In the first year after revascularization, patients who undergo coronary artery bypass graft (CABG) surgery are less diligent about taking standard medications to prevent subsequent events than their counterparts who receive percutaneous coronary intervention (PCI), according to an observational study published online December 12, 2012, ahead of print in the Journal of the American College of Cardiology.

Investigators led by Mark A. Hlatky, MD, of Stanford University College of Medicine (Stanford, CA), looked at 23,353 members of the Kaiser Permanente Northern California integrated health plan who underwent CABG (n = 8,837) or PCI (n = 14,516) for new-onset CAD between 2000 and 2007. Information on the filling of prescriptions for secondary prevention medications including ACE inhibitors and angiotensin receptor blockers (ARBs), beta-blockers, statins, and clopidogrel over the first year after revascularization was obtained from health plan databases.

CABG Patients Consistently Less Adherent

Most patients were prescribed a statin or a beta-blocker, while use of an ACE inhibitor or ARB was somewhat more variable. A higher percentage of CABG than PCI patients never filled a prescription for an ACE inhibitor/ARB or a statin, and among those who did, the medication possession ratios—the proportion of the first year for which prescriptions were filled—were lower for CABG patients. For beta-blockers, a similar proportion of the CABG and PCI groups never filled a prescription, although after adjustment for confounding factors, a difference emerged favoring PCI patients. And the medication possession ratio was lower for CABG patients (table 1).

Table 1. Secondary Prevention Medication Use in First Year After Revascularization

^a Adjusted for baseline characteristics.

Abbreviation: MPR, medication possession ratio.

To provide context for interpreting these data, use of clopidogrel, which is generally prescribed for PCI but not CABG patients, was compared between the groups. Most CABG patients did not fill a prescription (88.5%), whereas only 4.9% of PCI patients failed to do so (P < 0.0001). And the medication possession ratio was much lower among CABG than PCI patients even after adjustment for baseline characteristics (P < 0.0001).

The lower use of secondary prevention medications among CABG patients was generally consistent across subgroups, including those with chronic kidney disease, lung or liver disease, or prior MI. Among those with diabetes or heart failure, there were smaller differences between CABG and PCI patients, especially in use of ACE inhibitors or ARBs.

Overall use of secondary prevention medications increased progressively over the study period. The gap between CABG and PCI groups narrowed for statins and beta-blockers but persisted for ACE inhibitors and ARBs. In addition, the medication possession ratio rose steadily over time for all 3 medications, with the disparity between CABG and PCI patients narrowing slightly for beta-blockers, remaining the same for statins, and widening for ACE inhibitors and ARBs.

Opportunity to Improve Care

According to the authors, the findings “suggest that there might be systematic factors after CABG and PCI that contribute to lower medication use after CABG. Addressing these differences might provide an opportunity to further improve the quality of care after coronary revascularization.” They add that future studies should “test interventions to improve both the initial prescription and long-term adherence to proven medications for secondary prevention.”

In a telephone interview with TCTMD, Ajay J. Kirtane, MD, SM, of Columbia University Medical Center (New York, NY), said there are likely multiple explanations for the disparity in medication use between CABG and PCI patients. Often overlooked, he noted, is that patients treated with surgery may be demographically or clinically different from those who receive PCI. For example, CABG patients in the study were more than 5 years older, “a huge difference in a population study,” he commented.

Moreover, Dr. Kirtane noted, surgical patients are more likely to be taken off preventive medications during the post-op period, while PCI patients may only interrupt them briefly, and studies show that having to restart drugs at a later date is more difficult.

Sunil V. Rao, MD, of Duke University Medical Center (Durham, NC), concurred that differences between surgical and PCI patients can influence medication compliance. For example, he told TCTMD in an e-mail communication, CABG patients may have more severe disease, which could be due to more risk factors, which in turn could reflect lower socioeconomic status. And the latter is a barrier to adherence.

Predischarge Message May Play a Role

But the most likely explanation for the findings stems from the type of information CABG patients receive prior to discharge, Dr. Rao wrote. “While most surgical services do a good job of educating patients about their CAD and the importance of long-term preventive care, there is likely inconsistency in the intensity of this education across providers and hospitals,” he observed. “[On the other hand,] with PCI patients, concerns over stent thrombosis have prompted many interventional cardiologists to spend a lot of time with patients stressing the importance of medication adherence.”

In addition, Dr. Rao pointed out, CABG patients may get the message from the surgical care team that after revascularization their heart is “fixed,” which they can interpret to mean that ongoing medical therapy is less important.

Dr. Rao praised the study for calling attention to an important issue. Still, he noted, patient education is very challenging, and although most patients try to be conscientious about taking their medications, the number of secondary prevention agents prescribed keeps increasing. He suggested that a “polypill” might be an attractive option for nonadherent patients.

Study Details

Patients who underwent CABG were older and less likely to have had a recent MI or diagnosed depression than patients who underwent PCI. However, they were more likely to have a history of diabetes, hypertension, dyslipidemia, CKD, heart failure, or A-fib.

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