Acute Myocardial Infarction is the medical term for a “heart attack”. A heart attack is a permanent damage to the heart muscle that occurs when blood flow to the heart muscle is abruptly cut off. Myocardial infarction is the combination of three terms as below:
Myocardial Infarction = Myo + cardial + Infarction
“Myo” means muscle, “cardial” refers to the heart and “infarction” means death of tissue due to lack of blood supply.
Types of Infarcts:
Myocardial Infarction can be categorized in different ways as listed below:
1. According to Anatomic region of left ventricle involved:
- Combinations – Anterolateral, Posterolateral, Anteroseptal
2. According to degree of thickness of ventricular wall involved:
- Transmural (full thickness) – A transmural MI occurs when the myocardial necrosis is full thickness (extending from the endocardium through the myocardium to the epicardium.
- Nontransmural MI: A non-transmural MI includes necrosis of the endocardium or the endocardium and myocardium only.
3. According to age of infarcts:
- Newly formed (acute or recent)
- Advanced infarcts (old or healed)
4. Based on etiology and circumstances:
- Type 1: Spontaneous MI caused by ischemia due to a primary coronary event. (Example: plaque rupture, dissection, ulceration or erosion)
- Type 2: Ischemia due to increased oxygen demand or decreased supply to the heart. (Example: coronary artery spasm or embolism, arrhythmia, hypotension)
- Type 3: Related to sudden unexpected cardiac death.
- Type 4: Associated with coronary angioplasty or stents.
Type 4a: Myocardial Infarction occurring after percutaneous coronary intervention
Type 4b: Myocardial Infarction associated with stent thrombosis after PCI
- Type 5: Associated with coronary artery bypass graft.
5. Based on the ECG findings:
Electrocardiogram findings are more commonly used to identify the type of MI. This includes ST-elevation MIs (STEMI), non-ST-elevation MIs (NSTEMI), Q-wave MIs, and non Q-wave MIs. The terms Q-wave and non-Q-wave, transmural and non-transmural MIs are not often used by today’s clinicians. However STEMI and NSTEMI are widely used by the physicians and therefore it constitutes an important element in coding MIs.
Non–ST-segment elevation myocardial infarction (NSTEMI, subendocardial MI) is myocardial necrosis without acute ST-segment elevation. ECG changes such as ST-segment depression, T-wave inversion, or both may be present.
ST-segment elevation myocardial infarction (STEMI, transmural MI) is myocardial necrosis with ECG changes showing ST-segment elevation that is not quickly reversed by nitro-glycerine. Troponin I or troponin T and CK are elevated.
Factors involved in MI coding:
The below factors are essential to assign the appropriate codes for MIs.
- Anterior wall
- Inferior wall
- Arteries impacted
- Left main coronary artery
- Left anterior descending coronary artery
- Right coronary artery
- Left circumflex coronary artery
- Initial incident: up to 4 weeks (28 days)
- Subsequent incident: AMI occurring within 4 weeks (28 days) of previous AMI.
- Type of AMI
- ST elevation (STEMI)
- Non ST elevation (NSTEMI)
- Non-Q wave, Nontransmural
- Other, specified
The important guidelines for coding different types of MI are discussed below:
Type 1 STEMI and NSTEMI:
The ICD-10 codes for Type 1 acute myocardial infarction identify the site (anterior wall or posterior wall) or the coronary artery. The below table shows how the Type 1 STEMI codes are categorized based on the site. It is also significant to note that Type 1 NSTEMI codes have no such site specific codes and there is only one code to represent it.
Points to remember:
If a type 1 NSTEMI evolves to STEMI, assign the STEMI code.
If a type 1 STEMI converts to NSTEMI due to thrombolytic, code the STEMI.
Type 2, 3, 4 and 5:
Only type 1 MI has different codes to identify the site and arteries. Other types have a single code to represent the MI with “code first” and “code also” instructions.
This table will represent the codes for Type 2, 3, 4 and 5
Subsequent Acute MI:
A code from category I22, Subsequent ST elevation (STEMI) and non-ST elevation (NSTEMI) myocardial infarction is to be used when a patient who has suffered a type 1 or unspecified acute MI has a new acute MI within the four-week time frame of the initial acute MI.
Points to remember when coding I22:
· Category I22 should 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
· Category I22 should be used for subsequent MIs of type 1 or unspecified. For other types, do not use I22.
· For subsequent type 2 acute MI, assign only code I21.A1.
· For subsequent type 3, 4 or 5 acute MI, assign only code I21.A9
Figure: Type 1 or unspecified MI coding: (Both initial and subsequent)
Figure: 2 Subsequent MI codes