CLINICAL AND EXPERIMENTAL STUDIES OF PULMONARY EMBOLISM USING 111INDIUM-LABELED PLATELETS

Abstract

We studied the use of 111-labeled autologous platelets (111In-P) for diagnosis of pulmonary emboli (P.E.) in four humans and 41 dogs.

Canine thrombi were induced in jugular vein segments using thrombin and/or stasis; the results of the two methods were similar. The effect of short term bolus heparinization, thrombus age and embolus age were studied. Heparinization of the animal blocked visualization of emboli, but when heparin effect decayed (PTT returned towards normal) emboli could be detected. Detection of acutely embolized thrombi as old as 48 hours was possible in 50% of animals, but only 8% of 48 hour old emboli were localized. The ability of 111In oxine and 111InCl3 alone to detect emboli was investigated; no emboli were visualized with 111InCl3, but 27% of emboli were detected using intravenous injection of 111In oxine in saline solution. We also performed in vitro radiation counting and histologic studies of excised emboli which strongly suggest that emboli may propagate while lodged in the pulmonary arteries.

Four patients were studied. Two received infusion heparin for presumed emboli but did not have angiography; no persistent focal 111In activity was visible on scintigraphy. Two patients had angiography. In these two cases the patients' heparin therapy was interrupted prior to 111In-P injection (a routine precaution prior to angiography in our institution). One had a normal angiogram, but the second had both a positive angiogram and 111In-P scan. This is the first angiographically documented case in which P.E. was detected in man with 111-In-P. In other reported patients, heparin therapy has not been interrupted and the 111In-P studies have been negative. Future clinical studies of 111In-P should be performed either prior to initial anticoagulation or in conjunction with interruption of heparin therapy.

This work supported in part by NIH Grant NO1HR92904