Risk of mortality after acute myocardial infarction: Performance of model updating methods for application in different geographical regions

Using the large Hirulog and Early Reperfusion or Occlusion (HERO-2) trial a parsimonious multivariable model for 30-day mortality risk assessment in acute myocardial infarction (AMI) was developed. HERO-2 was an international randomized trial of two antithrombotic therapies–unfractionated heparin and bivalirudin–for the treatment of AMI. This trial recruited 17 073 patients from 46 countries from Europe, North and Latin America and Asia, including Australia, New Zealand and Russia. An important issue in applying findings from randomized clinical trials is the procedure to estimate risk among members of other patient populations. Methods for updating risk models for AMI are compared. Simple re-calibration (re-estimation of the intercept and slope of the linear predictor within regions) and model revision (re-estimation of all regression coefficients within regions) with and without shrinkage were compared to a global additive model with a built-in region effect. The relative performance of these methods in the different geographical regions, which vary in sample size, is of primary interest. Model revision only provided a slight improvement in predictive performance when applied with shrinkage in the smallest region Asia (N=756N=756). In conclusion, a global model with regional re-calibration is adequate: region-specific coefficients did not provide worthwhile improvements in any region.