Myocardial Injury or MI? New Universal Definition Aims for Clarity

MUNICH, Germany—The fourth iteration of the universal definition of MI, released to coincide with the European Society of Cardiology (ESC) Congress 2018 here last week, makes clear that not every cardiac troponin elevation is indicative of an infarction.

In the first update to the definition since 2012, an international group of experts representing the ESC, the American College of Cardiology, the American Heart Association, and the World Heart Federation make explicit the distinction between MI, which still requires the presence of both acute myocardial injury detected by abnormal cardiac biomarkers and evidence of acute myocardial ischemia, and nonischemic myocardial injury.

That latter entity—which can be caused by any number of factors, including heart failure, myocarditis, catheter ablation, cardiac contusion, sepsis, chronic kidney disease, and strenuous exercise—is defined by detection of an elevated cardiac troponin value above the 99th percentile upper reference limit and is classified as acute if there is a rise and/or fall in the measurement.

“This document really spends a lot of time clarifying the difference between a nonischemic myocardial injury and a myocardial infarction,” Joseph Alpert, MD (University of Arizona, Tucson), told TCTMD. Alpert was one of the joint chairs of the task force that wrote the update, along with Kristian Thygesen, MD, DSc (Aarhus University Hospital, Denmark), and Harvey White, MBChB, DSc (Auckland City Hospital, New Zealand).

Expanded Info on MI Subtypes

A classification system for MI was first described in the 2007 universal definition of MI, identifying infarctions as type 1, 2, 3, 4 (a-c), or 5. This new version, however, expands the discussions of the different subtypes and provides figures and flow charts to help physicians come to a diagnosis of MI or myocardial injury.

“The diagnosis of type 1 MI versus type 2 MI versus a nonischemic myocardial injury versus a combination of more than one of these entities requires considerable, careful, and rational clinical decision-making,” Alpert said during a presentation at the meeting. “Good clinical judgment is essential in this decision-making process.”

In addition to extensive consideration of the differences between the various MI subtypes and nonischemic myocardial injury, the new document contains additional information on the benefits of high-sensitivity troponin assays and on the use of rapid rule-out and rule-in protocols. There are also new sections on Takotsubo syndrome, myocardial infarction with nonobstructive coronary arteries (MINOCA), chronic kidney disease, A-fib, regulatory perspectives on MI, and silent or unrecognized MI.

New ICD-10 Codes to Ease Implementation

To TCTMD, Alpert said implementation of this new consensus statement into practice will take some time, noting that most European cardiologists but just under half of their US counterparts are currently using the universal definition.

That transition will be eased, however, by the introduction in October 2017 of new ICD-10 codes for the different MI subtypes, he said. A separate code for myocardial injury is expected next year.

When asked about the potential impact of the updated universal definition, Alpert said, “It’ll certainly help epidemiologists because there’s a lot of confusion about elevated troponins and a lot of those patients haven’t had a myocardial infarct and are being called MI. So that’ll help.

“The second thing is,” he continued, “with high-sensitivity troponin, we’re going to be able to pick up smaller myocardial infarcts and treat those patients appropriately as opposed to telling them there’s nothing wrong here.”

Taking a broader view, Alpert said the new consensus statement, published in the European Heart Journal, the Journal of the American College of Cardiology, Circulation, and Nature Reviews Cardiology, is consistent with a move toward more standardization in medicine.

“The guidelines are one piece of the puzzle to get medicine to be much more standardized compared to 50 years ago, but it’s always important to remember that between the guidelines and the patient needs to be physician that’s using their brain because the guidelines are not the ten commandments,” he said. “Clinical situations will differ a little bit so that sometimes you have to deviate from the guidelines, but they’re still a huge help for the overwhelming majority of patients.”