Type 2 MI Not Uncommon in the Emergency Department

Type 2 myocardial infarction (T2MI) occurs less frequently than type 1 myocardial infarction (T1MI) among patients presenting to the emergency department with chest pain, but clinical outcomes for the two types of MIs are similar in long-term follow-up, according to the results of a new study.

Properly identifying T2MI, which is the result of myocardial oxygen supply-demand mismatch brought on by an extracardiac stressor, such as anemia or sustained tachyarrhythmia, is critically important, investigators say, because treatment differs from T1MIs caused by an obstruction in a coronary artery.

“With type 2 MI patients, you should always first treat the trigger, the underlying cause,” Thomas Nestelberger, MD (University Hospital Basel, Switzerland), one of the lead researchers, told TCTMD. “In a patient with anemia, for example, you need to treat the anemia, to correct the hemoglobin level, or to stop the bleeding if there is ongoing bleeding. . . . If addressing the trigger alone resolves all the symptoms, that’s probably all you need to do.”

It can be tricky to accurately diagnose patients with T2MI, particularly since they’re also presenting with chest pain and elevations in cardiac troponin, he added. “What you’re thinking as an emergency physician is a type 1 MI and whether or not to activate the cath lab,” said Nestelberger, noting that that decision would include an assessment of family history and CVD risk factors. “It’s very important to follow the Universal Definition to make a diagnosis of type 2 MI—you always need a clear identification of a trigger.”

The Fourth Universal Definition criteria for T2MI include an increase of cardiac troponin levels and evidence of an imbalance between oxygen supply and demand. Such triggers include severe hypertension, hypotension, tachyarrhythmia, anemia, or hypoxemia, among others. The patient must also have at least one of the following criteria: symptoms of acute myocardial ischemia, new ischemic ECG changes, development of pathological Q waves, or imaging evidence of new loss of viable myocardium or new regional wall motion abnormality.

The study, which included Tania Coscia, MD (University Hospital Basel), as lead author, was published March 9, 2022, in JAMA Cardiology.

T2MI Not a Single Entity

To investigate the characteristics, management, and outcomes of T2MI patients, researchers turned to the APACE study, which was initially designed to assess a rapid diagnosis of MI. The study included 6,253 patients with acute chest discomfort who presented to 12 European emergency departments between 2006 and 2018. Adjudicated T2MI was diagnosed in 4.0% of patients and T1MI in 16.4% of cases. Patients with T2MI were more likely to be women (35.9% vs 26.0% with T1MI; P = 0.002) and had a lower prevalence of cardiovascular risk factors.

The trigger for T2MI was most commonly reported to be tachyarrhythmia (53.8%), followed by hypertension (18.7%), coronary artery spasm (5.6%), anemia (4.4%), bradyarrhythmia (4.0%), hypoxemia (3.6%), coronary artery dissection (1.2%), and coronary embolism (0.8%). Multiple triggers and unknown triggers were also documented in 2.8% and 3.6% of T2MI patients, respectively.

With type 2 MI patients, you should always first treat the trigger, the underlying cause. Thomas Nestelberger

The risk of all-cause and cardiovascular mortality at 2 years was similar between patients with T2MI and T1MI. The risk of death did differ based on the underlying trigger, however. For example, patients with tachyarrhythmia or hypertension as the stressor for T2MI had a lower risk of death from any cause at 2 years compared with patients with T2MI triggered by hypotension, hypoxemia, or anemia. Patients with T2MI were more than three times more likely to have a future T2MI compared with patients who had T1MI as the index event. Similarly, future T1MI was more common among those with T1MI as the first event.   

To TCTMD, Nestelberger noted that patients with T2MI triggered by tachyarrhythmia or a hypertensive emergency tend to be younger, which could explain their lower risk of mortality. In contrast, patients with anemia are more likely to be older—think of an elderly patient with a gastrointestinal bleed accompanied by a significant decline in hemoglobin. In the absence of coronary artery disease, patients with T2MI have a very low risk of death, the researchers note.  

Overall, the study shows that even in this cohort of patients with a common presentation in a homogenous setting, “T2MI is not a single entity but rather a heterogenous group of phenotypic clusters with myocardial oxygen supply-demand mismatch as the underlying mechanism,” the group writes. With the identification of the trigger, treatment should be individualized, with the focus first being the rapid reversal of the extracardiac stressor. Additional therapies should also include optimizing blood pressure control and lipid levels, say researchers.