Differences in the occurrence of carotid transient ischemic attacks associated with antiplatelet aggregation therapy

Plasminogen activators and ischemic stroke: conditions for acute delivery

Appropriate acute treatment with plasminogen activators (PAs) can significantly increase the probability of minimal or no disability in selected ischemic stroke patients. There is a great deal of evidence showing that intravenous recombinant tissue PAs (rt-PA) infusion accomplishes this goal, recanalization with other PAs has also been demonstrated in the development of this treatment. Recanalization of symptomatic, documented carotid or vertebrobasilar arterial territory occlusions have also been achieved by local intra-arterial PA delivery, although only a single prospective double-blinded randomized placebo-controlled study has been reported. The increase in intracerebral hemorrhage with these agents by either delivery approach underscores the need for careful patient selection, dose-appropriate safety and efficacy, proper clinical trial design, and an understanding of the evolution of cerebral tissue injury due to focal ischemia. Principles underlying the evolution of focal ischemia have been expanded by experience with acute PA intervention. Several questions remain open that concern the manner in which PAs can be applied acutely in ischemic stroke and how injury development can be limited.

Antithrombotic treatment of cerebrovascular disease

The most common type of cerebrovascular disease is ischaemia or infarction from atherothrombosis or cardiac embolism. Antithrombotic treatment with an antiplatelet agent or anticoagulant assumes a prior clinical classification into categories of transient ischaemic attack (TIA) or minor stroke, acute partial stable stroke, stroke-in-progression, and completed stroke. Aspirin reduces the risk of stroke, myocardial infarction, and death after TIA or minor stroke secondary to atherothrombosis. Aspirin is effective in both sexes at a dose of 300 or 1200 mg/day. Ticlopidine (500 mg/day), a new antiplatelet agent, is more effective than aspirin in preventing stroke and death in patients with TIA or minor stroke. Ticlopidine (500 mg/day) is effective in preventing recurrent stroke, myocardial infarction, or vascular death in patients with completed stroke. Aspirin has not been directly shown to be effective after completed stroke. No clear evidence exists for the use of anticoagulants in atherothrombotic cerebral vascular disease in patients presenting with TIA or minor stroke, acute partial stable stroke, stroke-in-progression, or completed stroke. Anticoagulation for rheumatic valvular heart disease is effective in preventing recurrent embolism. Long-term anticoagulation of patients with mechanical prosthetic valves protects against initial embolism and prevents recurrent embolism. The addition of aspirin (500-1000 mg/day) to warfarin reduces the rate of cerebral embolism from mechanical prosthetic heart valves but is associated with increased bleeding. The addition of dipyridamole (400 mg/day) to warfarin may be more effective than aspirin in reducing the rate of cerebral embolism from mechanical prosthetic heart valves and has fewer bleeding side-effects. Anticoagulation during the hospital phase of myocardial infarction reduces the incidence of systemic embolism/stroke. Long-term anticoagulation of patients after the hospital phase of myocardial infarction reduces the incidence of systemic embolism/stroke, recurrent myocardial infarction and death. Prophylactic anticoagulant treatment of patients with non-valvular atrial fibrillation reduces the incidence of embolism, but the optimal duration of treatment is not known. Immediate anticoagulation of patients with completed cardioembolic stroke is safe and effective in preventing recurrent embolism.

Thrombosis: the relationship of hemostatic mechanisms to drug therapy

The mechanism of action and present clinical role of drugs affecting hemostasis in the therapy of spontaneous, postoperative, and posttraumatic arterial thrombosis, arterial embolism, venous thrombosis, pulmonary embolism, and intracranial aneurysm have been reviewed. Both the management of neurosurgical problems and the development of antithrombotic regimens are improving. In regard to the use of drug therapy, discussed herein, each surgeon will reach his own decision based on his findings in the individual patient, and may wisely elect in specific situations not to employ drug therapy. The comments offered in ths analysis are to be construed as suggestions not mandates, as they will undoubtedly undergo modification with time. In closing, it is appropriate to recall a famous Chinese curse: "May you live," it reads, "in a time of transition."

An investigation of the effect on platelet function of acetylsalicylic acid, dipyridamole and the two drugs in combination in patients with transient attacks of ischaemia

Twenty patients suffering from transient attacks of ischaemia were studied. Seven received acetylsalicylic acid, six dipyridamole and seven a combination of the two drugs. No significant difference in platelet aggregation was shown in the acute phase between the three treatment groups using an adenosine diphosphate test method. Using Thrombofax platelet substitute, however, a significant difference was seen in all measures. On the seventh day following the ischaemic attack the Thrombofax values returned to normal but, in contrast, Platelet Factor 4 release was increased. Monthly testing of platelet activity during treatment shows that the combination of acetylsalicylic acid with dipyridamole was more effective in bringing about an early inhibition of Platelet Factor 4 release than either agent alone.

Are agents affecting platelet functions clinically useful?

Notwithstanding the large number of clinical trials, most of them designed and performed according to the requirements of modern clinical pharmacology, only a few firm clinical recommendations on drugs affecting platelet function in the prevention of arterial or venous thrombosis can be made at present. There is no good evidence for the clinical effectiveness of aspirin or any other drug affecting platelet function in patients with peripheral arterial occlusion or after vascular grafting. In cerebrovascular disease there is reasonable evidence that the administration of sulfinpyrazone can significantly reduce cerebral ischemia or mortality, but similar trials performed with aspirin, dipyridamole or clofibrate failed to reveal a significant difference in favor of the experimental treatment. Patients with angina only were shown to benefit from treatment with clofibrate, but prospective trials with dipyridamole or aspirin in the primary or secondary prevention of myocardial infarction did not reveal a significant reduction in morbidity or mortality in the experimental group. Use of a combination of the latter two drugs did, however, reveal a reduction in morbidity and mortality. In patients with prosthetic heart valves, there is firm evidence that dipyridamole and sulfinpyrazone therapy can normalize decreased platelet survival, an effect which has been shown to correlate well with the incidence of thromboembolism. Provided further trials lead to confirmatory conclusions, drugs inhibiting platelet function associated or not with oral anticoagulants may constitute an ideal prophylaxis in patients with a substitute valve. There is still much uncertainty as to whether dipyridamole, given in addition to conventional treatment, benefits patients with membranous or mesangiocapillary glomerulonephritis. The same holds for drugs inhibiting platelet function after kidney or heart transplantation in man. Only scanty reports are available on the usefulness of drugs affecting platelet function in thrombotic thrombocytopenic purpura and the hemolytic uremic syndrome. Three different types of antiplatelet drugs are available for the prevention of postoperative deep vein thrombosis: dextran, oral drugs also affecting platelet function and heparin administered subcutaneously in small doses. In orthopedic surgery dextran 70 administered before and every second day after surgery was the drug showing the most convincing reduction in the incidence of phlebographically proved deep vein thrombosis. Major orthopedic surgery is precisely the type of surgery in which the effectiveness of small dose heparin is much in doubt and in which the effectiveness of aspirin and dipyridamole is still to be confirmed. In general surgery, use of a combination of 1 g aspirin and 0.225 g dipyridamole daily was shown to offer approximately the same level of protection as small doses of heparin, land these two forms of prevention seem to offer a greater degree of protection than dextran...

Aspirin therapy in angina pectoris: effects on platelet aggregation, exercise tolerance, and electrocardiographic manifestations of ischemia

If altered platelet function contributes to poorly perfused zones of myocardium in patients with angina pectoris, then specific antiplatelet therapy might improve cardiovascular function and exercise performance. Exercise tolerance on a bicycle ergometer, heart rate-blood pressure product, and ischemic ECG changes at exercise end-point were compared before and during oral aspirin therapy (2.4 Gm. per day for 2 weeks) in 11 normal subjecs and in 11 patients with stable angina pectoris. Platelet aggregation threshold in response to ADP and epinephrine was measured. Untreated patients had increased platelet aggregability when compared to normal subjects...

Effect of aspirin on experimentally induced arterial thrombosis during the healing phase

Twenty dogs were treated with either acetylsalicylic acid or a lactose placebo for 5.5 ± 2.3 days before surgical or chemical injury to the carotid and femoral arteries and for the following 34.5 days. Only the laboratory diener had knowledge of the random table used to select type of treatment until after all determinations had been completed. Following sacrifice the arteries were classified for the presence of intimal proliferation, defects in the internal elastica, presence of organized thrombi and the percentage of recanalization, and the presence of fresh thrombi and the percentage of occlusion. Thrombi were present in 8% of the arteries of dogs treated with acetylsalicylic acid and in 36% of those treated with placebo. This difference is significant (P<0.01). The degree of intimal proliferation and defects in the internal elastica were not significantly different between the two groups. We conclude that in dogs acetylsalicylic acid therapy during the healing phase following arterial injury protects against thrombosis and does not retard the healing process.