A myocardial infarction occurs about every 40 seconds in this country. And because of this high number, it is likely, if you’re a medical coder, you will come across this heart condition at some point in your career. And you will definitely need to know ICD-10-CM coding for acute myocardial infarction for your coding exams.

acute myocardial infarction coding in ICD-10-CM

Coding For Acute Myocardial Infarction

In ICD-10-CM, there are quite a few guidelines related to acute myocardial infarction that we need to know in order to code for it accurately. However, it’s also important to have a basic knowledge of the condition, the different terms used to describe it, as well as the causes, symptoms, and diagnosis.    

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.

According to the National Heart, Lung, and Blood Institute, if an area of the heart muscle goes too long without the flow of blood 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 plague 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 completely block the flow of blood through a coronary artery.

Immediate treatment is necessary in order 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 serious 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

Heart attacks do 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 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)


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

In order 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 enroute 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

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 AMI

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

The different types include:

  • Type 1 (spontaneous MI related to ischemia)  
  • 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])

ICD-10-CM Coding

There are quite a few ICD-10-CM coding guidelines (FY2021) pertaining to the circulatory system and myocardial infarctions. Still, if you know the guidelines, what to look for in the documentation, and how to find the codes in your coding manual, your chance of errors is slim to none.

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 documentation should provide the site (wall) of the AMI, arteries affected, whether it is initial or subsequent, and the type of AMI. If any of these components are not documented, you may need to query the physician.

Acute MI

An acute MI is a myocardial infarction specified as acute or with a stated duration of 4 weeks (28 days) or less from onset.

Acute MI codes from category I21 include:

  • I21.01‑I21.09, ST elevation (STEMI) myocardial infarction of anterior wall
  • I21.11‑I21.19, ST elevation (STEMI) myocardial infarction of inferior wall
  • I21.21‑I21.29, ST elevation (STEMI) myocardial infarction of 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‑I21.A9, Other type of myocardial infarction

Before assigning codes from I21, be sure to review the “Includes,” “Code First,” “Code Also,” “Use additional,” and “Excludes2” notes.


An ST elevation myocardial infarction (STEMI) is caused by a sudden and long-term blockage of blood supply, according to the Cleveland Clinic. A large area of the heart muscle is damaged due to the blockage and an elevation of the ST segment on the electrocardiogram (ECG) occurs. Changes also occur in the blood levels of key chemical markers. A STEMI, the most serious type of MI, is also called a Q-wave or transmural myocardial infarction. 

A Non-ST elevation myocardial infarction (NSTEMI) is caused by a partial or temporary blockage. The extent of the damage to the heart muscle may be relatively small based on the blood supplied by the affected artery. On an ECG, an elevation of the ST segment may not occur, but the chemical markers in the blood show damage. An NSTEMI is less serious than a STEMI and is also referred to as a non-Q wave or non-transmural MI. 

Subsequent MI

A subsequent MI is an acute myocardial infarction occurring within 4 weeks (28 days) of a previous acute myocardial infarction, regardless of site.

Subsequent MI 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

There are some instructions to review at I22, such as “Includes,” “Use additional,” “Excludes1,” and “Excludes2” notes. Look them over closely before making your final code selections.

“Use Additional” Codes

The “Use additional” note provided at category I21 and category I22 indicates the following should be coded, if applicable:

  • exposure to environmental tobacco smoke (Z77.22)
  • history of tobacco dependence (Z87.891)
  • occupational exposure to environmental tobacco smoke (Z57.31)
  • status post administration of tPA (rtPA) in a different facility within the last 24 hours prior to admission to current facility (Z92.82)
  • tobacco dependence (F17.-)
  • tobacco use (Z72.0)
  • presence of hypertension (I10-I16)


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, including the “Use additional” notes.

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acute myocardial infarction coding in ICD-10-CM