111In platelet imaging of left ventricular thrombi. Predictive value for systemic emboli.

Abstract

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 "'1In 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%7o), platelet-inhibitory therapy during follow-up (50% vs. 33%), injected "1'In dose (330±+92 vs.344±118 ,uCi), 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=O0.07). 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. (Circulation 1990;81:1182-1189 L eft ventricular thrombi occur in approximately one third of patients with either transmural anterior myocardial infarction or advanced idiopathic congestive cardiomyopathy.1,2 Thrombi that are hematologically active with ongoing platelet deposition can be detected by indium 111 platelet imaging as localized areas of increased labeled plate-

Left ventricular thrombus formation after acute myocardial infarction

“…w42 In indium-111 platelet imaging studies most thrombi, regardless of age, have been observed to have externally detectable ongoing platelet accumulation, indicating continued surface activity. 20 The European guidelines recommend vitamin K antagonist for at least 3e6 months, while the American guidelines recommend indefinite treatment in patients without increased risk of bleeding.…”

Molecular imaging of platelet activation in thrombus

“…The method proved to be sensitive for the detection of left ventricular thrombi in humans, 49,50 and was predictive of the occurrence of systemic emboli. 51 Of note, the uptake of 111 In-labeled platelets declined with time in chronic thrombi, owing to a decreased platelet incorporation. 52,53 In infective endocarditis, the technique provided the means of directly observing the pathogenic role of blood cellular components within the vegetation.…”

Noninvasive arterial thrombus imaging with 99mTc monoclonal antifibrin antibody.

“…The variability in T2G1s uptake shown in the histological sections is reflected in the well-counting data. Figure 3 shows the results from a single dog of a well-counted femoral thrombus sectioned into 4. Bar graphs of artery-or thrombus-to-blood ratios (mean ±SEM) shown for control artery (n = 13), injured artery (n=23), and thrombus (n=23), using average uptake for all 5-mm segments or segment with maximal uptake of T2GJs.…”

“…The thrombi weighed 218±+140 mg. Antibody uptake in the thrombi was patchy, and the thrombi were closely adherent to the injured arterial wall. In the segment with maximal ex vivo antibody uptake, the ratio of control artery to blood counts/g/sec was 0.65 ±0.46, the injured artery-to-blood ratio was 2.35± 1.01 (p<0.0001 versus control), and the thrombus-to-blood ratio was 4 A novel imaging approach is the use of specific antibodies directed at various thrombus components. One such antibody, T2G1s, reacts specifically with the first seven amino acids of the fibrin fl-chain.5 A similar antifibrin antibody, 59D8, reacts with the same por-tion of the /3-chain.…”