Ian K. Bailey

Thallium-201 myocardial perfusion imaging at rest and during exercise. Comparative sensitivity to electrocardiography in coronary artery disease.

SUMMARYThe sensitivity of myocardial perfusion imaging (MPI) using thallium-201 injected both at rest and during peak exercise was compared to simultaneously recorded 12 lead electrocardiography (ECG) for the detection of transient ischemia in 20 normal subjects and 63 patients with coronary artery disease (CAD). No significant perfusion defects or ECG changes were seen on either the rest or exercise studies in any of the normal subjects. Fifty-six percent of patients with CAD developed new perfusion defects with exercise compared to 38% who developed ischemic ST-segment depression (P < 0.02). However, when chest pain and/or ST depression were considered indices of ischemia, the sensitivity of exercise testing and thallium-201 MPI was similar. The increased sensitivity of MPI compared to ST-segment depression on the ECG was due to patients with baseline ECG abnormalities and those who failed to achieve 85% of predicted maximum heart rate with exercise.Analysis of the exercise results according to the extent of coronary artery disease revealed a progressive increase in both positive ECGs and MPI with the number of vessels involved. In patients with single vessel disease the MPI was more sensitive than the ECG (P <0.02).The combination of the rest and exercise ECG, MPI and chest pain during exercise failed to identify 11% of patients with CAD.Exercise thallium-201 MPI is a useful adjunct to conventional exercise testing particularly when evaluating patients with abnormal resting ECGs, those who develop ventricular conduction defects or arrhythmias during exercise, and those who fail to achieve their predicted heart rate because of fatigue or breathlessness.

Analysis of left ventricular function from multiple gated acquisition cardiac blood pool imaging. Comparison to contrast angiography.

Global ventricular function was evaluated by both multiple gated cardiac blood pool scans (MUGA) and contrast ventriculograms in a group of 17 patients with suspected coronary artery disease. The contrast ventriculograms were analyzed frame by frame to generate a volume versus time curve for each patient, while the tracer data were analyzed by two methods: 1) the standard method, in which the left ventricle is identified on the end-diastolic frame and the background corrected activity under the region of interest obtained from the entire cardiac cycle, and displayed as a time versus activity curve; and 2) by a semi-automatic method in which the computer applies a threshold detection program to define the ventricular borders, and activity in the chamber at each point in the cardiac cycle is defined after background correction. The tracer data in each patient were analyzed independently by four observers. The tracer data correlated with the contrast data on a point by point basis r = 0.87 for the standard method, and 0.93 for the semi-automatic technique. An F test of variance revealed the semi-automatic method superior to the standard approach (P < 0.05).

Value and limitations of segmental analysis of stress thallium myocardial imaging for localization of coronary artery disease.

This study was done to determine the value of thallium-201 myocardial scintigraphic imaging (MSI) for identifying disease in the individual coronary arteries. Segmental analysis of rest and stress MSI was performed in 133 patients with arteriographically proved coronary artery disease (CAD). Certain scintigraphic segments were highly specific (97-100%) for the three major coronary arteries: anterior wall and septum for the left anterior descending (LAD) coronary artery; the inferior wall for the right coronary artery (RCA); and the proximal lateral wall for the circumflex (LCX) artery. Perfusion defects located in the anterolateral wall in the anterior view were highly specific for proximal disease in the LAD involving the major diagonal branches, but this was not true for “septal” defects. The apical segments were not specific for any of the three major vessels. Although MSI was abnormal in 89% of these patients with CAD, it was less sensitive for identifying individual vessel disease: 63% for LAD, 50% for RCA and 21% for LCX disease (narrowings > 50%). Sensitivity increased with the severity of stenosis, but even for 100% occlusions was only 87% for LAD, 58% for RCA and 38% for LCX. Sensitivity diminished as the number of vessels involved increased: with single-vessel disease, 80% of LAD, 54% of RCA and 33% of LCX lesions were detected, but in patients with triple-vessel disease, only 50% of LAD, 50% of RCA and 16% of LCX lesions were identified. Thus, although segmental analysis of MSI can identify disease in the individual coronary arteries with high specificity, only moderate sensitivity is achieved, reflecting the tendency of MSI to identify only the most severely ischemic area among several that may be present in a heart. Perfusion scintigrams display relative distributions rather than absolute values for myocardial blood flow.

Thallium 201 imaging and gated cardiac blood pool scans in patients with ischemic and idiopathic congestive cardiomyopathy. A clinical and pathologic study.

In ischemic cardiomyopathy (CM) fibrosis replaces large segments of myocardium, but in idiopathic congestive CM the myocardium contains only small foci of fibrosis or is morphologically normal. As coronary disease and myocardial infarction may be clinically silent, it is not always possible to distinguish ischemic from idiopathic congestive CM during life without cardiac catheterization. To determine whether noninvasive methods, thallium 201 myocardial (TI) imaging and technetium 99m gated cardiac blood pool scans (GCBPS), could separate the entities, we evaluated radioisotope images of the heart in 13 patients with ischemic, and eight patients with idiopathic congestive CM, and 14 patients with normal hearts. Diagnosis was established by cardiac catheterization and/or autopsy in each of the 35 patients. The 14 normals could be readily distinguished from CM, and ischemic could be distinguished from idiopathic dilated CM in 20 of 21 patients. All patients with myocardiopathy showed hypokinetic and dilated left ventricles, but right ventricular dilatation was evident mainly in those with idiopathic CM. TI images in the ischemic type had defects of greater than 40% of image circumference which corresponded to segmental wall motion abnormalities on GCBPS, whereas those with the idiopathic congestive form were homogeneous or had defects of less than 20% of image circumference. Autopsy studies in 7 of 35 patients correlated TI defects of greater than 20% of circumference with transmural myocardial fibrosis.

Exercise-induced ST-segment elevation. Correlation of thallium-201 myocardial perfusion scanning and coronary arteriography.

Exercise-induced ST-segment elevation was correlated with myocardial perfusion abnormalities and coronary artery obstruction in 35 patients. Ten patients (group 1) developed exercise ST elevation in leads without Q waves on the resting ECG. The site of ST elevation corresponded to both a reversible perfusion defect and a severely obstructed coronary artery. Associated ST-segment depression in other leads occurred in seven patients, but only one had a second perfusion defect at the site of ST depression. In three of the 10 patients, abnormal left ventricular wall motion at the site of exercise-induced ST elevation was demonstrated by ventriculography. Twenty-five patients (group 2) developed exercise ST elevation in leads with Q waves on the resting ECG. The site of ST elevation corresponded to severe coronary artery stenosis and a thallium perfusion defect that persisted on the 4-hour scan (constant in 12 patients, decreased in 13). Associated ST depression in other leads occurred in 11 patients and eight (73%) had a second perfusion defect at the site of ST depression. In all 25 patients with previous transmural infarction, abnormal left ventricular wall motion at the site of the Q waves was shown by ventriculography.In patients without previous myocardial infarction, the site of exercise-induced ST-segment elevation indicates the site of severe transient myocardial ischemia, and associated ST depression is usually reciprocal. In patients with Q waves on the resting ECG, exercise ST elevation way be due to peri-infarctional ischemia, abnormal ventricular wall motion or both. Exercise ST-segment depression may be due to a second area of myocardial ischemia rather than being reciprocal to ST elevation.

Influence of coronary collateral vessels on the results of thallium-201 myocardial stress imaging

Abstract Although collateral vessels are commonly seen in patients with coronary disease, their functional significance has been debated. In this study segmental analysis of thallium-201 perfusion scintigrams obtained at rest and after exercise was made in 124 patients with angiographically proved coronary artery disease to determine whether collateral vessels could provide protection front myocardial ischemia during stress. All 15 coronary arteries that were completely occluded and had no collateral vessels showed a corresponding stress perfusion abnormality, but only 65 of 92 occluded arteries with angiographically visualized collateral vessels showed a corresponding stress defect (P

Thallium-201 myocardial perfusion imaging in aortic valve stenosis

Abstract The clinical utility of thallium-201 myocardial perfusion imaging in aortic valve stenosis was evaluated at rest and after exercise in three groups of patients: (1) 20 normal subjects, (2) 11 patients with aortic valve stenosis and coronary artery disease (70 percent or greater narrowing of luminal diameter), 11 patients with aortic valve stenosis without coronary artery disease (30 percent or less narrowing). Seven of the latter 22 patients also had postoperative imaging studies. None of the normal subjects had perfusion abnormalities either at rest or after maximal exercise. Three patients with aortic stenosis and coronary artery disease and one with aortic stenosis alone had focal perfusion defects present at rest suggesting prior myocardial infarction. Five patients with aortic stenosis and coronary artery disease manifested new focal perfusion defects and also a pattern of widespread left ventricular wall “thinning” in the postexercise thallium image suggesting diffuse subendocardial ischemia; three had wall “thinning” alone, and two no change in resting focal defects. Five patients with aortic stenosis without coronary artery disease also manifested focal perfusion defects and wall thinning; one had wall thinning alone, and one a new focal defect alone. Two patients had new resting focal defects after surgery, suggesting perioperative damage, and four patients no longer had either the focal or the diffuse pattern of exercise ischemia seen preoperatively. Thallium-201 imaging is of value in assessing the results of surgery in aortic stenosis. However, the technique does not allow adequate separation of patients with aortic stenosis and coronary artery disease from those with aortic stenosis alone because (1) angiographically significant coronary artery disease may not always produce focal ischemia before diffuse subendocardial ischemia develops, and (2) angiographically insignificant coronary artery disease may become functionally critical in the presence of aortic stenosis and produce focal ischemia.

Stress thallium-201 myocardial scintigraphy for the detection of individual coronary arterial lesions in patients with and without previous myocardial infarction☆

The value of stress thallium-201 scintigraphy for detecting individual coronary arterial stenoses was analyzed in 141 patients with angiographically proved coronary artery disease, 101 with and 40 without a previous myocardial infarction. In patients without infarction, the sensitivity for detecting greater than 50 percent narrowing in the left anterior descending, the right and the left circumflex coronary artery was 66, 53 and 24 percent, respectively. In those with a previous infarction, the sensitivity for demonstrating disease in the artery corresponding to the site of infarction was 100 percent for the left anterior descending, 79 percent for the right and 63 percent for the left circumflex coronary artery. In patients with a prior anterior infarction, concomitant right or left circumflex coronary arterial lesions were detected in only 1 of 12 cases, whereas in those with previous inferior or inferolateral infarction, the sensitivity for left anterior descending coronary artery disease was 69 percent. Because of the reasonably high sensitivity for detecting left anterior descending arterial disease, irrespective of the presence and location of previous infarction, myocardial scintigraphy was useful in identifying multivessel disease in patients with a previous inferior infarction. However, because of its relative insensitivity for right or left circumflex coronary artery disease, scintigraphy proved to be a poor predictor of multivessel disease in patients with a prior anterior infarction and in patients without previous myocardial infarction.

Noninvasive prediction of multivessel disease after myocardial infarction.

In 65 patients with a previous transmural myocardial infarction (anterior in 33, inferior in 32), exercise thallium scanning was compared with 12-lead exercise electrocardiography to see if multivessel disease could be detected. At coronary arteriography 40 patients were shown to have multivessel disease (⩾70% diameter stenosis in two or three vessels) and 25 patients had one-vessel disease. On the exercise scan thallium defects corresponding to the electrocardiographic site of infarction were present in all patients. Patients with one-vessel and multivessel disease were separated by exercise-induced angina, perfusion defects on the exercise thallium scan in more than one specific vascular area, and a positive exercise ECG associated with angina, but not by a positive exercise ECG alone. Of the 40 patients with multivessel disease, 85% had defects in more than one vascular area on the thallium scan and 70% had a positive exercise ECG (p = NS). Of the 37 patients with thallium defects in more than one specific vascular area, 92% had multivessel disease, compared with 72% of the 39 patients who had a positive exercise ECG (p < 0.05). Periinfarctional ischemia was present in 38 of the 65 patients (58%) (14 of 25 with one-vessel disease and 24 of 40 with multivessel disease), and did not correlate with the severity of the corresponding coronary artery disease. When thallium defects that resolved were noted in a second vascular area, they were associated with a resolving rather than a constant defect in the vascular area where the infarction had occurred (p < 0.005). In patients after a transmural myocardial infarction, multivessel disease can be better differentiated from one-vessel disease by thallium scanning than by exercise electrocardiography.

Exercise-induced ST-segment elevation in leads V1 or aVL. A predictor of anterior myocardial ischemia and left anterior descending coronary artery disease.

Exercise-induced ST-segment elevation in leads V1 and/or aVL in the absence of anterior Q waves occurred in 46 of 190 patients (24%) who underwent 12-lead exercise electrocardiography with thallium-201 myocardial perfusion imaging and coronary arteriography. Significant left anterior descending coronary artery (LAD) disease was present in 38 of 46 patients (83%) with V1/aVL ST elevation and in 72 of 144 patients (50%) without V1/aVL ST elevation (p < 0.0005). Anterior myocardial ischemia, indicated by reversible anterior perfusion defects on thallium scanning, was present in 40 of 46 patients (87%) with V1/aVL ST elevation and in 25 of 144 patients (17%) without V1/aVL ST elevation (p < 0.0005). Exercise ST elevation in V1/aVL was detected in 38 of 110 of the patients (35%) with LAD disease, for a specificity of 90%, and in 40 of 65 of the patients (62%) with anterior myocardial ischemia, for a specificity of 95%.We conclude that during 12-lead exercise electrocardiography, ST-segment elevation in V1 and/or aVL in the absence of anterior Q waves predicts anterior myocardial ischemia and LAD disease.