ICD-10-CM Medical Coding: Ischemic Heart Diseases
ICD-10-CM Codes: This lecture reviews medical coding for ischemic heart diseases along with chapter-specific guidelines for atherosclerotic coronary artery disease and angina, and acute myocardial infarction (AMI).
Guest Author
Guest Author: Donna Maher, MS, RHIA
The lecture below was written by guest author Donna Maher, who is a faculty member at Renton Technical College teaching medical billing and coding.
Medical illustrations were provided by Donna Maher.
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ICD-10-CM: Chapter-Specific Coding Guidelines
This lecture will focus on Chapter 9: Diseases of the Circulatory System (I00-I99) from ICD-10-CM Official Guidelines for Coding and Reporting, FY 2023.
This lecture will specifically cover items from:
Section 1; C.9.b. Atherosclerotic Coronary Artery Disease and Angina
Section 1; C.9.e Acute Myocardial Infarction (AMI)
ICD-10-CM Codes: This lecture reviews Chapter 9: Diseases of the Circulatory System (I00-I99), specifically items from Section I.C.9.b. (atherosclerotic coronary artery disease and angina) and Sections I.C.9.e. (acute myocardial infarction)
ICD-10-CM: Ischemic Heart Disease
Let’s begin with a few definitions that are pertinent to coding for ischemic heart disease.
Definitions
“Heart Disease” is a generic term for a wide range of conditions affecting the heart.
The most common type of heart disease is coronary artery disease (CAD).
“Coronary Artery Disease (CAD)” is a condition in which the coronary arteries become narrow, hardened, or blocked which can result in decreased blood flow to the heart (ischemia).
As a result, CAD is often referred to as “ischemic heart disease”.
CAD is usually caused by atherosclerosis.
“Atherosclerosis” is a buildup of plaque inside the artery walls.
Atherosclerosis and arteriosclerosis are often used interchangeably, however, there is a slight difference between the terms.
“Arteriosclerosis” is when the arteries become hard, thick, and stiff.
Atherosclerosis is a specific type of arteriosclerosis.
Atherosclerosis, arteriosclerosis, and CAD are all intertwined and can lead to a decrease in blood supply/flow to the heart (ischemic heart disease).
“Native” artery refers to an original artery at that site, i.e. one that has not been replaced with a bypass graft.
“Lumen” refers to the inside space or channel within a tubular structure, in this case the hollow passageway within the artery in which blood flows.
“Patent” refers to the degree the lumen of the artery is open and clear for blood to flow.
“AMI or MI” refers to acute myocardial infarction or myocardial infarction i.e. heart attack.
Atherosclerotic Coronary Artery Disease
Let’s bring all these terms together starting with atherosclerotic coronary artery disease.
Atherosclerosis is the most common form of arteriosclerosis, which is a general term for several disorders that cause thickening and loss of elasticity in the arterial wall.
Atherosclerosis is also the most serious and clinically relevant form of arteriosclerosis because it causes coronary artery disease and cerebrovascular disease.
Atherosclerosis is characterized by patchy intimal plaques (atheromas) that encroach on the lumen of medium-sized and large arteries.
The plaques contain lipids, inflammatory cells, calcium, and other cellular waste products.
Atherosclerosis can affect most of the arteries in the body, including arteries in the heart, brain, arms, legs, pelvis, and kidneys.
Pertinent to this lecture, atherosclerosis of the coronary arteries can lead to atherosclerotic coronary artery disease.
Atherosclerotic coronary artery disease can cause decreased blood flow (ischemia) to the heart, called ischemic heart disease.
Coronary artery disease and ischemic heart disease are often used interchangeably.
Atherosclerotic Coronary Artery Disease: Plaque buildup in the coronary arteries can decrease the blood flow to the heart and cause ischemia.
What is Ischemic Heart Disease?
Ischemia refers to a lack of blood supply to tissues and organs.
If the ischemia persists, then the tissue without blood supply will die.
This is known as an infarct, which is an area of necrosis (dead tissue) resulting from insufficient blood supply.
Infarcts typically occur when a blood vessel gets blocked and can be caused by a thrombus (blood clot), embolus (blood clot, air bubble, fatty deposit, etc. that travels and gets lodged in a blood vessel), or atherosclerotic plaque rupture.
If an artery that supplies blood to the heart (coronary artery) becomes blocked, then this can lead to ischemia or ischemic heart disease.
A warning sign of ischemic heart disease can be angina, which is reversible chest pain due to ischemia (usually during physical activity that improves with rest).
Ischemic Heart Disease: Atherosclerotic coronary artery disease can cause decreased blood flow to the heart (ischemia) and a heart attack.
Atherosclerotic Coronary Artery Disease and Angina
Section 1; C.9.b.
Now that we understand atherosclerosis and ischemic heart disease along with its associated definitions, let’s review the chapter-specific coding guidelines for section 1; C.9.b. Atherosclerotic Coronary Artery Disease and Angina.
A causal relationship can be assumed in a patient with both atherosclerosis and angina pectoris, even if the provider does not state a relationship.
The category code range for Atherosclerotic Coronary Artery Disease and Angina are I20-I25.
Within these codes are combination codes for atherosclerotic heart disease with native or non-native vessels and with or without angina.
The atherosclerotic coronary artery disease and angina codes often appear contradictory and suggest multiple codes instead of combination codes.
Many times, abstracting the main terms from the documentation into a separate document to eliminate nonessential factors can help improve coding and simplify identification of combination codes.
The coding sequence depends on the reason for the encounter or “why did the patient come through the door”.
If the patient is currently having an acute myocardial infarction (AMI) then that condition is coded first before any coronary artery disease code.
Let’s review AMI next.
Acute Myocardial Infarction (AMI)
Section 1; C.9.e.
Let’s now review the chapter-specific coding guidelines for section 1; C.9.e. Acute Myocardial Infarction (AMI).
We will start with a general overview of myocardial infarctions (MI), and then work our way through the chapter-specific guidelines with examples.
Coding for an Acute Myocardial Infarction
An acute myocardial infarction is myocardial tissue death resulting from decreased or blocked blood flow to the heart, such as from an acute obstruction of a coronary artery.
Myocardial coding requires in-depth knowledge of the heart anatomy and physiology.
There are many variables to consider when coding myocardial infarctions.
Coding myocardial infarctions requires knowledge of the coronary arteries, the cause of the infarct, and the damaged section of the heart.
The major coronary arteries include the right coronary artery (RCA), the right marginal artery (RMA), the posterior descending artery (PDA), the left main coronary artery (LMCA), the left circumflex artery (LCx), and the left anterior descending (LAD) artery.
There are other branches as well, but these are the main ones.
Coronary Artery Diagram: Anatomy and location of the major coronary arteries of the heart
Types of Myocardial Infarctions (MIs)
Myocardial infarctions are classified by the cause and the resultant pathology.
There are 5 types of myocardial infarctions (MIs):
Type 1: Spontaneous myocardial infarction
Type 2: Myocardial infarction due to demand ischemia or secondary to an ischemic imbalance
Type 3: Myocardial infarction resulting in death when biomarker values are unavailable
Type 4: Myocardial infarction related to percutaneous coronary intervention - PCI (4a), stent thrombosis (4b), or restenosis (4c)
Type 5: Myocardial infarction related to coronary artery bypass grafting - CABG
Put simply: Type 1 and type 2 MIs are spontaneous, type 4 and 5 MIs are procedure related, and a type 3 MI is identified after death.
A type 1 MI is due to a primary coronary event (i.e. plaque rupture, erosion, fissuring) resulting in coronary artery thrombosis and acute coronary artery occlusion.
A type 2 MI is due to a mismatch between myocardial oxygen supply and demand unrelated to plaque disruption and coronary thrombosis (which would be a type 1 MI).
Causes of type 2 MIs may involve cardiac or non-cardiac conditions including coronary artery spasm, coronary embolism, arrhythmias, hypotension, severe anemia, sepsis, hypoxia, hypertension, pulmonary embolism, etc.
STEMI vs NSTEMI
Myocardial infarctions can present as either a STEMI or NSTEMI depending on the presence or absence of ST segment elevation on EKG.
ECG Waveform: A normal EKG wave along with its labeled parts including the ST segment
STEMI or NSTEMI refer to the presentation of the infarct on the patient’s EKG (particularly the ST segment) and indicate a ST-Elevation Myocardial Infarction (STEMI) or a Non-ST-Elevation Myocardial Infarction (NSTEMI).
Note: NSTEMIs may show ischemic changes on EKG such as ST depression or T wave inversions.
Caution: ST depressions in the anterior leads on EKG may indicate a STEMI (i.e. poster MI).
Generally speaking, a STEMI is typically the result of a complete (100%) blockage of a coronary artery whereas an NSTEMI is usually the result of a partial blockage.
If the partial occlusion is severe, remains occluded or becomes completely occluded, then the NSTEMI can convert to a STEMI.
STEMIs and NSTEMIs can be type 1 or type 2 MI depending on the underlying cause as outlined above.
Most patients with a STEMI and many patients with an NSTEMI are a type 1 MI.
Many of the type 2 MIs are NSTEMIs, but can also present as a STEMI too (i.e. cocaine induced MI from coronary artery vasospasm, hypertension, tachycardia, etc.).
A STEMI tends to be more severe than an NSTEMI, however both are potential cardiac emergencies.
STEMI vs NSTEMI: ECG changes for STEMIs and NSTEMIs including ST elevations, ST depressions, and T wave inversions.
Acute Myocardial Infarction (AMI)
Section 1; C.9.e.
Let’s now review the chapter-specific coding guidelines for AMI, starting with type 1 ST elevation myocardial infarction (STEMI) and non-ST elevation myocardial infarction (NSTEMI).
1) Type 1 ST elevation myocardial infarction (STEMI) and non-ST elevation myocardial infarction (NSTEMI)
As previously mentioned, a type 1 MI is due to coronary plaque disruption and subsequent coronary artery thrombosis.
A type 1 MI can present as a STEMI or NSTEMI.
The area of damage from an MI depends on the artery and the degree of blockage.
Coding an AMI depends on identifying the following:
The type of MI: STEMI or NSTEMI
Presence or absence of angina
Coronary artery involved
Location of the infarct i.e. transmural, nontransmural, anterolateral wall or true posterior
Initial or subsequent MI
Presence of an old or healed MI
Unspecified
First, determine the type of myocardial infarction.
The ICD10 categories I21.0-I21.2 and code I21.3 are used for type 1 STEMIs.
Code I21.4, is used for type 1 non-ST elevation myocardial infarction (NSTEMI) and nontransmural MIs.
Next, determine the coronary artery involved and the portion of the heart wall involved, such as anterolateral wall or true posterior wall.
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.
Site of Infarction
The two main branches of coronary circulation are the right coronary artery and the left main coronary artery.
Anterior infarcts are usually due to left coronary artery obstruction, especially in the left anterior descending artery (LAD).
Posterior infarction occurs when the posterior coronary circulation becomes disrupted.
Inferior infarcts are usually caused by occlusion of the right coronary artery.
Transmural infarcts involve the whole thickness of myocardium from epicardium to endocardium.
Nontransmural infarcts do not extend through the ventricular wall.
Subendocardial infarcts usually involve the inner one third of myocardium, where wall tension is highest and myocardial blood flow is most vulnerable to circulatory changes.
Myocardial Infarction: Location of MI and coronary arteries involved
Example:
This 87-year-old male was admitted for an acute MI STEMI of the left main coronary artery, in the anterior wall.
The code would be AMI, left main, anterior wall
The code: I21.01 ST elevation (STEMI) myocardial infarction involving left main coronary artery.
Acute Myocardial Infarction (AMI)
Section 1; C.9.e.
Let’s continue through the chapter-specific coding guidelines for AMI and discuss acute myocardial infarctions, unspecified.
2) Acute myocardial infarction, unspecified
An unspecified acute myocardial infarction is when the type and site of the infarct is not identified.
When the documentation is not more specific than an acute myocardial infarction, code to I21.9.
This code is the default for unspecified acute myocardial infarction or unspecified type.
Codes ending in .9 are typically classified to unspecified, in this case, an unspecified acute MI.
However, if the type of infarct is specified, but the site is not documented, the OGCR requires code I21.3 (STEMI of unspecified site) be assigned instead of I21.9.
ICD-10-CM Code Lookup: Medical coding for acute myocardial infarction including STEMI, NSTEMI, and unspecified.
Acute Myocardial Infarction (AMI)
Section 1; C.9.e.
Let’s continue through the chapter-specific coding guidelines for AMI and discuss AMI documented as nontransmural or subendocardial but site provided.
3) AMI documented as nontransmural or subendocardial but site provided
If an acute myocardial infarction is documented as nontransmural or subendocardial, and the site is provided, it is still coded as a subendocardial AMI.
The difference between an unspecified infarction, type and site not stated, and a specified myocardial infarction but the site within the heart is not specified is determined by the variation on the patient’s EKG.
Transmural vs Subendocardial Myocardial Infarction
Acute Myocardial Infarction (AMI)
Section 1; C.9.e.
Let’s continue through the chapter-specific coding guidelines for AMI and discuss subsequent acute myocardial infarction.
4) Subsequent acute myocardial infarction
The coding for a subsequent acute myocardial infarction depends on the timing between MIs.
Subsequent MI (< or = 4 Weeks)
For encounters occurring while the myocardial infarction is less than or equal to four weeks old, codes from category I21 may continue to be reported.
Determine if the current MI is the first MI the patient has had, and if this is the first MI in this episode of care.
If the MI is not the initial MI in this episode of care, determine the time between the MIs.
If the following MI is within 4 weeks of the initial, it is coded as a subsequent MI.
However, if the following MI occurred more than 4 weeks of the initial MI, it is coded as an old, or healed MI (see below).
If the subsequent MI is within 4 weeks of the first, I22 is used.
The initial MI is coded to I21.
The code I22 must be used with a I21 code.
You cannot code a subsequent MI, I22 without coding the initial MI, I21.
The order or sequencing of the I22 and I21 codes depends on the reason for the encounter.
I22 is only used when the initial and subsequent MI are of the same type or are unspecified.
If the initial and subsequent MIs are not of the same type, code both as initial MIs with I21.
Example:
This 87-year-old male was admitted for an acute MI STEMI of the left main coronary artery, in the anterior wall 5 days ago.
Today, day 6, the patient suffered another acute MI STEMI in the same location.
Since it has not been 4 or more weeks, the initial MI is coded as I21 and the subsequent MI would be coded as I22, subsequent MI.
The codes would be I21.01 followed by I22.0.
Old or Healed MI (> 4 Weeks)
Assign code I25.2, for old or healed myocardial infarctions not requiring further care.
An old MI is considered to be more than 4 weeks from the first MI.
Example:
This 87-year-old male was admitted for an acute MI STEMI of the left main coronary artery, in the anterior wall 5 days ago.
On day 6, the patient suffered another acute MI STEMI in the same location.
The patient was discharged on day 20 and suffered another MI on day 60 post MI.
It has been more than 4 weeks since the last MI, so the current MI is the one 60 days post MI.
The patient was discharged and with no follow-up care for the MIs, only the one 60 days out.
The sequence would be I21.01 for the MI 60 days out, followed by I25.2, old or healed MI for both the day 6 and initial MI.
Codes would be I21.01 followed by I25.2
ICD-10-CM Code Lookup: Medical coding for subsequent acute myocardial infarctions.
Summary
This is a very brief summary of the complicated coding for acute myocardial infarctions.
The ICD-10-CM provides codes for different types of myocardial infarction.
In order to accurately code MIs, a thorough reading of the documentation and of the codes is required.
It takes time to develop skill at coding myocardial infarctions.
The best guides are the guidelines for Chapter 9: Diseases of the Circulatory System (I00-I99) and a good source of the anatomy of the heart.
ICD-10-CM Codes: Summary of medical coding for ischemic heart diseases along with chapter-specific coding guidelines for atherosclerotic coronary artery disease and angina, and acute myocardial infarction (AMI).
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