Indium-111 platelet scintigraphy and two-dimensional echocardiography for detection of left ventricular thrombus: Influence of clot size and age

Two-dimensional echocardiography and indium-111 platelet scintigraphy were performed on 50 dogs to determine the influence of clot age and size on the detection of experimentally induced left ventricular mural thrombus. Thrombus was induced by apical infarction and injection of a sclerosing agent and thrombin. The animals were classified jnto four groups according to the time of indium-111 platelet injection after thrombus induction: Group I (17 dogs, ½ hour after induction; 3 dogs, before induction), Group II (12 dogs, 24 hours after induction) and Group III (12 dogs, 1 week after induction). In Group IV (six control dogs) apical infarction was produced, but thrombin was not injected; indium-111 platelets were injected ½ to 1 hour after infarction. The dogs were studied by indium-111 platelet scintigraphy and by two-dimensional echocardiography ½ to 5 hours (Group I) and 1 to 5 and up to 72 hours (Groups II to IV) after platelet administration and before death was induced. Two-dimensional echocardiography showed the best overall sensitivity for detection of acute thrombus (97% ; 29 of 30). The sensitivity of indium-111 platelet scintigraphy was 86% (18 of 21) for clots ≥ 0.08 ml in size, and 67% (20 of 30) for detection of all clots. Thrombus did not form in 14 dogs of Groups I to III and in 6 of 6 control dogs. The specificity of scintigraphy was 100% (20 of 20) compared with 80% (16 of 20) for echocardiography. Echocardiography was more sensitive than scintigraphy for detecting very small clots in this experimental model. Most thrombi were detected by scintigraphy within 24 hours of injection of the labeled platelets, and the best specificity was achieved with this technique. Indium-111 platelet scintigraphy should be a useful alternative to two-dimensional echocardiography for detecting acute left ventricular thrombus after myocardial infarction.