Type 1 STEMI and Type 2 MI Coding Challenge
** This was reviewed and updated on November 28, 2023. **
The Coding Challenge
Question:
A patient was previously admitted to the hospital with a Type 1 STEMI involving the right coronary artery. The patient was treated and discharged. Three weeks later, this same patient was admitted with a Type 2 MI and received treatment. The patient is still being treated for the Type 1 STEMI. Assign the appropriate diagnosis codes.
A. I22.2, I21.11
B. I21.11, I25.2
C. I25.2, I21.A1
D. I21.A1, I21.11
Answer:
D. I21.A1, I21.11
First of all, it’s important to know what these acronyms stand for:
- STEMI is the acronym for an ST elevation myocardial infarction.
- MI is short for myocardial infarction, also known as a heart attack.
The documentation indicates that both myocardial infarctions (MIs) were treated within 4 weeks of each other. The first MI was a type I STEMI with right coronary artery involvement, and the second one was a type 2 MI.
Difference Between Type 1 and Type 2 MI
According to the American College of Cardiology (ACC), “Type 1 MI is due to acute coronary atherothrombotic myocardial injury with either plaque rupture or erosion and, often, associated thrombosis. Most patients with ST-segment elevation MI (STEMI) and many with non-ST-segment elevation MI (NSTEMI) fit into this category.”
Type 2 MI, according to the ACC, “includes patients with evidence of acute myocardial ischemia who do not have acute coronary atherothrombotic injury but instead have oxygen supply-demand imbalance from other reasons. This occurs most often due to the presence of coronary artery disease, which limits increases in coronary perfusion in cases of severe anemia, significant arrhythmias, and other stressors.”
For more comprehensive information on coding for acute myocardial infarctions in ICD-10-CM, please see my article here.
Locate and Verify
Type 1 STEMI
In the ICD-10-CM coding manual Index, look under Infarct, infarction/myocardium, myocardial (acute) with a stated duration of 4 weeks or less/ST elevation (STEMI)/involving right coronary artery I21.11.
This code can be verified in the Tabular as:
I21.11, ST elevation (STEMI) myocardial infarction involving right coronary artery
I21.11 is also reportable when the documentation states, “Inferoposterior transmural (Q wave) infarction (acute).”
Be sure to review the “Includes,” “Excludes2,” and “Use Additional” notes before making your final coding selection.
For example, there is an “Includes” note at I21 that reads:
Includes:
- cardiac infarction
- coronary (artery) embolism
- coronary (artery) occlusion
- coronary (artery) rupture
- coronary (artery) thrombosis
- infarction of heart, myocardium, or ventricle
- myocardial infarction specified as acute or with a stated duration of 4 weeks (28 days) or less from onset
The “Use additional” note provided at I21.11 states an additional code should be assigned to identify:
- 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)
A “Code Also” note provided at I20-I25 indicates a code should be used to identify the presence of hypertension (I10-I16), if applicable.
The conditions listed at the “Excludes2” note at I21.11 are:
- old myocardial infarction (I25.2)
- postmyocardial infarction syndrome (I24.1)
- subsequent type 1 myocardial infarction (I22.-)
There is also an “Excludes2” note at I00-I99. These conditions should be coded if applicable:
- certain conditions originating in the perinatal period (P04-P96)
- certain infectious and parasitic diseases (A00-B99)
- complications of pregnancy, childbirth, and the puerperium (O00-O9A)
- congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)
- endocrine, nutritional, and metabolic diseases (E00-E88)
- injury, poisoning and certain other consequences of external causes (S00-T88)
- neoplasms (C00-D49)
- symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)
- systemic connective tissue disorders (M30-M36)
- transient cerebral ischemic attacks and related syndromes (G45.-)
Type 2 MI
In the coding manual Index, look under Infarct, infarction/myocardium, myocardial (acute) (with stated duration of 4 weeks or less)/ST elevation (STEMI)/type 2 I21.A1.
This code can be verified in the Tabular as:
I21.A1, Myocardial infarction type 2
Other clinical terms reportable with I21.A1 include:
- Myocardial infarction due to demand ischemia
- Myocardial infarction secondary to ischemic imbalance
Again, make sure to review the “Code First,” “Includes,” “Use Additional,” and “Excludes2” notes.
The “Code First” note indicates that the underlying cause should be sequenced first, such as:
- anemia (D50.0-D64.9)
- chronic obstructive pulmonary disease (J44.-)
- paroxysmal tachycardia (I47.0-I47.9)
- shock (R57.0-R57.9)
Just like for the “Use additional” note provided at code I21.11, the following should be assigned here, when applicable, to identify:
- 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)
The “Code Also” note tells us to assign a code for the presence of hypertension (I10-I16), if applicable.
The “Excludes2” notes are the same for this code as they are for I21.11. If the patient has any of the listed conditions, they will also need to be coded.
Coding Guidelines
According to the ICD-10-CM Official Guidelines for Coding and Reporting, a code from category I22 should not be assigned for subsequent myocardial infarctions other than for 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.
The coding guidelines further state, “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.”
Sequencing
According to the coding guidelines, the sequencing of these two codes is based on the circumstances of the encounter.
The second admission was due to the type 2 MI, which occurred less than 4 weeks after the first MI. Therefore, the type 2 MI (I21.A1) is sequenced first, followed by the type 1 MI (I21.11).
The second MI is not considered a “subsequent” MI, because the coding guidelines state that subsequent MIs are only assigned when both MIs are type 1 or unspecified. (A subsequent MI is then coded to category I22.) In this case, we have one type 1 and one type 2.
Incorrect Answers
A, B, and C are incorrect.
A. I22.2, I21.11. I22.2 refers to Subsequent non-ST elevation (NSTEMI) myocardial infarction.
B. I21.11, I25.2. I25.2 refers to Old myocardial infarction.
C. I25.2, I21.A1. Again, I25.2 refers to Old myocardial infarction.
How Did You Do?
Coding for acute myocardial infarctions can be tricky. But if you know what to look for in the documentation, it definitely reduces the errors. Things to look for include the location (which wall), arteries affected, whether it is an initial AMI (up to 4 weeks) or a subsequent AMI (AMI occurring within 4 weeks of initial AMI), and the type of AMI.
Also, documentation should include any tobacco use, dependence, and exposure when possible and should be assigned as secondary codes. Post-administration of tPA (rtPA) prior to admission and within the previous 24 hours should also be documented and coded, as should any hypertension. If there are any questions, be sure to query the physician.
