What is the ICD-10-CM code for the first episode of an acute myocardial infarction?

The ICD-10-CM code for the first episode of an acute myocardial infarction is I21.9, which represents "Acute myocardial infarction, unspecified." This code is used when the specific type of myocardial infarction cannot be determined from the clinical information available.

The other options correspond to specific types of myocardial infarctions. For instance, I21.1 pertains to "ST elevation myocardial infarction of the anterior wall," while I21.3 refers to "ST elevation myocardial infarction of the inferior wall." I21.5 is designated for "ST elevation myocardial infarction of the other specified sites." Therefore, the correct choice encompasses any acute myocardial infarction when no specified type is available, making it suitable for coding the first episode in a more general context, as indicated in the question.