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Ann Thorac Surg 2007;83:993-1001
© 2007 The Society of Thoracic Surgeons
a Duke Clinical Research Institute and Division of Cardiology, Duke University Medical Center, Durham, North Carolina
b Cardiothoracic Surgery Associates of North Texas, Dallas, Texas
c University of Cincinnati Surgeons, Inc, Cincinnati, Ohio
d Division of Cardiac Surgery, Brigham and Womens Hospital, Boston, Massachusetts
e Division of Cardiovascular and Thoracic Surgery, Missouri Baptist Medical Center, St. Louis, Missouri
f Corgentech, Inc, San Francisco, California
g Division of Cardiology, Beth Israel Deaconess Medical Center, Boston, Massachusetts
h Division of Cardiothoracic Surgery, Brody School of Medicine at Eastern Carolina University, Greenville, North Carolina
Accepted for publication October 16, 2006.
* Address correspondence to Dr Alexander, Duke University Medical Center, DUMC Box 3850, Durham, NC 27710 (Email: john.h.alexander{at}duke.edu).
| Drs Gennevois, Alexander, and Gibson disclose that they have a financial relationship with Corgentech, Inc.
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| Abstract |
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Methods: Patients undergoing coronary artery bypass graft surgery in the PREVENT IV trial (n = 2970) were surveyed for use of antiplatelet agents, ß-blockers, angiotensin-converting enzyme inhibitors or angiotensin receptor blockers, and lipid-lowering agents after hospital discharge and at 1 year. Patients were categorized based on their percentage use of indicated medications after hospital discharge. Cox modeling was used to determine the association between medication use categories and rates of death or myocardial infarction through 2 years after adjustment for clinical factors, the number of indicated medications, and treatment propensity.
Results: Rates of use of antiplatelet agents and lipid-lowering agents were high at discharge and at 1 year, but use of ß-blockers and angiotensin-converting enzyme inhibitors or angiotensin receptor blockers was suboptimal. There was a stepwise association between medication use at discharge and patient outcomes (p for trend = 0.014). Patients taking 50% or less of indicated medications at discharge had a significantly higher 2-year rate of death or myocardial infarction (8.0% versus 4.2%; adjusted hazard ratio, 1.69; 95% confidence interval, 1.12 to 2.55; p = 0.013) than those taking all indicated medications.
Conclusions: Greater use of indicated secondary prevention medications after coronary artery bypass graft surgery is associated with a lower 2-year rate of death or myocardial infarction. These data underscore the importance of appropriate secondary prevention measures to improve long-term clinical outcomes after coronary artery bypass graft surgery.
Coronary artery bypass graft surgery (CABG) is among the most commonly performed procedures in the United States, with almost 500,000 CABG operations performed annually [1]. During the past two decades, patients undergoing CABG have had an increasing burden of comorbidities and cardiac risk factors [2, 3]. Despite the higher-risk profile of patients undergoing CABG, perioperative mortality has declined in CABG patients as a result of advances in operative techniques and improvements in the in-hospital management of CABG patients [2]. However, long-term survival after CABG has not improved during the past two decades [3], underscoring the need for improvements in secondary prevention strategies in these patients [4].
The use of secondary prevention medications, such as antiplatelet agents [5, 6], angiotensin-converting enzyme (ACE) inhibitors [7, 8], ß-blockers [9], and lipid-lowering therapy [10, 11], have each been associated with a lower rate of adverse cardiac events in patients after CABG. However, whether greater use of multiple secondary prevention medications after CABG is associated with improved clinical outcomes is unknown. Recent studies have reported that appropriate medical therapies are underutilized after CABG surgery [12, 13]; however, they did not report the impact of medication use on clinical outcomes. In the PRoject of Ex-vivo Vein graft ENgineering via Transfection (PREVENT) IV trial of 3,014 patients undergoing first CABG surgery [14, 15], patients were surveyed for use of medications just after hospital discharge and at 1 year, and were followed for 2 years after CABG for the occurrence of death or myocardial infarction (MI). These data provide a unique opportunity to investigate the association between the use of multiple secondary prevention medications and clinical outcomes after CABG.
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Medication Use
Discharge medication use was collected between hospital discharge and 30 days by contacting patients by phone or in person during the first follow-up clinic visit within 30 days of CABG. Medications were collected and then coded into classes, including antiplatelet agents (aspirin or clopidogrel), ACE inhibitors or angiotensin receptor blockers (ARBs), ß-blockers, and lipid-lowering medications (statins or any nonstatin lipid-lowering agent). At 1-year follow-up, patients were again contacted by mail to document which medications they were taking. Those who did not respond by mail were subsequently contacted by phone to obtain medication use at 1 year.
Patient Population
Patients were included in this study if they were alive and free from MI at the time of 30-day follow-up. Of the 3,014 patients enrolled in PREVENT IV, 2,970 were included for rates of use and associated outcomes (Fig 1). Patients were then stratified on the basis of whether or not they were ideal candidates for each of the four classes of secondary prevention medications at the time of hospital discharge based on having a class IA indication for these medications according to the American College of Cardiology/American Heart Association guidelines for CABG [16] or for chronic heart failure in adult patients [17], and having no relative or absolute contraindications for that medication (Appendix). The numbers of patients considered ideal and nonideal candidates for each medication class are shown in Figure 1.
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To determine whether more complete use of multiple secondary prevention medications at discharge was associated with a lower rate of death or MI at 2 years, we used the KaplanMeier method to determine the unadjusted 2-year rate of death or MI among patients in each comparison group defined in Table 1. We then created another Cox proportional hazards model for 2-year death or MI in which patients taking half or fewer of the indicated medications at hospital discharge and patients taking more than half but not all indicated medications were compared with the reference group of patients taking all indicated medications at discharge. This model was adjusted for age, sex, recent MI, history of congestive heart failure, creatinine clearance, history of diabetes, the propensity to be taking all indicated medications, and the number of drugs for which patients had an ideal indication.
All analyses were performed using SAS statistical software, version 8.2 (SAS Inc, Cary, NC), and a probability value of 0.05 or less was considered statistically significant.
| Results |
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Rates of Use of Secondary Prevention Medications
In PREVENT IV, rates of use of antiplatelet agents, ß-blockers, and lipid-lowering agents were relatively high after discharge after CABG, but use of ACE inhibitors or ARBs was suboptimal. Rates of use of secondary prevention medications in PREVENT IV were notably higher than those reported from "real-world" CABG patients from the 2002 Society of Thoracic Surgeons National Database [14] (in which only 80%, 68%, 28%, and 55% of patients were receiving aspirin, ß-blockers, ACE inhibitors, and lipid-lowering therapy, respectively, at discharge), and from elderly patients who underwent CABG after acute MI in the Centers for Medicare/Medicaid Services database [12] (in which 88%, 62%, and 35% of patients with proven indications for aspirin, ß-blockers, or lipid-lowering drugs, respectively, actually received these drugs). These "real-world" registry data support the need to improve discharge processes to increase prescription rates for secondary prevention medications after CABG.
We were able to capture 1-year medication use data in more than 95% of the PREVENT IV patients who were alive at 1 year. Rates of use of secondary prevention medications were surprisingly well maintained at 1-year follow-up, particularly for antiplatelet and lipid-lowering agents, and use actually increased substantially for ACE inhibitors and ARBs. Furthermore, the overwhelming majority of patients taking secondary prevention agents at 1 year had also taken these agents soon after hospital discharge, and only a very small percentage of patients not taking these medications at discharge were started on these drugs de novo during the first year of follow-up. These data clearly attest to the critical importance of initiating appropriate secondary prevention therapies soon after CABG to ensure long-term adherence to these proven therapies.
Medication Use and Clinical Events
The benefit of antiplatelet therapy after CABG has been well established [5, 6]. In our study, the use of antiplatelet agents was associated with a 56% lower hazard of death or MI at 2 years. However, as only a very small proportion of the overall cohort (3%) was not on an antiplatelet agent at hospital discharge, it is likely that the lack of use of antiplatelet agents was mainly a marker of serious comorbidities that led to a high clinical event rate.
Use of ß-blockers at discharge in those with a proven indication (ie, prior MI or symptomatic congestive heart failure with left ventricular systolic dysfunction) was associated with a trend toward a lower hazard of death or MI at 2 years after CABG. These findings are consistent with studies demonstrating the survival advantage conferred by ß-blockers on patients after acute MI [18, 19] and congestive heart failure with left ventricular dysfunction [20, 21]. However, we did not demonstrate an association between ß-blocker use and improved outcomes in post-CABG patients who were not ideal candidates for these medications (ie, in most routine CABG patients). Although observational studies have suggested that preoperative ß-blocker use is associated with reduced rates of morbidity and mortality after CABG [22, 23], a randomized placebo-controlled trial demonstrated no clinical benefit from ß-blocker use for 2 years after CABG in a relatively low-risk group of post-CABG patients (similar to the PREVENT IV cohort) [24].
Use of ACE inhibitors or ARBs was not associated with improved 2-year outcomes in post-CABG patients in our study [16, 17]. The benefit of ACE inhibitors in patients with left ventricular systolic dysfunction is well established [25, 26]; however, the median ejection fraction (0.50) in our study was higher than that of patients in these prior studies. Use of ACE inhibitors in patients with prior MI [27, 28] or at high-risk for vascular events [29, 30] has also been shown to be beneficial, but two recent trials of lower-risk coronary heart disease patients with preserved left ventricular function [3133], including one in post-CABG patients [32, 33], failed to demonstrate a reduction in mortality or other vascular events with ACE inhibition.
Use of lipid-lowering therapy in our study was also not associated with improved 2-year outcomes. Although several trials have demonstrated that statins reduce mortality and other vascular events compared with placebo among patients with coronary heart disease [34, 35], a clinical benefit was not apparent during the first few years of follow-up. Furthermore, in a randomized trial of aggressive-intensity versus moderate-intensity lipid-lowering therapy in post-CABG patients, aggressive lipid-lowering therapy did not reduce the incidence of death or MI after 4 years [10]. Similarly, the 2-year follow-up of PREVENT IV may not be of sufficient duration after CABG to detect a clinical benefit from lipid-lowering therapy.
It is noteworthy (but not surprising) that we found an association between composite medication use and clinical outcomes, but not between the use of most individual medications and subsequent outcomes. Although almost 3,000 patients are included in our study, we did not expect to have sufficient power to detect an association between individual medications and clinical outcomes after only a 2-year follow-up period. However, it is reasonable that we detected an association between more complete use of multiple secondary prevention medications and clinical outcomes, inasmuch as the effect of any one secondary prevention medication is additive to the effect of others. A strong association between combinations of medications and clinical outcomes, despite an absent association between certain individual medications and outcomes, has been previously reported in ischemic heart disease patients [36].
Composite Medication Use and Clinical Events
Greater use of multiple indicated secondary prevention medications at discharge was associated with a lower rate of death or MI at 2 years. The number of secondary prevention therapies used in patients with coronary artery disease has been shown to predict improved outcomes in patients after coronary angiography [37], after percutaneous coronary intervention [38], and after acute coronary syndromes [39, 40]. Our study extends these prior observations by demonstrating that greater use of multiple indicated medications is also associated with improved outcomes after CABG as well. Despite advances in intraoperative technique and postoperative management, long-term outcomes after CABG have not improved in the past two decades [3, 4]. Recent reports documenting the underutilization of secondary prevention medications after CABG [12, 13] have identified a potential area in which improvement could lead to better long-term outcomes in post-CABG patients [4]. This study provides the needed complementary evidence that increased use of indicated medications at hospital discharge is associated with improved clinical outcomes after CABG surgery.
Limitations
First, our data are from a clinical trial database and thus may not accurately reflect the impact of medication use on outcomes in the "real world." However, a comparison of patients in PREVENT IV and patients undergoing first CABG from The Society of Thoracic Surgeons National Database suggests that the baseline demographics, medical history, and burden of coronary artery disease are remarkably similar [14]. Second, we evaluated the association between composite medication use at a single time period (hospital discharge) and 2-year clinical outcomes. However, we could not evaluate the effect of consistent medication use between discharge and 1 year on 2-year outcomes, as there were only 12 clinical events that occurred after the 1-year medication survey. We did, however, demonstrate that the great majority of use of secondary prevention medications at 1 year was among those taking these medications at discharge, and thus we believe a similar association would likely be found between more consistent use of medications and improved long-term clinical outcomes. Finally, although we adjusted for known confounders and treatment propensity, these data are observational in nature and thus may not account for the influence of unmeasured confounders. Therefore, it is possible that the observed association between more complete secondary prevention medication use and improved clinical outcomes may not be directly attributable to the medications effects, but may rather reflect better concomitant medical care, higher rates of other preventive measures (such as smoking cessation), or higher socioeconomic or educational status in the group taking all indicated medications. Nevertheless, this study provides evidence that increased use of indicated medications at hospital discharge is a valid measure of quality of care in patients undergoing CABG surgery.
Conclusions
Long-term use of proven secondary prevention medications in post-CABG patients is strongly linked to their use after hospital discharge, and greater use of these medications after CABG is associated with lower rates of subsequent death or MI. Strategies must be implemented to ensure greater adherence to appropriate secondary prevention therapies to improve long-term clinical outcomes after CABG.
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| Acknowledgments |
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| References |
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