Coding For Acute Myocardial Infarction

A myocardial infarction occurs about every 40 seconds in this country. And because of this high number, you will likely come across this heart condition at some point in your coding career. There are quite a few coding guidelines pertaining to the circulatory system and acute myocardial infarctions. Still, if you know them and how to find the codes in your coding manual, your chance of errors is slim to none.

coding for acute myocardial infarction

What is an Acute Myocardial Infarction and How Common is It?

An acute myocardial infarction (AMI), also known as a myocardial infarction (MI), is also referred to as a heart attack. An acute myocardial infarction occurs when the flow of oxygen-rich blood to an area of the heart muscle suddenly becomes blocked (occluded), preventing enough oxygen from getting to the heart. When the heart attack lasts for four weeks or less, it is considered acute.

According to the National Heart, Lung, and Blood Institute, if an area of the heart muscle goes too long without blood flow and is not immediately restored, that area starts to die.

Other names for myocardial infarction and heart attack are:

  • Acute coronary syndrome
  • Coronary thrombosis
  • Coronary occlusion

The term myocardial relates to the heart’s muscular tissue. “Myo” means muscle, and “cardial” means heart.

Infarction means death of tissue (necrosis) caused by lack of blood supply. 

The Centers for Disease Control and Prevention (CDC) reports that heart disease is the leading cause of death in the U.S. The CDC also provides these statistics as they relate to heart attacks:

  • Someone in the U.S. has a heart attack every 40 seconds.
  • Every year about 805,000 Americans experience a heart attack. Of these, 605,000 people have a first heart attack, and 200,000 people have already had a heart attack. 
  • About 1 in 5 heart attacks are silent, meaning the damage is done, but the person isn’t aware of it.
acute myocardial infarction coding in ICD-10-CM are located in chapter 9 are located in chapter 9

Causes of AMI

The main cause of most myocardial infarctions is ischemic heart disease. However, some MIs are caused by a coronary artery spasm, but on a less frequent basis.

Ischemic Heart Disease

Ischemic heart disease is a condition that occurs when fatty deposits (plaque) build up on the inside of the coronary arteries over many years. This plaque buildup is called atherosclerosis or hardening of the arteries.

Eventually, an area of plaque can break open inside an artery, causing the formation of a blood clot (thrombus). If the blood clot gets large enough, it can partially or entirely block blood flow through a coronary artery.

Immediate treatment is necessary to prevent the part of the heart muscle fed by the artery from dying (necrosis). Scar tissue replaces the healthy heart tissue, and it may or may not cause severe or long-term problems.

Other names for ischemic heart disease are:

  • Coronary Artery Disease
  • Coronary Microvascular Disease
  • Coronary Syndrome X
  • Non-obstructive Coronary Artery Disease
  • Obstructive Coronary Artery Disease

Coronary Artery Spasm

A severe spasm, or tightening, of a coronary artery can occur in coronary arteries that are not affected by atherosclerosis. The spasm cuts off the blood flow through the artery.

The cause of the spasm of a coronary artery  is uncertain but may be related to:

  • Taking drugs, such as cocaine
  • Emotional stress or pain
  • Exposure to extreme cold
  • Cigarette smoking

Myocardial infarctions tend to happen more in men than in women in early middle age. However, once menopause starts, a woman’s risk increases, according to Harvard Health Publishing.

Signs and Symptoms

A heart attack does not always have symptoms, which is why it is referred to as a silent heart attack. When an AMI does present with symptoms, the symptoms can vary from one person to another and from one heart attack to the other in the same person. Diabetics may have no symptoms or very mild ones.

The most common symptoms for both men and women include:

  • Chest pain or discomfort. A feeling of pressure, squeezing, fullness, or pain that is usually felt in the center or left side of the chest. The discomfort can be mild or severe and often lasts longer than a few minutes or comes and goes sporadically. It can be mistaken for heartburn or indigestion.   
  • Upper body discomfort. Pain or discomfort may occur in one or both arms, the back, shoulders, neck, jaw, or upper part of the stomach.
  • Shortness of breath. This may occur prior to or with chest pain or discomfort, or it may be the only symptom. It can happen while resting or during minimal physical activity.

Other common symptoms that may occur are:

  • Breaking out in a cold sweat
  • Unusual fatigue that can last for days (especially in women)
  • Nausea and vomiting
  • Sudden dizziness
  • Any sudden new symptoms or a change in the current symptoms such as those that become stronger or last longer than previously

Risk Factors

Major risk factors for a myocardial infarction include:

  • Smoking
  • Hypertension (high blood pressure)
  • Hypercholesterolemia (high blood cholesterol)
  • Unhealthy diet
  • High blood sugar due to insulin resistance or diabetes
  • Obesity
  • Lack of physical exercise
  • Age
  • Family history of early coronary artery disease
  • Preeclampsia (high blood pressure and excess protein in the urine during pregnancy)

Diagnosing a Heart Attack

A physician may suspect a heart attack based on the patient’s symptoms, medical history, and risk factors for cardiovascular disease.  

To make a diagnosis, the physician will perform the following:

  • Electrocardiogram (ECG or EKG). This 12-lead ECG is often done by paramedics on-site or on the way to the hospital. The leads (wires) are connected to the patient from a bedside monitor for continuous monitoring of the heart rate and rhythm.   
  • Physical Examination, with emphasis on the heart and blood pressure
  • Blood tests, which indicate if the heart muscle is damaged. Blood may be drawn to measure levels of biochemical markers. The most common blood test is called Troponin T (cTNT).  
Electrocardiogram to help diagnose myocardial infarction and how to code for acute myocardial infarction in ICD-10-CM

Other tests that may be required include:

  • Echocardiogram (echo) to listen to the heart muscle and heart valves. A handheld wand is placed on the chest, and ultrasound provides pictures of the heart’s valves and chambers to determine the pumping action.  
  • Cardiac catheterization (cath or coronary angiogram) may be performed during the first hours of a heart attack if the ischemia or symptoms are not relieved by medication. This is an invasive imaging procedure used to view the blocked artery and guide the procedure that will take place, such as an angioplasty, stent placement, or coronary artery bypass graft.

Types of Acute MI

There are different types of MI with varying underlying causes. The specific type of AMI should be diagnosed as quickly as possible so that the appropriate treatment can begin.

The different types include:

  • Type 1 (spontaneous MI))  
  • Type 2 (MI secondary to an ischemic imbalance)
  • Type 3 (MI resulting in death due to unavailable biomarker values)
  • Type 4a (MI associated with percutaneous coronary intervention [PCI])
  • Type 4b (MI associated with in-stent thrombosis)
  • Type 4c (MI  associated with restenosis of coronary artery after previous percutaneous coronary intervention [PCI])
  • Type 5 (MI associated with coronary artery bypass graft [CABG])
acute myocardial infarction coding in ICD-10-CM and coding for initial and subsequent AMI from categories I21 and I22

ICD-10-CM Coding

The ICD-10-CM codes for acute myocardial infarction are located in Chapter 9. Diseases of the Circulatory System (I00-I99) under Ischemic Heart Diseases (I20-I25).

The codes for acute MI are broken down into Initial and Subsequent MI.

Initial Acute MI

An initial AMI is coded to I21, Acute myocardial infarction, when a patient has suffered an initial ST elevation (STEMI) or non-ST elevation (NSTEMI) myocardial infarction that is specified as acute or with a stated duration of 4 weeks (28 days) or less from onset.

Initial AMI codes from category I21 include:

  • I21.01, ST elevation (STEMI) myocardial infarction involving left main coronary artery
  • I21.02, ST elevation (STEMI) myocardial infarction involving left anterior descending coronary artery
  • I21.09, ST elevation (STEMI) myocardial infarction involving other coronary artery of anterior wall
  • I21.11, ST elevation (STEMI) myocardial infarction involving right coronary artery
  • I21.19, ST elevation (STEMI) myocardial infarction involving other coronary artery of inferior wall
  • I21.21, ST elevation (STEMI) myocardial infarction involving left circumflex coronary artery
  • I21.29, ST elevation (STEMI) myocardial infarction involving other sites
  • I21.3, ST elevation (STEMI) myocardial infarction of unspecified site
  • I21.4, Non-ST elevation (NSTEMI) myocardial infarction
  • I21.9, Acute myocardial infarction, unspecified
  • I21.A1, Myocardial infarction type 2
  • I21.A9, Other myocardial infarction type

Based on the ICD-10-CM Official Guidelines for Coding and Reporting ( FY2022), keep the following in mind when coding from category I21:

  • The ICD-10-CM codes for type 1 STEMI and NSTEMI identify the site, such as the anterolateral wall or true posterior wall.
  • Codes I21.01-I21.3 are used for type 1 STEMI MI.
  • If the provider documents acute MI but does not include the specific location, the appropriate code is to assign is I21.3.
  • Code I21.4 is used for type 1 NSTEMI MI and nontransmural MIs.
  • Code I21.9 is used for unspecified AMI or unspecified type.
  • Code I21.A1 is used for type 2 MI.
  • Code I21.A9 is used for types 3, 4a, 4b, 4c, and 5 MI.
  • If a type 1 NSTEMI evolves to STEMI, assign the STEMI code.
  • If a type 1 STEMI converts to NSTEMI due to thrombolytic therapy, it is still coded as STEMI.
  • For encounters occurring while the MI is equal to or less than 4 weeks old, including transfers to another acute or postacute setting, and the MI meets the definition for “other diagnoses”, codes from category I21 may continue to be reported. For encounters after the 4-week timeframe and the patient is still receiving care related to the MI, the appropriate aftercare code should be assigned instead of a code from I21. Old or healed MIs not requiring further care should be coded to I25.2, Old myocardial infarction.
  • If an AMI is documented as nontrasmural or subendocarial, but the site is provided, it is still coded as a subendocarial AMI.

Subsequent Acute MI

A subsequent AMI is coded to I22, Subsequent ST elevation (STEMI) and non-ST elevation (NSTEMI) myocardial infarction, when a patient has suffered a type 1 or unspecied AMI and has a new AMI within the 4-week timeframe (28 days) of the initial AMI. A code from category I22 must be used in conjunction with a code from category I21. The sequencing of the I22 and I21 codes depends on the circumstances of the encounter. ”

Subsequent AMI codes from category I22 include: 

  • I22.0, Subsequent STEMI of anterior wall
  • I22.1, Subsequent STEMI of inferior wall
  • I22.2, Subsequent non-ST elevation (NSTEMI) myocardial infarction
  • I22.8, Subsequent STEMI of other sites
  • I22.9, Subsequent STEMI of unspecified site

Other coding guidelines to keep in mind when coding from category I22:

  • 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.
  • For subsequent type 4 or type 5 AMI, assign only code I21.A9.
  • If a subsequent myocardial infarction of one type occurs within 4 weeks of a myocardial infarction of a different type, assign the appropriate codes from category I21 to identify each type. Do not assign a code from I22. Codes from category I22 should only be assigned if both the initial and subsequent myocardial infarctions are type 1 or unspecified.

Before making your final code selection from categories I21 and I22, review the “Includes,” “Excludes,” “Code First,” “Code Also,” and “Use additional” notes.


Myocardial infarctions can be difficult to code if you don’t know the coding guidelines. Be certain to abstract the pertinent information from the medical record relative to the site of the AMI, arteries affected, whether the AMI is initial or subsequent, and the type of AMI. Finally, read all the instructional notes listed at the ICD-10 codes. This is critical to correct coding.

** This article has been updated to reflect the ICD-10-CM coding guidelines for FY 2022. **

Demonstrate your myocardial infarction coding knowledge by taking The Coding Challenge. Simply complete the form below.

acute myocardial infarction coding in ICD-10-CM



  1. I was quite excited to find this website and what it has to offered. Right now, I would like to take the test

  2. I am so happy that I found your website and You! I am currently doing my studies for the CPC test and find your information absolutely wonderful! Thank you for all your efforts, your website
    is so interesting. Thank you for sharing your knowledge!

  3. I have a question. This is the scenario.
    A patient presents with a non-healed myocardial infarction of the inferoposterior wall 6 weeks after initial treatment. What is the correct diagnosis code?
    I answered 122.1
    My other options are

    1. Hi Eva,

      I don’t know if this is a test question, but I don’t typically answer specific coding questions. However, pay close attention to the coding guidelines, which state, “A code from category I22, Subsequent ST elevation (STEMI) and nonST elevation (NSTEMI) myocardial infarction, is to be used when a patient who has suffered a type 1 or unspecified AMI has a new AMI within the 4 week time frame of the initial AMI. A code from category I22 must be used in conjunction with a code from category I21. The sequencing of the I22 and I21 codes depends on the circumstances of the encounter…”

      This scenario is describing a non-healed MI that is receiving treatment 6 weeks after initially receiving treatment for it.

      Be sure to read the other guidelines related to MI’s. There is one about a patient presenting to the physician 6 weeks after initial treatment.

      I hope this helps.

Leave a Reply

Your email address will not be published.