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August 1, 2011

Coding for Acute Myocardial Infarction
For The Record
Vol. 23 No. 14 P. 27

A myocardial infarction (MI) is myocardial cell death due to prolonged ischemia. While cell death can occur as quickly as 20 minutes after coronary artery occlusion, complete cell death is thought to take two to four hours. When myocardial cells do not receive adequate blood flow or oxygenation, the following three conditions can occur:

• Ischemia: may or may not present with electrocardiogram (EKG) changes or symptoms; usually no elevation of cardiac enzymes.

• Injury: may or may not have EKG changes or symptoms; zero to minimal rise in cardiac enzymes; practitioners may document acute coronary syndrome (ACS) or acute coronary injury (ACI).

• Infarct: EKG changes and symptoms usually present; definitive rise in cardiac enzymes; practitioners may document as ACS or ACI.

Acute MI (AMI) is classified to ICD-9-CM category 410. AMIs are frequently described as subendocardial, nontransmural, non-ST elevation myocardial infarction (NSTEMI); non-Q wave (minimal to mild cell death); or STEMI, transmural, or endocardial (moderate to extensive cell death).

Subendocardial infarctions that do not extend through the full thickness of the myocardial wall are classified to code 410.7x, which also includes NSTEMI. The initial EKG in patients with NSTEMI does not show ST segment elevation. The majority of patients who present with NSTEMI do not develop new Q waves on an EKG and are ultimately diagnosed as having had a non–Q-wave MI. NSTEMI is distinguished from unstable angina by the detection of cardiac markers indicative of myocardial necrosis and the absence of an abnormal elevation of such biomarkers in patients with unstable angina.

STEMI differs from NSTEMI in that it typically goes all the way through the heart wall muscle and is caused by a completely blocked artery. STEMIs are considered the most critical type of heart attack but can be quickly recognized and treated to reduce heart damage. The code assignment remains in category 410, and the fourth digit will depend on the specific location of the AMI.

Episode of Care
The fifth-digit subclassification for category 410 identifies the episode of care. A fifth digit of 1 indicates the first time the patient was seen and treated for MI. The fifth digit of 1 may be used at the first hospital where a patient received treatment and also at other acute care hospitals to which the patient is subsequently transferred (without interim discharge).

A fifth digit of 2 is assigned when a patient is admitted for subsequent care of an MI after the initial care but within eight weeks of the initial MI. Assign code 414.8 if the MI is described as chronic or with a duration of eight weeks or more.

Up to 25% of patients have no symptoms of an MI. If symptoms do occur, they may include substernal chest pain; left arm, neck, or jaw pain; shortness of breath; indigestion; and nausea or vomiting. Atypical or less prominent symptoms are usually found in diabetic, female, or older adult patients. Clinical presentation is usually based on the severity and presence of comorbid conditions and may include EKG changes, an elevation of cardiac markers, bradycardia or tachycardia, new arrhythmias or uncontrolled chronic arrhythmias, hypotension or hypertension, and cardiogenic shock.

Practitioners sometimes use the term “troponin leak”  when patients have elevated troponins and no evidence of an MI. There is still debate about whether troponin can “leak”  without myocardial cell damage. However, there are some conditions, including acute respiratory failure, aortic dissection, arrthymias, and burns, in which a rise in troponin is found.

The following antiplatelet agents may be used to treat AMI:

• Aspirin should be administered immediately on recognition of MI signs and symptoms unless a patient is allergic.

• Thienopyridines, such as Ticlid and Plavix, block adenosine diphosphate receptors and prevent platelets from aggregating and causing blood clot formation.

• Glycoprotein IIb/IIa inhibitors, such as Repro and Integrillin, prevent the clumping of platelets.

Other AMI treatments include the following:

• IV pain control with morphine;

• IV nitrites (rapid onset of action);

• IV thrombolytics unless contraindicated (eg, recent surgery, history of bleeding disorders);

• beta blockers, such as metoprolol or atenolol, to reduce MI mortality and limit infarct size; and

• angiotensin-converting enzyme inhibitors, such as lisinopril, enalapril, or quinapril, for long-term therapy.

Coding and sequencing for AMI are dependent on the physician documentation in the medical record and application of the Official Coding Guidelines for inpatient care. Also, use specific AHA Coding Clinic for ICD-9-CM and American Medical Association CPT Assistant references to ensure complete and accurate coding.

— This information was prepared by Audrey Howard, RHIA, of 3M Consulting Services. 3M Consulting Services is a business of 3M Health Information Systems, a supplier of coding and classification systems to more than 5,000 healthcare providers. The company and its representatives do not assume any responsibility for reimbursement decisions or claims denials made by providers or payers as the result of the misuse of this coding information. More information about 3M Health Information Systems is available at www.3mhis.com or by calling 800-367-2447.


Coding for AMI in ICD-10-CM
In ICD-9-CM, the initial time frame for acute myocardial infarction (AMI) treatment is within eight weeks of onset. In ICD-10-CM, the initial time frame for acute treatment is within four weeks of onset. Documentation of the time frame is critical for correct Medicare severity diagnosis-related group assignment.

In addition, ST elevation myocardial infarction AMIs are specific to site as well as artery involvement. Examples include left main coronary artery, left anterior descending coronary artery, other coronary artery of anterior wall, right coronary artery, and left circumflex coronary artery. Documentation of specific sites with specific artery involvement will be required for appropriate classification of patients with an AMI.

— Audrey Howard