Fourth Universal Definition Separates MI From Myocardial Injury

MUNICH — The fourth universal definition of myocardial infarction issued jointly by the European Society of Cardiology (ESC), the American College of Cardiology (ACC), the American Heart Association (AHA), and the World Heart Federation (WHF) provides important updates to the previous 2012 definition.

Notably, the document — which was simultaneously published in the European Heart Journal, in Circulation, and on the ESC website and is being presented here at the ESC 2018 Congress — clearly separates MI from myocardial injury.

"The main thing is an update of the [term] 'myocardial injury,'" Professor Kristian Thygesen, from Aarhus University Hospital, Denmark, one of three writing committee chairs, stressed in an interview with theheart.org | Medscape Cardiology.

"That is because of the increase in use of troponin, especially high-sensitivity troponin, which now is in common use" in Europe, Canada, the United States, and elsewhere, and which can detect more minute injury to heart muscle cells.

In this new definition, "patients with elevated blood troponin levels but without clinical evidence of ischemia are said to have had a 'myocardial injury,'" fellow chair Joseph S. Alpert, MD, from the University of Arizona College of Medicine, Tucson, explained in an editorial in the American Journal of Medicine.

To have a myocardial infarction requires both "an elevated troponin blood test together with clinical evidence of ischemia," such as ischemic patterns in the electrocardiogram (ECG), he noted.

The new universal definition of myocardial infarction has updated the descriptions of types 1, 2, 3, 4, and 5 covers other aspects of myocardial infarction, including the enhanced role of imaging.

The document also extends beyond the scope of the earlier version and includes sections on Takotsubo syndrome, myocardial infarction with nonobstructed coronary arteries, chronic kidney disease, atrial fibrillation, regulatory perspectives, and silent or unrecognized myocardial infarction.

"The 4th universal definition of MI has long been anticipated and provides much greater granularity than its predecessors," AHA spokesperson, Richard Becker, MD, director of the University of Cincinnati Heart, Lung, and Vascular Institute, Ohio, who was not involved with the document, told theheart.org | Medscape Cardiology in an email.

"Specifically, there is much greater emphasis on distinguishing myocardial injury, troponin elevation from a variety of causes, and myocardial infarction from one another, based on definitive evidence of underlying conditions and clinical and diagnostic testing."

Myocardial Infarction Definition Changes "Deserve Attention"

According to Alpert, the updates to the previous definition of myocardial infarction "deserve attention" from clinicians who treat patients who may have myocardial injury or an acute myocardial infarction.

A key point is that that all patients with an elevated blood troponin level have myocardial injury, but only patients with both a myocardial injury and clinical evidence of ischemia have myocardial infarction, Alpert reiterated.

The document defines the five subtypes of myocardial infarction as:

Type 1: Due to an atherosclerotic plaque rupture with subsequent coronary arterial thrombosis; patients can have an ST-elevation or a non-ST elevation myocardial infarction and are usually treated with antiplatelet medication and stenting of the culprit lesion in the coronary artery;
Type 2: Due to ischemia (oxygen deprivation) without any plaque disruption; for example, a patient may have hypotension (decreased myocardial oxygen supply) or a tachyarrhythmia (increased myocardial oxygen demand);
Type 3: Classic (such as typical ST elevation; electrocardiogram) but no troponin blood test result;
Type 4: In the setting of a percutaneous coronary intervention in the catheterization laboratory; and
Type 5: At the time of coronary bypass surgery.

"You can have myocardial injury and the release of troponin" that can be detected by high-sensitivity troponin assays if you have kidney disease or even if you are an athlete (eg, a runner), which is "certainly not myocardial infarction," Thygesen stressed. Other situations that can cause myocardial injury and a rise in troponin include Infection, sepsis, and heart surgery.

However, clinicians should not ignore myocardial injury because many studies show that this is associated with a worse prognosis, he added.

Distinguishing myocardial injury and type 2 myocardial infarction, Becker said, is important in several common clinical scenarios, including sepsis and hypertensive urgency and following trauma.

"In each case," he said, "a troponin elevation may prompt treatment that is either unproven or potentially deleterious — specifically, anticoagulation or dual antiplatelet therapy. Subsequent testing, such as a coronary angiogram (and PCI) may also be undertaken without strong evidence of benefit."

In a statement, the third chair of the new document, Professor Harvey D. White, MD, from Auckland City Hospital, New Zealand, noted that: "In the consensus document we have expanded the section on type 2 myocardial infarction and included three figures to help doctors make the correct diagnosis."

ICD-10 Codes Catching Up

The concept of subtypes of myocardial infarction was introduced in 2007, but this was only incorporated into the International Classification of Diseases codes in October 2017, as detailed in an editorial by Goyal and colleagues in Circulation.

"It is of considerable interest that all 5 subtypes of myocardial infarction and nonischemic myocardial injury now have associated International Classification of Diseases, 10th Revision codes for billing and epidemiologic purposes," Alpert noted.

According to Becker, this fourth universal definition of myocardial infarction provides an opportunity to fit different types of myocardial infarction into more specific ICD-10 codes.

"The incorporation of type 2 MI into the ICD codes," White noted, "is another step towards accurate recognition [of different presentations of MI or myocardial injury] followed by appropriate treatment."

He expects that "a code for myocardial injury will be added to the ICD next year."

The disclosure forms are available with the article.

European Society of Cardiology (ESC) Congress 2018. To be presented on Monday August 27, 2018.

Circulation. Published online January 1, 2018. Full text

Eur Heart J. Published online August 25, 2018. Full text

Am J Med. Published online August 11, 2018. Full text

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