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In the Fall of 2023, I received a message from a cardiology fellow about one of my twitter posts. He argued that I had used the term “Type 2 NSTEMI” but “STEMI” (ST-segment elevated myocardial infarction) and “NSTEMI” (non ST-segment elevated myocardial infarction) were terms that could only be used for Type 1 MIs. We respectfully exchanged ideas, neither really convincing the other.

But then I saw other cardiologists arguing the exact same point on social media. Then, in June 2024, I received a message from a fellow CDI physician advisor. His colleagues were also arguing that point. This made me pause.

Was I wrong?

Should I stop using the term “Type 2 NSTEMI”? I still saw it used all the time in practice, by cardiologists and non-cardiologists alike.

Were we ALL wrong?

I immediately asked a cardiac electrophysiologist friend of mine (and assistant professor at UAB) who confirmed my understanding…phew…

So where’s the misunderstanding? Let’s take a step back.

How Do We Define a Myocardial Infarction?

According to the 4th Universal Definition of Myocardial Infarction (4UDMI), two key criteria must be met:

1. Evidence of acute myocardial injury

2. Signs or symptoms of ischemia

Both criteria are required for a diagnosis of MI. 

Breaking down the definitions

• Acute Myocardial Injury: This occurs when cardiac troponin levels rise above the 99th percentile upper reference limit (URL). A rise and/or fall in troponin levels indicates an acute injury, while an unchanging pattern suggests chronic injury. 

• Evidence of Ischemia: The 4UDMI outlines four potential indicators, any one of which suffices: 

  • Symptoms of acute myocardial ischemia (e.g., angina or anginal equivalents) 

  • New ischemic ECG changes 

  • Development of pathological Q waves 

  • Imaging evidence of new loss of viable myocardium or regional wall motion abnormality consistent with ischemia 

If both criteria are met, then the diagnosis of MI is supported. The distinction between Type 1 and Type 2 MI depends on the underlying etiology: 

• Type 1 MI results from atherothrombotic coronary artery disease, often triggered by plaque disruption (rupture or erosion). 

• Type 2 MI stems from an oxygen supply-demand mismatch. 

Where does NSTEMI fit in?

The terms STEMI and NSTEMI describe ECG findings rather than MI types. Neither ECG finding is unique to a type. In fact, ST-elevation can occur in 3–24% of Type 2 MIs according to the 4UDMI.

So, let’s address that cardiology fellow’s question. Can you meet the criteria for a myocardial infarction with supply-demand mismatch aka “Type 2 physiology?”

Absolutely.

And if there’s no ST-elevation on ECG, then it is, by definition, a non-ST segment elevated myocardial infarction, aka NSTEMI. So, a Type 2 NSTEMI.

But here’s the catch (and where his argument originated): 

The 4UDMI does NOT use the term “Type 2 NSTEMI.” It only uses “Type 2 MI.” So, even though it’s an accurate descriptor, should we use “Type 2 NSTEMI” in documentation? The answer is actually no—and not just to avoid irking cardiologists but rather because there are important quality reporting implications at play. 

Quality Implications of NSTEMIs

CMS tracks 30-day unplanned readmissions for acute myocardial infarctions (AMIs) under the Hospital Readmissions Reduction Program (HRRP). This cohort isn’t based on DRG assignment but rather on the principal diagnosis code of the index admission:

Notice that the ICD-10-CM code I21.4 Non-ST elevation (NSTEMI) myocardial infarction is included in CMS’s AMI cohort, but I21.A1 Myocardial infarction Type 2 is not. The program is designed to track Type 1 MIs. So if providers document “NSTEMI” without specifying it as Type 2, it may be incorrectly coded as I21.4. This misclassification may negatively impact your hospital’s AMI readmission metrics.

To best mitigate this, encourage providers to document “Type 2 MI” explicitly and reserve “NSTEMI” for Type 1 MIs. CDI teams should query for clarification when necessary.

Other Common Issues: 

1. I5A Non-Ischemic Myocardial Injury (Non-Traumatic): This diagnosis is a CC (complication or comorbidity) whether acute or chronic, impacting DRG assignment and risk adjustment more significantly than terms like “troponinemia” or “troponin elevation.”

2. Overuse of NSTEMI: Providers frequently document “NSTEMI” in cases where troponin levels rise and/or fall due to supply-demand mismatch but without ischemic signs or symptoms. These cases meet the criteria for acute myocardial injury, not myocardial infarction. Given that Type 2 MI (I21.A1) is an MCC, it’s a prime target for clinical validation denials. Providers should avoid documenting myocardial infarction unless both 4UDMI criteria are met. 

Outdated Language

Behind all of this is a larger point. Many cardiologists have already moved away from the term “NSTEMI” and instead use NSTE-ACS (an umbrella term for a Type 1 event which includes NSTEMI and unstable angina).

…Doesn’t quite roll off the tongue, though. But if the coding and quality implications change, you know I’ll be here to keep you all updated.

Don’t forget to check out our CDI and Coding Village online community and access hours of recorded video content and attend monthly live webinars.

That’s all for now. Don’t hesitate to ask questions as they help inspire future issues!

Cheers,

Robert

Thanks to Dr. Sean Dunn (EP Cardiologist, Assistant Professor at UAB) for his help over the last year on this topic. Thanks to Erica Remer, MD, and Laura Samson, RN BSN CCDS for editing this newsletter!

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