ICD-10: Acute Myocardial Infarction
Under ICD-9-CM, a myocardial infarction
(MI) was considered acute for 8 weeks,
meaning that providers had to assign an
acute MI code for services performed
within 8 weeks following the date of the
infarct. In ICD-10-CM, the acute period
has been cut back to 4 weeks ( 28 days).
However, providers can still use the acute
MI code for multiple encounters within
this time period. If the patient undergoes
cardiac imaging studies on two different
dates within the 4 week period, an acute
MI code should be assigned for each study.
STEMI and NSTEMI
Treatment decisions for an acute MI hinge
on whether it is an ST elevation MI
(STEMI) or a non-ST elevation MI
(NSTEMI). This distinction is also recognized in the ICD-10-CM code assignment.
For coding purposes, a subendocardial,
nontransmural, or non-Q wave MI should
be coded as NSTEMI. “Subendocardial”
and “nontransmural” indicate that the
infarction does not extend through the
entire heart wall, while “non-Q wave”
means that the patient’s EKG does not
show pathologic Q waves, which are
another sign of heart damage.
There are separate categories for
STEMI in different areas of the heart. For
example, codes in subcategory I21.0- are
used to report STEMI of the anterior wall
of the heart, including the left main and
left anterior descending coronary arteries.
If the radiology report or requisition indicates the specific location of the patient’s
acute MI, the provider should assign the
most specific code possible.
There is only one code (I21.4) for
NSTEMI, regardless of where in the heart
the infarction occurs. If the physician
describes the MI as NSTEMI but gives a
specific heart location, such as the poste-rolateral wall, the NSTEMI code (I21.4)
should still be assigned.
As an example of code assignment for
acute MI, a portable chest x-ray is
ordered for a patient in the coronary care
unit. The clinical history is “Inferior ST
elevation MI.” In the ICD-10-CM Index,
“Infarction, myocardium, ST elevation,
inferior” refers you to code I21.19 [ST
elevation (STEMI) myocardial infarction
involving other coronary artery of inferior wall].
The ICD-10-CM guidelines (Section
I.C. 9.e. 1) state that if the patient presents
with NSTEMI but it evolves to STEMI, a
STEMI code should be assigned. However, if the patient presents with STEMI
and it converts to NSTEMI after the
patient receives thrombolytic medication, a STEMI code should be assigned.
ICD-10-CM contains specific codes for
subsequent STEMI occurring within 4
weeks of the initial MI. In this situation
codes should be assigned for both the
original MI and the subsequent MI, and
sequencing will depend on the circum-
stances. For example, a patient is brought
back to the hospital with new onset of
chest pain 2 weeks after suffering a
STEMI involving the left anterior
descending (LAD) coronary artery. On
his return the patient is found to have
sustained a STEMI involving the inferior
wall. The new MI is reported with code
I22.1 [Subsequent ST elevation (STEMI)
myocardial infarction of inferior wall].
The prior MI, which is still acute, is
reported with code I21.02 [ST elevation
(STEMI) myocardial infarction involving
left anterior descending coronary artery].
Finally, ICD-10-CM contains codes
for certain complications of acute MI,
including rupture of chordae tendineae
(I23.4), rupture of papillary muscle
(I23.5), and postinfarction angina (I23.7).
These codes should be assigned when the
complication occurs within the initial 4
week acute period of the MI.
Melody W. Mulaik is president and co-founder of
Coding Strategies, Inc. She is a nationally recognized
speaker and has delivered numerous presentations at
AHRA annual meetings and conferences. Melody is a
member of AHRA, has published extensively, and may
be contacted at email@example.com.
By Melody W. Mulaik, MSHS, CRA, FAHRA, RCC, CPC, CPC-H