Recommended Use of Aspirin and Other Antiplatelet Medications Among Adults — National Ambulatory Medical Care Survey and National Hospital Ambulatory Medical Care Survey, United States, 2005–2008

Mary G. George, MD1

Xin Tong, MPH1

Nancy Sonnenfeld, PhD2

Yuling Hong, MD, PhD1

1Division for Heart Disease and Stroke Prevention, National Center for Chronic Disease Prevention and Health Promotion

2National Center for Health Statistics

Corresponding author: Mary G. George, MD, National Center for Chronic Disease Prevention and Health Promotion, CDC, 4770 Buford Hwy, MS F-72, Atlanta, GA 30341. Telephone: 770-488-8092; Fax: 770-488-8334; E-mail: MGeorge@cdc.gov.

Introduction

Cardiovascular disease (CVD) is the most highly prevalent disease in the United States and remains the leading cause of death among adults aged ≥18 years despite advancements in treatment and prevention in recent decades (1). Each year, approximately 800,000 persons die from CVD, which includes coronary heart disease (CHD) (1,2); the majority of those persons who die from CVD had underlying atherosclerosis. Approximately 7.9 million U.S. adults have a history of heart attack, approximately 7 million U.S. adults have a history of stroke (1), and, approximately 16 million U.S. adults have received a diagnosis of CHD (2). CVD and CHD cause a substantial economic burden in the United States. In 2010, the estimated annual cost (direct and indirect) of CVD in the United States was approximately $450 billion, including $109 billion for CHD and $54 billion for stroke alone (3).

Preventive care and lifestyle interventions have proven to be effective in reducing atherosclerotic CVD (4,5). Taking aspirin or other antiplatelet medications is one of several preventive interventions that can provide substantial benefit for patients with ischemic vascular disease and is strongly recommended in practice guidelines (6,7). This report summarizes the estimated prevalence of physician prescription of aspirin and other antiplatelet medications for patients with or without ischemic vascular disease as recommended by the U.S. Preventive Services Task Force (USPSTF) and other major guidelines (8–15). Previous research has indicated that the use of aspirin among eligible patients is suboptimal, even for those patients at highest risk (16). In persons who do not have a history of ischemic vascular disease, the net benefit is dependent upon the patient's risk for suffering a stroke or myocardial infarction compared with their chances of harm from treatment.

The information in this report is intended for clinicians who treat patients with ischemic vascular disease and patients who are at high risk for suffering cardiovascular disease and stroke. In addition, this information can serve as a baseline to monitor progress and measure the impact of use of recommended clinical preventive services.

Methods

To estimate the prevalence of physician-prescribed aspirin and other antiplatelet medications (e.g., clopidogrel, ticlid, and dipyridamole) among adults aged ≥18 years with or without ischemic vascular disease as recommended by USPSTF and other major guidelines, CDC analyzed 2005–2008 data from the National Ambulatory Medical Care Survey (NAMCS) and the National Hospital Ambulatory Medical Care Survey (NHAMCS) (17). These two national surveys collect data annually on the provision of ambulatory care services to patients of all ages from office-based physicians and in-hospital outpatient departments. The methods and sampling frame of NAMCS and NHAMCS have been described in detail elsewhere (18). Pregnant women (ICD-9-CM codes: V22, V23, and V28), visits for pre- or postsurgery follow-up, patients with documented contraindications to chronic aspirin use (coagulation defects, purpura and other hemorrhagic conditions, subarachnoid hemorrhage, intracerebral hemorrhage, acute hepatic failure, and gastrointestinal hemorrhage), and persons prescribed anticoagulant medication (warfarin, heparin, or low molecular weight heparins) were excluded from this analysis of patients with or without ischemic vascular disease. In addition, patients without ischemic vascular disease who were prescribed nonsteroidal anti-inflammatory drugs (NSAIDs) were excluded from analyses because of the increased risk for bleeding complications when NSAIDs are used together with aspirin.

For both study groups (patients with and those without ischemic vascular disease), the unit of analysis used was a patient visit. With the exception of physician and clinic specialty (obtained from the provider interview and sampling frames), all data in this analysis were obtained through abstraction of patient visit records using a standardized patient record form. Key items included on the patient record form include major reason for visit (new problem [<3 months], chronic problem [routine or flare-up], and preventive care); a maximum of three ICD-9-CM diagnosis codes related to the visit); systolic blood pressure; regardless of visit diagnoses, separate checkboxes identifying patients with diagnoses of cerebrovascular disease, congestive heart failure, diabetes, hypertension, hyperlipidemia, and ischemic heart disease; check boxes to identify patient's tobacco use ("current," "not current," or "unknown"); and up to eight over-the-counter or prescription drugs that were "ordered, supplied, administered, or continued at this visit." Aspirin and other antiplatelet medications identified as either "new" or "continued at this visit" were considered as prescribed in this analysis.

Of a total of 198,042 patient visits among adults aged ≥18 years, 6,574 (4.0%) visits met the criteria for visits by patients having ischemic vascular disease. For patients with ischemic vascular disease, analysis was limited to visits to physicians in the following specialties: general medicine, family practice, general practice, general medicine, geriatric medicine, internal medicine, cardiovascular diseases, and neurology as well as to hospital outpatient department clinics specializing in general medicine or obstetrics and gynecology. Ischemic vascular disease was determined by the presence of an International Classification of Disease, Ninth Revision, Clinical Modification (ICD-9-CM) code for ischemic heart disease, ischemic stroke or carotid stenosis, peripheral vascular disease, or atheroembolic disease (ICD-9-CM codes: 410, 411, 412, 413, 414.0, 414.2, 414.8, 414.9, 429.2, 433, 434, 435, V12.54, 437.0, 437.1, 440.1, 440.2, 444, 445, V45.81, and V45.82) or by the presence of a current diagnosis of cerebrovascular disease or ischemic heart disease.

Of 198,042 patient visits among adults aged ≥18 years, 9,369 (6.1%) visits met the criteria for visits by patients without ischemic vascular disease. For patients without ischemic vascular disease, the analysis was limited to practitioners in general medicine, family practice, general practice, geriatric medicine, cardiovascular diseases, and internal medicine. The inclusion criteria for patients without ischemic vascular disease were defined so as to include men aged 45–79 years at risk for myocardial infarction and women aged 55–79 years at risk for stroke. The inclusion criteria were based on clinical guidelines (10,12–15) and USPSTF recommendations identifying the risk levels at which benefit of treatment outweighs the harm of treatment (e.g., gastrointestinal or cerebral hemorrhage) (8).

Sex-specific risk levels for myocardial infarction and stroke were based on Framingham risk for coronary heart disease risk for men and Framingham stroke risk for women (19). Visits by men aged 45–59 years with at least an intermediate risk (≥ 6% for a 10-year risk) for coronary heart disease were defined as one or more risk factors (hypertension, current tobacco user, hypercholesterolemia, or diabetes). Visits by men aged 60–79 years with a high risk (≥10% for a 10-year risk) for coronary heart disease were defined as having two or more risk factors (hypertension, current tobacco user, hypercholesterolemia, or diabetes). Visits by women aged 55–64 years with a moderate risk for stroke (i.e., ≥6% for a 10-year risk) were defined as having 1) atrial fibrillation, 2) left ventricular hypertrophy plus either hypertension or diabetes or current tobacco use, or 3) hypertension, diabetes, and current tobacco use. Visits by women aged 65–79 years with a high risk for stroke (i.e., ≥10% for a 10-year risk) were defined as having atrial fibrillation or any two risk factors (left ventricular hypertrophy, hypertension, diabetes, or current tobacco use).

Data from NAMCS and NHAMCS were combined, and two time intervals were selected for analysis: 2005–2006 and 2007–2008. Patient visit weights were used to extrapolate these findings to national estimates. Chi-square or the Fisher exact test was used to test for the statistical significance of the associations, and a two-tailed p-value at the p = 0.05 level was deemed statistically significant. If chi-square tests were statistically significant, a post hoc t-test procedure was used to make pairwise comparisons. All data analyses were performed with SAS (Release 9.2, Cary, North Carolina). To account for survey design features, including clustering and weighting, all statistical analyses were performed with the statistical software package SUDAAN (Release 9.2, Research Triangle Institute, Research Park, North Carolina).

Results

During 2007–2008, physicians prescribed aspirin and other antiplatelet medications at 46.9% of patient visits for patients with ischemic vascular disease, with no change compared with 2005–2006 (Table 1). Aspirin and other antiplatelet medications were prescribed less often at visits by female patients compared with visits by male patients (p = 0.002). Of the disease subgroups examined, physicians prescribed aspirin and other antiplatelet medications significantly more often when a patient had hyperlipidemia or ischemic heart disease and significantly less often for a patient with cerebrovascular disease. Cardiologists prescribed aspirin and other antiplatelet medications at 68% of visits compared with primary care specialists, who prescribed aspirin and other antiplatelet medications at only 35% of visits (p<0.001).

Although systolic blood pressure was measured as ≥160 mm Hg at only 9.4% of visits among those with ischemic vascular disease, physicians prescribed aspirin and other antiplatelet medications at 50% of these visits (Table 1). Aspirin use in the presence of uncontrolled hypertension increases the risk for hemorrhagic stroke (20). Among visits for preventive care or chronic disease care, physicians prescribed aspirin and other antiplatelet medications (both at 49%) compared with 38% for visits for a new problem (p<0.05 and p<0.01, respectively). During 2007–2008, the distribution of aspirin and other antiplatelet medications prescribed at visits among those with ischemic vascular disease (total: 1,732 sample visits when aspirin and other antiplatelet medications were prescribed), indicated that aspirin alone was prescribed at 59.3% of visits, aspirin and another antiplatelet medication was prescribed at 24.2% of visits, and an antiplatelet medication other than aspirin was prescribed at 16.6% of visits.

Physicians prescribed aspirin and other antiplatelet medications at 17.1% of visits during 2007–2008 for patients at risk for ischemic vascular disease (Table 2). If the analysis were limited to aspirin, with other antiplatelet medications excluded, the corresponding prescribing rate would be 14.9%. During 2007–2008, physicians prescribed aspirin and other antiplatelet medications at relatively few of the visits by patients in the USPSTF population recommended for consideration of aspirin for prevention of CVD and stroke (16.2% of visits by males and 21.7% of visits by females; p<0.05). Physicians prescribed antiplatelet medications at 14.1% of patient visits with a measured systolic blood pressure of ≥160 mm Hg for patients without ischemic vascular disease. Physicians were more likely to prescribe aspirin or other antiplatelet medications for patients seen for a chronic condition than they were for those seen for a new problem (19.5% versus 12.8%, respectively; p<0.01). Physicians were least likely to prescribe antiplatelet medication at visits paid by Medicaid (13.1%) whereas physicians prescribed these medications most often at visits paid by Medicare (21.9%; p<0.01).

During 2007–2008, the distribution of aspirin and other antiplatelet medications prescribed for patients without ischemic vascular disease (total: 1,030 sample visits at which aspirin and other antiplatelet medications were prescribed) indicated that aspirin alone was prescribed at 82.3% of visits, aspirin and another antiplatelet medication was prescribed at 6.7% of visits, and an antiplatelet medication other than aspirin was prescribed at 6.8% of visits (data not reported). At the visit level, among patients without ischemic vascular disease, physicians were most likely to prescribe aspirin and other antiplatelet medications for those patients with congestive heart failure (26.4%; p<0.05).

Discussion

The findings provided in this report indicate that prevalence of prescribing aspirin or other antiplatelet medications at outpatient health-care visits is low for patients who have been recommended to receive these medications based on the presence of ischemic vascular disease or certain risk factors. Despite the low prevalence of aspirin prescribing identified in this analysis, other studies using the same data sources have demonstrated that aspirin and other antiplatelet medication prescribing among patients with ischemic vascular disease was only 32.8% in 2003 (16). Previous reports have estimated that for every 10% increase in the use of antiplatelet medication among eligible adults aged 18–79 years, an estimated 8,000 deaths per year would be prevented (21). A 2006 study that ranked clinical preventive services based on cost effectiveness and the clinically preventable burden of disease demonstrated that aspirin prevention counseling was one of three prevention services that received the highest score among 25 studied preventive services (22).

Use of aspirin or other antiplatelet medications among patients with ischemic vascular disease is recommended by multiple guidelines addressing prevention of atherosclerotic heart disease, ischemic stroke and transient ischemic attacks, and peripheral vascular disease (8–15). The results of this analysis demonstrate that even among patient visits with evidence of ischemic or atherosclerotic heart, brain, and peripheral vascular disease, prescribing of aspirin and other antiplatelet medications is <50% despite many guidelines recommending treatment and multiple National Quality Forum (NQF)–endorsed measures of care supporting their use. Among patient visits by those with ischemic vascular disease, primary care providers prescribed antiplatelet medication at only 35% of visits. Cardiologists prescribed antiplatelet medications more frequently (at 68% of visits) than physicians in other specialties examined. Cardiologist prescribing practices were similar to that seen in the Reduction of Atherothrombosis for Continued Health (REACH) Registry (23) of 71% antithrombotic use among patients with established atherothrombosis or three or more risk factors for cardiovascular disease and stroke. Consistent with this finding, treatment by a cardiologist was associated with a higher frequency of prescribing antiplatelet therapy compared with prescribing by neurologists and primary care providers.

Differences in categorization of patients to those with or without ischemic vascular disease might explain lower rates of antiplatelet medication prescribed in the group at risk for ischemic vascular disease compared with other reports (24). Patients who had evidence of ischemic or atherosclerotic disease of the brain, heart, or peripheral vasculature but had not experienced a stroke or myocardial infarction were included in the ischemic vascular disease category (consistent with NQF quality measures #0068 [25], "Use of aspirin or other antithrombotic for ischemic vascular disease" and #0076 [26], "Percentage of adult patients aged 18–75 years who have ischemic vascular disease with optimally managed modifiable risk factors [low-density-lipoprotein (LDL), blood pressure, tobacco-free status, daily aspirin use.") Reasons for nonadherence to prescribing, whether at the patient or provider level, cannot be assessed; however, a recent study indicated that elderly patients frequently perceive the use of cardiovascular preventive medications as having greater risk for harm and side effects than benefit (27).

USPSTF recommends shared decision making between patient and physician for patients who are at risk for developing ischemic vascular disease. Patient-centered care regarding the use of aspirin for prevention of vascular disease events involves consideration of the individual patient's potential of experiencing a vascular event, their potential of sustaining harm from aspirin, and the patient's preference after discussing these considerations in consultation with their health-care provider (8,28–31). On the basis of this analysis, the opportunity exists for physicians to improve compliance with existing clinical guidelines for aspirin use to prevent the recurrence and progression of ischemic vascular disease.

Multiple reasons might account for low prevalence of prescribing aspirin or other antiplatelet medications. First, providers might lack knowledge of clinical guidelines. Second, different reasons for the visit might compete with counseling for physicians' time, and this might differ by provider type or payment source. Finally, physicians might be less likely to prescribe aspirin or other antiplatelet medications when they expect their patients not to adhere to their advice. These possibilities warrant future research.

Physician prescribing of aspirin requires a careful estimate of the benefit provided by aspirin and the potential harm attributable to aspirin, including shared decision making between patient and health-care provider. The American College of Cardiology and the American Heart Association recommend that patients have a comprehensive cardiovascular health assessment at least every 5 years starting at age 18 years and that those with cardiovascular risk factors (e.g., diabetes, hypertension, or tobacco use) should have their cardiovascular health risk assessed more frequently (14,29). The Patient Protection and Affordable Care Act of 2010 (as amended by the Healthcare and Education Reconciliation Act of 2010 and referred to collectively as the Affordable Care Act [ACA]) (32) provides several opportunities to assist in cardiovascular prevention with medications, promoting health risk assessment and patient-centered health care. The Affordable Care Act provides for a health-risk assessment in the annual wellness visit for Medicare patients, as well as counseling services aimed at reducing risk factors for chronic disease, including heart disease and stroke are provided in the Affordable Care Act (ACA §4103). In December 2011, CDC issued a framework for patient-centered health risk assessments (33). This framework is designed to provide health-care providers, payors, and policymakers with information on ways to increase adherence to evidence-based guidelines for prevention of chronic disease and to improve health outcomes through early identification of modifiable health risk factors and early implementation of behavior change interventions to prevent chronic disease such as heart disease and stroke.

The National Strategy to Improve Health Care Quality (ACA §3011) calls for promoting the most effective prevention and treatment practices for the leading causes of mortality, starting with cardiovascular disease, and includes efforts to decrease preventable hospitalizations such as those due to adverse drug events (e.g., hemorrhagic complications from antiplatelet use); promote treatment according to guidelines through quality improvement initiatives such as the Physician Quality Reporting System (ACA §3002), development of quality measures (ACA §3012), and meaningful use; accountable care organizations to better coordinate patient care and improve quality; create community health teams that coordinate prevention and disease management and support primary care providers (ACA §3502); and develop medication management services by pharmacists that can increase patient adherence (ACA §3503).

In September 2011, the U.S. Department of Health and Human Services launched Million Hearts (34), a national initiative to prevent 1 million heart attacks and strokes over the next 5 years. Led by CDC and the Centers for Medicare and Medicaid Services, the Million Hearts initiative aims to improve heart disease and stroke prevention by improving access to effective care, improving the quality of care, focusing more clinical attention on heart attack and stroke prevention, increasing public awareness of how to lead a heart-healthy lifestyle, and increasing the consistent use of high blood pressure and cholesterol medications. Improving appropriate use of aspirin through adherence to clinical guidelines, quality improvement initiatives, use of electronic medical records with programmed physician reminders, and academic detailing (academic educational outreach to physicians on current guidelines and best practices) has the potential to prevent cardiovascular events and improve the quality of life in patients with ischemic vascular disease. Coordinating disease management for patients with complex chronic disease can assist in optimizing vascular care and decreasing risk factors for vascular disease.

The findings in this report are subject to at least six limitations. Many of these limitations relate to the distinction between actual aspirin use in compliance with the USPSTF recommendations versus receipt of a prescription during the visit assessed by the survey. First, prescribing aspirin and other antiplatelet medications is contraindicated in patients with diseases that put them at high risk for bleeding or in combination with other medications that augment the risk for bleeding. An underestimation of aspirin use might have occurred because the ability to identify those conditions definitively is limited because only three ICD-9-CM codes per visit were permitted. Second, this analysis cannot assess instances in which providers considered aspirin use for patients who met the USPSTF guidelines but elected not to prescribe the medication based on a risk assessment and the patient's informed decision. Nonprescribing based on patient preference with respect to perceived benefit and harm is not captured in this analysis. Therefore, a higher percentage of physicians might be discussing aspirin with their patients than is reflected by what is documented as having been prescribed. Third, aspirin is an over-the-counter drug, so physicians might not be as likely to document aspirin use as they would be to document use of other prescription drugs. This might lead to an underestimation of providers' compliance with guidelines and recommendations. Fourth, data on required risk factors frequently were absent. For example, information on tobacco use was missing at 28.1% of visits during 2005–2006 and 27.5% of visits during 2007–2008 among those without ischemic vascular disease. For systolic blood pressure, the missing percentage was 3.8% during 2005–2006 and 7.1% during 2007–2008 for visits among those with ischemic vascular disease. In addition, certain risk factors (e.g., left ventricular hypertrophy and atrial fibrillation) would only be identified from one of the three visit ICD-9-CM visit diagnosis codes and might also be underestimated. This missing information might lead to underestimation of persons with a high enough risk for stroke or myocardial infarction to warrant consideration of aspirin or antiplatelet medications; it might also be differential with respect to patient characteristics. Fifth, the analysis was limited to primary care physicians and specialties most likely to care for patients with ischemic vascular disease or at high risk for ischemic vascular disease. Although this analysis indicated that cardiologists prescribed aspirin more frequently than primary care providers, this difference might reflect which provider assumes the prime role in addressing the patient's CVD rather than reflect awareness of USPSTF guidelines. Finally, NAMCS and NHAMCS are representative of patient visits rather than individual patients. Therefore, patients who visit their doctors most frequently such as those who are sicker could potentially be represented more often in the survey. This bias might lead to an overestimation of aspirin use although this bias is presumed to be small given that NAMCS and NHAMCS surveys each physician practice for only a 1-week period. NCHS has taken steps to address some of the limitations inherent in this current analysis by gathering more detailed information regarding care delivered to patients with cardiovascular disease risk factors over time. In particular, in 2012, NAMCS and NHAMCS will include modules to gather data regarding care delivered during the 12 months before the sampled visit for patients with cardiovascular disease risk factors such as hypertension, hypercholesterolemia, and prior stroke. For each prior visit, this new module includes data on medications prescribed, changes in medications, family history, and contraindications to certain medications. These changes in data collection methods should make it possible to better identify patients at risk for CVD per USPSTF guidelines who are without contraindication to aspirin therapy and better understand how prescribing aspirin and antiplatelet medications fits into patients' broader treatment patterns over time (35).

Conclusion

The findings provided in this report indicate that aspirin and other antiplatelet medication prescribing among patients with ischemic vascular disease increased from 32.8% in 2003 (16) to 46.9% during 2007–2008. Caution should be used in interpreting the magnitude of this change because of changes in the survey methods over time, which could bias comparisons with previous studies. However, these rates can serve as a baseline to track progress and measure the impact of use of preventive services as provided for in the Affordable Care Act. Increased use of aspirin and other antiplatelet medications according to established guidelines for patients with ischemic vascular disease is likely to reduce incident and recurrent myocardial infarctions and stroke substantially. Because CVD and stroke are leading causes of disability and death, efforts to improve access to prevention through health risk assessments and early identification of modifiable health risk behaviors, the implementation of accountable care organizations to better coordinate care and improve quality of care for patients with chronic disease, and medication therapy management services by pharmacists are important steps in providing appropriate aspirin and other antiplatelet medications to patients with or at risk for cardiovascular disease. The Affordable Care Act provides opportunities with respect to all these aspects of care. Continued public and private partnerships can provide opportunities to maximize use of clinical preventive services such as prescribing aspirin and other antiplatelet medications to reduce the incidence of CVD and stroke.

Acknowledgment

John E. Watts IV, Pharm D, National Center for Health Statistics, CDC, assisted in developing the medication file for the analysis.

References

1. Roger VL, Go AS, Lloyd-Jones DM, et al. Heart disease and stroke statistics—2012 update: a report from the American Heart Association. Circulation 2012;125:e12–230.
2. Miniño AM, Murphy SL, Xu JQ, Kochanek KD. Deaths: final data for 2008. Natl Vital Stat Rep 2011;59(10).
3. Heidenreich PA, Trogdon JG, Khavjou OA, et al. Forecasting the future of cardiovascular disease in the United States: a policy statement from the American Heart Association. Circulation 2011;123:933–44.
4. Ford ES, Ajani UA, Croft JB, et al. Explaining the decrease in U.S. deaths from coronary disease, 1980–2000. N Engl J Med 2007;356:2388–98.
5. National Institutes of Health. Third report of the National Cholesterol Education Program (NCEP) expert panel on detection, evaluation, and treatment of high blood cholesterol in adults (ATP III), final report. National Heart, Lung, and Blood Institute, National Institutes of Health; 2002. NIH Publication No. 02-5215.
6. Smith SC Jr, Allen J, Blair SN, et al. AHA/ACC guidelines for secondary prevention for patients with coronary and other atherosclerotic vascular disease: 2006 update: endorsed by the National Heart, Lung, and Blood Institute. Circulation 2006;113:2363–72.
7. Furie KL, Kasner SE, Adams RJ, et al. Guidelines for the prevention of stroke in patients with stroke or transient ischemic attack: a guideline for healthcare professionals from the American Heart Association/American Stroke Association. Stroke 2011;42:227–76.
8. US Preventive Services Task Force. Aspirin for the prevention of cardiovascular disease: U.S. Preventive Services Task Force recommendation statement. Ann Intern Med 2009;150:396–404.
9. Anderson JL, Adams CD, Antman EM, et al. 2011 ACCF/AHA focused update incorporated into the ACC/AHA 2007 guidelines for the management of patients with unstable angina/non-st-elevation myocardial infarction. Circulation 2011;123:e426–579.
10. Becker, RC, Meade, TW, Berger, PB, et al. The primary and secondary prevention of coronary artery disease: American College of Chest physicians evidence-based clinical practice guidelines. 8th ed. Chest 2008;133:776S.
11. Brott TG, Halperin JL, Abbara S, et al. 2011 ASA/ACCF/AHA/AANN/AANS/ACR/ASNR/CNS/ SAIP/SCAI/SIR/SNIS/SVM/SVS guidelines on the management of patients with extracranial carotid and vertebral artery disease. Circulation 2011;124:e54-e130.
12. Goldstein LB, Bushnell CD, Adams RJ, et al. Guidelines for the primary prevention of stroke. Stroke 2011;42:517–84.
13. Redberg RF, Benjamin EJ, Bittner V, et al. AHA/ACCF 2009 performance measures for primary prevention of cardiovascular disease in adults. Circulation 2009;120:1296–336.
14. Mosca L, Benjamin EJ, Berra K, et al. Effectiveness-based guidelines for the prevention of cardiovascular disease in women 2011 update. Circulation 2011;123:1243–62.
15. Pignone M, Alberts MJ, Colwell JA, et al. Aspirin for primary prevention of cardiovascular events in people with diabetes. Circulation 2010;121:2694–701.
16. Stafford RS, Monti V, Ma J. Underutilization of aspirin persists in US ambulatory care for the secondary and primary prevention of cardiovascular disease. PLoS Med 2005;2:e353.
17. Schappert SM, Rechtsteiner EA. Ambulatory medical care utilization estimates for 2007. Available at http://www.cdc.gov/nchs/data/series/sr_13/sr13_169.pdf. Accessed May 17, 2012.
18. CDC, National Center for Health Statistics. 2008 NAMCS Micro-data file documentation. Available at http://www.cdc.gov/nchs/ahcd/ahcd_questionnaires.htm. Accessed May 17, 2012.
19. Framingham Heart Study: risk profile scores. Available at http://www.framinghamheartstudy.org/risk/index.html. Accessed May 17, 2012.
20. Saloheimo P, Juvela S, Hillbom M. Use of aspirin, epistaxis, untreated hypertension as risk factors for primary intracerebral hemorrhage in middle-aged and elderly people. Stroke 2001;32:399–404.
21. Farley TA, Dalal MA, Mostashari F, Frieden TR. Deaths preventable in the U.S. by improvements in use of clinical preventive services. Am J Prev Med 2010;38:600–19.
22. Maciosek MV, Coffield AB, Edwards NM, et al. Priorities among effective clinical preventive services: results of a systematic review and analysis. Am J Prev Med 2006;31:52–61.
23. Cannon CP, Rhee KE, Califf RM, et al. Current use of aspirin and antithrombotic agents in the United States among outpatients with atherothrombotic disease (from the Reduction of Atherothrombosis for Continued Health [REACH] Registry). Am J Cardiol 2010;105:445–52.
24. Sanchez DR, Roux AVD, Michos ED, et al. comparison of the racial/ethnic prevalence of regular aspirin use for primary prevention of coronary heart disease from the Multi-Ethnic Study of Atherosclerosis. Am J Cardiol 2011;107:41–6.
25. National Quality Forum. 0068 IVD: use of aspirin or antithrombotics (NCQA). Available at http://www.qualityforum.org/Projects/Cardiovascular_Endorsement_and_Maintenance_2010.aspx#t=2&s=&p=6|4|. Accessed May 17, 2012.
26. National Quality Forum. 0076 optimal vascular care (MNCM). Available at http://www.qualityforum.org/Projects/Cardiovascular_Endorsement_and_Maintenance_2010.aspx#t=2&s=&p=6|4|. Accessed May 17, 2012.
27. Fried TR, Tinetti ME, Towle Va, et al. Effects of benefits and harms on older persons' willingness to take medication for primary cardiovascular prevention. Arch Intern Med 2011;17:923–8.
28. George MG, Hong Y. Aspirin for prevention of cardiovascular disease. In: National Business Group on Health. A purchaser's guide to clinical preventive services: moving science into coverage. Available at http://www.businessgrouphealth.org/preventive/topics/aspirin.cfm. Accessed May 17, 2012.
29. US Preventive Services Task Force. Aspirin for prevention of cardiovascular disease. Available at http://www.uspreventiveservicestaskforce.org/uspstf/uspsasmi.htm. Accessed May 17, 2012.
30. Wolff T, Miller T, Ko S. Aspirin for the primary prevention of cardiovascular events: an update of the evidence for the U.S. Preventive Services Task Force. Ann Intern Med 2009;150:405–10.
31. Wolff T, Miller T, Ko S. Aspirin for the primary prevention of cardiovascular events: an update of the evidence for the U.S. Preventive Services Task Force. AHRQ Publication No. 09-05129-EF.
32. Patient Protection and Affordable Care Act of 2010. Pub. L. No. 114–48 (March 23, 2010), as amended through May 1, 2010. Available at http://www.healthcare.gov/law/full/index.html. Accessed May 17, 2012.
33. Goetzel RZ, Staley P, Ogden L, et al. A framework for patient-centered health risk assessments – providing health promotion and disease prevention services to Medicare beneficiaries. Available at http://www.cdc.gov/policy/opth/hra. Accessed May 17, 2012.
34. Frieden TR; Berwick DM. The "Million Hearts" Initiative — Preventing Heart Attacks and Strokes. N Engl J Med 2011; 365:e27.
35. National Center for Health Statistics. Welcome NAMCS Patients. Available at http://www.cdc.gov/nchs/ahcd/namcs_participant.htm. Accessed May 17, 2012.