IN-111 PLATELET IMAGING OF LEFT-VENTRICULAR THROMBI - PREDICTIVE VALUE FOR SYSTEMIC EMBOLI

To determine whether a positive indium 111 platelet image for a left ventricular thrombus, which indicates ongoing thrombogenic activity, predicts an increased risk of systemic embolization, we compared the embolic rate in 34 patients with positive 111 In platelet images with that in 69 patients with negative images during a mean follow-up of 38∓31 (∓SD) months after platelet imaging. The positive and negative image groups were similar with respect to age (59∓11 vs. 62∓10 years), prevalence of previous infarction (94% vs. 78%, p<0.05), time from last infarction (28∓51 vs. 33∓47 months), ejection fraction (29∓14 vs. 33∓14), long-term or paroxysmal atrial fibrillation (15% vs. 26%), warfarin therapy during follow-up (26% vs. 20%), platelet-inhibitory therapy during follow-up (50% vs. 33%), injected 111 In dose (330∓92 vs. 344∓118 μCi), and latest imaging time (≥48 hours in all patients). During follow-up, embolic events occurred in 21% (seven of 34) of patients with positive platelet images for left ventricular thrombi as compared with 3% (two of 69) of patients with negative images (p=0.002). By actuarial methods, at 42 months after platelet imaging, only 86% of patients with positive images were embolus free as compared with 98% of patients with negative images (p<0.01). To determine whether platelet imaging, which detects active thrombosis, offered additional predictive value to two-dimensional echocardiography, which is less costly and more widely available, we compared the embolic rates in 30 patients with both a positive echocardiogram and a positive platelet image to the rate in 28 patients with a positive echocardiogram but a negative platelet image. Among patients with both studies positive, embolic events occurred in 23% (seven of 30) versus 4% (one of 28) in patients with a positive echocardiogram but a negative platelet image (p=0.03). The corresponding actuarial rates at 42 months were 85% and 100% (p=0.07). We conclude that a positive platelet image for a left ventricular thrombus predicts an increased embolic risk and appears more specific for subsequent embolization than a positive echocardiogram. Additionally, in patients with left ventricular thrombus by echocardiography, a negative platelet image predicts a low risk of subsequent embolization. These findings suggest that thrombosis imaging might be useful to assess the risk of thromboembolic complications in patients with arterial thrombosis.