Long-term mortality after percutaneous coronary intervention (PCI) is significantly elevated in patients with radiation therapy-associated coronary artery disease (CAD) relative to patients with typical atherosclerotic CAD, an observational cohort study from Cleveland Clinic has shown.
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Other findings from the study, published in the June 2016 issue of Circulation: Cardiovascular Interventions, suggest that drug-eluting stents might be the preferred revascularization strategy for reducing long-term mortality risk in CAD patients with previous external beam radiation therapy (XRT).
“Radiation therapy has brought substantial improvements to patients with thoracic malignancy, but it also confers many adverse cardiovascular effects,” says lead author Milind Desai, MD, a cardiologist in Cleveland Clinic’s Section of Cardiovascular Imaging. “We are only beginning to understand the pathophysiology of radiation-associated CAD. This is the first study to establish previous external beam radiation therapy as an independent risk factor for all-cause and cardiovascular mortality after PCI.”
Study design and results at a glance
Dr. Desai and colleagues identified 157 consecutive patients with radiation-associated CAD who underwent PCI at Cleveland Clinic over a 13-year period (XRT group) and matched them in a 1:1 fashion to 157 patients with atherosclerotic CAD (i.e., with no previous XRT exposure) who underwent PCI during the same period (control group). Matching was based on the following factors:
- Age (within five years)
- Target artery during PCI
- Type of PCI (balloon angioplasty, bare-metal stent or drug-eluting stent)
Across a mean post-PCI follow-up of 6.6 ± 5.5 years, 59 deaths occurred in the XRT group versus 42 deaths in the control group (P = .04).
Multivariate survival analysis revealed that prior XRT remained an independent predictor of both all-cause mortality (the primary end point) and cardiovascular mortality (the secondary end point), as follows:
- Hazard ratio of 1.85 for all-cause mortality (95% CI, 1.21-2.85), P = .004
- Hazard ratio of 1.70 for cardiovascular mortality (95% CI, 1.06-2.89), P = .03
Other independent predictors of death
Multivariate analysis also identified several other independent predictors of elevated all-cause mortality:
- Receiving balloon angioplasty or a bare-metal stent versus a drug-eluting stent
- SYNTAX score ≥ 11
- New York Heart Association functional class ≥ 3
- Current or previous smoking
- Age ≥ 65 years
Implications for practice
Dr. Desai notes that the finding of increased mortality among patients with radiation-associated CAD who received balloon angioplasty or a bare-metal stent relative to a drug-eluting stent “does not prove causation between PCI type and mortality, but it suggests it may be reasonable to consider drug-eluting stents in these patients whenever possible.”
He adds that further studies are needed to define the optimal revascularization strategy in this population — and that such studies may identify angiographic characteristics to help predict outcomes in this setting.
For now, Dr. Desai says this study adds to growing evidence that radiation-associated CAD must be recognized as an entity that’s different from what he terms “garden variety” CAD.
“It’s critical to keep this in mind when treating these patients,” he observes. “And it’s imperative that patients who have undergone radiation therapy be screened for CAD starting around five years after their radiation exposure.”