A ‘mess’ of a diagnosis: Is it type 2 MI or a nonischemic imposter?

Troponin ‘overdependence’

With many clinical settings in common and the presence or absence of myocardial ischemia to primarily distinguish them, type 2 MI and nonischemic myocardial injury both can be mistaken for the other. That can send management decisions in inappropriate directions.

A 2019 study looked at 633 cases that had been coded as type 2 MI at a major center and readjudicated them according to the fourth universal definition. Only 57% met all the type 2 criteria, 42% were reclassified as nonischemic myocardial injury, and a few were determined to have unstable angina.

“There’s overdependence on the easiest tool in the universal definition,” said Dr. Januzzi, a coauthor on that study. “Frequently people get seduced by the rise in a troponin value and immediately call it a myocardial infarction, lacking the other components of the universal definition that require evidence for coronary ischemia. That happens every day, where someone with an abnormal troponin is incorrectly branded as having an MI.”

It may not help that the current ICD-10-CM system features a diagnostic code for type 2 MI but not for myocardial injury.

“Instead, the new ICD-10-CM coding includes a proxy called ‘non-MI troponin elevation due to an underlying cause,’ ” wrote Kristian Thygesen, MD, DSc, and Allan S. Jaffe, MD, in a recent editorial. They caution against “using this code for myocardial injury because it is not specific for an elevated cTn value and could represent any abnormal laboratory measurements.” The code could be “misleading,” thereby worsening the potential for miscoding and “misattribution of MI diagnoses.”

That potential suggests there could be a growing population of patients who have been told they had an MI, which then becomes part of their medical record, when, actually, they experienced nonischemic myocardial injury.

“Having seen this occur,” Dr. Januzzi explained, “it affects people emotionally to think they’ve had an MI. Precision in diagnosis is important, which is why the universal definition is so valuable. If people would adhere to it more assiduously, we could reduce the frequency of people getting a misdiagnosis of MI when in fact they had injury.”

Still, he added, “if someone has an illness severe enough to cause myocardial injury, they’re at risk for a bad outcome regardless of whether they did or didn’t have an MI.”
 

The uncertain role of angiography

Angiography isn’t ordered nearly as often for patients ultimately diagnosed with type 2 MI or myocardial injury as for those with type 1 MI. Type 2 MI can hit some patients who have remained symptom free despite possibly unrecognized obstructive coronary artery disease (CAD) when myocardial demand is pushed past supply by a critical illness, tachyarrhythmia, or other acute conditions.

In such cases, “it’s reasonable to hypothesize that revascularization, something that really is not done in the vast majority of patients with type 2 MI, might actually be of benefit,” Dr. Januzzi said.

Whether these patients should routinely have angiography remains an open question. Without intervention, any newly identified obstructive CAD would continue to lurk in the background as a potential threat.

In efforts to differentiate type 2 MI from nonischemic injury, it can be “incredibly hard to know whether or not there’s actual ischemia in the mix. And that’s the only thing that defines the difference before taking an angiogram,” Derek P. Chew, MBBS, MPH, Flinders Medical Centre, Bedford Park, Australia, said in an interview.

Dr. Chew is principal investigator for the ongoing ACT-2 trial that is enrolling hospitalized, hemodynamically stable patients with cTn elevations but no suspicion of type 1 MI and “an unequivocal acute intercurrent diagnosis.” Qualifying diagnoses are prespecified on a list that includes sepsis, pneumonia, septicemia, a systemic inflammatory response, anemia, atrial tachycardia, acute kidney injury, and recent noncardiac surgery.

The patients are randomly assigned to a strategy of routine, usually invasive coronary angiography with discretionary revascularization, or to conservative care with noninvasive functional testing as appropriate. The sicker the patient, the greater the competing risk from other conditions and the less revascularization is likely to improve outcomes, Dr. Chew observed. Importantly, therefore, outcomes in the trial will be stratified by patient risk from comorbidities, measured with baseline GRACE and APACHE III scores.

Dr. Chew said the study aims to determine whether routine angiography is of benefit in patients at some identifiable level of risk, if not the whole range. One possible result, he said, is that there could be a risk-profile “sweet spot” associated with better outcomes in those assigned to angiography.

Enrollment in the trial started about 3 years ago, but “the process has been slow,” he said, because many potentially referring clinicians have a “bias on one side or another,” with about half of them preferring the angiography approach and the other half conservative management.