The hospital and postdischarge course of patients diagnosed with type 2 myocardial infarction, triggered when myocardial oxygen demand outstrips supply, differs in telling ways from those with the more common atherothrombotic type 1 MI, suggests a new registry analysis that aims to lift a cloud of confusion surrounding their management.
The observational study of more than 250,000 patients with either form of MI, said to be the largest of its kind, points to widespread unfamiliarity with distinctions between the two, and the diagnostic and therapeutic implications of misclassification. It suggests, in particular, that type 2 MI may be grossly underdiagnosed and undertreated.
The minority of patients with type 2 MI were more likely female and to have heart failure (HF), renal disease, valve disease, or atrial fibrillation, and less likely to have a lipid disorder, compared with those with type 1 MI. They were one-fifth as likely to be referred for coronary angiography and 20 times less likely to undergo revascularization.
Indeed, only about 2% of the type 2 cohort ultimately underwent percutaneous coronary intervention (PCI) or coronary bypass surgery (CABG). Yet the analysis suggests that cardiovascular risk climbs regardless of MI type and that in patients with type 2 MI, coronary revascularization might well cut the risk of death in half over the short term.
There were also disparities in clinical outcomes in the analysis, based on data from the final 3 months of 2017 in the Nationwide Readmissions Database, which reportedly documents almost 60% of hospitalizations in the United States.
For example, those with type 1 or type 2 MI – as characterized in the then-current third Universal Definition of Myocardial Infarction and today’s UDMI-4 – were comparably at risk for both 30-day all-cause readmission and HF readmission. But type 2 patients were less likely to die in the hospital or be readmitted within 30 days for recurrent MI.
Revascularization uncertainty
Importantly, the study’s 3-month observation period immediately followed the debut of a code specifically for type 2 MI in the ICD-10-CM system.
Type 2 accounted for about 15% of MIs during that period, the percentage climbing sharply from the first to the third month. That suggests clinicians were still getting used to the code during the early weeks, “undercoding” for type-2 MI at first but less so after some experience, Cian P. McCarthy, MB, BCh, BAO, Massachusetts General Hospital, Boston, said in an interview.
“I can imagine that as people become more aware of the coding, using it more often, the proportion of type 2 MI relative to the total MI cases will probably be much higher,” said McCarthy, lead author on the study published online Feb. 15, 2021, in the Journal of the American College of Cardiology.
What had been understood about type 2 MI came largely from single-center studies, he said. This “first national study of type-2 MI in the United States” sought to determine whether such findings are hospital specific or “representative of what people are doing nationally.”
The new analysis largely confirms that patients with type 2 MI are typically burdened with multiple comorbidities, Dr. McCarthy said, but also suggests that type 2 often was, and likely still is, incorrectly classified as type 1. So, it was “surprising” that they were rarely referred for angiography. “Only 1 in 50 received revascularization.”
Those diagnosed with type-2 MI were far less likely to receive coronary angiography (10.9% vs. 57.3%), PCI (1.7% vs. 38.5%), or CABG (0.4% vs. 7.8%) (P < .001 for all three differences), the report noted.
That, Dr. McCarthy said, “clearly shows that clinicians are uncertain about whether revascularization is beneficial” in type 2 MI.