Cardiology Coding Alert

ICD-10-CM Coding:

Billing Myocardial Infarction Claims? Focusing on These Types of Codes Can Help

Published on Fri May 24, 2024

Report I21.A9 for Type 3 MIs.

When you report myocardial infarctions (MIs) in your practice, you must consider multiple details including the type of MI, the age, and whether it is initial or subsequent. If you don’t get this information correct, you risk denials.

Take a look at the following expert advice to keep your MI coding on track.

Know What MI Is

An MI is also known as a “heart attack.” It is caused by decreased or complete cessation of blood flow to a portion of the myocardium, according to Rebecca Sanzone, CPC, CPMA, compliance administrator at St. Vincent Medical Group/Ascension Health in Indianapolis, Indiana.

Most MIs are due to underlying coronary artery disease, which is the leading cause of death in the United States. With coronary artery occlusion, the myocardium is deprived of oxygen, she adds. Prolonged deprivation of oxygen supply to the myocardium can lead to myocardial cell death and necrosis.

Patients can present with chest discomfort or pressure that radiates to the neck, jaw, shoulder, or arm. In addition to the history and physical exam, myocardial ischemia may be associated with electrocardiogram (ECG) changes and elevated biochemical markers like cardiac troponins, Sanzone says.

Follow Rules in ICD-10-CM Guidelines

The ICD-10-CM Official Guidelines for Coding and Reporting go into great detail about how to select the appropriate MI code (found in Chapter 9, section E 1-6), says Carol Hodge, CPC, CPMA, CDEO, CCC, CEMC, CPB, CFPC, COBGC, senior documentation specialist at St. Joseph’s/Candler Medical Group.

Here are different kinds of MIs you might see in your documentation.

Type 1: Spontaneous myocardial necrosis caused by an anatomic blockage of blood flow for a prolonged period.

Report I21.01 (ST elevation (STEMI) myocardial infarction involving left main coronary artery) through I21.29 (ST elevation (STEMI) myocardial infarction involving other sites) and I21.3 (ST elevation (STEMI) myocardial infarction of unspecified site) for type 1 ST elevation MIs (STEMIs), per the guidelines. And report I21.4 (Non-ST elevation (NSTEMI) myocardial infarction) for Type 1 non-ST elevation myocardial infarction (NSTEMI) and nontransmural MIs.

Don’t miss: If a Type1 NSTEMI evolves to STEMI, report the STEMI code. If a Type 1 STEMI converts to NSTEMI due to thrombolytic therapy, still report it as a STEMI.

Type 2: Also, cell death 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 2 MIs are those due to demand ischemia or secondary to ischemic imbalance. Report these types of MIs with I21.A1 (Myocardial infarction type 2). Note: Report the underlying cause coded first, per the guidelines. Never report I24.89 (Other forms of acute ischemic heart disease) for the demand ischemia.

Tip: If the Type 2 AMI is described as NSTEMI or STEMI, only report I21.A1.

For MI Types 3, 4a, 4b, 4c, and 5, report I21.A9 (Other myocardial infarction type), per the guidelines. Find out more about those different types below:

Type 3: Results in sudden cardiac death.
Types 4a, 4b, and 4c: 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: Associated with a coronary artery bypass graft (CABG).

Tip: 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).

MI with Coronary Microvascular Dysfunction Coronary: Microvascular dysfunction (CMD) impacts the microvasculature by restricting microvascular flow and increasing microvascular resistance. Report I21.B (Myocardial infarction with coronary microvascular dysfunction) MI with coronary microvascular disease, MI with coronary microvascular dysfunction, and MI with non-obstructive coronary arteries (MINOCA) with microvascular disease.

“The provider’s documentation is extremely important when coding myocardial infarctions,” says Robin Peterson, CPC, CPMA, senior consultant; compliance review, education, and training, Pinnacle Enterprise Risk Consulting Services in Centennial, Colorado. “We need to work closely with our providers to let them know what documentation is needed to accurately assign MI codes. Ideal documentation should include the type of AMI, the date of onset, dates of any historical myocardial infarctions, the site [wall] and arteries affected, and any underlying causes.”

Take MI’s Age Into Consideration

Knowing the age of the MI is vital because you will report different codes for MIs based on their age.

Four weeks or less than four weeks: If an MI is equal to or less than four weeks old, and the myocardial infarction meets the definition for “other diagnoses,” report the appropriate codes from category I21- (Acute myocardial infarction). This includes transfers to another acute setting or a postacute setting.

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

Old or healed: If the MI is old or healed and does not require further care, report I25.2 (Old myocardial infarction).

Subsequent MI: If a patient has a subsequent MI, you can consider category I22- (Subsequent ST elevation (STEMI) and non-ST elevation (NSTEMI) myocardial infarction). Report the appropriate code from this category when a patient who has suffered a Type 1 or unspecified MI has a new MI within the four-week time frame of the initial MI. You must also report a code from category I21- in conjunction with a code from category I22-, per the guidelines. Sequence these codes depending on the circumstances of the encounter.

However, if a patient has a subsequent Type 2 MI, report I21.A1.

If a patient has a subsequent Type 4a, b, c, or Type 5 MI, report I21.A9.

Tricky scenario: A patient has a subsequent MI of one type (a Type 2 MI) within four weeks of an MI of a different type (a Type 5 MI). Report the appropriate codes from category I21- to identify each type, per the guidelines. Do not report a code from category I22. Only report a code from category I22 if both the initial and subsequent MIs are Type 1 or unspecified.

Solution: Report I21.A1 and I21.A9 on your claim.