Identifying acute myocardial infarction: effects on treatment and mortality, and implications for National Service Framework audit

BACKGROUND: The National Service Framework (NSF) for Coronary Heart Disease requires annual clinical audit of the care of patients with myocardial infarction, with little guidance on how to achieve these standards and monitor practice. AIM: To assess which method of identification of acute myocardial infarction (AMI) cases is most suitable for NSF audit, and to determine the effect of the definition of AMI on the assessment of quality of care. DESIGN: Observational study. METHODS: Over a 3-month period, 2153 consecutive patients from 20 hospitals across the Yorkshire region, with confirmed AMI, were identified from coronary care registers, biochemistry records and hospital coding systems. The sensitivity and positive predictive value of AMI patient identification using clinical coding, biochemistry and coronary care registers were compared to a 'gold standard' (the combination of all three methods). RESULTS: Of 3685 possible cases of AMI singled out by one or more methods, 2153 patients were identified as having a final diagnosis of AMI. Hospital coding revealed 1668 (77.5%) cases, with a demographic profile similar to that of the total cohort. Secondary preventative measures required for inclusion in NSF were also of broadly similar distribution. The sensitivities and positive predictive values for patient identification were substantially less in the cohorts identified through biochemistry and coronary care unit register. Patients fulfilling WHO criteria (n=1391) had a 30-day mortality of 15.9%, vs. 24.2% for the total cohort. DISCUSSION: Hospital coding misses a substantial proportion (22.5%) of AMI cases, but without any apparent systematic bias, and thus provides a suitably representative and robust basis for NSF-related audit. Better still would be the routine use of multiple methods of case identification.