Randomised trial of prophylactic daily aspirin in British male doctors

Placebo-controlled, randomised trial of warfarin and aspirin for prevention of thromboembolic complications in chronic atrial fibrillation. The Copenhagen AFASAK study

From November, 1985, to June, 1988, 1007 outpatients with chronic non-rheumatic atrial fibrillation (AF) entered a randomised trial; 335 received anticoagulation with warfarin openly, and in a double-blind study 336 received aspirin 75 mg once daily and 336 placebo. Each patient was followed up for 2 years or until termination of the trial. The primary endpoint was a thromboembolic complication (stroke, transient cerebral ischaemic attack, or embolic complications to the viscera and extremities). The secondary endpoint was death. The incidence of thromboembolic complications and vascular mortality were significantly lower in the warfarin group than in the aspirin and placebo groups, which did not differ significantly. 5 patients on warfarin had thromboembolic complications compared with 20 patients on aspirin and 21 on placebo. 21 patients on warfarin were withdrawn because of non-fatal bleeding complications compared with 2 on aspirin and none on placebo. Thus, anticoagulation therapy with warfarin can be recommended to prevent thromboembolic complications in patients with chronic non-rheumatic AF.

In vivo measurement of thromboxane B2 and 6-keto-prostaglandin F1 alpha in humans in response to a standardized vascular injury and the influence of aspirin

The effects of smoking, aspirin ingestion, and sex differences on bleeding times and bleeding time thromboxane B2 and 6-keto-prostaglandin (PG)F1 alpha production were examined. Nonsmoking men produced more thromboxane B2 (3.99 +/- 0.76 ng/ml) than nonsmoking women (2.13 +/- 0.24 ng/ml). Female smokers produced more thromboxane B2 (5.01 +/- 0.97 ng/ml) than nonsmoking women. Twenty-four hours after a single dose of 600 mg aspirin, in vitro production of thromboxane B2 in response to collagen fell by 95%, whereas in vivo production of thromboxane B2 and 6-keto-PGF1 alpha in bleeding time blood fell by 87% and 66%, respectively. Subjects with the lowest absolute levels of thromboxane B2 24 hours after aspirin were also those with the longest postaspirin bleeding times. Recovery of 6-keto-PGF1 alpha production was faster than recovery of thromboxane B2 production, but 6-keto-PGF1 alpha production for most subjects was still below basal 72 hours after aspirin. The influence of two different doses of long-term aspirin (80 mg every other day and 325 mg daily) on the in vivo production of thromboxane B2 and 6-keto-PGF1 alpha was studied in normals and diabetics. After 14 days of 80 mg aspirin every other day, thromboxane B2 and 6-keto-PGF1 alpha production were both substantially inhibited (93% and 78%, respectively). After 14 days of 325 mg aspirin daily, thromboxane B2 production was similarly substantially inhibited (93%), whereas 6-keto-PGF1 alpha was significantly less affected (only 45% inhibition). Study of a second group of five normal subjects confirmed that 6-keto-PGF1 alpha production was significantly inhibited 24 hours after the first dose of 325 mg aspirin but was not significantly less than basal after 14 days of 325 mg aspirin. The results suggest that 325 mg aspirin daily is more antithrombotic compared with 80 mg every other day due to the superior preservation of prostacyclin production.

Aspirin and prevention of myocardial infarction

Determining the cardioprotective effects of aspirin (acetylsalicylic acid) remains a focus for both basic science and clinical investigation. Although other contributors are probably present, the favorable prostacyclin-to-thromboxane ratio induced by low-dose aspirin appears beneficial for reducing cardiovascular mortality associated with unstable angina and myocardial infarction. The precise dosage, frequency and timing of aspirin's administration to reduce the incidence of vaso-occlusive events remains to be determined. This article reviews aspirin's mechanism of action and use for the prevention of myocardial infarction.

Use of aspirin for prevention of cardiovascular disease--1981-82 to 1985-86: the Minnesota Heart Survey

The efficacy of aspirin to prevent ischemic cardiovascular disease has received considerable attention recently. To determine the prevalence of aspirin use for cardiovascular disease prevention, the Minnesota Heart Survey examined population-based samples of Twin Cities' adults in 1981 to 82 and 1985 to 86. Over the 4-year period, reported use of aspirin for cardiovascular disease prophylaxis increased from 0.6% to 2.4% in women (p less than 0.05) and from 1.7% to 3.3% in men (p = 0.10). Prophylactic aspirin use was more common in older than in younger adults, in whites than in blacks, in those with a history of cardiovascular disease or hypercholesterolemia, and in health professionals and nonsmokers. Some individuals were apparently taking aspirin for "primary" prevention, although it has not yet been approved for that reason. Use of aspirin for cardiovascular disease prevention has been increasing and is likely to increase more rapidly over the next few years. This could favorably impact on mortality rates of cardiovascular disease, but untoward side effects of aspirin may be expected to increase as well.

Effects of intermittent treatment with aspirin on thromboxane and prostacyclin formation in patients with acute myocardial infarction

Thromboxane and prostacyclin formation were monitored in twenty patients with acute myocardial infarction. Ten received 500 mg acetylsalicylic acid (ASA) orally starting 12 h after admission and then intermittently every third day for one month; the other ten did not receive ASA or any other drug known to interfere with the synthesis of prostanoids. In the ASA group thromboxane formation, initially raised, fell rapidly and remained low. In the control group thromboxane formation decreased very slowly and was not normal by the end of the study period. Prostacyclin formation seemed identical in the two groups. Thus intermittent ASA, in this dosage, efficiently inhibited the enhanced thromboxane formation in acute myocardial infarction without interfering with prostacyclin formation.

Role of arachidonic acid metabolites in cardiac ischemia and reperfusion injury

Myocardial reperfusion after prolonged periods of ischemia may result in the acceleration and exacerbation of ventricular injury. This is associated with intramitochondrial calcium overload and gross alterations in ultrastructure. Prostaglandins (PGs) (e.g., PGE2, PGE2 alpha, thromboxane A2, PGl2) are synthesized by the heart during myocardial infarction, and cardiotoxic influences of arachidonate on contractile recovery with enhanced efflux of enzymes occur after reperfusion. Accumulation of arachidonic acid in early ischemia indicates degradation of phospholipids as structural components of myocyte membranes. One major cause for reperfusion-induced exacerbation of ischemic damage is a free radical-induced peroxidation of lipids with cellular disruption. On reperfusion, both vasoconstrictive and dilator PGs are released from platelets, myocytes, and endothelium, and flushed downstream. This may cause additional vasoconstriction in the microcirculation of normally and/or hypoperfused cardiac regions. Locally released vasodilating PGs can improve cardiac perfusion and prevent plugging of blood elements, thereby antagonizing cell destruction during flow restoration. Several drugs are available that modify blood cell and myocyte arachidonate metabolism, and may favor synthesis of dilating and antiaggregatory PGs.