The inconsistent pattern of thallium defects: a clue to the false positive perfusion scintigram

Noninvasive testing in coronary artery disease. Selection of procedures and interpretation of results

In patients with acute chest pain, selection of diagnostic tests and admission to and discharge from the coronary care unit are critical decisions for which useful empirical guidelines are now available. In hospitalized patients, the serum level of the MB fraction of creatine kinase is particularly useful when the history strongly suggests infarction but the ECG is nondiagnostic. In patients with chronic chest pain, the gender of the patient and the character of the pain are the most important guides to selecting and interpreting exercise tests. In women and in men with nonanginal chest pain, the myocardial scintiscan is preferred to the exercise ECG because of its greater diagnostic accuracy. In men with atypical angina, the two tests are nearly equivalent, and the added cost of the scintiscan is a factor in test selection. Since nearly all men with typical angina have coronary artery disease, diagnostic tests are usually not needed.

Abnormal thallium-201 scans in patients with chest pain and angiographically normal coronary arteries

We reviewed the exercise thallium-201 (TI-201) scans and clinical data of 41 patients with chest pain and normal coronary arteries to identify clinical factors associated with "false-positive" studies. Exercise TI-201 studies were performed before angiography and often precipitated referral. Sex, beta-blocker therapy, anginal pattern, and results of exercise electrocardiography were evaluated and compared with TI-201 imaging. A negative TI-201 study was the most common finding (p less than 0.005). Of the 41 patients, 11 (27%) had abnormal exercise TI-201 scans. No clinical factor was significantly associated with a false-positive TI-201 scans. Of the 11 patients with abnormal scans, 9 had greater than or equal to 1 cardiac abnormality: right bundle branch block in 2, mitral valve prolapse in 3, paroxysmal atrial fibrillation in 2, abnormal left ventricular diastolic pressure in 3, and left bundle branch block in 1. Thus, (1) when results of exercise TI-201 imaging are used to refer patients for angiography, "false-positive" TI-201 studies are common; (2) sex, beta blockade, anginal pattern, and results of exercise electrocardiogram are not useful predictors of a false-positive TI-201 study; and (3) patients with chest pain, normal coronary arteries, and abnormal TI-201 scans frequently have other cardiac abnormalities.

Comparison of thallium-201 scanning in idiopathic dilated cardiomyopathy and severe coronary artery disease

To determine whether cardiomyopathy could be distinguished from coronary artery disease, we used thallium scanning to study 25 patients with severe left ventricular dysfunction and chronic heart failure. Ten patients had normal coronary arteries and idiopathic cardiomyopathy (ejection fraction 20 +/- 5%), and 15 patients had multivessel coronary disease and left ventricular dysfunction (ejection fraction 25 +/- 6%). The exercise time and maximal heart rate were similar in the two groups. Two patients with cardiomyopathy and 11 with coronary artery disease had a positive exercise ECG (p less than 0.05). Thallium scans showed perfusion defects in all 25 patients. The perfusion defects were complete in nine coronary artery disease patients (60%) and in one patient (10%) with cardiomyopathy (p less than 0.05). Extensive defects involving more than 40% of the left ventricular circumference, the number of segments involved, redistribution on the 4-hour scan, lung uptake and ventricular size were similar in the two groups. Perfusion defects on thallium scanning can occur in patients with idiopathic dilated cardiomyopathy and chronic heart failure. Thallium scanning cannot be reliably used in patients with chronic heart failure to distinguish coronary artery disease from cardiomyopathy unless complete defects are present.

Routine radionuclide techniques in evaluation of patients with suspected coronary heart disease

Myocardial scintigraphy with thallium-201 and electrocardiogram-gated left ventriculography with technetium-99m labelled red blood cells were applied in four groups of subjects: 25 with no signs or symptoms of cardiovascular disease (group 1), 28 with a "false" positive exercise electrocardiogram (group 2), 14 with angina pectoris and normal coronary angiograms (group 3), and 43 with angina pectoris and fixed coronary artery stenoses (group 4). In groups 1 and 4 the radionuclide findings were in accordance with clinical and invasive measurements. In groups 2 and 3 the most important finding was the lack of increase in left ventricular ejection fraction during exercise in about half of these subjects (even a decrease in 25%), indicating subnormal myocardial reserve. The additional finding of pathological myocardial biopsies in four of these patients suggests that asymptomatic ST depression in patients with normal coronary angiograms may in some cases represent an early, preclinical sign of cardiomyopathy.

Clinical indications for thallium-201 myocardial perfusion scanning

Thallium -201 myocardial perfusion scanning can assess regional myocardial perfusion noninvasively. As it is both time-consuming and expensive its use should be restricted to specific diagnostic problems. The clinical indications in known or suspected coronary artery disease are reviewed. In suspected coronary artery disease thallium scanning is most useful in patients with chest pain when the exercise ECG is uninterpretable, in men with probable angina but a negative exercise ECG, or conversely a positive exercise ECG without typical angina, and in women with probable angina and either a positive or a negative exercise ECG. In known coronary artery disease, thallium scanning may help determine the functional significance of a coronary obstruction found at angiography and may determine the site of myocardial ischaemia when multiple obstructions are present.