Use of relative survival to evaluate non-ST-elevation myocardial infarction quality of care and clinical outcomes

Abstract

Survival after non-ST-elevation myocardial infarction (NSTEMI) is high and non-cardiovascular death has become more frequent. Observational studies typically quantify quality of care and clinical outcomes using all-cause mortality, which nowadays may not reflect the impact of index NSTEMI. We review and investigate relative survival for quantifying longer term outcomes after NSTEMI. National cohort study of hospitalized NSTEMI (Myocardial Ischaemia National Audit Project; patients: n = 346 546, hospitals: n = 243, countries: England and Wales). Mortality rates derived from two relative survival techniques were compared with all-cause mortality, and the impact of relative survival adjusted patient characteristics compared with those from Cox proportional estimates. Cox proportional hazards models provide lower survival estimates because they include deaths from all causes, overestimate the impact of increasing age on survival, and underestimate temporal improvements in care. The Royston-Parmar model allows more accurate estimation of relative survival because it is flexible to the high early hazard of death after hospitalized NSTEMI. All-cause mortality gives an overall assessment of survival for a cohort of patients. Relative survival provides a more accurate and informed estimation of the impact of an index cardiovascular event and, if necessary, patient characteristics on survival.

Figure 1

All-cause Kaplan–Meier survival curve (A), relative survival curve from Royston–Parmar model (B), all-cause smoothed hazard function (C), and Royston–Parmar model hazard function (D) for non-ST-elevation myocardial infarction patients diagnosed between 2003 and 2013.

Figure 2

Net probability of death (1 – relative survival) (A), crude probability of death due to cardiovascular disease (B), and crude probability of death due to other causes (C) for ages 55, 65, 76, 85, and 90.