Clinical trials are “urgently needed” to define validated management strategies for type 2 myocardial infarction (MI), researchers on a registry study of more than 250,000 patients have stressed, after finding these patients have a unique cardiovascular phenotype from type 1 MI.
The registry showed that type 1 and 2 MI patients have been receiving heterogenous management, they warned.
The findings were published online Monday in the Feb. 23 issue of the Journal of the American College of Cardiology, with authors led by Cian P. McCarthy, MB, MCh, BAO, of Massachusetts General Hospital.
McCarthy and colleagues included 216,657 patients with type 1 MI and 37,765 patients with type 2 MI from the U.S. Nationwide Readmissions Database during the 3 months immediately following the October 1, 2017 introduction of an International Classification of Diseases-10th Revision Clinical Modification (ICD-10-CM) code specific for type 2 MI – used to indicate a diagnosis for reimbursement purposes.
The subset of patients defined as type 2 MI – referring to MI occurring in the absence of thrombus – was first recognized in the early 20th century, but was not formally termed as such until 2007, the researchers noted.
Several iterations of the Universal Definition of MI have since been published that define type 2 MI as myocardial necrosis resulting from a mismatch in myocardial oxygen supply-demand, occurring in the absence of acute coronary thrombosis, they added.
Yet, although small observational studies from single centers or hospital systems in the last decade have added to the understanding of these patients – suggesting they tend to be older and have more comorbidities than type 1 counterparts – uncertainties surrounding MI type 2 have prevailed.
There have been no national studies of type 2 MI patients in the U.S. published previously, McCarthy and team added.
The researchers, therefore, set out to compare type 1 and 2 MI patients across the U.S. in the early period after the introduction of ICD-10-CM, hypothesizing that type 2 would be common and have different characteristics and outcomes to type 1.
ICD-10-CM codes were used to identify patients with either primary or secondary diagnosis of type 2 MI, type 1 MI or both during the three months.
Patients with type 2 MI were older (mean age 71 years vs. 69 years), more likely to be women (47.3% vs. 40%) and had higher prevalence of heart failure (27.9% vs. 10.9%), kidney disease (35.7% vs. 25.7%), and atrial fibrillation (31% vs. 21%).
Type 2 MI patients had lower rates than type 1 for some comorbidities, however, including coronary angiography (10.9% vs. 57.3%), percutaneous coronary intervention (1.7% vs. 38.5%), and coronary artery bypass grafting (0.4% vs. 7.8%).
Although observed in-hospital mortality rates were similar between the two groups (both 8.9%), multivariable logistic regression analysis revealed a lower in-hospital mortality risk for type 2 patients (adjusted odds ratio [OR]: 0.57; 95% confidence interval [CI]: 0.54 to 0.60) and 30-day MI readmission (adjusted OR: 0.46; 95% CI: 0.35 to 0.59).
There was no difference in risk of 30-day all-cause or heart failure readmission, but patients with type 2 MI did have longer length of stay than type 1 patients at a median of 5 days vs. 3 days, respectively.
Despite shorter stays, type 1 MI patients were associated with higher hospital costs, with a median of $17,731 (interquartile range [IQR]: $10,356.8 to $29,872) compared to a type 2 median of $12,643.1 [IQR]: $7,561.1 to $23,266.9).
However, patients with type 2 MI were less likely to be discharged home without any services than patients with type 1 MI (40.8% vs. 56.6% respectively).
Patients with type 2 MI who underwent revascularization also had longer lengths of stay (median 6 days, IQR 4 to 11 days vs. 5 days, IQR 3 to 8 days) and higher hospital costs ($30,367 vs. $12,379.2) than those who did not. Multivariable logistic regression analysis showed the type 2 MI patients who did undergo revascularization had lower risk of in-hospital mortality than those who did not (adjusted OR: 0.51; 95% CI: 0.30 to 0.85).
The results provide greater clarity over type 2 MI, showing it is a prevalent diagnosis with a cardiovascular phenotype distinct from type 1, the researchers said.
“In contrast to type 1 MI, management strategies for type 2 MI are not well validated, reflected in heterogenous management in this study,” they added. “Clinical trials are urgently needed to determine optimal management strategies for type 2 MI patients.”
In an accompanying editorial, Kristian Thygesen, MD, DSc, from Aarhus University Hospital, Denmark, and Allan S. Jaffe, MD, from Mayo Clinic, highlighted persistent issues in coding practice flagged within the study.
They stressed that the substantial majority of type 1 MI patients recorded in the database seems to indicate compliance with the mandate that the terms “ST-segment elevated myocardial infarction” (STEMI) and “non-STEMI” (NSTEMI) should always correspond to this subset.
“Unfortunately, such a supposition could inadvertently distort the understanding of the clinical context and pathophysiological mechanisms of MI, and thus, they may not comport to the UDMI (Universal Definition of MI) criteria,” with which both editorialists were involved.
They added that, although the introduction of an ICD-10-CM code for type 2 MI did represent a major advancement in coding practices for the subtypes of MI, there remain limitations, such as the fact the code does not distinguish a type 2 NSTEMI from a type 2 STEMI.
“Therefore, there is a risk for misattribution of MI diagnoses. Furthermore, clinicians may not be accustomed to the recently established codes; therefore, miscoding practices may possibly occur. Nonetheless, despite its deficits, the new ICD-10-CM paves the way for eventually fitting the MI codes into the framework of the UDMI.”
McCarthy CP, Kolte D, Kennedy KF, et al. Patient Characteristics and Clinical Outcomes of Type 1 Versus Type 2 Myocardial Infarction. J Am Coll Cardiol 2021;77:848-57.
Thygesen K, Jaffe AS. Adjusting the MI Codes Into the Framework of the Universal Definition of Myocardial Infarction. J Am Coll Cardiol 2021;77:858-60.