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Myocardial infarction (MI) or heart attack involves necrosis of heart muscle secondary to prolonged ischemia. It is estimated that about 1.5 million cases of MI occur every year in the United States. Starting October 1, 2017, ICD-10 code updates and new documentation guidelines came into effect for reporting MI. To ensure accurate claim submission, cardiology practices and medical coding companies need to know how to use the new codes correctly.

Myocardial Infarction

MI Classification

MI is classified as follows:

  • Type 1 MI is spontaneous myocardial necrosis caused by an anatomic blockage of blood flow for a prolonged period of time. Mechanical coronary artery obstruction usually occurs due to plaque rupture or thrombotic occlusion.
  • Type 2 MI is also cell death, but is secondary to ischemia on the basis of “supply-demand mismatch”, i.e., an imbalance between oxygen demand and supply (e.g., coronary spasm, anemia or hypotension). Type 2 MI is always caused by underlying condition or disease process.
  • Type 3 is MI resulting in sudden cardiac death
  • Type 4a is an MI associated with percutaneous coronary intervention (PCI)
  • Type 4b is MI associated with in-stent thrombosis
  • Type 4c is MI related to restenosis
  • Type 5 is an MI associated with coronary artery bypass graft (CABG)

MI Code Changes FY 2018

ICD-10-CM provides codes for different types of myocardial infarction. The codes for type 1 acute myocardial infarction (AMI) identify the site, such as anterolateral wall or true posterior wall. Type 1 myocardial infarctions are assigned to codes I21.0-I21.4.

New MI Codes

New MI codes have been added, meaning that the physician will need to specify the type of MI for the medical coding service provider to assign the right code. The new ICD-10 codes for MI are:

  •  I21.A1 Myocardial infarction type 2, which describes MI due to demand ischemia or ischemic imbalance. Sequencing of type 2 acute MI or the underlying cause is dependent on the circumstances of admission. When a type 2 AMI code is described as non-ST elevation myocardial infarction (NSTEMI) or ST elevation myocardial infarction (STEMI), only code I21.A1 should be assigned.
  •  I21.A9 Other myocardial infarction type. Acute MI types 3, 4a, 4b, 4c and 5 are assigned to code I21.A9. This code should be used when documentation does not support using a more specific code.

New Guidelines

  • Codes I21.01-I21.4 should only be assigned for type 1 AMIs in 2018.
  • Notes have been added to specify that STEMI subcategories I21.0-, I21.1-, and I21.2- apply only to Type 1 MIs.
  • Code I21.3, STEMI of unspecified site: Acute MI, unspecified Code I21.9, Acute myocardial infarction, unspecified, is the default for unspecified acute myocardial infarction or unspecified type. If only type 1 STEMI or transmural MI without the site is documented, code I21.3 should be assigned.
  • NSTEMI code I21.4 should be reported for type 1 non ST elevation myocardial infarction (NSTEMI) and nontransmural MIs.
  • Myocardial InfarctionA STEMI code should be reported both when STEMI converts to NSTEMI and when NSTEMI converts to STEMI. This rule applies to type 1 MIs.
  • If an acute MI is documented as nontransmural or subendocardial, but the site is provided, it should be still coded as a subendocardial acute MI.
  • Subsequent acute MI: The existing rule about using a code from I22.- (Subsequent STEMI and NSTEMI) for AMI within four weeks of another AMI has not changed, but it now applies specifically to type 1 and unspecified AMI. Coders should continue to use Code I22.- in conjunction with the I21.- code, sequencing them based on the circumstances of the encounter.
  • Code I22 should be assigned for subsequent myocardial infarctions other than type 1 or unspecified. Only code I21.A1 should be assigned for subsequent type 2 AMI. Only code I21.A9 should be reported for subsequent type 4 or type 5 AMI.
  • MI due to demand ischemia or secondary to ischemic (im)balance” should be assigned to Type 2 MI and not I24.8, Other forms of acute ischemic heart disease.

The primary goal in the management of acute MI is to diagnose the condition accurately and quickly. Treatment acute MI is directed towards restoration of perfusion as soon as possible and prevent death, reinfarction, congestive heart failure, and other complications. ICD-10 provides the ability to code and capture the complications and this can be best accomplished with the help of a cardiology medical billing and coding company that is up-to-date with the ICD-10 coding changes and new guidelines.