Acute Myocardial Infarction

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:

  • Anterior
  • Posterior
  • Lateral
  • Septal
  • Circumferential
  • 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.

  1. Location
  2. Anterior wall
  3. Inferior wall
  4. Arteries impacted
  5. Left main coronary artery
  6. Left anterior descending coronary artery
  7. Right coronary artery
  8. Left circumflex coronary artery
  9. Timing
  10. Initial incident: up to 4 weeks (28 days)
  11. Subsequent incident: AMI occurring within 4 weeks (28 days) of previous AMI.
  12. Type of AMI
  13. ST elevation (STEMI)
  14. Non ST elevation (NSTEMI)
  15. Non-Q wave, Nontransmural
  16. Q-wave
  17. 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

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