Type 2 MI Diagnoses on the Rise, but Best Course of Action Unknown

While type 1 MIs continue to dominate, the prevalence of type 2 MIs has grown in recent years among Medicare beneficiaries, an observational study shows. The shift has implications for care, researchers say, given that patients with type 1 tended to fare worse in the short term and those with type 2 had poorer long-term outcomes.

Led by Amgad Mentias, MD (Cleveland Clinic Foundation and Bon Secours Mercy Health, Lorain, OH), the study was published online in Circulation: Cardiovascular Quality and Outcomes.

The Fourth Universal Definition of MI, released in 2018, separates MI into two types. Management of type 1 MIs, caused by atherothrombotic disease, is guided by a solid evidence base. Type 2 MIs, where the myocardial injury arises due to a mismatch between oxygen supply and demand, make up a more heterogeneous group that’s less well characterized.

Yet type 2 events are far from rare: Mentias and colleagues found that now, in their nationally representative dataset, more than a quarter of MI admissions were type 2.

Diagnosis has been on the rise thanks to the “advent of high-sensitivity troponin that can capture myocardial infarction [more easily], but also there has been an increasing emphasis on identifying type 2 MI,” senior author Ambarish Pandey, MD (University of Texas Southwestern Medical Center, Dallas), pointed out. He cited the introduction of new billing codes for these events and growing awareness about conditions like MI with nonobstructive coronary arteries, often called MINOCA, that fall under the type 2 category.

Here, Pandey said, the researchers sought to take a contemporary look at the type 2 population and better understand how its short- and long-term outcomes might differ from what’s seen with type 1 MIs.

“The thing is that we don’t really know how to take care of the type 2,” he noted, adding that there’s a dearth of therapies aimed specifically at this condition. So, with type 2 MI, long-term prognosis is primarily driven by patients’ high burden of comorbidities, such as frailty and chronic kidney disease.

“I think if we had better approaches to take care of type 2 MI, we would probably do better [in terms of outcomes], but unfortunately, as of now, we don’t have that,” Pandey said.

Medicare Beneficiaries, 2018 to 2021

Mentias and colleagues delved into Medicare Provider Analysis and Review, which tracks all beneficiaries with inpatient hospital stays, using ICD-10 codes to identify type 1 or 2 MI diagnoses from 2018 to 2021. In all, 1.8 million Medicare beneficiaries were admitted with acute MI during that time.

The proportion of type 2 MIs rose over the years, from 19.4% in 2018 to 26.8% in 2021 (P for trend < 0.001). This trend was seen across sex, race, and hospital types.

For patients with type 2 MI, the most common primary or first secondary diagnoses were hypertensive disorder (15%), sepsis and infection (13.7%), tachyarrhythmia (9.5%), respiratory failure (4.7%), and pneumonia/influenza (4.1%). For those with type 1 MI, most (77.5%) presented with NSTEMI, 14.5% with inferior STEMI, and 7.4% with anterior STEMI.

Type 2 MI patients tended to be older, were more likely to be female and nonwhite, and had a higher prevalence of comorbidities and frailty compared with type 1 patients. They also were more likely to be treated at major teaching hospitals but less likely to undergo a coronary angiogram (12.6% vs 63.2%), PCI (1.8% vs 40.8%), or CABG (0.4% vs 7.1%; P < 0.001) during the index admission.

To compare outcomes, the researchers then matched type 1 and type 2 MI cases 1:1 based on age, sex, race, and year of diagnosis. In this population of 94,132 patients (mean age 77.3 years; 53.3% male), those with type 2 MI had lower risks of all-cause mortality, recurrent MI, and heart failure hospitalization within the first month, but similar stroke risk, compared with type 1 patients. Beyond 1 month, however, the type 2 MI patients had higher risks of all-cause mortality and stroke than did type 1 MI patients, as well as slightly lower risks of recurrent MI and heart failure hospitalization.

Propensity-Matched Analysis: HR (95% CI)*

*Subdistribution hazard ratio for all endpoints except all-cause mortality

“These results highlight an urgent need for evidence-based strategies in this high-risk population,” the researchers conclude, adding that studies are “urgently needed to identify which patients would benefit most from coronary evaluation and aggressive cardiovascular risk modification versus those who might be better served by focusing on noncardiovascular comorbidities.”

The ongoing ACT-2 trial is looking at the role of invasive assessment, they note, “but additional research is needed to develop evidence-based pathways that can help standardize and optimize care for this growing, high-risk population.”

As for the next step, Pandey suggested, what’s most needed is a prospective study of type 2 MI that tracks phenotypes over time to clarify the factors driving long-term outcomes.