To make a global comparison for these variables, we performed a weighted summation of the selected variables for all patients in each group, where the weighting of each variable was determined by its association with the disease/disease group.We generated logistic regression models of myocardial infarction (group 3 versus group 1, excluding group 2 and group 4 patients) on baseline clinical characteristics and outcomes (age, hypertension, hyperlipidaemia, diabetes, vascular disease, previous coronary revascularisation, presentation with chest pain, smoking status, electrocardiographic findings on admission, drugs on admission, Killip class, and outcomes at 12 months).For example, evidence of myocardial ischaemia on electrocardiography could be used as such an “umpire test” wherein the discrepant group with the highest prevalence of ischaemia on electrocardiography would indicate the superior test.Consequently we compared a range of risk factor, clinical and outcome variables for all groups, which are likely to be independent of the assay under consideration but are conditional on the true disease state.Through requests for data from the National Records of Scotland we identified deaths occurring anywhere in the United Kingdom.We used these two sources to record all admissions to secondary and tertiary hospitals in our region and all deaths in the United Kingdom.18 test for between group comparisons and Mc Nemar’s test for within group comparisons.We used regional and national registries to ensure that follow-up was complete for the entire study population.Trak Care software application (Inter Systems, Cambridge, MA) is a regional electronic patient record system, which provides data on all hospital admissions to both tertiary and secondary care hospitals in south east Scotland.
Using a high sensitivity assay, the number of women classified as having type 1 myocardial infarction increased to 80 (16%) with the generic (26 ng/L) threshold and to 111 (22%) with the sex specific (women 16 ng/L) threshold (PFig 2 Proportion of men and women with diagnosis of type 1 myocardial infarction and type 2 myocardial infarction or myocardial injury using the contemporary troponin I assay (single threshold 50 ng/L) and high sensitivity troponin I assay (single threshold 26 ng/L, and sex specific threshold 34 ng/L for men and 16 ng/L for women)Overall, 20 women (4%) and 27 men (4%) received an adjudicated diagnosis of type 2 myocardial infarction using the contemporary troponin I assay with a threshold of 50 ng/L, and a further 15 women (3%) and 12 men (2%) had a diagnosis of myocardial injury (figs 1 and 2).
Myocardial injury was defined as evidence of myocardial necrosis in the absence of any clinical features of myocardial ischaemia.6 Unstable angina was defined as symptoms or signs of myocardial ischaemia in the absence of myocardial necrosis with evidence of myocardial ischaemia on resting electrocardiography or stress testing, or obstructive coronary artery disease on coronary angiography, or where the patient had a recurrent myocardial infarction or died within 30 days.
Any discrepancies in adjudication were resolved by consensus between the two cardiologists through in-depth review of source documents.
They then reclassified patients using troponin concentrations from the high sensitivity assay with both a single generic threshold (26 ng/L) and sex specific thresholds (34 ng/L for men and 16 ng/L for women).
Fig 1 Steps involved in adjudication and classification of patients with suspected acute coronary syndrome.