Iodine-123 phenylpentadecanoic acid and single photon emission computed tomography in identifying left ventricular regional metabolic abnormalities in patients with coronary heart disease: comparison with thallium-201 myocardial tomography.

Iodine-123 phenylpentadecanoic acid (IPPA) is a synthetic long chain fatty acid with myocardial kinetics similar to palmitate. Two hypotheses were tested in this study. The first hypothesis was that IPPA imaging with single photon emission computed tomography (SPECT) is useful in the identification of patients with coronary artery disease. Fourteen normal volunteers (aged 27 +/- 2 years) and 33 patients (aged 54 +/- 11 years) with stable symptomatic coronary artery disease and at least one major coronary artery with luminal diameter narrowing greater than or equal to 70% were studied with symptom-limited maximal exercise testing. The IPPA (6 to 8 mCi) was injected 1 min before the termination of exercise, and tomographic imaging was performed beginning at 9 min and repeated at 40 min after the injection of IPPA. Nine of the normal volunteers and 13 of the patients had a second examination performed at rest on another day. Using the limits of normal as 2 SD from the normal mean values, 27 of the 33 patients with coronary artery disease demonstrated abnormalities in either the initial distribution or the clearance of IPPA, or both. Nineteen of the 33 patients had a maximal variation of activity distribution of greater than or equal to 25% on the 9 min IPPA images. Twenty-two of the 33 patients had a maximal variation in IPPA washout greater than 17% and 17 had a washout rate less than or equal to 2%. There was good agreement between the location of significant coronary artery stenoses and abnormalities in the initial distribution and clearance of IPPA. The second hypothesis tested was that IPPA imaging is as or more sensitive and, therefore, complementary to thallium-201 imaging in the identification of exercise-induced ischemia in patients. Twenty-five of the 33 patients underwent both thallium-201 and IPPA tomographic imaging after symptom-limited maximal exercise testing. The amount of exercise performed by each patient during both studies was similar. Twenty-one of the 25 patients had abnormal IPPA tomographic studies, whereas 18 had abnormal thallium-201 tomographic studies (p = NS). The results of this study suggest the following conclusions: 1) iodine-123 phenylpentadecanoic acid imaging using single photon emission computed tomography and exercise provides a sensitive and relatively noninvasive method for identifying abnormalities in myocardial metabolism associated with significant coronary artery stenoses, and 2) iodine-123 phenylpentadecanoic acid is at least as sensitive as thallium-201 for this purpose using tomographic imaging and exercise testing.

Quantitation of postexercise lung thallium-201 uptake during single photon emission computed tomography.

To test the hypothesis that analysis of lung thallium uptake measured during single photon emission computed tomography (SPECT) yields supplementary clinical information as reported for planar imaging, quantitative analysis of lung thallium uptake following maximal exercise was performed in 40 clinically normal subjects (Group 1) and 15 angiographically normal subjects (Group 2). Lung thallium uptake was measured from anterior projection images using a ratio of heart-to-lung activities. Seventy subjects with coronary artery disease (CAD) (Group 3) determined by angiography (greater than or equal to 70% luminal stenosis) underwent thallium perfusion SPECT. Thirty-nine percent of these subjects had multivessel and 61% had single vessel CAD. Lung thallium uptake was elevated in 47 of 70 (67%) Group 3 subjects. Group 3 subjects with elevated lung thallium uptake did not differ from Group 3 subjects with normal lung thallium uptake with respect to extent or distribution of coronary artery disease, left ventricular function, or severity of myocardial ischemia as determined by exercise and redistribution thallium SPECT. Thus, the measurement of thallium lung uptake from anterior projection images obtained during SPECT frequently identifies patients with CAD, but it may not provide supplementary information regarding the extent of myocardial ischemia or ventricular dysfunction.

Estimation of jeopardized left ventricular myocardium in symptomatic and silent ischemia as determined by iodine-123 phenylpentadecanoic acid rotational tomography.

Whether patients with silent myocardial ischemia have a lesser mass of ischemic myocardium than patients with symptomatic ischemia is controversial. Forty-five patients with angiographic coronary artery disease (greater than or equal to 70% luminal diameter narrowing) were studied. All patients had ischemic patterns of myocardial uptake and clearance of the long-chain fatty acid perfusion/metabolic imaging agent iodine-123 phenylpentadecanoic acid after maximal exercise. Single-photon emission computed tomography was performed and 25 myocardial segments were analyzed using circumferential activity profile curves. The 21 patients with silent treadmill ischemia exercised longer than the 24 patients with painful treadmill ischemia (430 +/- 137 vs 337 +/- 96 seconds, p less than 0.01) and to a higher heart rate (138 +/- 21 vs 125 +/- 18 beats/min, p less than 0.05). Patients with treadmill silent ischemia had the same number of abnormally perfused myocardial segments as patients with painful treadmill ischemia (8.6 +/- 4.5 vs 6.5 +/- 4.1 segments, difference not significant) and the same number of reversibly ischemic myocardial segments (4.0 +/- 1.4 vs 4.2 +/- 3.0 segments, difference not significant). The angiographic severity and extent of coronary artery disease were similar in the 2 groups. Thus, in this selected group of patients, those with silent treadmill ischemia appear to have at least as great an extent of ischemic myocardium as patients with painful exertional ischemia.

Age- and sex-based nomograms from coronary artery calcium scores as determined by electron beam computed tomography.

We present data for 18,785 patients undergoing electron beam computed tomography, dividing them by sex and age (using 5-year age increments) to determine coronary artery calcium scores representing the 50th and 75th percentiles for each group. Because risk stratification is an integral part of determining therapies for coronary artery disease, age- and sex-based scores may be more clinically useful than total coronary artery calcium scores alone.

Predictive value of quantitative dipyridamole-thallium scintigraphy in assessing cardiovascular risk after vascular surgery in diabetes mellitus.

Cardiac complications represent a major risk to patients undergoing vascular surgery. Diabetic patients may be particularly prone to such complications due to the high incidence of concomitant coronary artery disease, the severity of which may be clinically unrecognized. Attempts to stratify groups by clinical criteria have been useful but lack the predictive value of currently used noninvasive techniques such as dipyridamole-thallium scintigraphy. One hundred one diabetic patients were evaluated with dipyridamole-thallium scintigraphy before undergoing vascular surgery. The incidence of thallium abnormalities was high (80%) and did not correlate with clinical markers of coronary disease. Even in a subgroup of patients with no overt clinical evidence of underlying heart disease, thallium abnormalities were present in 59%. Cardiovascular complications, however, occurred in only 11% of all patients. Statistically significant prediction of risk was not achieved with simple assessment of thallium results as normal or abnormal. Quantification of total number of reversible defects, as well as assessment of ischemia in the distribution of the left anterior descending coronary artery was required for optimum predictive accuracy. The prevalence of dipyridamole-thallium abnormalities in a diabetic population is much higher than that reported in nondiabetic patients and cannot be predicted by usual clinical indicators of heart disease. In addition, cardiovascular risk of vascular surgery can be optimally assessed by quantitative analysis of dipyridamole-thallium scintigraphy and identification of high- and low-risk subgroups.

Modulation of the QT interval: effects of graded exercise and reflex cardiovascular stimulation.

During exercise, as heart rate (HR) increases, the QT interval of the electrocardiogram shortens. The mechanism(s) involved in this QT shortening has not been clearly defined. To distinguish the influence of increased circulating catecholamines from myocardial efferent stimulation, the relationship between HR and QT interval was investigated during exercise and cardiovascular reflex stimulation in cardiac transplant patients and normal control subjects. Because of cardiac denervation, increases in HR in these patients are solely due to circulating catecholamines and thus allow isolation of their effect on the QT interval. Twenty-one cardiac transplant patients were studied and compared with 16 normal control subjects. The QT-HR relationship was determined according to an exponential model during treadmill exercise in both groups [QT = 0.12 + 0.492e(-0.008.HR) and QT = 0.12 + 0.459e(-0.007.HR) in normal subjects and transplant patients, respectively] and was statistically similar between groups, suggesting similar QT interval shortening in both groups. During cold pressor and Valsalva maneuvers, HR increased significantly in normal subjects only, whereas QT interval changed minimally in both groups. These results suggest that during exercise the QT interval is influenced predominantly by increases in circulating catecholamines rather than by neurally mediated reflex autonomic changes.

New radionuclide agents for cardiac imaging: description and application.

The introduction of three new radiopharmaceuticals into clinical research and practice has broadened the potential applications and scope of nuclear cardiology examinations. Technetium-99m labeled isonitrile perfusion agents have excellent imaging characteristics allowing the accurate identification of coronary artery disease. Simultaneous assessments of ventricular function are possible with these agents. Iodine-123 phenylpentadecanoic acid myocardial scintigraphy permits assessments of myocardial perfusion and fatty acid metabolism, and permits investigations of myocardial metabolism with conventional imaging equipment. Iodine-123 meta-iodobenzyl-guanidine serves as an indicator of the functional integrity of the sympathetic nervous system and permits evaluations of the effects of various disease states on catecholamine handling by the heart.

Effect of variation in heart size on quantitative thallium SPECT.

Quantitative single-photon emission tomographic (SPECT) thallium 201 (201Tl) cardiac studies are frequently used to improve test accuracy. One common technique uses polar mapping of relative tracer distribution to compare patient data to emplates from "normal" patient data. Commercial software does not correct for cardiac size variations. This study's purpose was to determine the effect of uncorrected variations in heart size on the variance of the normal population, which is the basis of template significance levels. Twenty-one male volunteers with low probability (less than 5%) for coronary disease underwent SPECT-Tl stress test. Data analysis with and without size correction was performed. Data were corrected for size by use of a three-dimensional compression/expansion algorithm. Quantitative data were generated by radial search to maximum activity in short-axis reconstructions. The mean activity and its variance was calculated from 288 points encompassing the myocardium. Mean and variance differences were analyzed by paired t test. There was no difference in activity means (pT greater than .9), indicating that size correction does not distort the data. The corrected data had, however, significantly lower variance (pT less than .0001). This shows that ventricular size variation contributes significantly to "normal" template variance and may adversely affect diagnostic accuracy in the absence of volume correction.

Assessment of thallium scintigraphy and echocardiography during dobutamine infusion for the detection of coronary artery disease.

Dobutamine infusion was performed in 16 patients following cardiac catheterization, and non-invasive assessment was performed with thallium SPECT and echocardiography. Dobutamine thallium scintigraphy was abnormal in 93% of patients with significant coronary artery disease. In addition, individual epicardial vessel involvement was identified by a corresponding perfusion defect with 88% sensitivity and 93% specificity. Dobutamine echocardiography revealed segmental wall motion abnormalities in 62% of patients with significant coronary disease. However, in six patients baseline segmental wall motion abnormalities on echocardiography improved during dobutamine infusion. Dobutamine thallium SPECT is a safe and useful test for the detection and localization of coronary artery disease. Dobutamine echocardiography is less useful in screening for coronary disease, but may detect areas of abnormally functioning myocardium having retained viability.

Incidental detection of preclinical renal tumors with electron beam computed tomography: report of 26 consecutive operated patients.

PURPOSE: The purpose of this work was to describe the positive predictive value of electron beam CT (EBCT) for diagnosis of solid renal tumors. METHOD: Among 11,932 consecutive patients undergoing screening EBCT, 27 cases met EBCT criteria for solid renal tumors. Twenty-six of 27 patients underwent surgery. RESULTS: Surgical pathology identified 25 solid renal tumors and 1 adrenal hemorrhage with thrombus. Twenty tumors were classified as T1N0M0, one was T2N0M0, and one was T3aN0M0. All tumor patients are clinically well at 1-41 months (mean 17 months) postoperatively. None of the patients had clinical signs or symptoms characteristic of renal malignancy. CONCLUSION: EBCT is an effective tool for detection of solid renal tumors in a healthy outpatient population (positive predictive value 0.96). The detection rate is low [0.2% (26/11,932) at our facility] in patients undergoing EBCT for other indications. The cost-effectiveness and sensitivity of this technique for solid renal tumor detection among various populations remain to be determined.

Abnormal I-123 metaiodobenzylguanidine myocardial washout and distribution may reflect myocardial adrenergic derangement in patients with congestive cardiomyopathy.

I-123 metaiodobenzylguanidine (MIBG) is a new radiopharmaceutical with properties that allow the characterization of the sympathetic innervation of several organ systems. In this study, we used MIBG with tomographic imaging to evaluate noninvasively the differences in myocardial sympathetic innervation in 14 healthy volunteers and 16 patients with severe dilated cardiomyopathy (CM). Initial (15-minute) images demonstrated no significant differences in MIBG concentration in the hearts of patients with CM and of healthy volunteers. However, the myocardial retention of MIBG was significantly reduced in the patients with CM. Expressed as the percent washout from 15 to 85 minutes, the patients with CM had a 28 +/- 12% washout rate compared with 6 +/- 8% in the controls (p less than 0.001). A small subset of patients from each group imaged at 4-hour intervals demonstrated even greater disparity in washout rates. In addition, the patients with CM had significantly greater heterogeneity in the MIBG activity distribution within the myocardial images. There was 47 +/- 15% intraimage variability in MIBG distribution in the patients with CM and 22 +/- 9% variation in the controls (p less than 0.001). We conclude from these data that the myocardial distribution and kinetics of MIBG in images obtained from patients with CM differ significantly from those of controls and that the MIBG patterns may be used as a relatively noninvasive means to evaluate the severity of altered adrenergic innervation in the hearts of these patients.