Hemodynamic, platelet and clinical responses to prostacyclin in unstable angina pectoris

Plasma thromboxane and prostacyclin are linear related and increased in patients presenting with acute myocardial infarction

The role of prostanoids in patients with ischemic heart disease including acute myocardial infarction (AMI) has been recognized. However, there is very limited knowledge of the baseline TXB2 and 6-keto-PGF1a plasma levels in patients with AMI before therapy has been administered. We compared plasma levels of TXB2 and 6-keto-PGF1a by enzyme immunoassay in 18 AMI patients before thrombolysis, with those of 13 healthy controls. Plasma levels of TXB2 (319.78+/-16.50 pg/ml) and 6-keto-PGF1a (536.72+/-56.71 pg/ml) were heterogeneous, but significantly higher in the AMI patients than in controls (175.92+/-17.29 pg/ml and 192.08+/-26.11 pg/ml, respectively). In some patients, long-term aspirin therapy mildly inhibits baseline prostanoid levels, however, limited data prevents us from further speculations on this issue. Although, the contributions by prostanoids to the pathogenesis of AMI have been well proposed, their plasma concentrations are not uniformly elevated, and it is still unclear whether the resultant changes are indicative of clinically meaningful effects.

New antiplatelet drugs

Antiplatelet drugs are used in a wide range of disorders, either as sole agents or as adjuncts to other therapies. Aspirin has been shown to be clinically effective in a number of ischaemic conditions and has been in use for many years. The newer agents, ticlopidine and clopidogrel (which are thought to inhibit ADP-mediated platelet reactions) are also effective and may prove to be superior to aspirin in certain indications. However, ticlopidine in particular has a different spectrum of side-effects, which may eventually limit its widespread use. The Gp IIb/IIIa antagonists have been most extensively investigated in the acute coronary syndromes, and shown to significantly improve outcome. Most of these studies have utilized agents which need to be given parenterally, and subsequently oral compounds are currently being developed. A number of other antiplatelet drugs such as prostacyclin and its analogues, as well as thromboxane inhibitors have been studied over the years, but overall they have failed to demonstrate any real clinical advantage.

Effects of beraprost sodium, a new prostaglandin I2 analog, on parameters of hemostasis, fibrinolysis, and myocardial ischemia in patients with exertional angina

The purpose of this study was to investigate the effects of beraprost sodium, a stable prostacyclin analog, on the parameters of hemostasis, fibrinolysis, and myocardial ischemia in patients with exertional angina. Thirty-one patients with exertional angina who had significant organic coronary artery stenosis in at least one of the three major coronary arteries were selected. All patients underwent quantitative exercise thallium-201 emission computed tomography before and 1 month after 120 micrograms per day of beraprost sodium administration. Before exercise, blood samples were collected from 8:30 a.m. to 9:30 a.m. after the patients had been lying in bed undisturbed for at least 10 minutes. Plasma platelet factor 4 (PF4), fibrinopeptide A (FPA), tissue plasminogen activator antigen (t-PA), and plasminogen activator inhibitor-1 activity (PAI-1) were measured. There were no significant differences in exercise parameters on both exercise tests. However, both the extent and severity scores of ischemia were significantly aggravated (p < 0.05 for both) during beraprost sodium administration. Plasma FPA levels decreased significantly during beraprost sodium administration (p < 0.01). Likewise, plasma PF4 levels decreased significantly during beraprost sodium administration (p < 0.05). As for plasma t-PA antigen levels, there was no significant difference before versus during beraprost sodium administration. Plasma PAI-1 activity levels decreased significantly during beraprost sodium administration (p < 0.05). The results indicate that beraprost sodium has strong antithrombogenic properties. However, its aggravation of myocardial ischemia may limit clinical usage.

Newer concepts in the treatment of unstable angina pectoris

Unstable angina patients should be hospitalized and treated with antianginal drugs to control their symptoms and with aspirin or heparin to reduce the risk of myocardial infarction. Heparin is probably preferable to aspirin acutely, because it also reduces the risk of refractory angina. However, aspirin therapy should be started before heparin is discontinued, to prevent the rebound in symptoms, and continued long-term. Unless specifically contraindicated, coronary arteriography should be performed to identify patients who might benefit from coronary bypass surgery or angioplasty. Control of risk factors is important for long-term outcome.

Antiplatelet and antithrombotic therapy in unstable angina

In 4 well-controlled clinical trials, aspirin reduced the incidence of coronary events in unstable angina. The benefits were present during the acute, subacute and more chronic phases of the disease and were independent of the doses and of other protocol differences. This benefit of aspirin can be extended to some, but not all, other antiplatelet drugs. In 4 clinical trials, heparin used acutely added substantial benefit to the management of unstable angina, reducing the event rate and also the incidence of refractory angina more than aspirin. The long-term benefit of antithrombin therapy remains to be more thoroughly investigated. Despite these successes, the failure rate of aspirin and of heparin remains high, justifying a continuing search for more potent and safe antiplatelet and antithrombotic drugs.