The following changes have been made at category I21, Acute myocardial infarction, to align with a new clinical classification of myocardial infarctions:
- New inclusion terms added at codes I21.0 to I21.4, to clarify that these codes refer to type 1 myocardial infarctions
- New code created for unspecified acute myocardial infarction (I21.9)
- New subcategory (I21.A) added for other types of myocardial infarctions with code I21.A1, Myocardial infarction type 2, and code I21.A9, Other myocardial infarction type
Codes from category I22, Subsequent ST elevation (STEMI) and non-ST elevation (NSTEMI) myocardial infarction, should not be assigned for subsequent myocardial infarctions other than type 1 or unspecified. Subsequent type 2, 4 or 5 myocardial infarctions are coded by type rather than using codes from category I22. For example, for subsequent type 2 acute myocardial infarctions, assign code I21.A1; for subsequent type 4 or type 5 acute myocardial infarction, assign code I21.A9. There is no subsequent type 3 myocardial infarction, as type 3 refers to myocardial infarction resulting in death when biomarker values are unavailable.
In addition, new Official Guidelines for Coding and Reporting have been created to clarify the usage of the new codes.
A global task force, which included the European Society of Cardiology, the American College of Cardiology, the American Heart Association and the World Heart Federation (WHF), developed a consensus clinical classification of myocardial infarctions. Referred to as the “Third Universal Definition of Myocardial Infarction,” it classifies acute myocardial infarction into the following subtypes:
- Type 1: Spontaneous myocardial infarction due to a primary coronary event like plaque rupture.
- Type 2: Myocardial infarction secondary to an ischemic imbalance as in coronary vasospasm, anemia or hypotension.
- Type 3: Myocardial infarction resulting in death when biomarker values are unavailable
- Type 4a: Myocardial infarction related to percutaneous coronary intervention (PCI)
- Type 4b: Myocardial infarction related to stent thrombosis
- Type 4c: Myocardial infarction due to restenosis ≥50% after an initially successful PCI
- Type 5: Myocardial infarction related to coronary artery bypass grafting (CABG)
How should a type 2 NSTEMI due to demand ischemia be coded?
Assign code I21.A1, Myocardial infarction type 2. Do not assign code I24.8, Other forms of acute ischemic heart disease for the demand ischemia. Code also the underlying cause, if known. According to the ICD-10-CM Official Guidelines for Coding and Reporting, “When a type 2 AMI code is described as NSTEMI or STEMI, only assign code I21.A1. Codes I21.01-I21.4 should only be assigned for type 1 AMIs.”
What code should be assigned when a patient is readmitted to the hospital with a new type 2 acute myocardial infarction occurring within four weeks of either a previous type 1 or type 2 acute myocardial infarction?
Assign code I21.A1, Myocardial infarction type 2. According to the ICD-10-CM Official Guidelines for Coding and Reporting, “Do not assign code I22 for subsequent myocardial infarctions other than type 1 or unspecified. For subsequent type 2 AMI assign only code I21.A1.” The Excludes1 note under category I22, Subsequent ST elevation (STEMI) and non-ST elevation (NSTEMI) myocardial infarction makes the point that a subsequent type 2 MI is assigned code I21.A1, not code I22.