Myocardial Infarctions

What’s with all the new codes for myocardial infarctions (MI), you may be asking yourself.  What differentiates a type 1 from a type 2 MI?  This edition of “In the kNOW” will delve into those questions and more.

As you have undoubtedly noticed, myocardial infarction codes now allow us to capture the “type” of MI that the patient experiences.  This is very useful as more and more cardiologists had been specifically documenting type 2 MI and leaving us with no way to distinguish that particular type of MI from any other.  1^st Qtr. 2017 Coding Clinic had instructed coders to use I21.4 for a type 2 MI which was the same code as a Non-ST elevation myocardial infarction.  We were instructed to assign the type 2 to NSTEMI unless there was documentation that the MI was a STEMI.  Now, however, we have a specific code, I21.A1, to assign when a patient has suffered a type 2 MI, regardless of whether they are specified as STEMI or NSTEMI.     

So how many different types of MIs are there, and what is the difference between them?  There are five different types of MIs, and they are categorized as follows:

Type 1- MI resulting from plaque rupture or dissection

Type 2- MI that occurs as a result of a supply/demand mismatch

Type 3- A sudden cardiac death, without biomarker evidence of MI, but with signs of ischemia

Type 4:

            Type 4a- MI related to percutaneous coronary intervention (PCI)

            Type 4b- MI related to thrombosis in a stent

            Type 4c- MI related to a restenosis (greater than 50%) post previously successful PCI

Type 5- MI associated with a coronary artery bypass graft

The corresponding ICD-10-CM codes for each type are:

Type 1- I21.9, or code for MI of specific site, or code for STEMI or NSTEMI

Type 2- I21.A1

Type 3- I21.A9

Type 4 (a, b, c) - I21.A9

Type 5- I21.A9

In the event there is an unspecified MI, then assign code I21.9. 

A further word regarding type 2 MIs; because this type of MI results from another condition which is placing the supply/demand of myocardial oxygenation into an imbalance, coders are directed to “Code also the underlying cause, if known and applicable”.   These conditions may include: heart failure, shock, renal failure, anemia, or chronic obstructive pulmonary disease (COPD) to name a few.  The sequencing of the codes would be dependent upon the circumstances of the admission. 

There are “Code first” and “Code also” notes associated with MI types 3-5 which must be followed as well.  The “Code first” note requires code assignment for postprocedural MI if applicable, whereas the “Code also” note is for capturing complications such as stent stenosis or thrombosis.

The expansion of the MI code set also impacts the code assignment for subsequent MIs that occur within four weeks of the initial MI.  Subsequent type 1 and unspecified MIs should be coded from the I22 category and will be coded along with a code from the I21 category with sequencing again dependent on the admission circumstances.  Subsequent type 2 MIs should be assigned to I21.A1, with types 4 and 5 coded to I21.A9.  Note that there would never be a subsequent type 3 MI since that type of MI results in a death.

Now you are in the kNOW!!

About the Author 

Dianna Foley, RHIA, CHPS, CCS  is OHIMA's Coding Education Coordinator. Dianna has been an HIM professional for 20 years. She progressed through the ranks of coder, department supervisor, and department director, to her current role as a coding consultant. 

She recently served as the program director for Medical Coding and HIT at Eastern Gateway Community College. Dianna earned her bachelor's degree from the University of Cincinnati subsequently achieving her RHIA, CHPS, and CCS certifications. She is an AHIMA Approved ICD-10-CM/PCS Trainer and a a presenter at regional HIM meetings and the OHIMA Annual Meeting.