Aspirin for Carotid Stent Continue Perioperative
Original Article
Aspirin in Patients Undergoing Noncardiac Surgery
List of authors.Abstract
Background
There is substantial variability in the perioperative administration of aspirin in patients undergoing noncardiac surgery, both among patients who are already on an aspirin regimen and among those who are not.
Methods
Using a 2-by-2 factorial trial design, we randomly assigned 10,010 patients who were preparing to undergo noncardiac surgery and were at risk for vascular complications to receive aspirin or placebo and clonidine or placebo. The results of the aspirin trial are reported here. The patients were stratified according to whether they had not been taking aspirin before the study (initiation stratum, with 5628 patients) or they were already on an aspirin regimen (continuation stratum, with 4382 patients). Patients started taking aspirin (at a dose of 200 mg) or placebo just before surgery and continued it daily (at a dose of 100 mg) for 30 days in the initiation stratum and for 7 days in the continuation stratum, after which patients resumed their regular aspirin regimen. The primary outcome was a composite of death or nonfatal myocardial infarction at 30 days.
Results
The primary outcome occurred in 351 of 4998 patients (7.0%) in the aspirin group and in 355 of 5012 patients (7.1%) in the placebo group (hazard ratio in the aspirin group, 0.99; 95% confidence interval [CI], 0.86 to 1.15; P=0.92). Major bleeding was more common in the aspirin group than in the placebo group (230 patients [4.6%] vs. 188 patients [3.8%]; hazard ratio, 1.23; 95% CI, 1.01, to 1.49; P=0.04). The primary and secondary outcome results were similar in the two aspirin strata.
Conclusions
Administration of aspirin before surgery and throughout the early postsurgical period had no significant effect on the rate of a composite of death or nonfatal myocardial infarction but increased the risk of major bleeding. (Funded by the Canadian Institutes of Health Research and others; POISE-2 ClinicalTrials.gov number, NCT01082874.)
Methods
Study Design
POISE-2 was an international, randomized, controlled trial with a 2-by-2 factorial design to separately evaluate the effects of aspirin versus placebo (reported here) and clonidine versus placebo (reported elsewhere in the Journal)20 in patients undergoing noncardiac surgery. Details of the trial objectives, design, and methods have been reported previously.21 All centers obtained ethics approval before starting recruitment.
Study Oversight
The study was funded by the Canadian Institutes of Health Research and others. The Population Health Research Institute was the study coordinating center and was responsible for the randomization design, maintenance of the database, data validation, analyses, and study-center coordination. Bayer Pharma provided the aspirin used in the study, and Boehringer Ingelheim provided the clonidine and some research funding; both companies were provided with the first draft of the manuscript. However, no donor or funder had a role in the design or conduct of the study, the collection or analyses of the data, or the preparation of the manuscript. The operations committee designed the trial, prespecified the statistical analysis plan, and vouches for the completeness and accuracy of the data and analyses and the adherence of the study to the protocol (available with the full text of this article at NEJM.org). The first author wrote the first draft of the manuscript, and the writing committee made revisions and made the decision to submit the manuscript for publication.
Patients
We recruited patients from July 2010 through December 2013 at 135 hospitals in 23 countries. Eligibility criteria are reported in Section 1 in the Supplementary Appendix, available at NEJM.org. Patients were then stratified according to whether they were not taking aspirin before study enrollment (initiation stratum) or they were already on an aspirin regimen (which was defined as daily use for at least 1 month within 6 weeks before surgery) (continuation stratum). Patients in the continuation stratum were required to stop taking aspirin at least 3 days before surgery to participate in the trial.
Procedures
After providing written informed consent before surgery, patients underwent randomization by means of a 24-hour computerized Internet system that used block randomization stratified according to study center and aspirin stratum. Patients were assigned in a 1:1:1:1 ratio to receive aspirin and clonidine, aspirin placebo and clonidine, aspirin and clonidine placebo, or aspirin placebo and clonidine placebo. Patients, clinicians, data collectors, and outcome adjudicators were all unaware of study-group assignments.
Patients started taking aspirin or placebo (at a dose of 200 mg) just before surgery and continued it (at a dose of 100 mg per day) for 30 days in the initiation stratum and for 7 days in the continuation stratum, after which patients resumed their regular aspirin regimen. Patients also started clonidine (0.2 mg per day) or placebo just before surgery and continued it for 72 hours. If a patient had life-threatening or major bleeding, the aspirin study drug was to be stopped. (Details regarding the follow-up process are provided in Section 2 in the Supplementary Appendix.)
Study Outcomes
The primary outcome was a composite of death or nonfatal myocardial infarction 30 days after randomization. Details regarding the two secondary composite outcomes, the tertiary outcomes, and the safety outcomes at 30 days are provided in Section 3 in the Supplementary Appendix, outcome definitions are provided in Section 4 in the Supplementary Appendix, and events evaluated by outcome adjudicators, which were used in the analyses, are provided in Section 5 in the Supplementary Appendix.
Statistical Analysis
We determined that enrollment of 10,000 patients would give the study a power of 84% to detect a hazard ratio of 0.75 in the aspirin group, at a two-sided alpha level of 0.05, on the assumption that the rate of the primary outcome in the placebo group would be 6.1%.16 An external data and safety monitoring committee reviewed the data when 25%, 50%, and 75% of the 30-day data were available.
We evaluated patients according to the group to which they were assigned, censoring the data for patients who were lost to follow-up on the last day that their status was known. Outcomes were analyzed with the use of Cox proportional-hazards models, stratified according to the aspirin stratum and status with respect to receipt of clonidine, except for the outcome of acute kidney injury with receipt of dialysis, for which we used logistic-regression analysis, and outcomes with respect to the length of the hospital stay, for which we used the log-rank test.
For the primary outcome, we performed subgroup analyses that were based on the aspirin stratum, type of surgery (vascular vs. nonvascular), and the number of criteria of the Revised Cardiac Risk Index that the patient met.22 We also performed subgroup analyses, according to the aspirin stratum, for one of the secondary composite outcomes and for the tertiary outcomes. In a prespecified analysis, we predicted the direction of potential subgroup effects. For the subgroup analyses, we used Cox proportional-hazards models that incorporated tests of interaction, with a P value of less than 0.05 indicating statistical significance. All analyses were performed with the use of SAS software, version 9.1.
Results
Patients
A total of 10,010 patients were enrolled (5628 in the initiation stratum and 4382 in the continuation stratum). Of these patients, 4998 were assigned to receive aspirin and 5012 to receive placebo. The 30-day follow-up was complete for 99.9% of the patients (Figure S1 in the Supplementary Appendix).
Table 1.
Table 1. Characteristics of the Patients at Baseline. The baseline characteristics were similar in the aspirin and placebo groups (Table 1). The mean age was 68.6 years; 52.8% of the patients were men, 32.7% had a history of vascular disease, and 4.3% had undergone previous coronary stenting. Among patients in the continuation stratum, aspirin was stopped a median of 7 days (interquartile range, 4 to 8) before surgery. In the first 3 days after surgery, 65.0% of the patients received prophylactic anticoagulation. Overall, 80.4% of the patients in the aspirin group and 82.4% of those in the placebo group took at least 80% of the doses of the study drug (Table S1 in the Supplementary Appendix).
Study Outcomes
Table 2.
Table 2. Effects of Aspirin on 30-Day Outcomes. Figure 1. 
Figure 1. Kaplan–Meier Estimates of the Primary Composite Outcome of Death or Nonfatal Myocardial Infarction at 30 Days. The inset shows the same data on an enlarged y axis.
The primary outcome (death or nonfatal myocardial infarction) occurred in 351 of 4998 patients (7.0%) in the aspirin group and in 355 of 5012 patients (7.1%) in the placebo group (hazard ratio in the aspirin group, 0.99; 95% confidence interval [CI], 0.86 to 1.15; P=0.92) (Table 2 and Figure 1). The use of aspirin did not significantly affect the secondary composite or tertiary outcomes. Myocardial infarction occurred in 309 patients (6.2%) in the aspirin group and in 315 patients (6.3%) in the placebo group (hazard ratio, 0.98; 95% CI, 0.84 to 1.15; P=0.85). Aspirin increased the risk of major bleeding, as compared with placebo, with major bleeding occurring in 230 patients (4.6%) versus 188 patients (3.8%) (hazard ratio, 1.23; 95% CI, 1.01 to 1.49; P=0.04) (Table 2, and Figure S2 in the Supplementary Appendix). The most common sites of bleeding were the surgical site (78.3%) and gastrointestinal tract (9.3%). Stroke occurred in 16 patients (0.3%) in the aspirin group and in 19 patients (0.4%) in the placebo group (hazard ratio, 0.84; 95% CI, 0.43 to 1.64; P=0.62). The median length of hospital stay was 4 days (interquartile range, 3 to 7) in both the aspirin and placebo groups (P=0.79). There was no significant difference between the study groups in the length of stay in the intensive care unit or cardiac care unit (P=0.23). There was no significant effect of clonidine on the results comparing aspirin with placebo (P≥0.12 for all interactions).
Figure 2.
Figure 2. Subgroup Analyses of the Primary Outcome. The primary composite outcome was death or nonfatal myocardial infarction at 30 days. The area of each square is proportional to the size of the corresponding subgroup. The Revised Cardiac Risk Index ranges from 0 to 6, with higher scores indicating greater risk.
The effect of aspirin was consistent across subgroups (P≥0.16 for all interactions) (Figure 2). The subgroup analysis of the secondary composite outcome also showed no significant heterogeneity (P=0.72 for interaction).
Differences between Strata
Aspirin use significantly increased the risk of major bleeding and decreased the risk of stroke in the initiation stratum (P=0.03 for both comparisons) and significantly increased the rate of acute kidney injury requiring dialysis in the continuation stratum (P=0.04) (Tables S2 and S3 in the Supplementary Appendix). However, the P value for strata interaction was significant only for stroke (P=0.01) (Table S4 in the Supplementary Appendix). In the initiation stratum, there were 3 strokes in the aspirin group and 12 in the placebo group (hazard ratio, 0.25; 95% CI, 0.07 to 0.89), whereas in the continuation stratum there were 13 strokes in the aspirin group and 7 in the placebo group (hazard ratio, 1.86; 95% CI, 0.74 to 4.66; P=0.19).
The effects of aspirin on myocardial infarction were similar in the initiation stratum and the continuation stratum (hazard ratio, 0.98; 95% CI, 0.79 to 1.22 in the initiation stratum; hazard ratio, 0.99; 95% CI, 0.79 to 1.24 in the continuation stratum; P=0.96 for interaction). In addition, the effects of aspirin on the composite of life-threatening or major bleeding were similar in the initiation stratum and the continuation stratum (hazard ratio, 1.24; 95% CI, 0.99 to 1.55 in the initiation stratum; hazard ratio, 1.20; 95% CI, 0.94 to 1.55 in the continuation stratum; P=0.87 for interaction).
Bleeding Risk
Table 3.
Table 3. Absolute Increase in the Risk of a Composite of Life-Threatening or Major Bleeding with Aspirin Therapy, Starting on Each of the First 10 Postoperative Days until 30 Days after Surgery. To better understand the risk of bleeding on the basis of the timing of administration of aspirin, we undertook post hoc analyses. Among patients who were alive and did not have life-threatening or major bleeding, we determined the subsequent risk of a composite of life-threatening or major bleeding until day 30, starting on the day of surgery and then starting on each day thereafter (Table 3). The absolute increase in the risk of a composite bleeding outcome associated with aspirin was 1.2% from the day of surgery up to 30 days and 0.9% from day 4 after surgery up to 30 days. If a patient survived without the composite bleeding outcome until day 8 after surgery, the increase in risk from day 8 to day 30 was 0.3% (3 in 1000 patients).
Table S5 in the Supplementary Appendix shows the results of the post hoc multivariable analysis investigating potential factors associated with perioperative myocardial infarction. The composite of life-threatening or major bleeding was an independent predictor of myocardial infarction (hazard ratio, 1.82; 95% CI, 1.40 to 2.36; P<0.001).
Discussion
In this trial, the use of low-dose perioperative aspirin, as compared with placebo, did not reduce the rate of a composite of death or nonfatal myocardial infarction (the primary outcome) or the rates of the two secondary composite outcomes. The use of perioperative aspirin increased the risk of major bleeding (hazard ratio, 1.23; 95% CI, 1.01 to 1.49). The results with respect to the primary and secondary outcomes were consistent in the initiation stratum and the continuation stratum.
In a meta-analysis of data from trials involving more than 110,000 patients who were not undergoing surgery, the use of aspirin, for primary and for secondary prevention, reduced the relative risk of myocardial infarction by 20% and 25%, respectively.9 In contrast, the Pulmonary Embolism Prevention (PEP) trial included 13,356 patients undergoing surgery for a hip fracture.13 Patients received 160 mg of aspirin or placebo before surgery and daily for 35 days. Aspirin was associated with an increased risk of myocardial infarction (hazard ratio, 1.33; 95% CI, 1.00 to 1.78), although the number of myocardial infarctions (184) was much lower than that in our study (624; hazard ratio with aspirin, 0.98; 95% CI, 0.84 to 1.15).
Consistent with our findings, the PEP trial and other perioperative trials have shown that aspirin significantly increases the risk of bleeding requiring a transfusion.13,14 In previous surgical trials with hundreds of venous thromboembolism events, the use of aspirin decreased the risk of deep-vein thrombosis and pulmonary embolism by one third.13,14 In our study, relatively few patients had deep-vein thrombosis (60 patients) or pulmonary embolism (64 patients), and more patients in our study than in the PEP trial received concomitant anticoagulant prophylaxis (65.0% vs. 44.4%).
Observational data suggest that the discontinuation of aspirin before surgery results in an increased thrombotic risk.19,23 In our study, among the 4382 patients in the continuation stratum, we found no increase in thrombotic events owing to preoperative withholding of aspirin.
In the nonoperative setting, aspirin prevents myocardial infarction in patients with or at risk for atherosclerotic disease. However, in our study, aspirin did not prevent perioperative myocardial infarction. We offer three potential explanations for this finding. First, previous studies and our post hoc multivariable analysis showed that major bleeding was associated with perioperative myocardial infarction.3,24 The absolute increase in bleeding risk with aspirin is greater in the perioperative setting than the nonoperative setting. It is possible that aspirin prevented some perioperative myocardial infarctions through thrombus inhibition and caused some myocardial infarctions through bleeding and subsequent mismatch between the supply of and demand for myocardial oxygen, thus resulting in the overall neutral effect in our study. Second, the lower boundary of the hazard ratio for myocardial infarction was 0.84, and we cannot exclude the possibility of a missed moderate effect that would be consistent with results of other aspirin trials.9 Third, coronary-artery thrombus may not be the dominant mechanism of perioperative myocardial infarction.5,6
The results with respect to the primary and secondary outcomes were similar across the two aspirin strata. There were significant between-group differences in one tertiary outcome (acute kidney injury with receipt of dialysis) and two safety outcomes (major bleeding and stroke) in one aspirin stratum but not the other (Table S4 in the Supplementary Appendix). The interaction P value for the aspirin stratum was not significant for two of these outcomes (i.e., acute kidney injury with receipt of dialysis and major bleeding), suggesting that there is no significant difference in effect across the aspirin strata for these two outcomes and that the results in the overall population provide the most reliable effect estimates.
Our data suggest that among patients on a long-term aspirin regimen, stopping aspirin 3 or more days before surgery may decrease the risk of major bleeding. Because we did not randomly assign patients according to the timing of aspirin cessation before surgery, we cannot determine the most effective timing to minimize bleeding risk. Studies have suggested that hemostasis is unimpaired if at least 20% of the platelets have normal COX-1 activity25,26 and 12% of circulating platelets are replaced every 24 hours.27,28 Therefore, stopping aspirin 72 or more hours before surgery may be adequate to minimize the risk of perioperative bleeding.
We observed one significant interaction: aspirin appeared to reduce the incidence of stroke in the initiation stratum but not in the continuation stratum (P=0.01 for interaction). Several considerations suggest that this is a spurious subgroup effect.29 First, there were only 15 strokes in the initiation stratum, so the power to detect a change is small. Second, the effect of aspirin on reducing the risk of stroke in the initiation stratum was large (hazard ratio, 0.25), an effect that was inconsistent with the effect in the nonoperative setting on the basis of analyses of more than 1000 strokes and the perioperative data from the PEP trial with 103 strokes (hazard ratio for aspirin, 1.10; 95% CI, 0.75 to 1.62).9,13 Third, since this analysis was 1 of 19 tertiary or safety subgroup analyses that we performed, the results may be a chance finding. Finally, our hypothesized direction was opposite to that observed (i.e., we expected more benefit in the continuation stratum because of an aspirin-withdrawal effect). Therefore, the best estimate of the effect of aspirin on stroke is probably reflected in the overall population (hazard ratio, 0.84; 95% CI, 0.43 to 1.64).
If clinicians plan to use an anticoagulant agent for perioperative prevention of venous thromboembolism, our results suggest that starting or continuing aspirin throughout the perioperative period will provide no additional benefit but will increase the risk of major bleeding. However, our findings do not resolve the issue of the relative merits of aspirin versus other anticoagulant agents for perioperative thromboprophylaxis.30 Although the POISE-2 trial is a large study by perioperative standards, the lower boundary (0.86) and upper boundary (1.15) of the hazard ratio for the primary outcome show that we have not excluded the possibility of appreciable benefit or harm.
It should be noted that we excluded patients who received a bare-metal coronary stent less than 6 weeks before surgery or a drug-eluting coronary stent less than 1 year before surgery. Observational data have suggested that perioperative aspirin prevents myocardial infarction and stent thrombosis in these two groups of patients.31
For patients on a long-term aspirin regimen, the most effective time to restart aspirin would be 8 to 10 days after surgery, when the bleeding risk has diminished considerably. If physicians consider starting aspirin after surgery to treat a thrombotic event (e.g., stroke or myocardial infarction), they can expect an absolute increase of 1.0 to 1.3 percentage points in the risk of life-threatening or major bleeding if aspirin is administered within the first 2 days after surgery. Physicians and their patients will have to weigh this risk against the high risk of death from the thrombotic event and the potential benefits of aspirin.3,12,16
In conclusion, the administration of aspirin before noncardiac surgery and throughout the early postsurgical period had no significant effect on the rate of death or nonfatal myocardial infarction but increased the risk of major bleeding. These findings apply both to patients who were not already receiving aspirin and to those who were on a long-term aspirin regimen.
Appendix
The authors' affiliations are as follows: the Population Health Research Institute, Hamilton Health Sciences and McMaster University (P.J.D., M.M., A.R., F.B., G.L.B., J.E., Y.L.M., P.G., J.P., R.W., A.L., S.P., S.C., S.Y.), the Departments of Clinical Epidemiology and Biostatistics (P.J.D., G.G., D.C., J.E., Y.L.M., J.P., C.K., S.Y.), Medicine (P.J.D., G.G., M.T., D.C., J.E., R.M., C.K., S.Y.), Anesthesia (T.V., Y.L.M.), Surgery (R.W., A.L.), and Critical Care (R.W.), McMaster University, Hamilton, ON, the Department of Medicine, London Health Sciences Centre, London, ON (M.M.), the Department of Anesthesiology and Perioperative Medicine, Kingston General Hospital and Queen's University, Kingston, ON (J.L.P.), the Department of Medicine, Division of Nephrology, University of Western Ontario, London, ON (A.X.G.), the Department of Surgery, University of Manitoba, Winnipeg (S.S.), and the Department of Medicine, University of Alberta, Edmonton (M.G.) — all in Canada; the Department of Outcomes Research, Anesthesiology Institute, Cleveland Clinic, Cleveland (D.I.S., A.K.); the Department of Anaesthesia and Pain Management, Royal Melbourne Hospital, Melbourne, VIC, Australia (K.L.); Iberoamerican Cochrane Center (P.A.-C.) and the Anesthesiology Department (P.P.), Biomedical Research Institute, Barcelona; Universidad Autónoma de Bucaramanga and Fundación Cardioinfantil, Bogota, Colombia (J.C.V.); the Department of Pharmacology, Division of Clinical Research and Training, St. John's National Academy of Health Sciences, Bangalore, India (A.S., D.X.); the Department of Anaesthetics, Perioperative Research Group, Nelson R Mandela School of Medicine, University of KwaZulu-Natal, Durban, South Africa (B.M.B., R.N.R.); the Department of Anesthesiology, Herlev Hospital, University of Copenhagen, Herlev, Denmark (C.S.M.); Estudios Clínicos Latino América, Instituto Cardiovascular de Buenos Aires, Buenos Aires (F.B.); the Department of Anesthesia, University Hospital Basel, Basel, Switzerland (G.L.B.); the Department of Anaesthesia and Intensive Care, Chinese University of Hong Kong, Hong Kong (M.T.V.C.); the Department of Anesthesiology, University of North Carolina, Chapel Hill (P.A.K.); Anesthesiology, Cliniques universitaires Saint-Luc, Brussels (P.F.); Universidad Peruana Cayetano Heredia, Lima, Peru (G.M.); the Department of Anesthesia and Intensive Care, Medical University of Vienna, Vienna (E.F.); the Department of Surgery, Shifa International Hospital, Islamabad, Pakistan (M.A.); the Department of Anesthesiology, Clinica Santa Maria, Santiago, Chile (D.T.); the Department of Anesthesiology, University of Malaya, Kuala Lumpur, Malaysia (C.Y.W.); Research Institute HCor (Hospital do Coracão), São Paulo (O.B.); Anesthesia and Intensive Care, San Raffaele Scientific Institute, Milan (L.P.); Clinical Trial Service Unit and Epidemiological Studies Unit, University of Oxford, Oxford, United Kingdom (C.B.); and the George Institute for Global Health and the University of Sydney, Sydney (C.C.).
Supplementary Material
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Source: https://www.nejm.org/doi/full/10.1056/NEJMoa1401105
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