Usefulness of fish oil supplements in preventing clinical evidence of restenosis after percutaneous transluminal coronary angioplasty

The restenosis paradigm revisited: an alternative proposal for cellular mechanisms

Coronary restenosis is a reparative response to arterial injury during angioplasty, and remains a major clinical problem. The reasons for treatment failures likely stem from our incomplete understanding of the cellular mechanisms in restenotic neointimal formation. Restenosis is thought to result from migration and replication of medial smooth muscle cells to form an obstructive neointima, a concept neither observed nor demonstrated in humans. An alternative hypothesis for restenosis is based on observations in the porcine coronary injury model. In this model, there are three cellular stages in neointimal formation: thrombotic (stage I), cellular recruitment (stage II) and proliferative (stage III). The thrombotic stage occurs early and consists of platelets, fibrin and red blood cells accumulating at the vessel injury site. In the recruitment stage, the mural thrombus itself develops an endothelium, followed by a mononuclear leukocytic infiltrate beginning on the lumen side of the vessel. In the proliferative stage, a "cap" of actin-positive cells forms on the lumen surface and progressively thickens. These cells do not arise from media at the injury site. Extracellular matrix secretion and additional recruitment likely add to neointimal volume during this phase. Thrombus assumes a major role in restonosis by providing an absorbable matrix into which smooth muscle cells proliferate. Further studies are needed to validate or modify this hypothesis.

Plasma lipid levels and platelet and neutrophil function in patients with vascular disease following fish oil and olive oil supplementation

This double-blind study was designed to examine and compare the effects of supplementing the existing diet with fish oil or olive oil on lipids and cell function in patients with peripheral vascular disease. Thirty-two patients with symptomatic and angiographically demonstrated peripheral vascular disease were screened, matched, and randomly allocated to take either 15 g/d fish oil or olive oil for 4 weeks. Fish oil reduced serum triglyceride levels by 26%, but increased total cholesterol levels due to a significant increase in both low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein-2 cholesterol (HDL2-C). There was a nonsignificant decrease in HDL3-C levels. Olive oil reduced total cholesterol levels, accountable to a significantly decrease in LDL-C levels. Serum thromboxane B2 (TXB2) levels remained unchanged following fish oil, but were significantly increased by olive oil. Urinary excretion of TXB2 and 6-keto-PGF1 alpha was unaffected by either oil supplement. Platelet aggregation, which was measured in platelet-rich plasma in response to two doses of collagen or platelet-activating factor (PAF), was significantly reduced after fish oil, but was increased by olive oil. Following fish oil, there was a significant increase in eicosapentaenoic acid (EPA, 20:5) and docosahexaenoic acid (DHA, 22:6) levels and a decrease in arachidonic acid content of platelet phospholipids. The platelet fatty acid composition after olive oil was unchanged. Fish oil decreased neutrophil leukotriene B4 (LTB4) generation following calcium ionophore stimulation by 33%, while leukotriene B5 levels increased significantly. Neutrophil PAF production and plasma lyso-PAF were unaffected by either oil.(ABSTRACT TRUNCATED AT 250 WORDS)

The acute effect of a single very high dose of N-3 fatty acids on coagulation and fibrinolysis

The objective of the study was to investigate the acute effect of a single very high dose of n-3 PUFA on coagulation and fibrinolysis. Forty healthy volunteers were randomized into two groups to receive either 20 grams of n-3 PUFA or 20 grams of n-6 PUFA as a single dose at 6 p.m. with their evening meal. Coagulation and fibrinolysis were evaluated in the fasting state at 8 a.m. the next morning and compared to values obtained at 8 a.m. the day before, when the participants were on their habitual diets. PAI-1 activity in plasma increased by a mean of 62% in subjects randomized to receive n-3 PUFA despite that no changes could be demonstrated in t-PA antigen levels. PAI-1 activity was unaltered in the 20 controls receiving n-6 PUFA. Plasma fibrinogen, coagulation factor VII, thrombin-antithrombin complexes and D-dimer did not significantly change after either supplement. The substantial increase in levels of PAI-1 activity in plasma after a single very high dose of n-3 PUFA may limit the usefulness of single very high doses of n-3 PUFA in acute clinical conditions.

Fish oil supplements for prevention of restenosis after coronary angioplasty

We have evaluated the effect of fish oil supplementation in the prevention of restenosis after percutaneous transluminal coronary angioplasty by a randomised trial conducted in 107 patients. The treatment group (n = 58, 96 significant coronary narrowings) received 10 capsules of fish oil (1.8 g eicosapentaenoic acid, 1.2 g docosahexaenoic acid) besides aspirin and calcium blockers, beginning 4.3 (SD 2.9) days before coronary angioplasty. The conventional medical treatment group (n = 49, 81 significant coronary narrowings) received only aspirin and calcium blockers. Enrollment required the presence of angina pectoris and successful dilatation of all significant coronary narrowings. All patients were followed-up for at least 6 months. Restenosis was identified by symptoms and exercise testing and confirmed by angiography. The incidence of angiographic restenosis was 32% in the fish oil group and 27% in the conventional treatment group. Biochemical investigations showed a greater decrease in serum triglyceride levels in fish oil group as compared to the conventional treatment group. There was no significant difference in the cholesterol levels over the treatment period. Administration of fish oil in a dose of 3 g per day did not reduce the incidence of early restenosis after coronary angioplasty.

Double-blind, randomized, controlled trial of fish oil supplements in prevention of recurrence of stenosis after coronary angioplasty

BACKGROUND

Previous studies suggest that recurrence of coronary stenosis after percutaneous transluminal coronary angioplasty (PTCA) might be prevented with dietary supplements rich in omega-3 fatty acids. The purpose of the present study was to evaluate this hypothesis. In addition, the relation between usual dietary consumption of omega-3 fatty acids and restenosis was assessed.

METHODS AND RESULTS

A double-blind, randomized, controlled trial was conducted in which 205 patients undergoing a first PTCA received 15 capsules per day containing 1 g of either fish oil (2.7 g/day of eicosapentaenoic acid, 1.8 g/day of docosahexaenoic acid) or olive oil. The treatment was started 3 weeks before PTCA and continued for 6 months thereafter. Dietary intake was assessed by food frequency questionnaire. At 6 months after PTCA, patients underwent a control angiography. All angiographic lesions were measured by quantitative computer analysis. Four criteria were used to define restenosis. Restenosis occurred less often in the fish oil group (22.0-35.6% depending on the definition) than in the control group (40.0-53.3%). After controlling for other risk factors of restenosis, the association of fish oil supplementation with a lower frequency of restenosis was statistically significant (p = 0.03) for three of four definitions. After adjustment, a dietary intake of omega-3 fatty acids of more than 0.15 g/day was also associated with a lower frequency of restenosis (p less than or equal to 0.03).

CONCLUSIONS

This trial documented the protective effect of fish oil supplements on the recurrence of coronary stenosis 6 months after PTCA. The study results suggest that a dietary intervention could be useful in preventing restenosis.

The paradoxical effects of dietary fish oil on blood pressure

Dietary fish oil supplementation has received considerable interest as a non-pharmacological adjuvant in the treatment of several diseases, especially hypertension. However, epidemiological, clinical, and experimental evidence conflict. A hypothesis is proposed that fish oil, may have a variable effect on vascular reactivity and consequently, blood pressure. A mechanism is proposed and reasons for the variation in the literature suggested. On the basis of this analysis a potentially adverse effect of dietary fish oil on blood pressure in some individuals is suggested.

Fish oils in the prevention of atherosclerosis

The hypothesis that oils derived from the flesh of fish and marine mammals inhibit the atherosclerotic process is critically reviewed. Populations consuming a diet rich in fish have low rates of coronary heart disease. Dietary fish oil is associated with changes in serum lipids, prostaglandin and leukotriene metabolism, enhanced endothelial function and effects on growth factors released from platelets, leukocytes and endothelial cells. Dietary fish oil supplementation has been associated with inhibition of atherosclerosis experimentally induced by dietary hyperlipidemia and balloon injury. Results of studies of the use of fish oil to inhibit postangioplasty restenosis in human subjects have been inconclusive.

Lipids and fatty acids and their relationship to restenosis

One hundred consecutive patients had fasting lipids and percutaneous fat biopsy performed at the time of percutaneous transluminal coronary angioplasty to determine if there was an association between restenosis and lipids or fatty acids. Angiographic follow-up and complete lipid and fatty acid results were available in 82 patients. Restenosis occurred in 37/82 (45%). Total cholesterol, triglyceride, high density lipoprotein, low density lipoprotein, and apolipoproteins A1 and B were not associated with restenosis. There was a significantly lower level of the monounsaturated fat palmitoleic acid (p less than 0.02), a trend towards a lower level of the monounsaturated fat oleic acid (p less than 0.09), and a trend towards a higher level of the saturated fat palmitic acid (p less than 0.08) in the restenosis group. The polyunsaturated fatty acids were not associated with restenosis. We conclude that lipids are not significantly associated with restenosis, and that lower levels of monounsaturated fatty acids may increase the risk of restenosis.

Effects of low-dose aspirin on restenosis after coronary angioplasty

After angioplasty of a previously untreated native coronary artery and after 2 weeks of aspirin therapy, 216 subjects (aged less than 70 years without acute infarction) were randomized to treatment with soluble aspirin, 100 mg/day, or placebo to study the effect on restenosis. Follow-up, defined as angiography at 6 months, earlier angiographic restenosis or coronary bypass surgery was completed by 108 aspirin- and 104 placebo-treated patients. Restenosis (stenosis greater than or equal to 50% plus loss of greater than or equal to 50% of gain, or surgery) occurred in 38 (35%) aspirin- and 45 (43%) placebo-treated subjects (p = not significant). No patient died. Restenosis occurred in 42 of 168 (25%) aspirin- and 51 of 135 (38%) placebo-treated lesions (p less than 0.025). Aspirin-treated lesions (n = 163) had lost 16 +/- 22% (mean +/- standard deviation) of lumen and placebo-treated lesions 22 +/- 25% of lumen (n = 134) at angiography (p less than 0.01). There were more left anterior descending lesions in the placebo group and these had a higher recurrence rate than other lesions. The beneficial effect of aspirin was not dependent on this, although significance was reduced in subgroup analysis. Loss of lumen in left anterior descending lesions was 20 +/- 24% (n = 57) in the aspirin-treated and 27 +/- 25% (n = 70) in the placebo-treated lesions (p less than 0.1). It is concluded that there is a small beneficial effect of low-dose aspirin on restenosis after coronary angioplasty.(ABSTRACT TRUNCATED AT 250 WORDS)

[New developments of antiplatelet drugs]

A better knowledge of platelet activation mechanisms has made it possible to develop antiplatelet agents that are capable of inhibiting primary haemostasis at very precise levels. Many of these agents block the synthesis or receptor of an hemostasis I agonist. Thus, the thromboxane A2 receptor can be blocked, or its synthesis can be interrupted, by thromboxane synthetase inhibitors, by cyclooxygenase inhibitors, or by omega 3 fatty acids which are competitive inhibitors. Inhibitors of thrombin (hirudin), PAF acether and serotonin (ketanserin) also are available. Other antiplatelet agents secreted by endothelial cells act as haemostasis I antagonists by elevating platelet cAMP or cGMP levels (prostacyclins and analogues, nitrate derivatives). Monoclonal antibodies and RGD peptides directly inhibit the glycoproteins that are responsible for platelet adhesion or aggregation, but their users are faced with problems of cost and route of administration. Of all these new antiplatelet agents, only ticlopidine, which has an imperfectly known mode of action, has proved effective in multiple situations, but its use is limited by its side-effects.

Clinical, physiologic, anatomic and procedural factors predictive of restenosis after percutaneous transluminal coronary angioplasty

In a recent prospective double-blind placebo-controlled trial, a combination of aspirin and dipyridamole was not associated with a reduction in the rate of restenosis within the 1st 6 months after coronary angioplasty. The purpose of this study was to determine whether clinical, anatomic or procedural factors were predictive of the observed restenosis rates in that prospective trial. A total of 247 patients and 280 segments underwent follow-up angiography and quantitative coronary angiographic analysis between 4 and 7 months after coronary angioplasty. Two baseline clinical characteristics--angina class and duration of angina in months--were related to the rate of restenosis by univariate analysis. Patient-related stepwise logistic regression analysis identified severity of angina as the only clinical predictor of restenosis. Three univariate baseline anatomic characteristics--percent diameter stenosis before angioplasty, stenosis greater than 10 mm in length and calcific stenosis--and two early postangioplasty characteristics--residual percent diameter stenosis and residual mean pressure gradient--were predictive of restenosis. Of these, only two--length of stenosis and residual percent diameter stenosis--were independently related to restenosis by multivariate analysis and only the former is identifiable before the procedure. It is concluded that in prospective studies in contrast to retrospective studies, few clinical and anatomic factors appear to be predictive of restenosis after coronary angioplasty.

Suppression of eicosanoid biosynthesis during coronary angioplasty by fish oil and aspirin

BACKGROUND

Percutaneous transluminal coronary angioplasty (PTCA) is an acute, localized stimulus to platelet and vascular function. Periprocedural cardiovascular complications are reduced by moderate-dose aspirin (ASA), presumably due to inhibition of thromboxane (TX) A2.

METHODS AND RESULTS

Excretion of TXA2 and prostacyclin (PGI2) metabolites in urine increased during PTCA. Pretreatment for 3 days with either moderate- (325 mg/day) or low-dose (80 mg/day) ASA inhibited the increase in both eicosanoids. Pretreatment for 3 weeks with fish oil (10 g/day) only partially suppressed TXA2. Formation of trienoic eicosanoids and accumulation of omega-3 fatty acids in platelet membranes confirmed fish oil ingestion. Although basal PGI2 was not inhibited, the PTCA-related increment was suppressed.

CONCLUSIONS

PTCA results in an acute, transient alteration of eicosanoid biosynthesis consistent with accelerated platelet-vascular interactions. Pretreatment for 3 days with moderate or low doses of ASA suppresses TXA to a similar extent during PTCA, and their effects on acute cardiovascular complications of this procedure are likely to be comparable. It is unlikely that even prolonged pretreatment with fish oil can substitute for the platelet inhibitory action of ASA during PTCA. Suppression of PGI2 may contribute to the residual acute periprocedural complication rate in patients taking ASA.

Prevention of restenosis by lovastatin after successful coronary angioplasty

Prevention of restenosis after successful percutaneous transluminal coronary angioplasty (PTCA) remains a major challenge. To determine whether lovastatin could prevent restenosis, between December 1987 and July 1988, a total of 157 patients undergoing successful PTCA were randomly and prospectively assigned to the lovastatin group or a control group. Seventy-nine patients received lovastatin (20 mg daily if the serum cholesterol level was less than 300 mg/dl and 40 mg daily if the serum cholesterol level was greater than or equal to 300 mg/dl) in addition to conventional therapy (lovastatin group). Seventy-eight patients received conventional therapy alone (control group). Fifty patients in the lovastatin group and 29 in the control group were evaluated with coronary angiography at an interval of 2 to 10 months (mean 4 months). The restenosis rate was evaluated according to the number of patients showing restenosis, the number of vessels restenosed, and the number of PTCA sites restenosed. Restenosis was defined as the presence of greater than 50% stenosis of the PTCA site. In the lovastatin group 6 of 50 patients (12%) had restenosis compared with 13 of 29 patients (44.4%) in the control group (p less than 0.001). When the number of vessels restenosed was considered, only 9 of 72 vessels (12.5%) restenosed in the lovastatin group compared with 13 of 34 vessels (38.2%) in the control group (p less than 0.002). Similarly, 10 of 80 (12.5%) PTCA sites restenosed in the lovastatin group compared with 15 of 36 (41.7%) in the control group (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary restenosis: what have we learned from angiography?

Coronary restenosis remains a major problem for interventional cardiology not only by virtue of its frequency, but also because of the current inability to prevent it. Symptomatic status and non-invasive evaluation have been used to study restenosis, but both lack specificity and sensitivity, particularly in patients with multivessel disease. Angiography remains the reference standard. Several arbitrary definitions have been used, some related to visual estimates of coronary stenosis and others to quantitative angiographic techniques. In another approach, linear modeling is used to assess minimal luminal diameter of lesions on restudy. Although angiographic studies have been essential in the study of restenosis, questions concerning the underlying mechanism and pathophysiology remain. The development of animal models that closely resemble human restenosis should allow evaluation of pathophysiologic mechanisms and development of new strategies to prevent the problem.

Restenosis after coronary angioplasty: an overview

Despite substantial basic and clinical efforts to address the problem of restenosis after percutaneous coronary intervention, effective preventive therapies have not yet been developed. Nevertheless, the accumulated information has provided much insight into the process of restenosis in addition to allowing standards to be developed for adequate clinical trials. The pathophysiology of restenosis increasingly appears to be distinct from that of primary atherosclerosis. Restenosis involves elastic recoil, incorporation of thrombus into the lesion and fibrocellular proliferation in varying degrees in different patients. Lack of an animal model that satisfactorily mimics restenosis is a major impediment to further understanding of the process. Clinical studies are hampered by difficulties in finding a single unifying definition of restenosis and by variable methods of reporting follow-up. Reporting of clinical outcomes of all patients in angiographic substudies would allow a more satisfactory interpretation of the results of clinical trials. Current noninvasive test results are not accurate enough to substitute for angiographic and clinical outcome data in intervention trials. In the majority of observational studies, only diabetes and unstable angina have emerged as consistently associated with restenosis; whereas most of the standard risk factors for atherosclerosis have a less consistent relation. Disappointingly, the new atherectomy and laser technologies have not affected restenosis rates. The one possible exception is coronary stenting, as a result of the larger luminal diameter achieved by the placement of the stent. In conclusion, although substantial continued effort is necessary to explore the basic aspects of cellular proliferation and mechanical alteration of atherosclerotic vessels, attention to the principles of clinical trials and observation are required to detect the impact of risk factors and interventions on the multifactorial problem of restenosis. Adequate sample sizes, collection of clinical and angiographic outcomes and factorial study designs hold promise for unraveling this important limitation of percutaneous intervention.

Effect of lovastatin on intimal hyperplasia after balloon angioplasty: a study in an atherosclerotic hypercholesterolemic rabbit

Restenosis, the major limitation of balloon angioplasty, is the result of intimal hyperplasia after the procedure. Lovastatin, a 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) inhibitor, may influence intimal hyperplasia by lowering serum cholesterol and by blocking deoxyribonucleic acid (DNA) synthesis. To determine whether lovastatin reduces intimal hyperplasia, a prospective, randomized blinded study was performed in 60 atherosclerotic New Zealand White male rabbits. Atherosclerosis was produced by air desiccation injury followed by a 28 day diet of 2% cholesterol and 6% peanut oil that was terminated before balloon angioplasty was performed. Angioplasty could not be performed in 14 rabbits with bilateral femoral artery occlusion, and in one rabbit the procedure was a technical failure. Forty-five rabbits underwent balloon angioplasty performed with use of a 2.5-mm balloon inflated to 10 atm for three 1 min dilations at 1 min intervals. Seven rabbits died during the procedure. Thirty-eight rabbits were randomized to either a lovastatin group (6 mg/kg body weight per day) or a control group. Angioplasty was performed on all patent vessels (n = 54); the procedure was bilateral in 16 rabbits and unilateral in 22. Fifteen lovastatin-treated and 15 control rabbits survived 39 days after angioplasty and were then killed. Angiograms, obtained before and 10 min and 39 days after balloon angioplasty, were read with use of electronic calipers by two observers who had no knowledge of treatment data. After the rabbits were killed, vessels were pressure perfused using a standardized protocol to maintain in vivo dimensions for blinded quantitative histologic analysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Polyunsaturated fatty acids and coronary heart disease

Polyunsaturated fatty acids can be used to replace saturated fatty acids in the diet in order to decrease plasma cholesterol concentrations. Intakes of up to 12% of the energy intake as linoleic do not decrease HDL cholesterol. Animal studies show a decreased incidence of atherosclerosis in animals fed polyunsaturated fats compared with saturated fats. Linoleic acid is required for the synthesis of eicosanoids, which are important in the regulation of platelet aggregation, blood pressure and coronary flow. Small amounts of linoleic acid are required for normal eicosanoid synthesis but larger intakes may lead to overproduction of eicosanoids. Dietary eicosapentaenoic and docosahexaenoic acids, which are provided by fish oils, have a protective effect on experimental myocardial infarction. Epidemiological evidence and secondary prevention trials suggest that these marine-derived polyunsaturates offer protection from CHD. Current advice on fat intake needs to be revised to take into account the neutrality of monounsaturated fatty acids and the need to balance the different types of polyunsaturated fatty acids.

Dietary fish oil accelerates the response to coronary thrombolysis with tissue-type plasminogen activator. Evidence for a modest platelet inhibitory effect in vivo

To assess the platelet inhibitory effect of high doses of fish oils and relate it to alterations in eicosanoid synthesis, we used a canine model in which coronary thrombosis, the time to reperfusion induced by recombinant tissue-type plasminogen activator (rt-PA), and the rate of spontaneous reocclusion are sensitive to platelet inhibition. In the animals fed fish oil, the time to rt-PA induced thrombolysis was accelerated (mean, 63 vs. 27 minutes; p less than 0.003). The time to thrombotic occlusion and the rate of reocclusion were unaltered. The ratio of eicosapentaenoic acid (EPA) to arachidonic acid rose in platelet and endothelial cell membranes, whereas serum thromboxane (Tx) B levels fell a mean 86%, and basal excretion of 2,3-dinor-TxB2 (TxA2-M) declined. Basal prostaglandin (PG) I2 formation was unaltered, whereas biosynthesis of EPA-derived TxA3 and PGI3 increased. In control animals, TxA2 formation increased during thrombosis; there was a further, more marked rise during reperfusion. PGI2 formation also increased, probably as a response to platelet-vascular interactions. Stimulated production of both eicosanoids was strikingly suppressed in the animals fed fish oil. Fish oils significantly enhance the efficacy of rt-PA in vivo, albeit to a modest extent. Because the time to reperfusion is highly sensitive to Tx-dependent platelet activation, this effect is likely to reflect the demonstrated suppression of TxA2 biosynthesis by fish oils.

Effect of short-term prostacyclin administration on restenosis after percutaneous transluminal coronary angioplasty

The effect of short-term prostacyclin (PGI2) administration on the incidence of restenosis after coronary angioplasty was studied in a prospective single-blind randomized trial of 286 patients. Of the 270 patients in whom dilation was successful, 134 received prostacyclin and 136 received placebo. Intracoronary prostacyclin was administered before and after dilation and then intravenously for 48 h. The control group received intracoronary placebo infusions before and after dilation. All patients received aspirin and dipyridamole before and after angioplasty, at least until follow-up angiography. Follow-up angiograms were obtained in 93% of patients in whom angioplasty was successful. Restenosis of one or more lesions was present in 34 patients (27%) who were given prostacyclin compared with 40 patients (32%) in the control group (p = NS). Acute vessel closure and ventricular tachyarrhythmias were more common in the control group than in the patients who received prostacyclin (acute vessel closure occurred in 14 [10.3%] of 136 versus 4 [3.0%] of 134, respectively, p less than 0.01; ventricular tachyarrhythmias occurred in 5 [3.4%] of 147 versus 0 of 139 respectively, p less than 0.05). Short-term administration of prostacyclin did not significantly lower the risk of restenosis after coronary angioplasty.

Platelet inhibitor agents in cardiovascular disease: an update

Platelets interact with the coagulation and fibrinolytic systems in the maintenance of hemostasis. However, these physiologic mechanisms may become pathologic, requiring prevention and treatment. In this review, the following clinical developments are analyzed: 1) the role of platelets in thrombogenesis; 2) the pharmacology of platelet inhibitory agents; and, most important, 3) the results of recent randomized trials of platelet inhibitor agents in different cardiovascular disorders. Aspirin reduces mortality and infarction rates in unstable angina and significantly decreases vascular mortality in acute myocardial infarction. Platelet inhibitors decrease mortality and recurrent cardiovascular events in the chronic phase after myocardial infarction. They also decrease vein graft occlusion rates after coronary bypass surgery. Although platelet inhibitors are beneficial in preventing acute vessel occlusion during coronary angioplasty, they are ineffective in preventing chronic restenosis. Antiplatelet agents, combined with warfarin, reduce thromboembolic events in patients with a mechanical prosthesis. Platelet inhibitors are also effective in secondary prevention of vascular events in patients with cerebrovascular disease. Finally, the use of aspirin for primary prevention of cardiovascular disease is still evolving, particularly in individuals at high risk. In conclusion, platelet inhibitors are effective in patients with a variety of cardiovascular disorders. The best studied, most inexpensive and least toxic agent is aspirin at a daily dose of 160 to 325 mg. Studies using new platelet inhibitor agents with different mechanisms of action are currently underway.