Cardiology Coding Alert

I21.4 will become your go-to code for nontransmural MIs.

Cardiology coders can look forward to a number of diagnoses actually having fewer options under ICD-10. Case in point: All three ICD-9 subendocardial infarction codes crosswalk to a single ICD-10 code.

ICD-9-CM Code

• 410.7x, Acute myocardial infarction; subendocardial infarction

Fifth digit options:

• 0, … episode of care unspecified
• 1, … initial episode of care
• 2, … subsequent episode of care

ICD-10-CM Code

• I21.4, Non-ST elevation (NSTEMI) myocardial infarction

           Acute subendocardial myocardial infarction
           Non-Q wave myocardial infarction NOS
           Nontransmural myocardial infarction NOS

Often called a heart attack, myocardial infarction (MI) refers to when the heart’s blood supply is cut off, leading to a lack of oxygen that causes muscle death. “ST” refers to a specific portion of an electrocardiogram (ECG). ST elevated away from the baseline suggests a heart attack is occurring (STEMI). But this elevation won’t appear on ECGs for more than half of patients experiencing an MI, so the physician will classify them as NSTEMI. All of the above codes are NSTEMI codes.

ICD-9 coding rules: Under ICD-9, you choose your fifth digit for 410.7x based on the episode of care. As a result, you have three code options for NSTEMI.

ICD-10 changes: In contrast to ICD-9’s “acute myocardial infarction” (AMI) terminology, ICD-10 uses STEMI and NSTEMI as the main terms in its code descriptors. You have just one code to represent acute NSTEMI in ICD-10. (Some ICD-10 MI codes do have fifth digit options, but they typically relate to the coronary artery involved. For instance, see I21.21, ST elevation [STEMI] myocardial infarction involving left circumflex coronary artery.)

Be sure to note that ICD-10 official guidelines state, “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.”

Documentation: Clear documentation that the patient suffered a non-ST elevation MI (as opposed to STEMI) is crucial for proper coding. Documentation should indicate whether the MI is initial and acute. You’ll code subsequent MIs within 28 days of the original using I22.- (Subsequent ST elevation [STEMI] and non-ST elevation [NSTEMI] myocardial infarction). For old MIs, you’ll use I25.2 (Old myocardial infarction) for healed MIs that no longer require care. 

Coder tips: Other than updating your coding tools, your practice shouldn’t have to deal with too much hassle to switch to I21.4. As with the other MI codes, determine whether you can easily locate the information in the file that you need. If not, alert the clinical staff to the increased documentation details, and create tools that you can use for MI patients to ease gathering that documentation.

Also take time to read through the official guidelines, and pay close attention to guidelines for diagnoses you code most often. Both the ICD-9 and ICD-10 guidelines offer multiple pages on coding MIs. For example, both tell you, “If NSTEMI evolves to STEMI, assign the STEMI code. If STEMI converts to NSTEMI due to thrombolytic therapy, it is still coded as STEMI.”

Remember: CMS has announced Oct. 1, 2015, as the new compliance date for ICD-10. When ICD-10-CM goes into effect, you should apply the code set and official guidelines in effect for the date of service reported. Learn more at www.cms.gov/ICD10/ and www.cdc.gov/nchs/icd/icd10cm.htm#10update.