Acute coronary syndrome is a very popular diagnosis frequently documented when a patient presents to the hospital with chest pain thought to be cardiac in origin. When further evaluation indicates whether the pain is due to unstable angina or myocardial infarction (MI), physicians often continue to use “acute coronary syndrome,” an all-inclusive term. For accurate coding, physicians should document unstable angina or acute MI.
Patients with ischemic discomfort may present with or without ST-segment elevation on electrocardiography (ECG). Most patients with ST-segment elevation ultimately develop a Q-wave acute MI, whereas a minority develop a non-Q-wave acute MI. Patients who present without ST-segment elevation are experiencing either unstable angina or non-ST-segment elevation MI (NSTEMI). The distinction between these two diagnoses is ultimately made based on the presence or absence of a cardiac marker in the blood. Most patients with NSTEMI do not evolve a Q-wave on 12-lead ECG and are subsequently referred to as having sustained a non-Q-wave MI; only a minority of NSTEMI patients develop a Q-wave and are later diagnosed as having Q-wave MI. The ICD-9-CM code for acute NSTEMI is 410.71.
Acute coronary syndrome and unstable angina are both coded as ICD-9-CM code 411.1. When the principal diagnosis is acute coronary syndrome in a patient with established coronary artery disease, the coder must report coronary artery disease as a principal diagnosis with a secondary diagnosis of unstable angina to comply with the 2009 Official Guidelines for Coding and Reporting of Diagnoses for an inpatient claim.
The following are the principal presentations of unstable angina (Circulation. 1989;80:410-4)
Rest angina. Angina occurring at rest and prolonged, usually more than 20 minutes.
New-onset angina. New-onset angina of at least Canadian Cardiovascular Society (CCS) class III severity.
Increasing angina. Previously diagnosed angina that has become distinctly more frequent, longer in duration, or lower in threshold (i.e., increased by ≥ one CCS class to at least CCS class III severity).
The CCS grades angina according to the following criteria (Circulation. 1976;54:522-3).
Grade I: Not caused by ordinary physical activity, such as walking or climbing stairs. Occurs with strenuous, rapid, or prolonged exertion.
Grade II: Slightly limits ordinary activity. Occurs on walking or climbing stairs rapidly; walking uphill; walking or stair climbing after meals; walking more than two blocks on level ground and climbing more than one flight of ordinary stairs at a normal pace and under normal conditions; in cold, in wind, or under emotional stress; or only during the few hours after awakening.
Grade III: Ordinary physical activity is markedly limited. Occurs on walking one to two blocks on level ground and climbing one flight of stairs under normal conditions and at a normal pace.
Grade IV: Involves inability to perform any physical activity without discomfort. Symptoms may be present at rest.
Six Medicare Severity-Based diagnosis-related groups (MS-DRGs) have been established to classify patients admitted to an acute care facility with a principal diagnosis of acute MI (initial episode of care) who do not have an interventional procedure other than cardiac catheterization during the admission. The difference in payment between “unstable angina due to coronary artery disease or acute coronary syndrome” and “acute MI” can be quite large (see Table).
According to an expert consensus document published by the Journal of the American College of Cardiology in October 2007, “the term myocardial infarction should be used when there is evidence of myocardial necrosis in a clinical setting consistent with myocardial ischemia.”
The diagnosis of MI is based on detection of rise and/or fall of cardiac biomarkers (preferably troponin) with evidence of ischemia, defined as the following
- symptoms of ischemia;
- ECG changes indicative of new ischemia (new ST-T changes or new left bundle-branch block);
- pathological Q-waves on ECG; and
- imaging evidence of new loss of viable myocardium, or new regional wall motion abnormality.
For patients with normal baseline troponin after percutaneous coronary intervention (PCI), troponin elevation greater than three times the upper reference limit defines PCI-related MI.
In patients with normal baseline troponin after coronary artery bypass grafting (CABG), a CABG-related MI may be defined as a troponin increase of five times the upper reference limit plus
- new pathological Q-waves,
- new left bundle-branch block,
- angiographic evidence of new graft or coronary artery occlusion, or
- imaging evidence of new loss of viable myocardium.
When cardiac biomarkers (such as troponin or CK-MB) are elevated in the absence of clinical evidence of ischemia, the provider should document the condition determined to have been the cause of the myocardial necrosis, such as myocarditis, pulmonary embolism, or congestive heart failure.
For example, a patient is admitted with a condition such as congestive heart failure that progresses to acute MI. After study, the principal diagnosis in this example is the infarction, with an additional diagnosis of acute on chronic systolic heart failure. The diagnosis would be coded as MS-DRG 280, acute MI discharged alive with major CC, according to the 2009 Official Guidelines for Coding and Reporting of Diagnoses.
In a patient with chronic diastolic heart failure who is admitted with unstable angina and experiences an infarction three days later, the correct MS-DRG would be MS-DRG 281, the infarction with a CC (acute MI discharged alive with CC).
If either of these patients died, the MS-DRG assignment would be changed to MS-DRG 283-285, acute MI expired.