James H. Caldwell

Prospective versus Retrospective ECG Gating for 64-Detector CT of the Coronary Arteries: Comparison of Image Quality and Patient Radiation Dose

PURPOSE To compare image quality and patient radiation dose in a group of patients who underwent 64-detector computed tomography (CT) coronary angiography performed with prospective electrocardiographic (ECG) gating with image quality and radiation dose in a group of patients matched for clinical features who underwent 64-detector CT coronary angiography performed with retrospective ECG gating. MATERIALS AND METHODS Institutional review board approval was obtained for this HIPAA-compliant study, and the informed consent requirement was waived due to the retrospective study design. Two independent reviewers separately scored coronary artery segment image quality and overall image quality for 100 cardiac CT studies (50 in each group). Interobserver variability was calculated. Patient radiation dose for the actual examination z-axis length was recorded, and a normalized dose was calculated for a 12-cm z-axis length of a typical heart. RESULTS The two groups matched well for clinical characteristics and CT parameters. There was good agreement for coronary artery segment image quality scores between the independent reviewers (kappa = 0.72). Of the 1253 coronary artery segments scored, the number of coronary artery segments that could not be evaluated in each group was similar (1.1% [seven of 614] in the prospective group vs 1.5% [10 of 647] in the retrospective group, P = .53). Image quality scores were not significantly different when matched for chest cross-sectional area (P > .05). Mean patient radiation dose was 77% lower for prospective gating (4.2 mSv) than for retrospective gating (18.1 mSv) (P < .01). CONCLUSION Use of 64-detector CT coronary angiography performed with prospective ECG gating has similar subjective image quality scores but 77% lower patient radiation dose when compared with use of retrospective ECG gating.

A new digital electronic caliper for measurement of coronary arterial stenosis: Comparison with visual estimates and computer-assisted measurements☆

Visual analysis of the severity of coronary stenosis is limited by observer variability. However, more complex techniques of proved accuracy are tedious and costly. Therefore, a new digital electronic caliper (DEC) was evaluated as a potentially more accurate, rapid and less costly alternative for measuring stenosis severity. Stenosis minimum diameter (Dmin) and percent diameter reduction (% S) were measured from the screen of the cine projector using a DEC. These measurements were compared with visual estimates (VIS) by 4 experienced angiographers and with measurements made by a computer-assisted method (QCA) of proved accuracy. In routine cineangiograms from 7 patients, 10 lesions were significant (greater than 50% S) and 8 were mild (less than 50% S). Variability, the standard deviation of multiple estimates of Dmin and % S, averaged 0.09 mm and 3.1% for QCA; 0.18 mm and 5.9% for DEC; and 0.26 mm and 7.4% for VIS. Compared with QCA, the visual determination of % S significantly underestimates (-5%; p less than 0.02) mild and overestimates (+11%; p less than 0.002) significant stenosis. VIS underestimates Dmin in significant lesions by 20% (p less than 0.04). In contrast, the mean error for DEC measurement of Dmin and % S was not significantly different from 0 in either lesion group. For the entire group of lesions, and particularly in significant lesions, the mean error for measurement of these 2 indexes of disease was significantly less with DEC than with VIS. Thus, variability and error with DEC are acceptably low for clinical use.(ABSTRACT TRUNCATED AT 250 WORDS)

Patient management after noninvasive cardiac imaging: Results from SPARC (Study of myocardial perfusion and coronary anatomy imaging roles in coronary artery disease)

OBJECTIVES This study examined short-term cardiac catheterization rates and medication changes after cardiac imaging. BACKGROUND Noninvasive cardiac imaging is widely used in coronary artery disease, but its effects on subsequent patient management are unclear. METHODS We assessed the 90-day post-test rates of catheterization and medication changes in a prospective registry of 1,703 patients without a documented history of coronary artery disease and an intermediate to high likelihood of coronary artery disease undergoing cardiac single-photon emission computed tomography, positron emission tomography, or 64-slice coronary computed tomography angiography. RESULTS Baseline medication use was relatively infrequent. At 90 days, 9.6% of patients underwent catheterization. The rates of catheterization and medication changes increased in proportion to test abnormality findings. Among patients with the most severe test result findings, 38% to 61% were not referred to catheterization, 20% to 30% were not receiving aspirin, 35% to 44% were not receiving a beta-blocker, and 20% to 25% were not receiving a lipid-lowering agent at 90 days after the index test. Risk-adjusted analyses revealed that compared with stress single-photon emission computed tomography or positron emission tomography, changes in aspirin and lipid-lowering agent use was greater after computed tomography angiography, as was the 90-day catheterization referral rate in the setting of normal/nonobstructive and mildly abnormal test results. CONCLUSIONS Overall, noninvasive testing had only a modest impact on clinical management of patients referred for clinical testing. Although post-imaging use of cardiac catheterization and medical therapy increased in proportion to the degree of abnormality findings, the frequency of catheterization and medication change suggests possible undertreatment of higher risk patients. Patients were more likely to undergo cardiac catheterization after computed tomography angiography than after single-photon emission computed tomography or positron emission tomography after normal/nonobstructive and mildly abnormal study findings. (Study of Perfusion and Anatomys Role in Coronary Artery [CAD] [SPARC]; NCT00321399).

Cardiovascular Effects of Tricyclic Antidepressants in Depressed Patients with Chronic Heart Disease

Twenty-four depressed patients with heart disease were treated for four weeks in a double-blind trial of imipramine, doxepin, or placebo to assess the effects of tricyclic antidepressants on ventricular function and rhythm. The tricyclic antidepressants had no effect on left ventricular ejection fraction at rest or during maximal exercise, as measured by radionuclide ventriculograms obtained before and after treatment. Premature ventricular contractions were reduced by imipramine but were not consistently changed by doxepin or placebo. Treatment with imipramine and doxepin, but not placebo, was associated with significant improvement (P less than 0.001) in standard ratings of depression. Our findings underscore the need for a reappraisal of the cardiovascular risks of tricyclic antidepressants and suggest that in the absence of severe impairment of myocardial performance, depressed patients with preexisting heart disease can be effectively treated with these agents without an adverse effect on ventricular rhythm or hemodynamic function.

Global and regional left ventricular function and tomographic radionuclide perfusion: the Western Washington Intracoronary Streptokinase In Myocardial Infarction Trial.

The Western Washington Intracoronary Streptokinase In Myocardial Infarction Trial enrolled 250 patients with acute myocardial infarction. After the coronary angiographic diagnosis of thrombosis, patients were randomly assigned to receive either conventional therapy with heparin or intracoronary streptokinase followed by heparin. Of the 232 patients who survived at least 60 days, 207 (89%) underwent radionuclide ventriculographic determination of global and regional ejection fraction at a single institution at 62 +/- 35 days after infarction. In the first 100 patients, infarct size was also determined by quantitative single-photon emission tomographic imaging with thallium-201 (201Tl) and expressed as a percentage of the left ventricle with a perfusion defect. Overall, global ejection fraction did not differ between patients treated with streptokinase (45.9 +/- 13.9%; n = 115) and control patients (46.1 +/- 14.4%; n = 92, p = NS). Similarly, the regional posterolateral, inferior, and anteroseptal ejection fraction did not differ between the two groups. Infarct size as measured by 201Tl tomography was 19.4 +/- 12.8% (n = 52) of the left ventricle for the streptokinase group and 19.6 +/- 11.8% (n = 48; p = NS) for the control group. When patients were compared within groups by electrocardiographic location of infarction, time to treatment, or the presence or absence of vessel opening, there were no significant differences between streptokinase and control patients. Statistical inclusion of the 18 patients who died early and were unavailable for study also failed to modify the results, except for a possible reduction in inferior infarct size as measured by 201Tl tomography.(ABSTRACT TRUNCATED AT 250 WORDS)

Congestive heart failure symptoms in patients with preserved left ventricular systolic function: Analysis of the CASS registry

The clinical characteristics and long-term survival of 284 patients from the Coronary Artery Surgery Study (CASS) registry data base who had moderate to severe congestive heart failure symptoms and a left ventricular ejection fraction greater than or equal to 0.45 were studied. A control group consisting of registry patients with an ejection fraction greater than or equal to 0.45 who did not have heart failure was used for comparison. Patients who had heart failure were older and more likely to be female and to have a higher incidence of hypertension, diabetes and chronic lung disease than registry patients who did not have heart failure. As a group, patients with heart failure had more severe angina and were more likely to have had a prior myocardial infarction than were registry patients without heart failure. At 6 year follow-up, 82% of patients in the heart failure group survived compared with 91% of patients in the control group (p less than 0.0001). Multivariate analysis using the Cox proportional hazards model identified the following independent predictors of mortality: regional ventricular systolic dysfunction, number of diseased coronary arteries, advanced age, hypertension, lung disease, diabetes, increased left ventricular end-diastolic pressure and heart failure symptoms. Among patients with heart failure, the 6-year survival rate of those who had three-vessel coronary artery disease was 68% compared with 92% for the group without coronary artery disease. However, the 6-year survival rate for patients with heart failure who underwent surgical revascularization of diseased coronary arteries was not significantly improved compared with that of patients treated medically.(ABSTRACT TRUNCATED AT 250 WORDS)

Serial exercise radionuclide angiography. Validation of count-derived changes in cardiac output and quantitation of maximal exercise ventricular volume change after nitroglycerin and propranolol in normal men.

R–wave–synchronous radionuclide angiography provides time–activity curve information that is assumed to be proportional to ventricular volumes. We performed serial 2-minute time–activity curves and simultaneous Fick cardiac outputs before and during graded, maximal, supine exercise in nine normal subjects; each subject exercised without drug intervention, after nitroglycerin and after intravenous propranolol. Imaging was performed using an R–wave–synchronized gamma camera–computer system, a high–sensitivity collimator and autologous 99mTc–labeled red blood cells. Fick cardiac output was determined from pulmonary and radial artery blood samples and oxygen consumption. Changes in count–derived cardiac output, expressed as percent change from baseline, closely paralleled changes in Fick output at all levels of exercise for nondrug and nitroglycerin studies. After propranolol, agreement was maintained between both methods for low–tomoderate levels of exercise. Changes in count–defined end–diastolic volume, end–systolic volume and stroke volume agreed well with simultaneous heart rate, wedge pressure and Fick measurements and were in accord with known hemodynamic effects of exercise, nitroglycerin and propranolol. We conclude that radionuclide count data accurately reflect true hemodynamic change as determined by the Fick technique and may aid in defining the mechanisms of ventricular dysfunction in coronary and valvular heart disease, thereby providing a better understanding of the effects of interventions in these disorders.

The detection of coronary artery disease with radionuclide techniques: a comparison of rest-exercise thallium imaging and ejection fraction response.

Fifty–two patients with suspected coronary artery disease underwent coronary angiography, thallium-201 myocardial imaging, and ECG–gated blood pool ventriculography at rest and at maximal exercise. In 11 patients without coronary artery disease, all thallium images were normal. The resting ejection fraction (EF) was normal in all 11 patients and increased during exercise in six, was unchanged in three, and decreased in two. Of the 41 patients with coronary artery disease, the thallium image was normal at rest and at exercise in six (15%), whereas the exercise EF was abnormal in these six. A new (18 patients) or enlarged (11 patients) defect appeared on the thallium image in 29 of 41 patients (71%) with coronary disease. Six of 41 patients (15%) had an abnormal rest thallium image that was unchanged with exercise. An abnormal rest and/or exercise image defect identified 35 of 41 patients (85%) with coronary artery disease. The resting EF was normal in 26 of the 41 patients (63%) and in 24 patients demonstrated an abnormal response to exercise. Fifteen patients (37%) had an abnormal resting EF, and 14 of these 15 demonstrated persistent abnormalities. Thus, an abnormal exercise EF response identified 38 of 41 (93%) patients with coronary disease. The specificity of the thallium image was 100% and for the exercise EF determination, 54% (p < 0.02). We conclude that an abnormal exercise EF response and the rest–exercise thallium image have similar sensitivities for detecting coronary disease; however, an abnormal exercise ejection fraction was significantly more sensitive than was a new thallium abnormality alone (93% vs 71%). Combined, the two studies detected all patients with coronary disease.

Cine CT for Attenuation Correction in Cardiac PET/CT

In dual-modality PET/CT systems, the CT scan provides the attenuation map for PET attenuation correction. The current clinical practice of obtaining a single helical CT scan provides only a snapshot of the respiratory cycle, whereas PET occurs over multiple respiratory cycles. Misalignment of the attenuation map and emission image because of respiratory motion causes errors in the attenuation correction factors and artifacts in the attenuation-corrected PET image. To rectify this problem, we evaluated the use of cine CT, which acquires multiple low-dose CT images during a respiratory cycle. We evaluated the average and the intensity-maximum image of cine CT for cardiac PET attenuation correction. Methods: Cine CT data and cardiac PET data were acquired from a cardiac phantom and from multiple patient studies. The conventional helical CT, cine CT, and PET data of an axially translating phantom were evaluated with and without respiratory motion. For the patient studies, we acquired 2 cine CT studies for each PET acquisition in a rest–stress 13N-ammonia protocol. Three readers visually evaluated the alignment of 74 attenuation image sets versus the corresponding emission image and determined whether the alignment provided acceptable or unacceptable attenuation-corrected PET images. Results: In the phantom study, the attenuation correction from helical CT caused a major artifactual defect in the lateral wall on the PET image. The attenuation correction from the average and from the intensity-maximum cine CT images reduced the defect by 20% and 60%, respectively. In the patient studies, 77% of the cases using the average of the cine CT images had acceptable alignment and 88% of the cases using the intensity maximum of the cine CT images had acceptable alignment. Conclusion: Cine CT offers an alternative to helical CT for compensating for respiratory motion in the attenuation correction of cardiac PET studies. Phantom studies suggest that the average and the intensity maximum of the cine CT images can reduce potential respiration-induced misalignment errors in attenuation correction. Patient studies reveal that cine CT provides acceptable alignment in most cases and suggest that the intensity-maximum cine image offers a more robust alternative to the average cine image.

Comparative plasma catecholamine and hemodynamic responses to handgrip, cold pressor and supine bicycle exercise testing in normal subjects

Serial hemodynamic and plasma catecholamine responses were compared among 10 healthy men (27 +/- 3 years) (+/- 1 standard deviation) during symptom-limited handgrip (33% maximal voluntary contraction for 4.4 +/- 1.8 minutes), cold pressor testing (6 minutes) and symptom-limited supine bicycle exercise (22 +/- 5 minutes). Plasma catecholamine concentrations were measured by radioenzymatic assays: ejection fraction and changes in cardiac volumes were assessed by equilibrium radionuclide angiography. During maximal supine exercise, plasma norepinephrine and epinephrine concentrations increased three to six times more than during either symptom-limited handgrip or cold pressor testing. Additionally, increases in heart rate, systolic blood pressure, rate-pressure product, stroke volume, ejection fraction and cardiac output were significantly greater during bicycle exercise than during the other two tests. A decrease in ejection fraction of 0.05 units or more was common in young normal subjects during the first 2 minutes of cold pressor testing (6 of 10 subjects) or at symptom-limited handgrip (3 of 10), but never occurred during maximal supine bicycle exercise. The magnitude of hemodynamic changes with maximal supine bicycle exercise was greater, more consistent and associated with much higher sympathetic nervous system activation, making this a potentially more useful diagnostic stress than either handgrip exercise or cold pressor testing.