Type 2 Myocardial Infarction Is Prevalent in U.S., Has a Distinct Clinical Profile

Type 2 myocardial infarction (MI)—which occurs with mild or no plaque, or fixed atherosclerosis—was formally recognized in 2007, and an ICD-10-CM code was introduced in October 2017. This permitted better research into the incidence of type 2 MI as well as patient characteristics, management and outcomes.

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Cian P. McCarthy, MD, cardiology fellow, and James L. Januzzi, Jr, MD, director of the Dennis and Marilyn Barry Fellowship in Cardiology Research at Massachusetts General Hospital Corrigan Minehan Heart Center, and colleagues recently conducted the first nationwide study of type 2 MI patients hospitalized in the U.S., the largest cohort of type 2 patients published to date. They concluded that type 2 MI is common and has distinctly different characteristics and outcomes than type 1. Their report is published in the Journal of the American College of Cardiology.

Study Methods

The research team analyzed the Nationwide Readmissions Database, maintained by the U.S. government, which in 2017 included data from 28 geographically dispersed states on 58% of all hospitalizations in the country that year. They identified 255,947 patients hospitalized for MI between October 1 and December 31, 2017.

Incidence of Type 2 MI

84.6% of patients had type 1 MI alone, 14.8% had type 2 alone and 0.6% had both types during their admission. The latter finding might represent miscoding, but a prior prospective study, published in Circulation, demonstrated that patients do on occasion experience both types of events.

The number of type 2 MI cases per month doubled during the three-month study period, presumably as clinicians became familiar with the new code, so 14.8% may be an underestimation.

Patient Characteristics

Patients with isolated type 2 MI were significantly different from those with isolated type 1 in that they:

• Were older
• Were more likely to be female
• Had a higher prevalence of serious cardiac comorbidities such as heart failure, valvular heart disease and atrial fibrillation
• Had a higher prevalence of chronic kidney disease, liver disease, deficiency anemia, depression, alcohol use disorder and substance use disorder

Patients with type 1 MI were significantly more likely than those with type 2 to have traditional atherosclerotic risk factors, including smoking, dyslipidemia, prior MI, prior percutaneous coronary intervention (PCI) and prior coronary artery bypass grafting (CABG).

Management

Patients with type 1 MI were substantially more likely than those with type 2 to undergo:

• Coronary angiography (57% vs. 11%; P<0.001)
• PCI (39% vs. 1.7%; P<0.001)
• CABG (8% vs. 0.4%; P<0.001)

Patients with type 2 MI patients who did undergo revascularization were younger, more likely to be men with atherothrombotic risk factors, more likely to have private insurance and more likely to be treated at a teaching hospital than those who did not undergo revascularization.

Mortality

In-hospital mortality was identical for type 1 and 2 MI at 8.9%. However, on multivariable analysis patients with type 2 MI had lower in-hospital mortality than those with type 1 (adjusted OR, 0.57).

Readmissions

Patients with type 2 MI were at significantly lower adjusted odds of 30-day readmission for MI compared to patients with type 1 MI (adjusted OR, 0.46). The two groups had similar risks of 30-day all-cause readmission and readmission for heart failure.

Decision on Revascularization Should Be Individualized

Although revascularization was associated with lower adjusted odds of in-hospital mortality, there may have been confounders that were not measured in this database study. Length of stay was significantly longer and hospital costs were two-fold higher for the type 2 MI patients who underwent revascularization than those who did not.

Until evidence from randomized, controlled trials is available, decision-making about revascularization for patients with type 2 MI should continue to be based on clinical judgment about each case.

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