Arm exercise-thallium imaging testing for the detection of coronary artery disease.

Patients with lower limb impairment are often unable to undergo a standard bicycle or treadmill test for the evaluation of coronary artery disease. To establish an alternative method of testing, 50 subjects (aged 56 +/- 10 years) performed arm ergometry testing in conjunction with myocardial thallium scintigraphy. All underwent coronary angiography; significant coronary artery disease (greater than or equal to 70% stenosis) in at least one vessel was present in 41 (82%) of the 50 patients. Thallium scintigraphy was found to have an 83% sensitivity and 78% specificity for detecting coronary disease, compared with a sensitivity and specificity of 54% (p less than 0.01) and 67% (p = NS), respectively, for exercise electrocardiography. In the subgroup of 23 patients who had no prior myocardial infarction or left bundle branch block and were not taking digitalis, thallium scintigraphy had a sensitivity of 80% versus 50% for exercise electrocardiography. Scintigraphy yielded a sensitivity of 84, 74 and 90% for one, two and three vessel disease, respectively. Noninvasive arm ergometry exercise-thallium imaging testing appears to be reliable and useful and should be considered in the evaluation of coronary artery disease in patients with lower limb impairment.

Persistent left superior vena cava and right superior vena cava drainage into the left atrium without arterial hypoxemia.

A 46 year old patient who presented with an acute myocardial infarction was discovered to have a systemic venous communication with the left heart during attempted insertion of a pulmonary flotation catheter. There was no evidence of cyanosis or systemic arterial desaturation. A right superior vena cava that emptied into the right superior pulmonary vein and a persistent left superior vena cava draining into the coronary sinus were confirmed pathologically after death related to a brain abscess. The embryology, physiology and noninvasive diagnostic approach to this unique venous anomaly are discussed.

Evaluation in dogs of a new double-dose technique for imaging changes in myocardial perfusion.

Assessment of myocardial perfusion with thallium immediately before and after an intervention that alters blood flow has been difficult due to presence of residual activity from the first tracer dose at the time of the second imaging. In a canine model we investigated a technique using two separate thallium injections during an intervention and after its reversal. Images were obtained after each injection, and a difference image was obtained by subtracting the first from the second image to correct for tracer persisting from the first injection. Interventions on coronary blood flow included: transient occlusion, subcritical stenosis with dipyridamole infusion, and permanent occlusion. The first images showed defects corresponding to the occlusion or stenosis, while the "difference" images correlated with myocardial perfusion at the time of the second injection. This technique allows rapid evaluation of changes in perfusion in response to interventions, and may find application in several clinical procedures.

Diagnosis of pericardial effusions from routine gated blood-pool imaging.

Gated blood-pool scintigraphy (GBPS) is often obtained as the initial test to evaluate symptoms suggestive of left ventricular dysfunction. Since large pericardial effusions may also cause such symptoms, the ability to recognize them on routine GBPS is of clinical importance. Characteristic features of the "halo" sign surrounding the cardiac blood pool were developed, based on the GBPS of patients with known pericardial effusions. These criteria were then applied blindly to 154 consecutive patients who underwent both GBPS and echocardiography. All five patients with large effusions (approximately greater than 500 ml) were correctly identified by GBPS (sensitivity 100%); for patients with moderate effusions (approximately 150-500 ml), the sensitivity was only 33% (3/9). There were three false positives (specificity 98%). We conclude that large pericardial effusions can be identified with high sensitivity and specificity on routine GBPS. Although echocardiography remains the method of choice for the diagnosis of effusions, inspection for characteristics suggesting their presence on GBPS should be part of routine interpretations.

Effect of a delay in commencing imaging on the ability to detect transient thallium defects.

Sixty patients, 42 with coronary disease and 18 normals, were studied to assess the impact of a delay following exercise in commencing thallium imaging on the sensitivity for detecting ischemic transient defects. Three sets of images were obtained beginning 2 min, 18 min, and 2 hr after exercise. Each patient's images were separated into two pairs of studies for analysis: 2 min-2 hr and 18 min-2 hr. Of the 42 patients with coronary disease, a greater number had transient defects detected on the 2 min-2 hr compared with the 18 min-2 hr study (22 compared with 14, p less than 0.05). False positives were not increased by earlier imaging. We conclude that a modest (18 min) delay obtaining the first set of images causes a significant reduction in the ability to detect transient thallium defects, and that imaging should begin several minutes after exercise.

Derivation of systolic time intervals from Doppler measurement of temporal arterial blood flow.

The carotid pulse method of recording systolic time intervals is limited by significant motion-induced artifact, making it unsuitable for studying patients during exercise. As an approach to overcoming this limitation, a new method utilizing the blood velocity profile of the superficial temporal artery measured by Doppler ultrasound has been developed. When compared with the values obtained from the conventional carotid pulse method, Doppler-derived left ventricular ejection time and preejection period showed excellent correlation (r = 0.99 for both) and the Doppler-derived measurements showed little intra- or interobserver variability. Studies performed during treadmill exercise showed that in 8 of 10 subjects, suitable tracing could be recorded through stage 3 of the Bruce protocol, confirming the enhanced stability of the technique compared with the carotid pulse method.

Technique for dual transducer echocardiography.

Circuitry for simultaneous recording from dual transducers on a single echocardiogram is presented. The technique may be used to compare the motion pattern and time intervals of separate intracardiac structures. The technique may be difficult, is limited by the size of the cardiac window, and may be most useful for research purposes.

Dipyridamole-thallium-201 scintigraphy in the prediction of future cardiac events after acute myocardial infarction.

To evaluate the safety and usefulness of serial thallium scanning immediately after intravenous dipyridamole, we studied 51 patients recovering from acute myocardial infarction. Eight patients experienced angina during the procedure, but there were no serious complications. Patients were followed for a mean period of 19 months after hospital discharge. Eleven of 12 patients who died during follow-up or had another infarction had shown transient defects (redistribution) on their predischarge scan, as had 22 of the 24 patients who needed readmission for management of angina. Among all the other clinical or scintigraphic criteria tested, the presence of redistribution on the dipyridamole-thallium scan was the only significant predictor of these serious cardiac events. Twenty-six patients were also given a submaximal exercise test before discharge, of whom 13 subsequently had serious cardiac events. The exercise test had been positive in only 6 of these 13 patients, whereas the dipyridamole-thallium scan had shown a redistribution pattern in 12 (P less than 0.001). We conclude from this preliminary study that dipyridamole-thallium scintigraphy after myocardial infraction is relatively safe. It appears to be a more sensitive predictor of subsequent cardiac events than a submaximal exercise test and may therefore prove useful in evaluating patients after recovery from a myocardial infarction.

Decrease in the ability to detect elevated lung thallium due to delay in commencing imaging after exercise.

Post-exercise elevation of the lung/myocardial thallium ratio and a high lung clearance rate between initial and delayed images have been reported to be markers for exercise-induced left ventricular (LV) dysfunction associated with coronary artery disease (CAD). We performed thallium exercise tests on 60 patients, 42 with CAD, in order to determine the effect of delaying initial imaging on detection of elevated lung thallium. In addition to images obtained at 2 minutes and at 2 hours after exercise, 18-minute images were also obtained to simulate such a delay. Because of rapid isotope clearance in those with initially elevated lung activity, there was decreased sensitivity of both the initial lung/myocardial ratio and lung thallium clearance for detecting CAD, using the 18-minute image as the initial post exercise study. We conclude that initial imaging should be done in the anterior view early after exercise to optimize detection of elevated lung thallium.

Evaluating diagnosis-based case-mix measures: how well do they apply to the VA population?

BACKGROUND: Diagnosis-based case-mix measures are increasingly used for provider profiling, resource allocation, and capitation rate setting. Measures developed in one setting may not adequately capture the disease burden in other settings. OBJECTIVES: To examine the feasibility of adapting two such measures, Adjusted Clinical Groups (ACGs) and Diagnostic Cost Groups (DCGs), to the Department of Veterans Affairs (VA) population. RESEARCH DESIGN: A 60% random sample of veterans who used health care services during FY 1997 was obtained from VA inpatient and outpatient administrative databases. A split-sample technique was used to obtain a 40% sample (n = 1,046,803) for development and a 20% sample (n = 524,461) for validation. METHODS: Concurrent ACG and DCG risk adjustment models, using 1997 diagnoses and demographics to predict FY 1997 utilization (ambulatory provider encounters, and service days-the sum of a patient's inpatient and outpatient visit days), were fitted and cross-validated. RESULTS: Patients were classified into groupings that indicated a population with multiple psychiatric and medical diseases. Model R-squares explained between 6% and 32% of the variation in service utilization. Although reparameterized models did better in predicting utilization than models with external weights, none of the models was adequate in characterizing the entire population. For predicting service days, DCGs were superior to ACGs in most categories, whereas ACGs did better at discriminating among veterans who had the lowest utilization. CONCLUSIONS: Although "off-the-shelf" case-mix measures perform moderately well when applied to another setting, modifications may be required to accurately characterize a population's disease burden with respect to the resource needs of all patients.