Abstract 221: How an ICD-10 Code for Type 2 Myocardial Infarction Impacts Patient Inclusion in Acute MI Cohorts for Value-based Programs

Background: The Center for Medicare and Medicaid Services uses primary discharge ICD-10 codes for Acute Myocardial Infarction (AMI) to define inclusion in value-based payment programs such as the hospital readmissions reduction program. Prior studies have shown that a significant number of hospitalizations with an ICD-10 code for AMI actually represent a Type 2 MI (T2MI) or non-ischemic myocardial injury (NIMI). Yet, the care of such patients may differ from those with AMI, and their inclusion in value-based payment programs risks inaccurately assessing hospital care and even unwarranted financial penalties. In October 2018, a new ICD-10 code for T2MI was introduced (I21.A1). It is unclear what effect, if any, this new code has had on Type 1 MI (T1MI) representation among discharges assigned an ICD-10 code for AMI.

Methods: We screened all discharges from 8 UCHealth hospitals between January 1, 2017 and June 30, 2019 for a primary discharge ICD-10 code of AMI (n=3,445). Hospitalizations occurring during a six month period prior to the introduction of I21.A1 (January 1, 2017 to June 30, 2017) and a six-month period after the introduction of I21.A1 (January 1, 2019 to June 30, 2019) were selected for chart review. Using the 4th Universal Definition of MI, hospitalizations were assigned a gold-standard clinical diagnosis of T1MI, T2MI, or NIMI. The cohorts were compared according to the primary outcomes of readmission and mortality at 30 and 90 days.

Results: Of 1,364 discharges reviewed, 676 occurred in the pre-I21.A1 period and 667 occurred in the post-I21.A1 period. In the pre-I21.A1 cohort, 86% (585 of 676) of discharges met clinical criteria for T1MI, 10% (67 of 676) were deemed T2MI and 4% (24 of 676) represented NIMI. In the post-I21.A1 group, 93% (626 of 676) were deemed T1MI, while 5% (33 of 667) were deemed T2MI and 2% (12 of 667) met criteria for NIMI. The post-I21.A1 cohort had significantly fewer readmissions at 30 and 90 days when compared to the pre-I21.A1 cohort, but had similar rates of mortality.

Conclusions: After the introduction of an ICD-10 code for T2MI, fewer patients with T2MIs and NIMIs were eligible for inclusion in value-based programs. Concomitantly, we observed lower readmission rates among patients with an ICD-10 code for AMI after the T2MI code was introduced.