From the Journals

New light cast on type 2 MI aims to sharpen diagnosis, therapy


 

Coding not in sync with UDMI

If there is confusion in practice about differentiating type 2 from type 1 MI, it likely has multiple sources, and one may be inconsistencies in how the UDMI and relevant ICD codes are applied in practice.

For example, the coding mandate is always to classify ST-segment elevation MI and non-STEMI as type 1, yet UDMI-4 itself states that a type 2 MI may be either STEMI or non-STEMI, noted Dr. McCarthy, as well as an editorial accompanying the report.

“It also can be difficult at times to distinguish type 2 MI from the diagnosis of myocardial injury,” both of which are partly defined by elevated cardiac troponin (cTn), adds the editorial, from Kristian Thygesen, MD, DSc, Aarhus (Denmark) University Hospital, Aarhus, Denmark, and Allan S. Jaffe, MD, Mayo Clinic, Rochester, Minn.

Crucially, but potentially sometimes overlooked, a diagnosis of infarction requires evidence of ischemia along with the biomarker elevation, whereas myocardial injury is defined by raised cTn without evidence of ischemia. Yet there is no ICD-10-CM code for “nonischemic myocardial injury,” Dr. Thygesen and Dr. Jaffe observed.

“Instead, the new ICD-10-CM coding includes a proxy called ‘non-MI troponin elevation due to an underlying cause,’ ” they wrote. “Unfortunately, although some have advocated using this code for myocardial injury, it is not specific for an elevated cTn value and could represent any abnormal laboratory measurements.” The code could be “misleading” and thus worsen the potential for miscoding and “misattribution of MI diagnoses.”

In the current study, 84.6% of the cohort were classified with type 1 MI, 14.8% with type 2, and 0.6% with both types. Of those with type 1 MI, 22.1% had STEMI, 76.4% had non-STEMI with the remainder “unspecified.”

“I think the introduction of ICD codes for type-2 MI is helpful in that we can study type 2 MI more broadly, across institutions, and try and get a better sense of its outcomes and how these patients are treated,” Dr. McCarthy said. But the coding system’s deficiencies may often lead to misclassification of patients. Especially, patients with type 2 STEMI may be miscoded as having type-1 STEMI, and those with only myocardial injury may be miscoded as having type 2 MI.

Most type 2 MI is a complication

A profile of patients with type 2 MI may be helpful for making distinctions. The analysis showed that, compared with patients with type 1 MI, they were slightly but significantly older and more likely to have clinical depression, alcohol or other substance abuse disorder, and to be female. They also had more heart failure (27.9% vs. 10.9%), kidney disease (35.7% vs. 25.7%), atrial fibrillation (31% vs. 21%), and anemia (26% vs. 18.9%) (P < .001 for all differences).

Type 2 patients were less likely to have CV risk factors usually associated with plaque instability and atherothrombosis, including a history of smoking, dyslipidemia, MI, PCI, or CABG (P < .001 for all differences), the group noted.

Of the 37,765 patients with type 2 MI, 91% received the diagnosis as secondary to another condition, including sepsis in 24.5%, hypertension in 16.9%, arrhythmias in 6.1%, respiratory failure in 4.3%, and pneumonia in 2.8% of cases.

In multivariate analyses, patients with type 2 MI, compared with type 1, showed lower risks of in-hospital death and readmission for MI within 30 days. Their 30-day risks of readmission from any cause and from MI were similar.

Study outcomes by MI type and revascularization status

In-hospital mortality was lower for patients with type 2 MI who underwent revascularization, compared with those who did not, “but they were a very select, small proportion of the patient group. I would say there are probably unmeasured confounders,” Dr. McCarthy said.

“There’s a real kind of equipoise, so I think we desperately need a trial to guide us on whether revascularization is beneficial.”

Dr. McCarthy has disclosed no relevant financial relationships. Dr. Thygesen disclosed no relevant financial relationships. Dr. Jaffe disclosed serving as a consultant for Abbott, Roche, Siemens, Beckman-Coulter, Radiometer, ET Healthcare, Sphingotec, Brava, Quidel, Amgen, Novartis, and Medscape for educational activities.

A version of this article first appeared on Medscape.com.

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