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 United States and most often occurs in patients 40 to 70 years of age. Approximately 1.5 million cases of AMI are reported in the United States 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.
As stated above, an AMI is the death of heart muscle from the sudden blockage of a coronary artery by a blood clot. This 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
Shortness of breath
Nausea, vomiting or general abdomen discomfort
Heartburn or indigestion
Arm or upper back pain
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.
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
Inclusion terms of ST elevation (STEMI) and non-ST elevation (NSTEMI) myocardial infarction are included 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 in order 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
1 - Initial episode of care:
2 -Subsequent episode of care
"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.
"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 eight-week time frame.
"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 eight weeks old.
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 healthcare 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.
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 of MI coding 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?
2. A patient was discharged following an acute inferior wall myocardial infarction. The patient is readmitted four 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?
- 410.41, 428.0
- 428.0, 410.42
- 410.42, 428.0
This month's column has been prepared by Cheryl D'Amato, RHIT, CCS, director of HIM, hospital solutions, and Melinda Stegman, MBA, CCS, clinical technical editor, OptumInsight (formerly Ingenix).
Coding Clinic is published quarterly by the American Hospital Association.
CPT is a registered trademark of the American Medical Association.
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. 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.