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ICD-10 Codes for Myocardial Infarction (Type 1 and Type 2)

Myocardial Infarction has defined six types of MI. The two most commonly encountered are type 1 (primarily due to CAD) and type 2 (primarily due to myocardial supply/demand mismatch). For these two types, MI is defined as myocardial necrosis identified by a rise and/or fall of cardiac biomarkers to or from a level greater than the 99th percentile of the upper reference limit.

Definition of Myocardial Infarction (Type 1)

Type 1 is the classic spontaneous MI, primarily due to coronary artery disease (CAD) with atherosclerotic plaque rupture, ulceration, fissuring, erosion, or dissection causing intraluminal thrombosis. Occasionally type 1 occurs in the absence of CAD with spontaneous thrombosis of a coronary artery (particularly in women). Type 1 includes Q-wave infarction, ST-elevation MI, and non-ST elevation MI.

ICD-10 Code for Myocardial Infarction (Type 1)

An acute type 1 MI is now by a group of codes in category I21 for ST-elevation MI (STEMI), including Q-wave MI, and non-ST-elevation MI (NSTEMI). An MI is coded as acute for a period of four weeks following onset; after that, it is assigned code I25.2 (old MI). Codes in category I22 are also provided for a subsequent type 1 MI (STEMI or NSTEMI), defined as another MI occurring within four weeks of a previous (initial) MI. In this situation, a code from I21 is also assigned for the initial MI.

Definition of Myocardial Infarction (Type 2)

Type 2 MI is commonly known as supply/demand infarction where the supply of oxygenated blood to the myocardium does not meet the physiologic demand for oxygen (supply/demand mismatch or ischemic imbalance), causing myocardial necrosis primarily due to a condition other than CAD. Common examples include severe anemia, tachyarrhythmia, hypertensive emergency, and shock states.

Demand ischemia is supposed to be reserved to describe supply/demand mismatch causing ischemia without necrosis where biomarkers remain below the 99th percentile of the upper reference limit, but the term is often used by clinicians to describe what is technically a type 2 MI.

ICD-10 Code for Myocardial Infarction (Type 2)

With 2018 ICD-10-CM, we finally have codes to identify type 2 MI and make the important distinction between it and type 1. Type 2 MI (whether a new initial or subsequent) is assigned to one code (I21.A1). The code also includes any description of MI due to ‘demand ischemia’ or ‘ischemic imbalance.’

The diagnosis of type 2 MI may have a major impact on severity classification, affecting diagnosis-related group (DRG) assignment, quality reporting, and reimbursement, just as type 1 MI does. A diagnosis of ‘demand ischemia’ has assigned to code I24.8 (other forms of acute ischemic heart disease).

Demand ischemia is supposed to be reserved for supply/demand mismatch causing ischemia without necrosis where biomarkers remain below the 99th upper reference limit, but instead, it is often used by clinicians to describe what is technically a type 2 MI. A clinically correct distinction between demand ischemia and type 2 MI is crucial because demand ischemia has far less impact on severity classification.

Clinical Scenario

The patient is admitted to the hospital on June 1 and is diagnosed with acute myocardial infarction, unspecified (ICD-10 code I21.9). On July 7, the provider sees the patient for a follow-up visit and the patient receives care related to the myocardial infarction.

In the scenario described above, applying the appropriate aftercare code rather than the I21.9 code is appropriate.

  • Encounters related to the treatment of the myocardial infarction that is equal to or less than four weeks old can be assigned the appropriate I21 code.
  • Any services provided beyond 28 days would require an appropriate aftercare code to be assigned.
  • Old or healed Myocardial Infarctions not requiring further care may be assigned ICD-10 code I25.2 if supported by documentation in the chart.

In summary, acute type 1 MI (Q-wave, STEMI, and NSTEMI) is assigned to codes in category I21 and, if occurring as a subsequent MI, in category I22. Type 2 MI (supply/demand mismatch) is coded as I21.A1 whether initial or subsequent. All other MI types are assigned code I21.A9.

The code for demand ischemia is still I24.8. A clinically correct distinction between demand ischemia and type 2 MI is crucial. Correct documentation and coding of the specific types of MI are clinically important and essential for billing, compliant reimbursement, and reporting for the national health care database.

Coordinating with providers for accurate use of diagnostic codes is the crucial step of clean claim submission. Insurance companies review provider documentation to ensure the accuracy of diagnosis codes reported. Connecting with professional medical billing company like Medical Billers and Coders (MBC) could help in streamlining your billing activities. Contact us at: 888-357-3226/ for more information.


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