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ICD-10 training: A physician's guide to coding for heart disease


Outlining the differences and changes in coding for ischemic heart disease in the International Classification of Diseases-10th Revision-Clinical Management (ICD-10-CM)

is reported in ICD-10-CM with categories I20-I25. This includes angina pectoris, myocardial infarction, current complications following myocardial infarction, and chronic ischemic heart disease. Physicians and coders need to understand how the organization of codes, current definitions, and coding rules have changed. This will enable the provision of accurate documentation, and the selection and proper sequencing of codes.

This article provides a quick, but important, look at the major differences in reporting ischemic heart disease in ICD-10-CM in comparison with ICD-9-CM.

The provision of many more codes in ICD-10-CM as well as changes in definitions require the coder and the physician to understand the rules for code selection and sequencing, and the documentation specificity required to prevent delays in claim submission, rejection, and revenue loss.

Related E-Book | The Complete ICD-10 Training Checklist

Atherosclerotic coronary artery disease

Coronary atherosclerosis codes in ICD-9-CM are found in subcategory 414.0.

Code selection is by type of vessel or graft: unspecified whether native or grafted vessel, native coronary artery, autologous vein bypass graft, arterial bypass graft, nonautologous biological bypass graft, unspecified type of bypass graft, or native artery or bypass graft of a transplanted heart. Codes for angina pectoris are reported in addition to coronary atherosclerosis codes when both conditions are present.

In ICD-10-CM, there is an assumed causal relationship in a patient with both coronary atherosclerosis and angina pectoris. ICD-10-CM provides combination codes for these two conditions that are selected when both are documented in the patient, unless the documentation specifically states that the angina pectoris is due to some other condition or disease process besides the atherosclerosis.


Next: ICD-10-CM codes differentiated by subcategories


These ICD-10-CM combination codes for coronary atherosclerosis with angina pectoris are also selected by subcategories that distinguish between:

  • I25.11: native coronary artery,

  • I25.70: unspecified coronary

  • artery bypass graft, 

  • I25.71: autologous vein bypass graft, 

  • I25.72: autologous artery bypass graft,

  • I25.73: nonautologous biological

  • bypass graft,

  • I25.75: native coronary artery

  • of transplanted heart,

  • I25.76: bypass graft of transplanted

  • heart, and

  • I25.79: other coronary artery bypass graft.

These combination code subcategories are further broken down to the level of granularity valid for reporting. For example, I25.71 atherosclerosis of autologous vein coronary artery bypass graft(s) with angina pectoris is subdivided to report the type of angina pectoris:

  • I25.710: Atherosclerosis of autologous vein coronary artery bypass graft(s) with unstable angina pectoris,

  • I25.711: Atherosclerosis of autologous vein coronary artery bypass graft(s) with angina pectoris with documented spasm,

  • I25.718: Atherosclerosis of autologous vein coronary artery bypass graft(s) with other forms of angina pectoris, and

  • I25.719: Atherosclerosis of autologous vein coronary artery bypass graft(s) with unspecified angina pectoris.

When angina pectoris is not present, the appropriate atherosclerosis code that states ‘without angina pectoris’ should be reported.

Next: Codes for treatment of angina pectoris


Angina pectoris

Cases of angina without coronary atherosclerosis require documentation regarding specific characteristics such as stable, unstable, or the presence of spasm. Differences to note when coding cases of angina alone in ICD-10-CM versus ICD-9-CM include:

  • Code I20.0 unstable angina, is listed under angina pectoris and includes intermediate coronary syndrome and preinfarction syndrome, which are coded to 411.1 in ICD-9-CM under Other acute and subacute forms of ischemic heart disease, not under angina pectoris.

  • There is no specific code for angina decubitus in ICD-10-CM, as there is in ICD-9-CM. This type is reported with the code for other forms of angina pectoris, I20.8.

  • Prinzmetal angina and variant angina are coded as angina pectoris with documented spasm, code I20.1 in ICD-10-CM.

Myocardial infarction

The time frame for coding an acute myocardial infarction in ICD-10-CM has been cut in half from that used for reporting an acute myocardial infarction in ICD-9-CM.

An acute myocardial infarction is defined in ICD-10-CM as one that is specified as acute or with a stated duration of 4-week (28 days) or less from onse. A subsequent myocardial infarction code is used when a patient who has already suffered an acute myocardial infarction has a new acute myocardial infarction within the 4-week time frame of the initial one. This new definition time frame is much shorter than that used in ICD-9-CM coding, where an acute myocardial infarction is specified as acute in the documentation or with a stated duration of 8 weeks or less from onset.

Also of note in coding myocardial infarctions in ICD-10-CM is the provision of a new code category, I22, for reporting subsequent, new myocardial infarctions that occur within the 4-week time frame of healing from an initial acute myocardial infarction. Use of this category requires a knowledge of proper sequencing since a code from category I22 can only be used when the patient suffers a new acute myocardial infarction within the 4-week time frame of the initial myocardial infarction, and must be used in conjunction with a code from category I21, never alone.

In ICD-9-CM, the fifth digit of ‘2’ is used to designate a subsequent episode of care whenever the patient is admitted for an myocardial infarction that has received initial treatment but is less than 8 weeks old.

Another difference in myocardial infarction codes is the code descriptions themselves and their further subdivisions. Subcategory code descriptions for segment elevation myocardial infarction (STEMI) are stated as such for the particular wall site, e.g., the anterior wall, then further subdivided into valid codes for reporting by the specified artery involved.

In ICD-9-CM, the code descriptions remain as acute myocardial infarction of the specified wall site, then a fifth digit is used to denote episode of care. For example, subcategory I21.0  ST elevation (STEMI) myocardial infarction of anterior wall is further subdivided into three valid codes for reporting:

  • I25.01:  ST elevation (STEMI) myocardial infarction involving left main coronary artery

  • I25.02:  ST elevation (STEMI) myocardial infarction involving left anterior descending coronary artery

  • I25.09: ST elevation (STEMI) myocardial infarction involving other coronary artery

  • of anterior wall.

Subendocardial infarction is coded to I21.4 non-ST elevation (NSTEMI) myocardial infarction.

Next: Coding complications


A final note on classification system differences in reporting and documenting myocardial infarctions relates to coding complications.

In ICD-9-CM, subcategory 429.7- reports certain sequelae of myocardial infarction-either acquired cardiac septal defect, or other sequelae.

In ICD-10-CM, category I23 is provided for reporting certain current complications following acute myocardial infarction within the 28 days and contains codes for hemopericardium, atrial septal defect, ventricular septal defect, rupture of the cardiac wall without hemopericardium, rupture of chordae tendineae, rupture of papillary muscle, thrombosis of atrium, auricular appendage, and ventricle, postinfarction angina, and other current complications.

Documentation of the specific complication is necessary for proper code selection.

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Jennifer N. Lee, MD, FAAFP
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