Cardiology Coding Alert


How To Confidently Report Myocardial Infarctions In Your Practice

Hint: For old or healed MI, report I25.2.

When it comes to coding for acute myocardial infarctions (AMIs), the ICD-10-CM Official Guidelines for Coding and Reporting give you a lot of rules to follow. It can be hard to keep them straight.

Read on to learn more about how to keep your MI coding on the up and up.

Highlight ICD-10-CM Rules for Age of MIs

You should report different codes for MIs depending on their age.

The ICD-10-CM Official Guidelines tell us that for MIs of four weeks or less, use codes from category I21- (Acute myocardial infarction), along with other diagnoses as applicable, said Sharon Jane Oliver, CPC, CDEO, CPMA, CRC, Approved-Instructor, in her presentation “Pathophysiology of Heart Diseases” at AAPC’s Healthcon 2023 conference in Nashville, Tenn.

For encounters after four weeks and when the patient is still receiving care related to the MI, report the appropriate aftercare code (Z51.89) rather than a code from I21-.

For old or healed MI, report I25.2 (Old myocardial infarction), Oliver added. Subsequent MIs require the use of category I22- (Subsequent ST elevation (STEMI) and non-ST elevation (NSTEMI) myocardial infarction) to be used when the patient who has suffered a Type I or unspecified AMI has a new AMI within the four-week timeframe of the original.

You must report a code from category I22- in conjunction with a code from category I21-, Oliver said.

“We have to pay attention to our doctors to classify the type of MI because we have five types that we need to report for, and the codes are different,” Oliver added.

Oliver gave this coding example: On March 10, the patient arrived with a diagnosis of MI of the left main (LM) coronary artery — I21.01. On March 12, the patient was discharged home. But on April 2, the patient comes back with a diagnosis of MI of the inferior wall. The coding when they discharge is I22.1 (Subsequent ST elevation (STEMI) myocardial infarction of inferior wall) because it’s within the four weeks and I21.01 (ST elevation (STEMI) myocardial infarction involving left main coronary artery) to tell the payer the history and that the patient had another heart attack within the four-week timeframe. The same patient comes back on May 15 and arrives with an MI of the right coronary artery — I21.11. On May 17, the patient is discharged home. Now their diagnosis is I21.11, I25.2. The MIs were outside four weeks of each other; therefore, the old MI is reported in addition to the initial MI.

Observe Different Types of MIs

These are the five types of MIs, according to Oliver.

Type 1: A Type 1 MI is spontaneous myocardial necrosis caused by an anatomic blockage of blood flow for a prolonged period.

Type 2: A Type 2 MI is also cell death but is secondary to ischemia based on a “supply-demand” mismatch, i.e. an imbalance between oxygen demand and supply, e.g. coronary spasm, anemia, or hypotension.

Type 3: A Type 3 MI results in sudden cardiac death.

Type 4: Type 4 MIs have three different types, a, b, and c:

  • Type 4a is associated with percutaneous coronary intervention (PCI).
  • Type 4b is MI associated with in-stent thrombosis.
  • Type 4c is related to restenosis.

Type 5: A Type 5 MI is associated with a coronary artery bypass graft (CABG).

Code Different Types of MIs This Way

It’s very important to know the types of MIs because we have different coding for them, Oliver said.

“The typical MIs we normally see are Type 1 or Type 2,” Oliver added. “All of this matters. We want to be sure that the doctors tell us the history of the patient. So, we are continuously having to read that history to be sure that the doctor has addressed everything.”

According to the guidelines, you should only report codes I21.01 through I21.4 (Non-ST elevation (NSTEMI) myocardial infarction) for Type 1 AMIs.

For Type 2 MIs, which are those due to demand ischemia or secondary to ischemic imbalance, report I21.A1 (Myocardial infarction type 2) with the underlying cause coded first, per the guidelines. You should not report I24.8 (Other forms of acute ischemic heart disease) for the demand ischemia. Note: If the type 2 AMI is described as NSTEMI or STEMI, only report I21.A1.

For AMIs that are Type 3, 4a, 4b, 4c, and 5, report I21.A9 (Other myocardial infarction type), according to the guidelines. With I21.A9, you will see a “Code also” note telling you to code complications if known and applicable. You should also “Code first” a postprocedural MI following cardiac surgery (I97.190) or postprocedural MI during cardiac surgery (I97.790).

“The provider’s documentation is extremely important when coding myocardial infarctions,” says Robin Peterson, CPC, CPMA, manager of professional coding and compliance services, Pinnacle Enterprise Risk Consulting Services, LLC in Centennial, Colorado. “We need to work closely with our providers to let them know what documentation is needed to accurately assign codes. Ideal documentation should include the type of AMI, the site (wall), arteries affected, any underlying causes, and whether it is initial or subsequent.”