Maynard L. Freeman

Thallium scintigraphy during dobutamine infusion: Nonexercise-dependent screening test for coronary disease

Exercise thallium scintigraphy has proven to be a sensitive method for detecting coronary artery disease (CAD). However, early redistribution of thallium and inadequate exercise can reduce its sensitivity. In this study, dobutamine was infused in incremental doses (5, 10, 15, and 20 micrograms/kg/min) in 24 patients being evaluated for chest pain. Thallium scintigraphy was completed during the maximum dose of dobutamine tolerated and repeated 4 hours later. Significant CAD was present in 16 patients; the remaining eight had normal coronaries. Exercise ECG was obtained in 23 patients. During dobutamine thallium scintigraphy, reversible perfusion defects occurred in 15 of 16 CAD and in one of eight non-CAD patients, resulting in a sensitivity of 94% and a specificity of 87%. Exercise ECG had a sensitivity of 60% and a specificity of 63%. We conclude that: (1) dobutamine thallium scintigraphy appears to be a sensitive method for detecting significant CAD and provided a more sensitive screening test than exercise ECG; (2) dobutamine thallium scintigraphy is especially useful in patients who cannot exercise; and (3) because imaging occurs during dobutamine infusion, the problem of early redistribution may be mitigated.

A comparison of dobutamine infusion and supine bicycle exercise for radionuclide cardiac stress testing

We have compared the inotropic drug dobutamine to supine bicycle exercise as a means of inducing stress in radionuclide ventriculography studies. Dobutamine has the following properties, making it favorable for widespread usage: 1) ability to be given safely in a peripheral vein, 2) rapid onset, and 3) short duration of action. Each patient underwent supine bicycle progressive resistance testing of 2 minutes per stage followed 30 minutes later by dobutamine administration. Accuracy of diagnosis was 0.93 and sensitivity was 0.89 with dobutamine, while with bicycle the accuracy was 0.93 and sensitivity was 0.94. While not designed to replace supine bicycle testing, incremental infusions of dobutamine appear to be nearly equal in accuracy and sensitivity, providing a satisfactory technique for cardiac evaluation of previously excluded patients.

Visualization of metastatic liver disease on technetium-99m bone scintigraphy.

To determine the frequency with which liver metastases are visualized on bone scintigraphy, 425 pairs of liver and bone scans, performed within one month of each other, were reviewed. Sixty-three of the 425 liver scans showed metastases. Of these 63, five cases of carcinoma of the colon and six cases of carcinoma of the lung also visualized by Tc-99m MDP scintigraphy. This represented 46% of colon metastases and 15% of lung metastases detected on liver scan. Liver metastases from other primary tumors were not detected on bone scan, but the numbers for these tumors were small. The liver metastases which were detected on bone scan were significantly larger than those which were not. The literature was reviewed and the primary and secondary tumors of liver with uptake of Tc-99m phosphate compounds listed.

The effects of acute hypertriglyceridemia and high levels of free fatty acids on left ventricular function

The effects of acute hypertriglyceridemia and of high levels of free fatty acids on the left ventricular ejection fraction were studied by radionuclide ventriculography in 20 subjects with and without coronary artery disease. An infusion of approximately 125 ml of a 20% fat emulsion over 25 minutes resulted in an increase of plasma triglycerides to the mean of 820 mg/dl and a fall of the left ventricular ejection fraction from the baseline mean of 62% to 58% (p less than 0.05). Ninety minutes after the intravenous administration of 5000 units of heparin, plasma free fatty acids rose to the mean of 4.6 mmol/L and the mean left ventricular ejection fraction increased to 69% (p less than 0.001). The observed changes in blood lipids were not associated with clinical or ECG evidence of myocardial ischemia. We conclude that acute hypertriglyceridemia causes slight depression of left ventricular performance, while high levels of free fatty acids augment it. However, neither hypertriglyceridemia per se nor its rapid conversion to free fatty acids are likely to cause angina in stable patients with coronary artery disease.

Doughnut sign on bone scintigraphy in angioblastic meningioma

Bone imaging was performed in a patient with a rapidly expanding parietal bone lesion. The findings on the nuclear medicine study showed a doughnut type lesion. The underlying abnormality was found to be an angioblastic meningioma causing local bone destruction.

Time-based multiple organ functional images

Computer generation of functional images has gained recognition as a valuable method of analyzing physiologic data. However, most mathematical models used to produce these images are frequency-based, which requires that the entire function be examined. Because frequency-based characteristics are only indirectly related to physiologic characteristics, this technique has inherent deficiencies that may be minimized through various manipulations. Our technique is to base such images on time-related features, rather than frequency-based. This technique deals directly with regional count rate behavior, which in turn reflects function. Benefits from such an approach include the ability to generate images from isolated portions of an event and the removal of sinusoidal models that may or may not accurately represent function. Our experience with such an approach to the generation of functional images of the heart, lungs, and liver has been highly successful.

Effect of acute postinfusion lipemia and free fatty acids on myocardial contractility: Assessment with radionuclide ventriculography

Equilibrium gated radionuclide ventriculography was used to evaluate the effect of intravenous fat-emulsion overload and excess of free fatty acids (FFA) on left ventricular ejection fraction (LVEF) in 20 patients with and without coronary artery disease (CAD). Fifteen of these patients had normal (>50%) baseline LVEF and 5 had low (<50%) baseline LVEF. From 100 to 150 ml of 20% artificial fat emulsion (Liposyn) was infused over 20–25 min. At the end of the infusion, triglyceridemia reached 820±220 mg% and left ventricular ejection fraction decreased from baseline 62±19% (mean±SD) to 58±16% (P<0.05, paired t-test). After completion of Liposyn infusion, 5,000 U of heparin was administered intravenously and monitoring of LVEF was continuod. One and one-half hours following heparin administration, plasma FFA levels reached 3.7+2.0 mmol/l and LVEF rose to 69±19% (P<0.001, paired t-test). Our data indicate that acute intravenous fat overload can suppress and high pathophysiologic levels of FFA can increase LVEF. This effect is more uniform and statistically more reliable in patients with normal LVEF. The study failed to demonstrate any significant difference in the effect of this pharmacologic intervention between patients with and without CAD.