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What to expect when coding CAD, MI with ICD-10-CM

JustCoding News: Outpatient, September 19, 2012

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Let's get to the heart of the matter.

ICD-10-CM coronary artery disease (CAD) and myocardial infarction (MI) codes will undoubtedly differ from their ICD-9-CM counterparts in some ways, but certain aspects will remain the same.

Native and bypass grafts
In ICD-9-CM, CAD appears in category 414. ICD-10 code I25.- denotes CAD. Both ICD-9-CM and ICD-10-CM codes indicate whether CAD is in the native artery or a bypass graft. The term "native artery" describes an artery with which a patient is born and that has not been grafted during a coronary artery bypass graft (CABG) procedure. A "bypass graft" is a graft inserted by a surgeon during a CABG procedure to bypass a blocked coronary artery.

ICD-10-CM code category I25.1 denotes CAD of a native artery. Patients can also have CAD of several types of bypass grafts, including:

  • Unspecified (I25.700-I25.709)
  •  Autologous vein (i.e., a vein that originates from the patient, such as the saphenous vein graft in the leg that is used to create a bypass in the coronary ¬artery) (I25.710-I25.719)
  • Autologous artery (i.e., an artery that originates from the patient, such as an internal mammary artery graft that is used to create a bypass in the coronary artery) (I25.720-I25.729)
  • Non-autologous biological (i.e., the grafting material doesn't originate from the patient) (I25.730-I25.739)

Patients can also have CAD in a transplanted heart. In this scenario, coders should report I25.75- for CAD of the native artery and I25.76- for CAD of a bypass graft.

Documenting the specific type of bypass graft is important because it affects code assignment, says Shannon E. McCall, RHIA, CCS, CCS-P, CPC, CPC-I, CEMC, CCDS, director of HIM and coding at HCPro, Inc., in Danvers, Mass. Most physicians tend to only document "patient had a CABG or history of CABG"-and not the specific graft that was used.

If a patient has both CAD and angina, coders using ICD-9-CM must assign a code for each condition separately. They report a code from category 414.0 for CAD and either code 411.1 (unstable angina) or code 413.9 (other and unspecified angina pectoris) for angina. However, this has always raised a question about sequencing, particularly because code assignment order affects MS-DRG assignment.

"What usually prompts the person to come in the facility is the angina. Angina is basically a thoracic chest pain when the heart muscle doesn't get enough blood," says McCall. "So the question is, although the angina is what brought them in, what's the underlying cause of the angina? In many cases, it's the underlying CAD. The person wouldn't have likely had the angina if they didn't have CAD."

The good news is that coders using ICD-10-CM won't need to worry about sequencing these two conditions because CAD codes are combination codes. They include additional characters that denote the presence or absence of angina pectoris. For example, ICD-10-CM code I25.110 denotes CAD of the native artery with unstable angina. ICD-10-CM code I25.721 denotes CAD of autologous artery coronary artery bypass graft(s) with angina pectoris with documented spasm. ICD-10-CM code I25.751 denotes CAD of native coronary artery of ¬transplanted heart with angina pectoris with documented spasm.

Similarly, ICD-10-CM code I25.10 denotes CAD of native artery without angina pectoris. ICD-10-CM code I25.81- denotes CAD of other coronary vessels without angina pectoris.

Coders using ICD-10-CM must remember that they may not assign unstable angina separately when a patient also has CAD, says McCall. "Coders are so used to assigning separate codes for CAD and angina, so we have to be very careful because technically if you look up the main term angina, unstable in the Alphabetic Index … it gives you one option: I20.0-that is, unless you notice the entry stating 'angina, with atherosclerotic heart disease,' which provides a cross-reference to the CAD entry in the index. If you go to I20.0, it says unstable angina." Although patients can have unstable angina without CAD, this is not a common occurrence, she says.

Coders should note that an Excludes1 note in ICD-10-CM category I20 precludes coders from assigning this code with a code from the I25.1- or I25.7- categories or with code I23.7 (postinfarction angina), says McCall. Code category I20 is reserved for patients with angina not related to CAD.

Coders can and should make assumptions about causal relationships between CAD and angina when both are documented, says McCall. This liberty doesn't often occur in the coding world. However, the ICD-10-CM Official Guidelines for Coding and Reporting, Chapter 9 (Diseases of the Circulatory System), subsection b (Atherosclerotic CAD and angina) state:

A causal relationship can be assumed in a patient with both atherosclerosis and angina pectoris, unless the documentation indicates the angina is due to something other than the atherosclerosis.

"If the documentation states that the patient has both CAD and angina pectoris, the combination code can be used," says Melanie Endicott, MBA/HCM, RHIA, CCS, CCS-P, director of professional practice at AHIMA in Chicago. "Since the combination code for CAD and angina doesn't exist in ICD-9-CM, it may take some time for coders to remember the rule to combine these two conditions when coding in ICD-10-CM."

Default code changes
Coding Clinic, Fourth Quarter 2004, instructs coders using ICD-9-CM to default to code 414.01 (CAD of a native artery) for patients with CAD who have never undergone a CABG procedure, says McCall. The publication also instructs coders to default to 414.00 (CAD of unspecified artery) for patients with CAD who have undergone a CABG when documentation doesn't indicate whether the CAD is in the native artery or the bypass graft.

"This has always raised an eyebrow because techni¬cally, when you perform a bypass graft, you don't get rid of the atherosclerosis that's in the native artery," says McCall. "So it seemed kind of odd that Coding Clinic would say if you've got a bypass graft and CAD, you have to use the unspecified vessel even though you know the patient still has CAD in their native artery. That's why the physician performed the bypass initially."

ICD-10-CM remedies this; the Alphabetic Index maps CAD, not otherwise specified, to the default code for CAD of the native artery (I25.10), says McCall.

However, clarifying whether CAD is of the native artery or a bypass graft is important because this information can have financial ramifications in ICD-10-CM, she says.

Consider the following scenario. A patient has CAD without angina pectoris. The patient previously underwent a CABG procedure. The physician didn't document whether CAD is in the bypass graft or the native vessel. When documentation is unclear, coders using ICD-10-CM should default to I25.10, which is a non-CC condition. If a physician had clarified that the patient had CAD of a bypass graft without angina pectoris, coders could report I25.810 (atherosclerosis of CABG without angina pectoris) or I25.812 (atherosclerosis of bypass graft of coronary artery of transplanted heart without angina pectoris) if the patient had a transplanted heart. Both of these ICD-10-CM codes are CC conditions.

MIs and anatomical specificity
MIs appear in ICD-9-CM code categories 410.x (acute MI), 414.8 (chronic MI), and 412 (old MI). ICD-10-CM MI codes include I21.- (ST elevation MIs and non-ST elevation MIs [STEMI and NSTEMI, respectively]), I22.- (subsequent STEMI and NSTEMI), I25.2 (old MI), and I25.9 (chronic MI). A STEMI is due to a sudden occlusion of a coronary artery, says McCall. The usual treatment is thrombolytic therapy.
An NSTEMI is generally due to unstable plaque with an accumulation of platelets and is treated with anticoagulants and platelet inhibitors, she says.

Code I21.- denotes the specific wall and specific ¬coronary artery involved in an MI. Although ICD-9-CM denotes the specific wall (i.e., the fourth digit), the specificity in ICD-10-CM regarding the coronary artery is new. For example, ICD-10-CM code I21.01 denotes left main coronary artery, and code I21.02 denotes left anterior descending coronary artery.

This information helps capture exactly where an infarction is occurring, says McCall. Coders typically find this information in cardiac catheterization reports.

Coders should review current MI documentation to determine whether it specifies both the wall and specific coronary artery, says Endicott. "If all necessary documentation is not present, then this is an opportunity to work together with the cardiac physicians to share with them what documentation is required with the new codes."

Note that ICD-10-CM guidelines provide additional information about the evolution of an NSTEMI to a STEMI. The ICD-10-CM Official Guidelines for Coding and Reporting, Chapter 9 (Diseases of the circulatory system), subsection e (Acute MI) state:

If NSTEMI evolves to STEMI, assign the STEMI code. If STEMI converts to NSTEMI due to thrombolytic therapy, it is still coded as STEMI.

Acute and subsequent MIs
Among the most noticeable differences between ICD-9-CM and ICD-10-CM is that the latter defines an acute MI as one in which the patient's symptoms last for fewer than four weeks, says McCall. This differs from ICD-9-CM, which classifies an acute MI as one with a stated duration of eight weeks or fewer.

If patients have a second, subsequent MI during the acute phase (i.e., during the four-week period after the first MI), coders must assign a code for the subsequent MI (I22.-) as well as a code for the first MI (I21.-), says Endicott. The ICD-10-CM Official Guidelines for Coding and Reporting, Chapter 9 (Diseases of the Circulatory System), subsection e(4) (Subsequent acute MI) reiterate this.

Before assigning a code from category I22, coders must confirm that the patient suffered two MIs within four weeks, says McCall. ICD-10-CM specifies that a subsequent MI is one that occurs within four weeks (28 days) of a previous MI, regardless of site.

"It's very different from ICD-9. In ICD-10, it's really showing the true picture," says McCall. "When patients have MIs, it's not uncommon for them to have another one a short time after having the first one. In ICD-9, we don't have a way to address this. We may end up coding it as two separate episodes of care—initial and subsequent."

Coders are not familiar with assignment of a separate code for a subsequent MI, says McCall. In ICD-9-CM, the term "subsequent" refers to a subsequent episode of care and is included as a part of the fifth digit for the MI code. In ICD-10-CM, it refers to a second MI rather than an episode of care.

ICD-9-CM MI codes are considered MCCs only if they have a fifth digit of 1 (initial episode of care), says McCall. In ICD-10-CM, the MS-DRG remains the same regardless of whether a patient is being treated for a first MI or a subsequent one, she says. 

Coders may need to clarify documentation that doesn't specify the date of the first MI, says McCall. This date determines whether the subsequent MI is truly subsequent to the first MI or whether it is considered a new MI, which should be reported with I21.-, she says.

Old MI
Coders should report I25.2 for an old MI (i.e., a personal history of MI), says Endicott. This code would apply to any MI that occurred more than four weeks before admission. As in ICD-9-CM, this code remains in the disease-specific chapter rather than with other codes that denote personal history (i.e., ICD-10-CM Z codes), says McCall.

Coders must exercise caution when documentation states "history of MI," particularly if it doesn't specify when the MI occurred, says McCall. "Technically, coders should be coding that with I22 and I21, but I could see how someone could [incorrectly assign] that and code I21 and I25.2 instead," she says.

Editor’s note: This article was originally published in the September issue of Briefings on Coding Compliance Strategies. Email your questions to Senior Managing Editor Michelle A. Leppert, CPC, at

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