Coding Corner: Myocardial infarction

It’s estimated that 1.5 million people are affected by a myocardial infarction (or MI) every year in the United States. Updates to the 2018 ICD-10-CM now require MI to be coded by type. MI codes have now been expanded to reflect clinical classifications, as defined by the Task Force for the Universal Definition of Myocardial Infarction.

The five types of MI classifications and corresponding codes:

• Type 1 Acute myocardial infarction (AMI) represented by codes from I21.0-I21.4, is spontaneous myocardial necrosis caused by a blockage of blood flow in the heart for a prolonged period. This most frequently occurs due to a plaque rupture or thrombotic occlusion.
• Myocardial infarction type 2 is represented by code I21.A1, pertains to a demand ischemia or ischemic imbalance that is “supply-demand mismatch”, an imbalance between oxygen demand and supply (e.g., coronary spasm, anemia or hypotension). Since a type 2 MI is always caused by an underlying condition or disease process a “code also” note is included, instructing you to code this condition as well, if it’s known and applicable.
• Types 3-5, represented by code I21.A9, generally apply to an MI associated with a revascularization procedure and are all “other myocardial infarction type.” They are described as follows:
• Type 3 - MI that results in sudden cardiac death (when biomarker values are unavailable)
• Type 4a - MI associated with percutaneous coronary intervention (PCI)
• Type 4b - MI associated with stent thrombosis
• Type 4c - MI due to restenosis > 50% after an initially successful PCI
• Type 5 - MI related to coronary artery bypass graft (CABG)

Clarification related to coding these new classifications (1-5) of MI can be found in ICD-10-CM guideline I.C.9.e, Acute Myocardial Infarction (AMI). Subsequently, you’ll find the official guidelines we were accustomed to using now only apply to a type 1 MI.

The guideline includes the following directions for coding MI:

• Don’t assign code I22 for subsequent myocardial infarctions other than type 1 or unspecified
• For subsequent type 2 AMI assign only code I21.A1
• For subsequent type 4 or type 5 AMI, assign only code I21.A9

Specificity within provider documentation is essential when choosing the correct MI code to represent the patient’s condition. Only when the documentation doesn’t specify the type of MI, the code I21.9, Acute myocardial infarction, unspecified, should be assigned. If further clarification is needed on a patient’s condition the physician should be queried.

Some important points when coding an MI:

• AMI described as acute or with duration of 4 weeks (28 days) or less, is classified and coded as an acute myocardial infarction.
• For encounters after the four week time frame, with the patient still receiving care related to the myocardial infarction, the appropriate aftercare code should be assigned, not a code from category I21.
• If an AMI is documented as non-transmural or subendocardial, but the site is provided, it’s still coded as a subendocardial AMI.
• For old or healed myocardial infarctions not requiring further care, code I25.2, old myocardial infarction, may be assigned.**
• Old myocardial infarction is a history code and should be reported to identify a “healed or old MI” whether the patient is currently experiencing problems or not. This history code for a myocardial infarction is significant because an old, or “healed” MI, typically requires ongoing monitoring to address any long-term complications or new symptoms that can arise as a result of the damage caused by the myocardial infarction.

**Important-The note under the code I25.2 mentioning “currently presenting no symptoms” refers to symptoms specifically related to the old/healed MI, not cardiac symptoms in general (AHA Coding Clinic for ICD Detail; Year: 2003; Second Quarter).