Chapter 9-10: Unstable Angina (UA) or Non-ST-Segment Elevation Myocardial Infarction (nSTEMI)

TEXTBOOK PRESENTATION

UA and nSTEMI classically present with new or worsening symptoms of CHD and are only differentiated by the absence (UA) or presence (nSTEMI) of myocardial enzyme elevation in peripheral blood samples.

DISEASE HIGHLIGHTS

1. UA is defined as angina that is new, worsening in severity or frequency, or occurs at rest.

2. Pathophysiology

   1. Primarily caused by acute plaque rupture followed by platelet aggregation

      1. 67% of episodes occur in arteries with < 50% stenosis.

      2. 97% occur in arteries with < 75% stenosis.

   2. Caused less commonly by changes in oxygen demand or supply (eg, hyperthyroidism, anemia, high altitude)

3. The diagnosis of UA can be difficult, often depending on a careful history to differentiate stable angina from UA.

4. The clinician seeing a patient with UA or a nSTEMI must

   1. Recognize that the patient has an ACS

   2. Initiate care

   3. Determine the patient’s risk of progressing to an MI or death

   4. Treat accordingly

5. Vasospastic angina

   1. Vasospastic angina (also called Prinzmetal or variant angina) is a phenomenon that presents similarly to UA.

   2. Patients periodically have episodes of cardiac ischemia with ST elevation.

   3. The attacks

      1. Are often associated with chest pain or other ischemic symptoms

      2. Resolve spontaneously or with nitroglycerin

      3. May occur in normal or diseased coronary arteries

      4. Can result in MI or death (often secondary to arrhythmia)

      5. Often occur at the same time each day

   4. Vasospastic angina is usually diagnosed clinically but can also be diagnosed by inducing it with ergonovine infusion in the catheterization laboratory.

   5. Vasospastic angina is treated effectively with calcium channel blockers and nitrates.

Vasospastic angina should be considered in patients whose symptoms are consistent with cardiac ischemia and occur at about the same time each day. The diagnosis should also be considered when transient ST elevations develop.

EVIDENCE-BASED DIAGNOSIS

1. There are 3 presentations of UA:

   1. Rest angina

   2. New-onset (< 2 months) angina

   3. Increasing, or accelerating, angina

2. The American College of Cardiology and American Heart Association have endorsed a number of features or findings that increase the likelihood that a patient’s symptoms represent an ACS, including

   1. Chest or left arm pain that reproduces prior angina

   2. History of CHD

   3. Transient mitral regurgitation murmur

   4. Hypotension

   5. Diaphoresis

   6. Pulmonary edema

   7. Crackles

3. Appropriate risk stratification ensures that the patient is triaged to the proper location for care (ICU, inpatient ward, home) and receives the most beneficial therapy.

4. Clinical risk scores can be helpful for stratifying patient cardiac risk. The TIMI score (Table 9-8) for UA/nSTEMI is probably the most widely known of these scores. It was originally derived from a cohort of patients receiving treatment for ACS and thus should not be applied to patients with undifferentiated chest pain. However, it can be useful in risk stratifying patients to different treatment (conservative versus invasive) once the diagnosis of ACS has been established.

   1. Modern calculators like the HEART Score (Table 9-9) are more useful for estimating the risk of a major ...