Robert D. Burow

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).

Measurement of absolute left ventricular volume from gated blood pool studies

A new method for obtaining absolute left ventricular volume from gated blood pool studies was evaluated in a torso phantom and in 35 patients who also underwent single-plane contrast ventriculography. Gated 400 left anterior oblique and static anterior views were acquired. Left ventricular volume at end-diastole was given by the ratio of the attenuation-corrected end-diastolic count rate from the gated study to the count rate per milliliter from a blood sample. Attenuation correction was made by dividing the end-diastolic count rate by e ud, where u = the linear attenuation coefficient of water and d = the distance from the skin marker to the center of the left ventricle in the anterior view divided by sin 400 to yield the depth of left ventricle in the left anterior oblique view. In the phantom studies, the correlation between radionuclide and true volume was 0.99 (radionuclide = 1.03 true − 3 ml); the standard error of the estimate was 8 ml. In the patient studies, the radionuclide end-diastolic volume was used to calibrate the left ventricular time-activity curve, yielding left ventricular volume throughout the cardiac cycle. The correlation between radionuclide and angiographic enddiastolic volume was 0.95 (radionuclide = 0.97 angiographic + 3 ml); the standard error of the estimate was 36 ml. The correlation between radionuclide and angiographic end-systolic volume was 0.95 (radionuclide − 1.01 angiographic + I ml); the standard error of the estimate was 33 ml. This method permits direct determination of absolute left ventricular volume without assumptions about the shape of the ventricle or the necessity of using regression equations to convert volume “units” to true volume.

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.

Value of early thallium-201 scintigraphy for predicting mortality in patients with acute myocardial infarction.

To determine whether the severity of thallium-201 scintigraphic defects present within hours of acute myocardial infarction (MI) could he used to predict subsequent mortality, thallium-201 imaging was performed within 15 hours of the onset of symptoms in 42 patients with acute MI. Patients with pulmonary edema or shock were excluded. The extent of perfusion defect was determined in three views (anterior and 400 and 600 left anterior oblique) by both objective computer-assisted and subjective methods, and expressed as a summed defect score. Mortality for the patient group as a whole was 17% in hospital, 24% at 6 months, and 33% at last follow-up (average 9 months). Using the objective method, a high thallium defect score (7.0 or greater, corresponding to at least a moderate reduction of activity involving 40% of the left ventricle in two views) identified a subgroup of 13 patients in which mortality was 46% in hospital, 62% at 6 months, and 92% at last follow-up. Corresponding values for the 29 patients with lower objective defect scores were 3%, 7% and 7%, respectively (all p < 0.001). Similar results were obtained with the subjective scoring method. Certain clinical variables, including a history of prior myocardial infarction, anterior location of the current infarct, peak CK > 1000 IU/I and moderate (vs none or mild) left ventricular failure were also associated with mortality. However, a high thallium defect score was significantly more predictive than any of these variables. Stepwise, multivariate analysis showed that the thallium score alone was a better predictor than the best combination of these clinical variables, and no variable added to the predictiveness of the high defect score. These results suggest that thallium-201 scintigraphy may provide an accurate, rapid, noninvasive method for separating high-risk and low-risk subgroups of hemodynamically stable patients admitted with acute MI.

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.

Pathologic basis of thallium-201 scintigraphic defects in patients with fatal myocardial injury.

Using a quantitative, computer-aided circumferential profile technique, we have shown that thallium-201 scintigrams with large defects can identify a group of patients with a high mortality after acute myocardial infarction. To determine whether high-risk thallium scintigrams predict poor survival because of a critical loss of myocardium, we correlated infarct size in 24 autopsied patients with the extent of thallium defect in three views. Of 13 patients with large defects (computer score 7.0) eight (62%) had > 25% loss of left ventricular (LV) myocardium, but five (38%) had smaller infarcts (4-24% of LV myocardium), suggesting that part of the scintigraphic defect was related to ischemia without necrosis. Eight of nine patients with loss > 25% LV myocardium had large defects. In 10 of 11 patients with small defects (computer score < 7.0), infarcts involved < 20% of LV myocardium. Although scintigrams with large defects predicted a critical loss of myocardium in over 60% of our patients, they included an important second group, in which the scintigraphic defect appeared to reflect a small infarct and a large surrounding area of reversibly ischemic myocardium.

Quantification of left ventricular volume in gated equilibrium radioventriculography

We have developed a simple method for measuring left ventricular volume based on semi-automated analysis of 40° left anterior oblique images obtained with a standard scintillation camera after equilibrium of an intravenous injection of 20 mCi of technetium-99m in vivo labeled red blood cells. The essence of the method is the use of the dimensions and radioactivity within a segment of aorta to convert observed left ventricular count rates to volume. Four assumptions were made: 1) the aortic arch is nearly parallel to the collimator face when a patient is in the proper left anterior oblique position; 2) a segment at the top of the aortic arch, approximately 1 cm wide, is a right cylinder, 3) the edges of the aorta can be delineated as the lines where the second derivative of a cross sectional profile equals zero; 4) left ventricular and aortic arch counts undergo the same attenuation because they are nearly the same distance from the chest wall in the proper left anterior oblique position. By measuring the counts and volumes of two regions of known shape, one in the middle, the other at the edge of the aortic arch, and calculating their differences a background-independent volume count ratio (Δv/ΔC) can be obtained. The left ventricular and diastolic volume (LVEDV) is calculated with the equation: LVEDV=(Δ/ΔC) LVEDC, where LVEDC represents left ventricular end diastolic counts. Twenty-six patients were evaluated by equilibrium radio- and contrast-ventriculography, the latter analyzed by planimetry. The radionuclide method yielded an end diastolic volume that correlated well with contrast ventriculography (r=0.96, Y=0.91 X+21 ml). In addition to its simplicity and objectivity, a major advantage of this method of determining ventricular volume is that it does not require a blood sample.