Both techniques helped identify patients at high risk who required admission and those who could be safely discharged.     

Influence of coronary artery disease on pulmonary uptake of thallium-201

An increased pulmonary thallium-201 concentration has been observed in exercise stress thallium perfusion imaging in patients with coronary artery disease. To understand the cause of this lung uptake, studies were performed in experimental animals and in patients undergoing stress thallium perfusion imaging. The extraction fraction of thallium-201 by the lungs was measured in a group of eight dogs using a dual isotope technique. Basal thallium-201 extraction fraction at rest was 0.09 ± 0.009. After administration of isoproterenol, it decreased to 0.06 ± 0.02 (difference not significant). After balloon obstruction of the left atrium (which increased mean left atrial pressure and pulmonary transit time) and after administration of acetylcholine as a bolus injection (which prolonged pulmonary transit time only) it increased to 0.19 ± 0.02 (p <0.01).Lung thallium-201 activity was measured in 86 patients who had undergone cardiac catheterization and stress-redistribution myocardial perfusion imaging. The initial/final lung activity ratio was 1.41 ± 0.03 in patients with no significant coronary artery disease, 1.52 ± 0.03 (difference not significant) in patients with single vessel coronary disease, 1.60 ± 0.05 (p <0.05) in those with two vessel disease and 1.59 ± 0.05 (p <0.05) in those with triple vessel disease. Quantitation of lung activity in 30 of these patients indicated that the increased ratio in patients with multivessel coronary artery disease was due to a transient absolute increase in the thallium-201 concentration immediately after maximal exercise. The data imply that increased pulmonary concentration of thallium-201 during exercise is a consequence of left ventricular failure.     

The predictive value of a strongly positive stress test in patients with minimal symptoms

The ability of a strongly positive stress test to predict left main coronary artery disease in people with suspected coronary artery disease but with minimal or no angina was investigated in 40 such patients. Nine had a history of myocardial infarction but no angina. Thirty-one had mild angina or a history of mild angina. The stress electrocardiograms were analyzed according to criteria known to be associated with left main coronary artery disease in moderately or severely symptomatic patients; (1) early S-T segment changes (stage I or II of exercise), (2) 2 mm or more S-T segment depression, (3) downsloping S-T segments, (4) associated exercise-induced hypotension, (5) prolonged S-T segment changes after the test (≥8 minutes) and (6) anterior and inferior S-T segment depression. The prevalence of left main coronary artery disease was 35 percent and that of any severe coronary artery disease 75 percent. The criterion of anterior and inferior electrocardiographic changes with exercise was most predictive of left main coronary artery disease (P < 0.01 by χ²). Exercise electrocardiography is useful in the prediction of left main or other severe coronary artery disease even when performed in patients who have minimal angina or in those who are asymptomatic after myocardial infarction.