Study Examines Influence of Baseline Factors on Outcomes After CABG, PCI

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Older patients with multivessel disease and baseline clinical factors including male sex and diabetes may have better long-term outcomes with coronary artery bypass graft (CABG) surgery than with percutaneous coronary intervention (PCI), according to an observational study presented May 11, 2012, at the American Heart Association’s Quality of Care and Outcomes Research Scientific Sessions 2012 in Atlanta, GA.

Researchers led by Mark Hlatky, MD, of the Stanford University School of Medicine (Stanford, CA), used propensity score matching in 105,612 Medicare patients, with an average age of 75 years, who received either multivessel CABG or PCI between 1992 and 2008.

At 5 years, survival was 74.7% in the CABG group and 71.8% in the PCI group, showing a mortality advantage with CABG (adjusted HR 0.90; 95% CI 0.88-0.93).

Compared with PCI, several baseline clinical factors had a greater influence in reducing mortality with CABG, including male sex, diabetes, tobacco use, heart failure, and procedures performed prior to 2004 (table 1).

Table 1. Baseline Clinical Factors and Mortality

 

HR for CABG

HR for PCI

P Valuea

Male Sex

0.88

0.94

0.009

Diabetes

0.87

0.93

0.02

Tobacco Use

0.82

0.92

0.0004

Heart Failure

0.86

0.92

0.03

Procedures Prior to 2004

0.88

0.94

0.008

a P for interaction.

There was no significant interaction between age and treatment. Results were consistent whether examined as hazard ratios, differences in 5-year survival, or life-years added.

Similarities with ASCERT

The findings are similar to those of the ASCERT trial, which analyzed outcomes for patients with 2- or 3-vessel disease who underwent CABG (n = 86,244) or PCI (n = 103,549) from 2004 through 2007. At 1 year, there was no difference in adjusted mortality between the CABG and PCI groups (6.2% vs. 6.6%; RR 0.95). However, at 4 years, the CABG group showed a survival advantage (16.4% vs. 20.8%; RR 0.79).

The 4-year risk ratios in ASCERT showed a benefit of CABG across subgroups defined according to sex, age, presence or absence of diabetes, body-mass index, presence or absence of chronic lung disease, ejection fraction, and glomerular filtration rate in both high- and low-risk groups. CABG was also associated with a benefit across subgroups defined according to propensity score quintile. Thus, survival was improved with CABG even among patients whose propensity scores were more consistent with selection for PCI.

In a telephone interview with TCTMD, William S. Weintraub, MD, of the Christiana Care Health System (Newark, DE), the lead investigator for ASCERT, said while the new study is consistent with the basic findings of that trial, he does not feel the baseline clinical factors are of much relevance in such a large study population.

“When you have such large numbers, the P values don’t mean very much, and in fact we decided not to use P values when looking at interactions of these various subgroups in ASCERT,” he said.

Dr. Weintraub observed that the new data provide confirmatory evidence that better survival is associated with CABG, not PCI, in older patients with greater disease burden.

“All the observational studies and the more recent meta-analyses and clinical trials have shown this,” he said. “It’s also consistent with what we know so far from SYNTAX. Generalizing beyond the Medicare population, however, is something we cannot do. Also, because this study only used Medicare data, the ability to correct for baseline differences is not as strong as it was in ASCERT.”

In ASCERT, the CABG population was taken from the Society of Thoracic Surgeons National Database and the PCI population from the American College of Cardiology National Cardiovascular Data Registry. To obtain long-term follow-up, patient records were linked to administrative data from the Centers for Medicare and Medicaid Services. Propensity scores and inverse probability weighting were used and numerous clinical subgroups were prespecified.

Dr. Weintraub also questioned why Dr. Hlatky and colleagues used data as far back as 1992.

“There have been so many changes in methods and technology since then, so I don’t think that was the best choice,” he said. “I would have restricted it at the very least to the coronary stent era and better yet, restrict it to drug-eluting stents, which is what we did in ASCERT. By going back as far as they did, they were able to get 5-year data, which we were not able to do, but when you get down to it, I don’t think it adds that much.”

 


Sources:
1. Hlatky M, Boothroyd D, Baker L, et al. Comparative effectiveness of coronary angioplasty and bypass surgery among Medicare beneficiaries. Presented at: American Heart Association’s Quality of Care and Outcomes Research Scientific Sessions 2012; May 9-11, 2012; Atlanta, GA.

2. Weintraub WS, Grau-Sepulveda MV, Weiss JM, et al. Comparative effectiveness of revascularization strategies. N Engl J Med. 2012;Epub ahead of print.

 

 

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Disclosures
  • Dr. Hlatky reports no relevant conflicts of interest.
  • Dr. Weintraub reports serving as lead investigator for the ASCERT trial.

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