Implications of changing definitions of myocardial infarction on number of events and all-cause mortality: the WHO 1979, ESC/ACC 2000, AHA 2003, and Universal 2007 definitions revisited.

PURPOSE: To analyse the impact of four different definitions of acute myocardial infarction (AMI) on number of events and all-cause mortality after AMI.

METHODS: We retrospectively examined number of AMI events and mortality according to four different definitions of AMI, among 1494 patients admitted to Haukeland University Hospital in Norway from March 2002 to February 2003. Eligible for analysis were 815 patients with a discharge diagnosis of an AMI, and 679 patients without any AMI discharge diagnosis but with elevated cardiac troponin I level during admission.

RESULTS: Applying the WHO 1979 definition resulted in 566 definite AMIs among the 1494 patients and was used as reference. According to the other definitions, there were 455 (-20%) definite AMIs by the original troponin 'rise and fall' version of the ESC/ACC 2000 definition, 729 (+29%) by the troponin 'rise or fall' interpretation of the ESC/ACC 2000 definition, 761 (+34%) by the AHA 2003 definition, and 743 (+31%) by the Universal 2007 definition (all p < 0.001). The 28-day, 1-year, 5-year, and 8-year mortality for definite AMI applying the WHO 1979 definition was 12, 19, 32, and 40%, whereas applying the Universal 2007 definition resulted in a mortality of 14, 21, 35, and 43%, respectively.

CONCLUSIONS: The change of definitions of AMI during the last decades has had a significant impact on the number of AMI events and a moderate impact on the AMI mortality among hospitalized patients.