Grant W Reed, Milind Y Desai (both Department of Cardiovascular Medicine, Centre for Radiation Heart Disease, Cleveland Clinic, Cleveland, USA) and others report in Circulation Cardiovascular Interventions that prior external beam radiation therapy is an independent predictor of both all-cause and cardiovascular mortality in patients undergoing percutaneous coronary intervention (PCI).
The authors report that radiation-associated coronary artery disease is “a poorly understood process”, noting it is “thought to have a unique pathophysiology separate from standard atherosclerotic coronary artery disease”. They add that while a “few small studies” have indicated that prior radiation therapy is associated with worse outcomes after PCI, “these studies have generally been underpowered and limited in follow-up duration and scope.” Therefore, Reed & Desai et al conducted an observational study to compare outcomes of patients with radiation-associated coronary artery disease undergoing PCI with those of standard coronary artery disease patients undergoing PCI.
Of patients who underwent PCI at a tertiary centre between January 2000 and December 2012, the authors identified 157 patients with radiation-associated coronary artery disease and 157 matched controls. After an average follow-up of 6.6±5.5 years, there were significantly more deaths in the prior radiation therapy group: 38% vs. 27% for the standard coronary artery disease group (p=0.04). After multivariate analysis, prior radiation therapy was an independent predictor of all-cause mortality (p=0.004). Other predictors of mortality included PCI type (balloon angioplasty or bare metal stent), SYNTAX score ≥11, New York Heart Association class ≥3, current and previous smoking, and age ≥65 years. Furthermore in a multivariable conditional Cox proportional hazards model stratified by matched group, prior radiation exposure remained the only significant predictor of all-cause mortality (p=0.028).
Reed & Desai et al report that in matched analysis, after adjustment, prior radiation therapy was also a significant independent predictor of cardiovascular mortality (p=0.047). “Our results are supportive of the premise that cardiovascular death is more common among patients with malignancy who initially survive external beam therapy, particularly those previously treated with thoracic radiation that have developed concomitant coronary artery disease requiring PCI,” they comment.
The authors add that, in a previous study of theirs, long-term mortality in patients with radiation-associated coronary artery disease who underwent coronary artery bypass grafting (CABG) was 46%—ie. a higher figure than the 38% observed in the prior radiation patients in this study. They state that these results suggest that alternative treatment strategies should be considered in patients with previous radiation therapy requiring cardiac surgery but note: “There has not yet been a study directly comparing outcomes in patients with radiation-associated coronary artery disease treated with CABG or PCI and thus, the optimal revascularisation strategy in this patient population remains uncertain.”
According to Reed & Desai et al, studies focused on determining the optimal revascularisation strategy in patients with radiation-association coronary artery disease “may identify which angiographic characteristics are most predictive of cardiovascular events among patients with external beam radiation therapy and how PCI outcomes compare with CABG in outcomes in this patient population.”