Moreover, patients who have had vascular interventions are at high risk not just of subclinical occlusion but also of major vascular events such as myocardial infarction, stroke, or vascular death. Treatment for only six months of patients who have had coronary revascularisation procedures might therefore not only prevent several dozen from having coronary artery occlusions but, even more important, might avoid a few dozen serious or fatal clinical vascular events.
Among haemodialysis patients antiplatelet therapy reduced the risk of occlusion of fistulas and shunts by about two thirds. It is relevant that these patients also suffer a particularly high incidence of serious vascular events 6 that could be reduced by prolonged antiplatelet treatment.
Risk of bleeding Many patients at very high risk of subclinical occlusion or vascular events for example, those with unstable angina or with suspected acute myocardial infarction who are having emergency coronary artery bypass surgery or angiography have been denied antiplatelet therapy for fear of perioperative bleeding. Detailed analysis of bleeding complications in a trial of aspirin started preoperatively in patients having coronary artery bypass surgery found a small but significant increase in drainage from the chest tube, in perioperative transfusion requirements, and in the reoperation rate, but there was no excess mortality due to bleeding complications.
It has been suggested that starting antiplatelet therapy after invasive vascular procedures may reduce the risk of bleeding while still preventing occlusion. More recently, the results of a trial have been reported among patients randomly allocated to receive aspirin starting preoperatively or six hours after coronary artery bypass graft surgery. But there were no statistically significant differences between the treatment groups in graft occlusion at an average of eight days after surgery 30 of patients allocated preoperative antiplatelet therapy versus 27 of allocated postoperative therapy , reinforcing - if on smaller numbers - the conclusion suggested by figure 3 that treatment started just after the vascular procedure may be about as effective as treatment started preoperatively.
Comparisons between different antiplatelet regimens may be based on several factors, including efficacy, ease of use, severity of side effects, and cost. This overview provides some direct and indirect randomised comparisons of the effects of different drug regimens on the prevention of occlusion but finds no evidence of any differences in efficacy.
Consequently, the choice of which regimen to use must be determined by other factors. At present medium dose aspirin is the most widely tested, most convenient, and least expensive antiplatelet treatment, with direct evidence of substantial reductions in occlusion and in important vascular events 5 that would generally far outweigh any small risks of bleeding. The choice of which antiplatelet regimen to use is, however, of secondary importance: what chiefly matters is that some such treatment should routinely be considered for the vast majority of patients having vascular procedures.
It remains uncertain how long antiplatelet therapy should be continued after vascular procedures. As yet there are no large directly randomised comparisons of different durations of treatment though a recent small trial comparing two weeks versus six months of aspirin after coronary angioplasty suggested some additional effect on restenosis with continued treatment The highest absolute risk of occlusion generally occurs during the first few months, while any traumatic damage is healing, but even after those first few months a small percentage of patients per year may suffer late occlusions, as well as other more serious vascular events.
The average duration of treatment in these trials was only about one year, but indirect evidence from studies in other settings suggests that more prolonged treatment may be more effective see part I.
It may therefore be prudent to consider continuing antiplatelet therapy after vascular procedures for as long as the risk of occlusive vascular events remains high. Individual results of unconfounded randomised comparisons of antiplatelet therapy with control A upisilon C for maintaining vascular patency. Individual results of unconfounded randomised comparisons of one antiplatelet regimen with another A1 upsilion A2 for maintaining vascular patency.
Skip to main content. Research Collaborative overview Collaborative overview of randomised trials of antiplatelet therapy - II: Maintenance of vascular graft or arterial patency by antiplatelet therapy. Article Related content Metrics Responses Peer review. Accepted 29 November Abstract Objective : To determine the efficacy of antiplatelet therapy in maintaining vascular patency in various categories of patients.
Introduction After coronary artery revascularisation, whether by coronary artery bypass grafting or by percutaneous transluminal coronary angioplasty, 1 angiographic studies show substantial rates of reocclusion.
Materials and methods data acquisition Identification of all unconfounded randomised trials The aim was to include all unconfounded randomised trials of antiplatelet therapy versus no antiplatelet therapy, or of one antiplatelet regimen versus another, that could have been available for review by March and in which vascular graft or arterial patency was monitored systematically see appendices 1 and 2.
Definition of outcome measures Methods used to assess vascular patency varied widely between trials: angiography in all coronary artery trials; clinical examination, Doppler ultrasonography, limb plethysmography often with confirmatory radionuclide scanning or angiography , or systematic angiography in peripheral artery trials; and clinical examination in all haemodialysis access trials see appendices 1 and 2.
Statistical methods: proportional and absolute reductions Statistical methods used to obtain an overview of the results from the trials were detailed in part I. Results Effects of antiplatelet therapy on vascular graft or arterial occlusion Information on vascular graft or arterial occlusion was available from 46 trials of antiplatelet therapy.
FIG 2 Absolute effects of antiplatelet therapy on occlusion. Effects in different categories of patients Coronary artery trials Thirty trials of antiplatelet therapy versus control were identified among patients who had had coronary artery bypass grafting or percutaneous transluminal coronary angioplasty see part I , but vascular occlusion was monitored systematically in only 23 of these trials.
Peripheral artery trials Thirty nine trials of antiplatelet therapy versus control were identified among patients having peripheral vascular procedures or with peripheral vascular disease see part I but vascular occlusion was monitored systematically in only 14 of them.
Haemodialysis access trials Ten trials of antiplatelet therapy versus control were identified among renal patients having surgery to establish haemodialysis access, and vascular occlusion was monitored systematically in nine of these trials all evenly balanced and placebo controlled among a total of only patients. Avoiding bias when assessing efficacy Systematic assessment of patency was planned in all patients randomised in these trials, but the methods to be used differed widely appendices 1 and 2.
Comparisons of different antiplatelet regimens Indirect comparisons of when to start therapy During the period covered by this overview there were no direct randomised comparisons of starting treatment before the invasive vascular procedure versus starting treatment after it.
FIG 3 Indirect comparisons of proportional effects of antiplatelet therapy started before or after vascular procedures on occlusion. FIG 4 Direct comparisons of proportional effects on occlusion of different antiplatelet regimens. FIG 5 Indirect comparisons of proportional effects on occlusion of different antiplatelet regimens.
Effects of antiplatelet therapy on bleeding The table summarises the bleeding complications reported in all trials comparing antiplatelet therapy with control in patients who were to undergo, or had just undergone, a vascular procedure, irrespective of whether vascular patency was to be monitored systematically.
View this table: View popup View inline. Choice of antiplatelet regimen Comparisons between different antiplatelet regimens may be based on several factors, including efficacy, ease of use, severity of side effects, and cost. Duration of antiplatelet treatment It remains uncertain how long antiplatelet therapy should be continued after vascular procedures. Appendix 1 Individual results of unconfounded randomised comparisons of antiplatelet therapy with control A upisilon C for maintaining vascular patency.
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Results: In each of four main high risk categories of patients antiplatelet therapy was definitely protective. Reductions in vascular events were about one quarter in each of these four main categories and were separately statistically significant in middle age and old age, in men and women, in hypertensive and normotensive patients, and in diabetic and nondiabetic patients.
There was no evidence that non-vascular deaths were increased, so in each of the four main high risk categories overall mortality was significantly reduced.
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