Effect of suloctidil on tomographically quantitated platelet accumulation in Dacron aortic grafts

Selective uptake of radiolabeled annexin V on acute porcine left atrial thrombi

BACKGROUND

Annexin V is a human phospholipid binding protein that binds to activated platelets in vitro. We sought to determine the potential of this agent for imaging intracardiac thrombi in swine.

METHODS AND RESULTS

Left atrial thrombi were formed by crush injury. In initial nonimaging experiments using intravenous 125I-labeled human annexin V, the mean thrombus/whole blood ratio was 13.4 +/- 4.8 for the entire thrombus using well counting of resected specimens (n = 8). Using intravenously injected 99mTc-labeled human annexin V, the left atrial thrombus/blood ratio by well counting was similar (14.2 +/- 10.6 for the entire thrombus and 26.2 +/- 14.9 for the peak section) (n = 12). The ratio for a control protein, 125I-ovalbumin, was only 1.0 +/- 0.2. 99mTc tomographic imaging was positive (n = 10) or equivocal (n = 2) in all experiments with but negative in 10 controls without left atrial thrombi. By region-of-interest analysis of the tomographic images, the mean left atrial appendage/blood ratio at 2 hours in animals with a thrombus was 3.90 +/- 1.12 compared with 0.84 +/- 0.10 in closed chest controls and 1.01 +/- 0.23 in open chest controls (P < .001).

CONCLUSIONS

We conclude that 99mTc-labeled human annexin V detects acute left atrial thrombi in vivo in swine. The combination of a new thrombus detection agent, annexin V, with a 99mTc label may allow in vivo imaging of thrombi in humans.

Collaborative overview of randomised trials of antiplatelet therapy--I: Prevention of death, myocardial infarction, and stroke by prolonged antiplatelet therapy in various categories of patients. Antiplatelet Trialists' Collaboration

OBJECTIVE

To determine the effects of "prolonged" antiplatelet therapy (that is, given for one month or more) on "vascular events" (non-fatal myocardial infarctions, non-fatal strokes, or vascular deaths) in various categories of patients.

DESIGN

Overviews of 145 randomised trials of "prolonged" antiplatelet therapy versus control and 29 randomised comparisons between such antiplatelet regimens.

SETTING

Randomised trials that could have been available by March 1990.

SUBJECTS

Trials of antiplatelet therapy versus control included about 70,000 "high risk" patients (that is, with some vascular disease or other condition implying an increased risk of occlusive vascular disease) and 30,000 "low risk" subjects from the general population. Direct comparisons of different antiplatelet regimens involved about 10,000 high risk patients.

RESULTS

In each of four main high risk categories of patients antiplatelet therapy was definitely protective. The percentages of patients suffering a vascular event among those allocated antiplatelet therapy versus appropriately adjusted control percentages (and mean scheduled treatment durations and net absolute benefits) were: (a) among about 20,000 patients with acute myocardial infarction, 10% antiplatelet therapy v 14% control (one month benefit about 40 vascular events avoided per 1000 patients treated (2P < 0.00001)); (b) among about 20,000 patients with a past history of myocardial infarction, 13% antiplatelet therapy v 17% control (two year benefit about 40/1000 (2P < 0.00001)); (c) among about 10,000 patients with a past history of stroke or transient ischaemic attack, 18% antiplatelet therapy v 22% control (three year benefit about 40/1000 (2P < 0.00001)); (d) among about 20,000 patients with some other relevant medical history (unstable angina, stable angina, vascular surgery, angioplasty, atrial fibrillation, valvular disease, peripheral vascular disease, etc), 9% v 14% in 4000 patients with unstable angina (six month benefit about 50/1000 (2P < 0.00001)) and 6% v 8% in 16,000 other high risk patients (one year benefit about 20/1000 (2P < 0.00001)). Reductions in vascular events were about one quarter in each of these four main categories and were separately statistically significant in middle age and old age, in men and women, in hypertensive and normotensive patients, and in diabetic and nondiabetic patients. Taking all high risk patients together showed reductions of about one third in non-fatal myocardial infarction, about one third in non-fatal stroke, and about one third in vascular death (each 2P < 0.00001). There was no evidence that non-vascular deaths were increased, so in each of the four main high risk categories overall mortality was significantly reduced. The most widely tested antiplatelet regimen was "medium dose" (75-325 mg/day) aspirin. Doses throughout this range seemed similarly effective (although in an acute emergency it might be prudent to use an initial dose of 160-325 mg rather than about 75 mg). There was no appreciable evidence that either a higher aspirin dose or any other antiplatelet regimen was more effective than medium dose aspirin in preventing vascular events. The optimal duration of treatment for patients with a past history of myocardial infarction, stroke, or transient ischaemic attack could not be determined directly because most trials lasted only one, two, or three years (average about two years). Nevertheless, there was significant (2P < 0.0001) further benefit between the end of year 1 and the end of year 3, suggesting that longer treatment might well be more effective. Among low risk recipients of "primary prevention" a significant reduction of one third in non-fatal myocardial infarction was, however, accompanied by a non-significant increase in stroke. Furthermore, the absolute reduction in vascular events was much smaller than for high risk patients despite a much longer treatment period (4.4% antiplatelet therapy v 4.8% control; five year

Role of platelets and thrombosis in mechanisms of acute occlusion and restenosis after angioplasty

The vascular disruption produced by angioplasty initiates platelet deposition through the processes of platelet adhesion and recruitment of circulating platelets to form an enlarging mural platelet thrombus. Thrombin produced by simultaneous activation of the coagulation cascade by subendothelial connective tissue structures enhances platelet deposition and stabilizes the forming thrombus with enmeshing fibrin. Platelet recruitment involves the expression of the glycoprotein IIb/IIIa receptor for fibrinogen and other cytoadhesive proteins including fibronectin, thrombospondin and von Willebrand factor. Platelet deposition and thrombus formation caused by angioplasty appear to be important in the development of 2 complications: acute thrombotic occlusion and restenosis. Experimental mechanical vascular injury produces a predictable, although rather variable, amount of vascular narrowing due to transient smooth muscle cell proliferative intimal lesion formation. This intimal thickening by proliferating smooth muscle cells is in part mediated by platelet mitogens, particularly platelet-derived growth factor, which are released into the damaged vessel from platelets at the time of angioplasty. Platelet-derived growth factor may also be released from other associated vascular and blood cells in response to mechanical injury, e.g., endothelium, monocyte/macrophage and smooth muscle cells themselves. The actual mitogens, and their cells of origin, that mediate restenosis after therapeutic angioplasty remain to be established. Various oral antiplatelet agents have been shown to reduce arterial thrombotic occlusion in a number of controlled clinical trials, e.g., aspirin in transient ischemic attacks and unstable angina, aspirin and dipyridamole in saphenous vein coronary artery bypass and progression of peripheral vascular disease and dipyridamole in artificial heart valves. Acute arterial thrombosis may require more potent, immediate and transient intervention, e.g., monoclonal antibody to platelet receptor expression.(ABSTRACT TRUNCATED AT 250 WORDS)