Coding AMIs and Related Conditions

An acute myocardial infarction (AMI) is the death of heart muscle from the sudden blockage of a coronary artery by a blood clot. AMI is a leading cause of morbidity and mortality in the U.S. and most often occurs in patients 40-70 years of age. Approximately 1.5 million cases of AMI are reported in the U.S. each year. This column will cover various aspects of coding AMIs and related conditions and will prepare you for questions on the certified coding specialist (CCS) or CCS-P (physician-based) exams related to them.

AMI is most commonly due to occlusion or blockage of a coronary artery following the rupture of atherosclerotic plaque. Blockage of a coronary artery deprives the heart muscle of blood and oxygen, causing injury to the heart muscle.

Approximately 50 percent of patients who develop an AMI have warning symptoms. Severe chest pain or pressure is the most common symptom. However, patients may experience a variety of more mild symptoms including: pain, fullness, and/or squeezing sensation of the chest; jaw pain; shortness of breath; nausea, vomiting or general abdomen discomfort; sweating; heartburn or indigestion; arm or upper back pain; and general malaise.

Approximately one quarter of all heart attacks are silent, without any symptoms. Silent heart attacks are most common in patients with diabetes. Women more often than men have AMIs without the typical symptoms noted above. This might explain why the diagnosis of AMI is sometimes delayed in women. Regardless of age, sex or severity of symptoms, a delay in treatment can lead to extensive damage to the heart muscle.

If blood flow is not restored to the heart muscle within 20-40 minutes, irreversible death of the heart muscle will begin to occur. Muscle continues to die for 6-8 hours at which time the AMI is “complete.”

Myocardial infarctions that show an ST segment change on electrocardiogram (ECG) are referred to as ST elevation myocardial infarctions (STEMI) and generally involve the whole thickness of myocardium from epicardium to endocardium. Myocardial infarctions that do not show an ST segment change on ECG are referred to as non-ST elevation myocardial infarctions (NSTEMI) and generally do not involve the whole thickness of myocardium.

Codes Assignment
To correctly assign an ICD-9-CM code, the infarction site must be documented by the physician in the medical record. Once the site is identified the episode of care must then be determined.

Codes from category 410, Acute myocardial infarction are used to identify the site.

410.0 Acute myocardial infarction of anterolateral wall

410.1 Acute myocardial infarction of other anterior wall

410.2 Acute myocardial infarction of inferolateral wall

410.3 Acute myocardial infarction of inferoposterior wall

410.4 Acute myocardial infarction of other inferior wall

410.5 Acute myocardial infarction of other lateral wall

410.6 Acute myocardial infarction, true posterior wall infarction

410.7 Acute myocardial infarction, subendocardial infarction

410.8 Acute myocardial infarction of other specified sites

410.9 Acute myocardial infarction, unspecified site

Category 410 has a use additional code note to identify the presence of hypertension (401.0-405.9).

Category 410 includes cardiac infarction; coronary (artery) embolism; occlusion; rupture; thrombosis; infarction of heart, myocardium or ventricle; rupture of heart, myocardium or ventricle; STEMI and NSTEMI myocardial infarction; any condition classifiable to 414.1-414.9 specified as acute or with a stated duration of 8 weeks or less.

The inclusion terms of STEMI and NSTEMI myocardial infarction were added as descriptive terms to mirror the national standard guidelines of The American College of Cardiology and the American Heart Association for classifying patients with acute coronary syndrome.

NSTEMI is coded to 410.7X, Subendocardial myocardial infarction. STEMI is coded to 410.0X, 410.1X, 410.2X, 410.3X, 410.4X, 410.5X, 410.6X, or 410.8X depending on the site of the infarction.

Subcategory 410.9 is the default for the unspecified term acute myocardial infarction. If only STEMI without the site is documented, assign a code from subcategory 410.9

If an AMI is documented as nontransmural or subendocardial, but the site is provided, it is still coded as a subendocardial MI, 410.7X. If NSTEMI evolves to STEMI, assign the STEMI code. If STEMI converts to NSTEMI due to thrombolytic therapy, it is still coded as STEMI.

The site of the infarction should be clearly documented to assign the correct diagnosis code. Query the physician if the site is unclear.

Episode of Care
The fifth-digit assignment for codes in category 410 is dependent on the episode of care:

0 – Episode of care unspecified: “0” is assigned as a fifth digit when the documentation does not contain sufficient information to determine the episode of care. The fifth digit of “0” should rarely be used. The physician should be queried to appropriately classify the episode of care as initial or subsequent.

1 – Initial episode of care: “1” is used to identify the first episode of care provided to a newly diagnosed AMI patient. The fifth digit “1” is used until the patient is discharged from medical care. This includes any transfers to and from other acute care facilities occurring within the 8-week time frame.

Example: A patient was admitted to hospital “A” with a diagnosis of acute anteroseptal myocardial infarction and transferred to hospital “B” 2 days later for continued care and further diagnostic work-up. The patient received diagnostic cardiac catheterization in hospital “B” and was discharged home following further treatment of the myocardial infarction. Assign code 410.11, Acute anteroseptal wall myocardial infarction, initial episode of care, as the principal diagnosis for both admissions.

2-Subsequent episode of care: “2” is assigned to designate an encounter or episode of care following the initial episode of care when the patient is readmitted for further observation, evaluation or treatment for a AMI that has received initial treatment but is still less than 8-weeks old.

Example: A patient was admitted for diagnostic work-up following an acute myocardial infarction 4 weeks ago. A cardiac catheterization was performed; percutaneous transluminal coronary angioplasty was attempted and failed, followed by a coronary bypass. Assign code 410.92, Acute myocardial infarction, unspecified site, subsequent episode of care.

If the patient is readmitted more than 8 weeks after the initial onset of the AMI, a code from category 410 should not be assigned. If a patient is transferred to another health care facility more than 8 weeks after the myocardial infarction, a code from category 410 would also not be assigned.

Multiple Myocardial Infarctions: More than one code from category 410 may be assigned for each patient encounter. If a patient had an AMI of the inferior wall and the anterior wall during the same admission, then both 410.41 and 410.11 may be assigned. However, if a reinfarction or extension of the AMI occurs at the same site of the initial AMI, it is only coded once.

Impending Myocardial Infarction: If a patient is admitted for treatment of an impending MI and documentation indicates that the MI is averted do not assign a code from category 410. When the physician documents the diagnosis as an impending, aborted or averted MI use code 411.1, Intermediate coronary syndrome, to identify the condition. The myocardial injury may have been averted due to early treatment intervention.

Postinfarction Angina: Postinfarction angina is assigned with a code from category 411, Other acute and subacute forms of ischemic heart disease, regardless of whether it occurs during the same hospitalization as the treatment for the AMI or later. Coders should only assign a code if the term postinfarction angina is documented by the physician. Unstable postinfarction angina is assigned to code 411.1, Intermediate coronary syndrome. Do not assign a code for angina when the angina leads to MI.

Coronary Occlusion: Code 411.81, Acute coronary occlusion without myocardial infarction, is assigned when a coronary occlusion, thrombosis or embolism is documented but the condition has not progressed to an AMI. Patients can have occlusions without going on to develop an AMI.

The correct coding and sequencing of an AMI is dependent upon the physician’s documentation of the site of the AMI and the episode of care as well as the application of the ICD-9-CM Official Coding Guidelines and Coding Clinic instructions.

Test your knowledge with the following quiz:

1. A patient is transferred from a hospital to a skilled nursing facility (SNF) for continued recovery following an acute inferior wall AMI? Would this be considered a “subsequent episode of care”?

a. Yes

b. No

2. A patient was admitted to hospital A with an AMI. Four days after admission a heart cardiac catheterization was performed and revealed severe coronary artery disease. The patient was transferred to hospital B for a CABG. The surgery was performed, and 2 days later the patient was transferred back to hospital A for continued care. The final diagnoses are listed as follows for each hospital stay:

Hospital A (#1): AMI, Severe coronary artery disease

Hospital B: Severe coronary artery disease, Recent MI

Hospital A (#2): Recent MI, S/P coronary artery bypass graft, coronary artery disease

Which of the following would be the appropriate diagnosis code(s) for each admission?

a. Hospital A #1: 410.91, 414.00

Hospital B: 410.91, 414.00

Hospital A#2: 410.91, 414.00, V45.81

b. Hospital A #1: 410.91, 414.00

Hospital B: 414.00, 410.91

Hospital A#2: 414.00, 410.91, V45.81

c. Hospital A #1: 410.91, 414.00

Hospital B: 414.00, 410.91

Hospital A#2: 414.00, 410.92, V45.81

3. A patient was discharged following an acute inferior wall myocardial infarction. The patient is readmitted 4 days later with substernal chest pressure associated with severe dyspnea. The physician indicates that the patient refused CABG during the previous admission and is now being admitted with congestive heart failure. Final diagnoses are congestive heart failure. Which of the following would be the appropriate diagnosis code(s) selection?

    1. 410.41, 428.0

    2. 428.0, 410.42

    3. 410.42, 428.0

This month’s column has been prepared by Cheryl D’Amato, RHIT, CCS, director of HIM, facility solutions, Ingenix, and Melinda Stegman, MBA, CCS, clinical technical editor, Ingenix ( Ingenix develops software and e-commerce solutions for managing coding, reimbursement, compliance and denial management in the health care marketplace.

Coding Clinic is published quarterly by the AHA.

1. a: Yes, this would be considered a subsequent episode of care. In this case, it would be appropriate to assign code 410.12, Acute myocardial infarction, other anterior wall, subsequent episode of care, for the transfer to this non-acute care facility or SNF.

2. a: 410.01 is assigned as the principal diagnoses for all three hospital stays. The patient was still being treated in all three stays for his acute MI. 414.00 is assigned as a secondary diagnosis in all three stays because this is a secondary condition that is also being treated. Code V45.81 is assigned as a secondary diagnosis for the second visit to hospital A to identify that the patient is status CABG.

3. b: Assign code 428.0, Congestive heart failure, as the principal diagnosis and code 410.42, Acute myocardial infarction, of inferior wall, subsequent episode of care, as a secondary diagnosis. It would be incorrect to list code 410.42 as the principal diagnosis since this patient was admitted because of congestive heart failure. The fifth digit of 2 is assigned because this is the second episode of care for this MI and not part of the first.

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