Stress cardiac single-photon emission computed tomographic imaging late after coronary artery bypass surgery for risk stratification and estimation of time to cardiac events

ObjectiveWe assessed predictors and temporal characteristics of cardiac risk in patients undergoing stress single-photon emission computed tomography after coronary artery bypass grafting.MethodsStress cardiac tomography was performed in 362 patients 5 years after coronary artery bypass grafting. Cardiac death and myocardial infarction were considered as events. Cox proportional hazards analysis was used to identify predictors of events and parametric survival analysis to predict time to events.ResultsDuring a median follow-up of 27 months, 22 cardiac events occurred (6.1% cumulative event rate). At multivariable Cox analysis, ischemia at cardiac tomography (hazards ratio 3.7, 95% confidence interval 1.5–9.1; P = .004), and diabetes (hazards ratio 3.6, 95% confidence interval 1.5–8.5; P = .006) resulted in independent predictors of events. Event-free survival was 96% in patients with normal cardiac tomography, 86% in those with abnormal tomography without ischemia, and 70% in those with (log–rank 10.6, P for trend = .008). The parametric survival model revealed that the cardiac risk was greater for all time intervals and accelerated more over time in patients with ischemia than in those without (χ2 21.4, P < .0001). Patients without diabetes and normal cardiac tomography remained below a defined risk level (5%) for the entire follow-up period.ConclusionStress cardiac tomography performed 5 years after coronary artery bypass grafting is useful to characterize the risk of cardiac events and its temporal variation. Parametric survival model estimates the predicted time to risk and the level of risk at specific time intervals after coronary artery bypass grafting.