Understanding the different types of myocardial infarction can be challenging. In this article, we share the authoritative definitions for each of the six types of myocardial infarction and explain their distinct differences to help you guide proper physician documentation, correct coding, and successfully query your physicians.
The table below lists the six types of myocardial infarction (MI) based on the Third Universal Definition of Myocardial Infarction with corresponding ICD-10 codes for 2018:
|1||Spontaneous MI primarily due to coronary artery disease (CAD)
|2||MI due to supply/demand mismatch||I21.A1|
|3||Death from MI when biomarkers not available||I21.A9|
|4a||MI related to percutaneous coronary intervention||I21.A9|
|4b||MI related to stent thrombosis||I21.A9|
|5||MI related to coronary artery bypass grafting||I21.A9|
Types 1 and 2 are by far the most commonly encountered in clinical practice and 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 limit of reference range.
Cardiac troponin (I or T) is the most reliable biomarker for all types of MI because it has high myocardial specificity and high clinical sensitivity. Other cardiac biomarkers include MB fraction of creatinine phosphokinase (CK-MB) and myoglobin.
Type 1 MI is the classic spontaneous MI primarily due to CAD with atherosclerotic plaque rupture, ulceration, fissuring, erosion, or dissection causing coronary thrombosis. Occasionally Type 1 occurs in the absence of CAD with spontaneous thrombosis of a coronary artery (particularly in women). Type 1 includes both STEMI (Q-wave) and NSTEMI.
Treatment of STEMI usually requires immediate reperfusion therapy or percutaneous coronary intervention (PCI), such as coronary stent. NSTEMI treatment usually includes: nitroglycerin, aspirin, Plavix, a beta-blocker (e.g. atenolol, metoprolol), heparin or Lovenox, and Integrilin or Aggrastat.
Type 1 MI (STEMI and NSTEMI) is assigned to one of several codes in category I21 having specificity for the location of STEMI. NSTEMI is not specified to location and is assigned to code I21.4.
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 causes include severe anemia, rapid tachyarrhythmia, hypertensive emergency, and shock states. Also included as Type 2 are non-thrombotic occlusions like coronary spasm or embolism from another site.
Treatment of Type II MI is directed at the cause, not the MI itself, for example fluid resuscitation, anti-arrhythmics, blood transfusion, IV anti-hypertensives.
Type 2 MI (either initial or subsequent) is assigned to one code (I21.A1). The code also includes any mention of MI or infarction with “demand ischemia” or “ischemic imbalance.” However, a diagnosis of “demand ischemia” alone is assigned to code I24.8, other forms of acute ischemic heart disease, comparable to unstable angina primarily due to CAD.
Now that a specific code exists for Type 2 MI (supply/demand infarction), it should not be described as NSTEMI, which is a Type 1 MI primarily due to CAD. Incorrectly documenting NSTEMI rather than Type 2 results in many undesirable consequences for providers, patients, classification and data analysis.
Type 2 MI vs. Demand Ischemia. Demand ischemia is supposed to be reserved for supply/demand mismatch causing ischemia (without necrosis) where biomarkers remain below the 99th percentile of the upper limit of reference range. The term “demand ischemia” may be used indiscriminately even when patients experience Troponin or CK-MB release above the 99th percentile, which is technically a Type 2 MI.
A physician query is appropriate for the possibility of Type 2 MI when the diagnosis of demand ischemia is associated with elevated troponins above 99th percentile range. It may be necessary to verify what the 99th percentile reference range is for your hospital’s lab.
Example: A patient is admitted with acute GI bleed, severe anemia, hypotension and chest pain. Troponins 0.17, 0.20, 0.225 (all greater than 99th percentile). Treatment is control of bleeding, fluid resuscitation, and blood transfusion. The cardiologist diagnosed “demand ischemia with elevated troponins.” The circumstances in this case clearly confirm Type 2 MI with treatment directed at the underlying causes and not a coronary thrombosis, and the physician should be queried.
Type 3 MI is rarely encountered since biomarkers are usually obtained, but sometimes the patient dies of an MI before the biomarkers have risen above the 99th percentile of the upper limit of reference range. The MI may have been identified by symptoms that suggested MI and were associated with presumed new changes on electrocardiogram, such as Q-waves, ST elevation, or new left bundle-branch block.
Type 4 MI identifies a complication related to percutaneous coronary intervention (PCI) or a coronary stent. Type 4a is an MI related to PCI. It has a complicated technical definition with six separate criteria, including one that requires an elevation of cardiac troponin to a level five times greater than the 99th percentile of the upper limit of reference range from a normal pre-procedural baseline. Type 4b is simply a Type 1 MI associated with acute stent thrombosis.
Type 5 is MI related to coronary artery bypass grafting. It also has a complex technical definition with four separate diagnostic criteria, one of which is an elevation of biomarkers to a level 10 times greater than the 99th percentile of the upper limit of reference range from a normal preoperative baseline.
Types 3, 4a, 4b, and 5 are lumped together in a single code (I21.A9) that includes either initial or subsequent MI. This a little disappointing since distinction among these Types would be really useful for the national health care database, allowing precise, meaningful analysis of clinical outcomes, resource utilization, and other important data on these different Types of MI.
A Type 4c MI is also identified by ICD-10 under code I21.A9. Type 4c is not included in the Universal Definition Types but is recognized for use in clinical trials to describe infarction due to PCI-related restenosis.
ICD-10 Coding. Coding of the various Types of MI is not difficult once the definitions and causes are understood. All codes for all Types of MI are classified as MCCs and demand ischemia (without MI) is a CC.
An MI is coded as acute for a period of four weeks following onset for both the initial episode of care or for continued care of an MI that occurred within the past 4 weeks; after that it is assigned code I25.2 (old MI). A subsequent MI (“reinfarction”) is defined as another MI occurring within 4 weeks of the occurrence of a previous “initial” MI. Whenever a subsequent MI occurs, two codes are assigned: a subsequent MI code in category I22 and initial MI code (I21.-).
Summary. The Third Universal Definition of Myocardial Infarction has defined six Types of MI. The two most commonly encountered are Type 1 (STEMI and NSTEMI) primarily due to CAD and Type 2 primarily due to a condition other than CAD. Types 3-5 are much less common and describe unique circumstances primarily related to procedures.
Documentation of the specific Type of MI is clinically important and essential for correct coding, billing, reimbursement, and reporting to the national health care database. An accurate database allows precise, meaningful analysis of clinical outcomes, resource utilization, and other important data.
Always query regarding the possibility of Type 2 MI when the diagnosis of demand ischemia is associated with elevated troponins above 99th percentile range, and for NSTEMI when associated with unstable angina or acute coronary syndrome and elevated troponins above 99th percentile range.
It may be necessary to educate your hospitalists and cardiologists regarding the various MI definitions, particularly for Type 2 MI. A clinically correct distinction between Type 2 MI and demand ischemia is necessary to accurately describe the clinical circumstances.
Reference: Thygesen K, Alpert JS, Jaffe AS, Simoons ML, Chaitman BR, White HD, et al; Joint ESC/ACCF/AHA/WHF Task Force for the Universal Definition of Myocardial Infarction. Third universal definition of myocardial infarction. Circulation 2012;126:2020-35.
Sample Query for Demand Ischemia with Elevated Troponins
Documentation in the medical record indicates that this patient has been admitted with or
diagnosed as having ___________________________.
The following is also documented in the medical record [include only those that apply]:
- Serial troponin levels = [list all]
- Associated conditions: [include potential causes, e.g., severe anemia, sepsis, hypotension or shock, rapid tachycardia, hypertensive crisis]
- Treatment: [any treatment or management of associated conditions]
- EKG showing:
- History of CAD or MI
Based on your medical judgment, can you further clarify in the progress notes which, if any,
of the following this condition is intended to indicate:
- Type 2 MI
- Type 1 MI (NSTEMI)
- Demand ischemia only
- Unstable angina only
- Other, please specify:
- None of the above / Not applicable
In responding to this request, please exercise your independent professional judgment. The
fact that a question is asked does not imply that any particular diagnosis is desired or