SMI often escapes clinical detection, yet its long-term risk depends strongly on how myocardial infarction (MI) is defined on the ECG. Using data from the Atherosclerosis Risk in Communities (ARIC) study, an analysis published in the Journal of Electrocardiology assessed how different Minnesota Code (MC) ECG definitions influence SMI detection rates and prognostic significance.

The analysis included 9,188 adults without prior cardiovascular disease (CVD) who underwent serial ECG recordings between 1987–1989 and 1996–1998. The cohort comprised 57.4% women and 20% Black participants, with a mean age of 62.6 ± 6.0 years. Individuals with baseline ECG evidence of MI or bundle branch block, or adjudicated MI events during the ECG observation window, were excluded.

Six ECG-based SMI definitions were derived using MC criteria in the absence of adjudicated MI. These included standard MC MI, major Q-wave abnormality alone, standard and expanded serial Q-wave changes, combined serial Q-wave or ST/T changes, and evolving BBB. Cox proportional hazards models evaluated associations with fatal or non-fatal MI events through December 2016.

Both the estimated prevalence and prognostic associations of SMI depend on the ECG criteria used to define MI. These findings indicate that SMI assessment in population studies is sensitive to definition choice, supporting the need for harmonized and context-specific ECG criteria.