Question: What are the rules for coding an old myocardial infarction? Pennsylvania Subscriber Answer: You have a few rules to follow for old myocardial infarctions, according to the ICD-10-CM Official Guidelines for Coding and Reporting. If the myocardial infarction is equal to or less than four weeks, then you would report a code from category I21- (Acute myocardial infarction) through category I22- (Subsequent ST elevation (STEMI) and non-ST elevation (NSTEMI) myocardial infarction). After that four-week time frame and if the patient is still receiving care related to the myocardial infarction, then you would instead report the appropriate aftercare code. If the old or healed myocardial infarction does not require further care, then you would report I25.2 (Old myocardial infarction).