Q&A: Differentiating treatment for an initial MI from a subsequent MI

Q: How would you determine if the treatment is for the initial myocardial infarction (MI) as a secondary diagnosis versus the treatment for the subsequent MI?

A: Whenever a patient has two MI events in a 28-day period and is being admitted for the new MI, the principle will always be the subsequent MI. If a patient had an MI within the past 28 days and is admitted for a different medical problem such as chronic obstructive pulmonary disease (COPD), the MI (or both MIs) would always be secondary diagnoses. 

If a patient is being admitted for subsequent treatment of a single MI which has occurred within 28 days (for example, a patient who was stabilized, discharged, and then admitted three weeks later for a coronary artery bypass graft), you would code the coronary artery disease (CAD) as the principle diagnosis, the initial MI(s) with a present on admission code of Y (for yes, this condition was present on admission) as a secondary diagnosis, and the DRG will still be for the MI.

If you were really trying to dig down to the level of the cause of admission as the example you mentioned, you could do so by identifying the specific lesion being treated. For example, if the patient had a right coronary artery (RCA) MI and then two weeks later had a circumflex occlusion and the current admission is to address the RCA (with an intervention), then you have identified which lesion and cardiac event was related to the admission. 

Coding Clinic, Second Quarter, 2015, p. 16, reiterates that when a patient with CAD is admitted for treatment of an MI, the MI is always the principal diagnosis. Therefore, in the above example, you have identified that the initial MI appears to be the principal diagnosis. I have encountered some in the industry who believe the subsequent admission for a bypass after the care of the infarction is rendered should revert back to a principal diagnosis of CAD, but I do not believe this has been addressed in the official guidance. 

If the care was addressing the lesion at the circumflex (with an intervention), then you would have identified the subsequent MI as the cause of the admission. If they are just using general medical therapy for CAD but not directed at a specific lesion (or treating both with an intervention), then they are treating both. In such situations, however, the specific sequencing really has no effect on DRG assignment.

Editor’s note: Allen Frady, RN, BSN, CCDS, CCS, CDI education specialist for BLR Healthcare in Middleton, Massachusetts, answered this question. Contact him at AFrady@hcpro.com. For information regarding CDI Boot Camps visit http://hcmarketplace.com/clinical-doc-improvement-boot-camp-1.