How Do I Code a Myocardial Infarction? I21 for Four Weeks, I22 for a Second MI Within Them, and I25.2 After

Category I21, Acute myocardial infarction, is defined by time. Its Includes note reads myocardial infarction specified as acute or with a stated duration of 4 weeks (28 days) or less from onset. The Guidelines turn that into the sequencing rule coders actually need (Section I.C.9.e.1):

Official source

“For encounters occurring while the myocardial infarction is equal to, or less than, four weeks old, including transfers to another acute setting or a postacute setting, and the myocardial infarction meets the definition for ‘other diagnoses’ (see Section III, Reporting Additional Diagnoses), codes from category I21 may continue to be reported. For encounters after the 4-week time frame and the patient is still receiving care related to the myocardial infarction, the appropriate aftercare code should be assigned, rather than a code from category I21. For old or healed myocardial infarctions not requiring further care, code I25.2, Old myocardial infarction, may be assigned.”

So the same infarction moves through three codes as time passes: I21 during the four weeks, an aftercare code when care continues beyond them, and I25.2 — whose inclusion terms are healed myocardial infarction and past myocardial infarction diagnosed by ECG or other investigation, but currently presenting no symptoms — once it is history. I25.2 is a disease-chapter code, not a Z86 history code; the Alphabetic Index sends “Infarct, myocardium, past” straight to it.

Within the four weeks, the code also carries the type. Type 1 STEMI is coded by site (I21.0- anterior wall by artery, I21.1- inferior wall, I21.2- other sites, I21.3 unspecified site); type 1 NSTEMI is I21.4, whose inclusion terms take in acute subendocardial, non-Q wave and nontransmural infarctions. I21.9 is the default when type or site is not documented. The Guidelines resolve the two common edge cases: “If only type 1 STEMI or transmural MI without the site is documented, assign code I21.3”; and “If an AMI is documented as nontransmural or subendocardial, but the site is provided, it is still coded as a subendocardial AMI” — I21.4, with the site adding nothing. An NSTEMI that evolves to STEMI is coded as STEMI; a STEMI converted to NSTEMI by thrombolytics is still STEMI.

Types 2 to 5 have their own codes. I21.A1, Myocardial infarction type 2 (demand ischemia, ischemic imbalance), carries a Code First note for the underlying cause — anemia, COPD, paroxysmal tachycardia, shock — so the cause leads. I21.A9, Other myocardial infarction type, covers types 3, 4a, 4b, 4c and 5, with Code First for a postprocedural MI following or during cardiac surgery (I97.190, I97.790) and a Code Also list for the stent or graft complication that caused it. Category I21 also carries Use Additional Code notes for tobacco exposure, use and dependence, and for Z92.82 when tPA was given at another facility within the previous 24 hours — Z92.82 in turn says Code First the acute MI.

Category I22 exists for one situation, stated in its Includes note: acute myocardial infarction occurring within four weeks (28 days) of a previous acute myocardial infarction, regardless of site. The Guidelines add the constraints (Section I.C.9.e.4):

Official source

“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 AMI has a new AMI within the 4 week time frame of the initial AMI. A code from category I22 must 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.”

Official source

“Do not assign code I22 for subsequent myocardial infarctions other than type 1 or unspecified. For subsequent type 2 AMI assign only code I21.A1. For subsequent type 4 or type 5 AMI, assign only code I21.A9.”

The tabular says the same from the other end: I22 carries an Excludes1 for subsequent type 2 (I21.A1) and for subsequent types 3, 4 and 5 (I21.A9). And when the two infarctions are of different types within the four weeks, I22 is not used at all — the Guidelines assign a code from I21 for each type instead. I22 is reserved for the case where both the initial and the subsequent infarction are type 1 or unspecified.

1. Establish when the infarction began. Inside four weeks (28 days) → category I21. Beyond four weeks with care still directed at it → the appropriate aftercare code. Healed and untreated → I25.2.
2. Inside the four weeks, read the type. Type 1 STEMI → I21.0-–I21.3 by documented site (I21.3 when only “STEMI” or “transmural” is documented). Type 1 NSTEMI, subendocardial or nontransmural → I21.4, whatever site is named. No type or site → I21.9.
3. Type 2 → I21.A1 with the documented cause coded first. Types 3, 4 or 5 → I21.A9, with the postprocedural MI code first if applicable and the causing complication coded also.
4. A second type 1 or unspecified MI within four weeks of the first → add the I22 code to the I21 code; order by the circumstances of the encounter. A second MI of a different type → two I21 codes, no I22.
5. Add the Use Additional codes the record supports: Z92.82 for tPA at another facility within 24 hours, and the tobacco codes.

1. Admitted with NSTEMI, day 3 of stay.I21.4. The site, if documented, does not change the code.
2. Transferred to inpatient rehabilitation two weeks after an anterior-wall STEMI involving the LAD. The infarction is still inside its four weeks and meets the definition of an other diagnosis, so I21.02 continues to be reported — the Guidelines say so explicitly for transfers to a postacute setting.
3. Cardiac rehabilitation visit six weeks after the infarction. No code from I21: after four weeks, care related to the infarction takes the appropriate aftercare code.
4. ECG at an unrelated visit shows an old infarction; no symptoms, no treatment.I25.2 — its inclusion term names exactly this.
5. Second type 1 NSTEMI ten days after a STEMI. The I21 code for the first infarction plus I22.2 for the subsequent NSTEMI, sequenced by the circumstances of the encounter.
6. Type 2 MI documented as due to severe anemia. The anemia code first, then I21.A1 — the Code First note at I21.A1 orders it.

• Reporting a past infarction with a Z86.7- history code. ICD-10-CM classifies a healed infarction to I25.2 in the circulatory chapter; the Index entry “Infarct, myocardium, past” points there.
• Continuing category I21 beyond four weeks. After 28 days it is an aftercare code, or I25.2.
• Assigning I22 for a subsequent type 2 MI — only I21.A1 is assigned — or for a second infarction of a different type, where two I21 codes are used instead.
• Using I21.9 when the record documents “STEMI” without a site: that is I21.3.
• Sequencing a type 2 MI ahead of its documented cause; I21.A1 carries Code First.
• Adding a chest-pain symptom code beside a confirmed MI — the symptom is integral to the diagnosis.

• The date of onset, or the number of days since the infarction — the four-week boundary.
• Type 1, 2, 3, 4 or 5; STEMI or NSTEMI; the site for a STEMI.
• A second infarction within four weeks, and its type.
• Whether the current encounter treats the infarction, treats its aftermath, or merely records it as history.
• The underlying cause of a type 2 MI, and the procedure or device complication behind a type 4 or 5 MI.
• tPA given at another facility within the previous 24 hours; tobacco use, dependence or exposure.