Understanding ICD-10-CM Codes: The Important, Comprehensive, and Distinct Facts [Part 3 of 6]

Welcome back to our blog series!

The International Classification of Diseases, Tenth Revision, Clinical Modification, or ICD-10-CM, is a morbidity classification published by the United States for classifying diagnoses and reasons for visits in all healthcare settings. The Centers for Medicare and Medicaid Services (CMS) ICD-10-CM Official Guidelines for Coding and Reporting for Fiscal Year 2023 have the updated condition guidelines for coding and reporting.

First, what is the difference between an Active medical condition and a History of a condition?

• The medical condition is considered Active when the illness is causing or a contributory factor to the patient’s present clinical issues affecting the functional and cognitive status, mood or behavior, monitoring, and treatment(s). The active medical condition(s) is/are the reported ICD-CM code(s).
• If the physician (or physician assistant, nurse practitioner, clinical nurse specialist) documentation has a History of, then the medical condition has been resolved, no longer requires clinical management and/or is not reported as an active medical condition. Typically, the history of an illness is included in the notes to provide information about the patient’s past medical problems.

Acute Myocardial Infarction versus Subsequent Myocardial Infarction:

• An Acute Myocardial Infarction (AMI) is a condition equal to, or less than 28 days or four (4) weeks from onset. Assigning the Category I21, AMI, of the ICD-10-CM includes transfers to another acute care or post-acute care setting.
• Subsequent Myocardial Infarction is used when a patient had suffered an AMI has a new AMI within four (4) weeks or 28 days of the previous AMI. The Subsequent MI under the ICD-10-CM Category I22 must be reported with a code from Category I21 (AMI); the reporting sequence of the Category codes I21 and I22 depends on the circumstance of the patient’s condition.

Myocardial Infarction (MI) type is determined using an electrocardiogram (ECG) that evaluates the heart’s rhythm and abnormalities in the heart’s electrical system.

• STEMI or ST-segment Elevation Myocardial Infarction is the medical term for a major heart attack, and it is also referred to as a Q-wave or transmural myocardial infarction. The condition is caused by long-term blockage of blood supply to a large area of the heart muscle.
• NSTEMI or Non-ST Elevation Myocardial Infarction also called a non-Q wave or non-transmural MI. The condition involves a partial or temporary blockage of one of the coronary arteries, causing the reduced blood supply to the heart muscle.

Here are coding tips:

• Other names for MI or heart attack – Acute coronary syndrome; Cardiac or Coronary infarction; Coronary rupture; Coronary thrombosis; Coronary occlusion. cardiac infarction.
• Assign the ICD-10-CM to the highest specificity level – review the medical record to identify the AMI site, such as anterolateral wall or true posterior wall.
• Type 1 STEMI – use ICD-10-CM codes I21.0-I21.2 and code I21.3.
• NSTEMI and nontransmural MI- assign ICD-10-CM code I21.4.
• If a type 1 NSTEMI evolves to STEMI –  use the STEMI code.
• If a type 1 STEMI converts to NSTEMI due to thrombolytic therapy – code as STEMI.
• If the patient is still receiving care related to the MI  after the 4-week time frame, the appropriate aftercare code should be assigned.
• Default code for unspecified AMI, acute myocardial infarction or unspecified type – ICD-10-CM Code I21.9, Acute myocardial infarction, unspecified.
• If only type 1 STEMI or transmural MI without the site is documented – ICD-10-CM code I21.3, ST elevation (STEMI) myocardial infarction of unspecified site.
• If the AMI is documented as nontransmural or subendocardial, but the site is provided – code as a subendocardial AMI.

Let us discuss coding scenarios:

• The patient was admitted to a Skilled Nursing Facility (SNF) following hospitalization related to the STEMI of the left anterior descending coronary artery two (2) weeks ago.
• The patient is within four (4) weeks or 28 days from the onset and still requires care – assign ICD-10-CM code  I21.02, ST elevation (STEMI) myocardial infarction involving left anterior descending coronary artery.
• A patient is readmitted to the hospital due to a STEMI of the anterior wall. Three (3) weeks ago, the patient had a STEMI of the left anterior descending coronary artery.
• The second STEMI is within four (4) weeks or 28 days from the onset of the first AMI – it is a subsequent MI. It is listed first, coded as ICD-10-CM I22.0, Subsequent ST elevation (STEMI) myocardial infarction of anterior wall.
• The first STEMI is coded next – ICD-10-CM code  I21.02, ST elevation (STEMI) myocardial infarction involving left anterior descending coronary artery.

It is best practice to always refer to the updated ICD-10-CM Guidelines in assigning and sequencing the appropriate ICD-10-CM codes based on the physician documentation in the medical record.