Effects of dipyridamole and acetylsalicylic acid on platelet functions in patients with aortic ball-valve prostheses

A Critical Reappraisal of the Bleeding Time

Seminars in Thrombosis and Hemostasis (STH) celebrates 50 years of publishing in 2024. To celebrate this landmark event, STH is republishing some archival material. This manuscript represents the second most highly cited paper ever published in STH. The manuscript published without an abstract, and essentially represented a State of the Art Review on the bleeding time, a relatively invasive procedure that required an incision on the skin or earlobe of a patient, and timing how long it took for the incision to stop bleeding. The bleeding time test was first described in 1901 by the French physician Milian, who presented three studies of bleeding from stab wounds made in the fingertips of healthy and diseased subjects. In 1910, Duke observed the duration of bleeding from small incisions of the ear lobe, and pointed out that the duration of bleeding was increased in instances of reduced platelet counts. The test was subsequently repeatedly modified, and numerous variants of the test, including semiautomated methods, were described by several workers. The most frequently utilised test reflected one described by Ivy and coworkers, who shifted the location of the incision to the volar aspect of the forearm and applied a blood pressure cuff to the arm to maintain a standard venous pressure. The bleeding time has been proposed for use as a diagnostic test for platelet-related bleeding disorders, a measure of efficacy in various forms of therapy, and as a prognosticator of abnormal bleeding. The authors to the current review reevaluated the bleeding time literature using methods to assess the performance of the test in 1990, locating 862 printed documents that discussed the bleeding time, the majority in peer-reviewed professional journals. As this is a republication of archival material, transformed into a modern format, we apologise in advance for any errors introduced during this transformation.

The effect of a loading dose (300 mg) of clopidogrel on platelet function in patients with peripheral arterial disease

Clopidogrel acts on the P2Y12 adenosine diphosphate (ADP) purinergic receptors on human platelets. The aim of this study was to establish if a loading dose of clopidogrel inhibits platelet activation in patients with peripheral arterial disease (PAD). Two indices of platelet activation were considered: platelet shape change (PSC) and aggregation. Citrated blood was collected from ten PAD patients who were not on aspirin, at baseline (0 hours) and 2 and 4 hours after these patients ingested a loading dose (300 mg) of clopidogrel. ADP (5 micromo/L)-induced platelet aggregation in whole blood was inhibited after 2 hours (free platelet count, 47% +/- 19% vs. 68% +/- 15%; p < or = 0.001) and 4 hours (47% +/- 19% vs. 66% +/- 16%; p < or = 0.001). There was also a significant inhibition of 5- hydroxytryptamine (SHT, 5.0 micromol/L)-induced platelet aggregation at 2 hours. This trend was also observed for 10-micomol/L ADP-induced aggregation. ADP (0.3-0.4 micromol/L)-induced PSC was significantly inhibited at 4 hours (increase in median platelet volume, 6.3%, 1.8-10.7 vs. 1.2%, 0-5.3; p = 0.01). 5HT (0.5 micromol/L)-induced PSC at 4 hours was also significantly inhibited (8.1, 5.3-10.6 vs. 3.0, 0-8.2; p = 0.03). A loading dose of clopidogrel (300 mg) inhibits platelet activation in PAD patients, as early as 2 hours. To the authors' knowledge, no other study considered the effect of a loading dose of clopidogrel in PAD.

Antiplatelet therapy

The major clinical indication for antiplatelet therapy has been the prevention of arterial thrombosis. Arterial thrombi are composed of predominantly platelets formed under conditions of elevated shear stress at sites of atherosclerotic vascular injury and disturbed blood flow. Aspirin, the prototype antiplatelet agent, has been in clinical use as an antithrombotic for almost a half century. However, clinical trials have exposed the limitations of aspirin, and there has been considerable recent progress in the development of more effective antiplatelet agents. These newer agents are rationally based on interrupting specific sites in the sequence of platelet activation. Inhibitors of the initial step of platelet adhesion remain experimental. Inhibitors of specific platelet agonist-receptor interactions include antithrombins, thromboxane A2 receptor antagonists, and adenosine diphosphate (ADP) receptor blockers including ticlopidine and clopidogrel. Inhibitors of arachidonic acid metabolism and thromboxane A2 include omega-3 fatty acids, aspirin and other nonsteroidal antiinflammatory drugs that inhibit cyclooxygenase, and thromboxane synthase inhibitors. The clinical efficacy of many of these agents may be limited by their actions, which are restricted to single, specific platelet receptors or metabolic pathways. Global interruption of the final step of platelet aggregation can be achieved with monoclonal antibodies and RGD (arginine-glycine-aspartic acid) analogs that block ligand binding to the platelet glycoprotein IIb/IIIa complex. Initial clinical trials with these novel agents have demonstrated superior efficacy in preventing reocclusion and restenosis following coronary angioplasty and atherectomy.

Aspirin in cardiovascular disease

Although other mechanisms may be contributory, the antithrombotic properties of aspirin derive predominantly from its platelet-inhibitory effects. These are mediated via irreversible acetylation of platelet cyclo-oxygenase with subsequent blockade of platelet thromboxane synthesis. Long term administration of doses of aspirin as low as 20mg daily depresses platelet thromboxane formation by more than 90%; however, higher doses appear to be necessary to prevent thromboxane-dependent platelet activation in vivo. While there is evidence of biochemical selectivity with low doses of aspirin, significant reduction of the platelet-inhibitory eicosenoid, prostacyclin, occurs even at dosages ranging from 20 to 40mg daily. The ability of aspirin to prevent the occurrence or recurrence of vaso-occlusion has been extensively investigated. In the secondary prevention of myocardial infarction 7 placebo-controlled trials involving more than 15,000 patients have been completed. The dose of aspirin varied from 300 to 1500mg daily. Although none of the individual trials produced statistically significant reductions in total or coronary mortality, taken together the results are highly suggestive of a beneficial effect of aspirin. Similarly, 2 recent studies in patients with unstable angina demonstrated a protective effect of aspirin against acute myocardial infarction and death. While each study employed widely different doses of aspirin (324mg and 1250mg daily) similar reductions in mortality were reported. The effects of aspirin on the prevention of coronary artery bypass graft occlusion have been evaluated in 9 trials. Aspirin in doses of 100 to 975mg daily was shown to be of benefit in preventing early (less than 6 months) graft occlusion, particularly when therapy was started within 24 hours of operation. In patients with prosthetic vascular grafts of the lower limbs, aspirin has been shown to reduce platelet deposition, however further controlled trials will be required to establish the patient population most likely to benefit and, as in all these studies, the optimum dose of aspirin to employ. In patients with prosthetic heart valves it is clear that aspirin alone is insufficient to prevent thromboembolic complications and when administered as an adjunct to anticoagulant therapy it is associated with a high incidence of bleeding. In contrast, there is convincing evidence from several studies for the efficacy of aspirin in doses of 990 to 1300mg daily in the prevention of stroke and death in patients with transient ischaemic attacks.(ABSTRACT TRUNCATED AT 400 WORDS)

Thrombotic and bleeding complications of prosthetic heart valves

A review of articles published since 1979 indicates that thrombotic and bleeding complications account for about 50% of valve-related complications in patients with bioprosthetic aortic and mitral valves and for approximately 75% of the complications in patients with mechanical valves. Although compromised by lack of standard definitions and by variability in reporting and follow-up, the data suggest that the linearized rate of both thrombotic and bleeding complications in patients with aortic bioprostheses is approximately half that for aortic mechanical prostheses (2% versus 4%), but is approximately equal for both bioprostheses and mechanical valves in the mitral position (approximately 4%), and for mechanical and bioprosthetic aortic and mitral valves in combination. However, linearized rates for fatal thrombotic and bleeding events are two to four times higher in patients with mechanical prostheses. The adequacy of warfarin anticoagulation is the most important factor affecting thrombotic and bleeding complications in patients with mechanical valves and over shadows the dubious importance of other phenomena such as atrial fibrillation and left atrial thrombus. Short-term warfarin anticoagulation or the use of long-term platelet inhibitors, or both, do not appear to reduce the incidence of thrombotic complications in patients with aortic bioprostheses but increase bleeding. For mitral bioprostheses, the postoperative use of warfarin for three months or aspirin indefinitely is as effective in preventing thromboembolism as long-term warfarin. Acute prosthetic valve endocarditis is associated with a 13 to 40% incidence of thrombotic complications. Likewise, the recurrence rate of cerebral emboli is high (20-30%) in patients with prosthetic valves who are not anticoagulated. Bioprostheses are strongly preferred for women who wish to bear children; fetal wastage occurs in 25 to 30% of pregnant women with mechanical heart valves who receive either warfarin or heparin, or a combination of the two. Heparin, however, greatly increases the risk of maternal bleeding. In children, the efficacy of platelet inhibitors without warfarin anticoagulation is unproven; nearly all serious strokes occur when warfarin is omitted; and permanent disability from warfarin-related bleeding is rare. All prosthetic cardiac valves initiate coagulation and affect the dynamic equilibrium between activated procoagulants and endogenous anticoagulants. Warfarin is the only available oral exogenous anticoagulant.(ABSTRACT TRUNCATED AT 400 WORDS)

Aspirin and other antiplatelet drugs in the prophylaxis of thrombosis

Aspirin is of proven value as an antithrombotic drug. In unstable angina it reduces the risk of death and myocardial infarction by half. After a myocardial infarction it reduces the risk of death by about 10% and of coronary incidence (coronary death or definite myocardial infarction) by about 25%. These effects appear to be additive with those of beta-blocking drugs. Aspirin also reduces the risk of occlusion of aortocoronary saphenous vein grafts by about half. In transient cerebral ischaemia, aspirin may reduce the risk of stroke and death by 50%. In most clinical trials to date the daily dose of aspirin ranges from 325 mg to 1400 mg. Interest in very low doses of aspirin (less than 60 mg daily) is considerable but has yet to be translated into proven clinical benefit. Dipyridamole has not been shown to be effective as an antithrombotic when used alone. Its antiplatelet action ex vivo may be enhanced by combination with aspirin but clinical trials have shown relatively little advantage of the combination over aspirin alone. Sulphinpyrazone has not become established as a first line antithrombotic drug. Epoprostenol is useful in extracorporeal circulations to prevent platelet consumption and possibly in severe inoperable peripheral vascular disease.

Dipyridamole: a critical evaluation

Dipyridamol is a vasodilator that is used primarily in clinical practice as an antiplatelet agent. It increases coronary blood flow and was originally introduced as an antianginal agent. An ability to prolong a shortened platelet survival has been used to justify its value in preventing thromboembolic complications. Conditions characterized by a reduction in platelet survival and where dipyridamole has been used include heart valve replacement, arterial grafting, cerebrovascular disorders, and disorders of peripheral circulation. The in vivo effect of dipyridamole on platelet aggregation has not been well defined and may depend on additional factors. Prostaglandins appear to have important roles in platelet homeostasis; their relationships to the action of dipyridamole are discussed. Dipyridamole usually is combined with aspirin for synergistic anti-aggregatory purposes. However, the nature of the interaction has not been elucidated and benefit from the addition of dipyridamole has not been demonstrated in clinical studies. A review of clinical studies using dipyridamole indicates that it currently has limited value.

Effect of suloctidil on platelet function in patients with shortened platelet survival time

The effect of suloctidil (600 mg/day) on platelet survival time (PST) and plasma and urine betathromboglobulin (BTG) was studied in a double-blind, placebo-controlled six-week crossover trial in 13 patients with shortened PST (less than 110 hrs, exponential model). Mean PST after suloctidil (110.6 hrs) was significantly higher than in the placebo phase (94.5 hrs) (p = 0.04). Mean plasma BTG was significantly lower during the suloctidil phase (42.8 ng/ml) compared with the placebo phase (65.8 ng/ml) (p = 0.02), but there was no significant difference in urine BTG. These results suggest that suloctidil provides a platelet protective effect and therefore may be of benefit in reducing the frequency of platelet mediated thromboembolic events.

Indexes of intravascular hemolysis, quantification of coagulation factors, and platelet survival in patients with porcine heterograft valves

Ten patients with porcine heterograft valves who were not receiving anticoagulant agents were evaluated to determine the effect of the valve on red blood cell survival and on platelet activation and consumption as measured by (1) quantification of the coagulation mechanism, (2) platelet function studies, and (3) 51-chromium platelet survival time. There was no evidence of significant intravascular hemolysis as determined by the reticulocyte count, serum iron and iron binding capacity, serum bilirubin level, or lactic dehydrogenase activity. The coagulation profile and the platelet function studies were normal. No statistically significant difference was found in the platelet survival time in the 10 patients with porcine heterograft valves (half-life 3.2 +/- 0.8 days) and the 11 normal control subjects (half-life 3.6 +/- 0.6 days) (p greater than 0.2). The finding of a normal platelet survival time in patients with porcine heterograft valves is consistent with clinical experience indicating that this device is associated with a low incidence of systemic embolization, approximating 3% per year.

The effects of nifedipine, a calcium antagonist, on platelet function

Platelet function was studied before and 1 hour after ingestion of 20 mg nifedipine, a new calcium antagonist, in 20 patients with coronary heart disease. Platelet counts remained unchanged. Platelet adhesiveness, measured as retention in glass bead columns with Hellem's method for native blood, did not drop significantly eigher when 0.9 or 3.6 ml of blood was used. Platelet aggregation, which is dependent on extracellular calcium, was induced in citrated platelet-rich plasma. The mean maximal rate of primary aggregation, initiated with three different concentrations of adenosine diphosphate, was reduced by 20% to 26%. The rate of irreversible collagen-induced aggregation was on average 23% lower after nifedipine. The mean bleeding time was 36 seconds, or 12%, longer after ingestion of the drug. The moderate, but significant reduction of platelet aggregation and prolongation of the bleeding time by nifedipine may be mediated through inhibition of calcium transport across the platelet membrane.

Toxicity of combined therapy with carbonic anhydrase inhibitors and aspirin

A 67-year-old woman and a 75-year-old woman taking carbonic anhydrase inhibitors for therapy of glaucoma and high doses of aspirin for therapy of arthritis developed severe acid-base imbalance and salicylate intoxication. Neither patient exhibited ill effects when taking high aspirin doses without carbonic anhydrase inhibitor. Carbonic anhydrose inhibitor-induced acidemia increases the risk of developing salicylate intoxication in patients receiving high aspirin doses.

Anticoagulants and the Björk-Shiley prosthesis. Experience of 390 patients

From September 1972 to January 1975, 390 patients underwent valve replacement using the Björk-Shiley tilting disc prosthesis. For the group as a whole hospital mortality was 13.3 per cent and was lowest in those undergoing isolated mitral or aortic valve replacement (5.3 and 9.4%, respectively). Available for follow-up were 209 patients of whom 123 were maintained on dipyridamole and 96 on warfarin. Thromboembolic complications were significantly (P less than 0.01) commoner in the dipyridamole (28 of 123, 22%) than warfarin (6 of 86, 7%) treated group. In the dipyridamole treated group the incidence of thromboembolic complications was similar whichever valve was replaced and thromboembolic complications were responsible for 14 of the 28 late deaths. In the warfarin treated group thromboembolic complications only occurred in patients with a mitral prosthesis. Anticoagulation is indicated for all patients with this prosthesis wherever inserted.

Influence of sulphinpyranzone (Anturan) on thrombo-elastography

Sulphinpyrazone (Anturan, 200 mg four times daily) was administered orally to 10 patients for two weeks. Thrombo-elastographic determinations revealed no disturbance of coagulation and it may therefore be concluded that Anturan can also be safely administered pre-operatively.

Platelet functions in patients with aortic ball valves

Platelet functions were studied in normal subjects and patients with single Staff-Edwards aortic ball valves of series 1200 and 2300. The most pronounced changes were found in platelet adhesiveness, measured with Hellem's modified method. The mean percentage of adhesive platelets was reduced from 71.8 in normal subjects to 50.9 in patients with valve type 1200 and to 27.2 in those with type 2300. An inverse correlation was found between platelet adhesiveness and the degree of intravascular hemolysis, as reflected by serum LDH levels. The mean bleeding time was significantly prolonged in patients with valve 2300, and the individual values correlated inversely to the adhesiveness. The mean values of platelet counts, or irreversible aggregation induced by collagen or epinephrine, and of platelet survival were all moderately-but significantly-reduced as compared to normal. The most important mechanism behind the disturbed platelet reactivity is probably mechanical damage of the platelets by the valve, whereas refractoriness of platelets toward ADP liberated from red cells as well as consumption of adhesive platelets by thrombus formation is thought to have limited influence on platelet behavior. Platelet function was altered to the same extent in patients with a history of arterial thromboembolic complications as in those without. The disturbed platelet reactivity may predispose to bleeding, but may also offer some protection against arterial thromboembolism.

Prevention of arterial thromboembolism with acetylsalicylic acid. A controlled clinical study in patients with aortic ball valves

Prevention of arterial thromboembolism with acetylsalicylic acid (ASA) was studied in 148 patients with single Starr-Edwards aortic ball-valve prostheses. These patients are suitable for such a study because they have a high incidence of arterial emboli derived mainly from thrombi formed on the valves. They were given either 1 Gm. of ASA daily or placebo in combination with anticoagulants, and were observed for 2 years. Only two emboli occurred in patients receiving ASA, none of them severe. In the placebo group 12 thromboembolic episodes were diagnosed in 10 patients, and three with cerebral emboli died; in one a subdural hematoma unrelated to the embolus was found. In addition, one fatal and the one nonfatal intracranial bleeding occurred in each group, whereas gastrointestinal complications were seen more frequently in patients taking ASA. It is concluded that ASA combined with anticoagulants offered a significantly better protection against arterial thromboembolism than did anticoagulant therapy alone.

Surface ultrastructure of silicone rubber aortic valve poppetts after long-term implantation. A scanning electron microscope study of four poppets

The surface ultrastructure, demonstrated by scanning electron microscopy, is described in four implanted Silastic aortic valve poppets. Ball variance was discovered at necropsy in two patients and clinically in one in whom the poppet was replaced. The fourth patient underwent reoperation, but ball variance was neither suspected nor found. All four poppets were densely coated with biological debris and microthrombi. The 'coat' was soluble in a weak solution of sodium hydroxide. The true Silastic surface beneath the coat was little altered compared with unimplanted poppets, even after 10 years' implantation.