(1)
Division of Pulmonary and Critical Care Medicine, Eastern Virginia Medical School, Norfolk, VA, USA
Keywords
Acute coronary syndrome (ACS)Acute myocardial infarction (AMI)Unstable anginaNon-ST elevation Myocardial infarction (NSTEMI)Revascularization therapyAnginaTroponinsMorphineNitroglycerinHeparinPatients with acute coronary syndromes (ACS) are classified as having either:
i)
Unstable angina/myocardial infarction without ST-segment elevation (NSTEMI) or
ii)
Acute myocardial infarction with ST elevation (STEMI).
The distinction between these two entities is made basis of the 12-lead electrocardiogram and is crucial in formulating the therapeutic plan. As a general rule patients with NSTEMI are treated with aggressive medical therapy followed by coronary angiography (when “cooled down”) while patients with STEMI usually undergo immediate coronary angiography and revascularization.
Unstable Angina/NSTEMI
Unstable angina (UA) is characterized by the clinical presentation of angina with or without ischemic ECG changes (ST segment depression or new T-wave inversion). NSTEMI is similar to UA but is characterized by positive biomarkers (troponin or creatine kinase-MB [CK-MB]) in the setting of angina or ECG changes. The presence of myonecrosis as evident by positive cardiac markers portends a higher risk than those presenting with just UA. UA and NSTEMI pathophysiologically and clinically are related and initially may be indistinguishable, as biomarkers may not be elevated at presentation. Rupture of an atherosclerotic plaque and subsequent formation of a thrombus usually is the triggering event in the pathogenesis of most cases of ACS.
Canadian Cardiovascular Classification of Angina
Class 1: pain is precipitated only by severe and unusually prolonged exertion
Class 2: pain on moderate effort. There is slight limitation of ordinary activity
Class 3: marked limitation of ordinary activity; pain occurs on mild exertion, usually restricting daily chores. Patient is unable to walk two blocks on the level at a comfortable temperature and at a normal pace
Class 4: chest discomfort on almost any physical activity
Types of Presentations of Unstable Angina
Rest angina
Angina occurring at rest and prolonged, usually >20 min
New-onset angina
New-onset angina of at least 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 ≥1 CCS class to at least CCS class III severity)
Differential Diagnosis
ST elevation AMI (STEMI)
aortic dissection
esophagitis
pleurisy
leaking or ruptured thoracic aneurysm
acute pericarditis
pulmonary embolism
pneumothorax
esophageal rupture
Electrocardiography
Most patients who have unstable angina/NSTEMI have some ECG changes. The ECG is important for diagnostic and risk stratification purposes. Specific characteristics and the magnitude of pattern abnormalities increase the likelihood of CAD. ST–T-segment depression portends a poorer prognosis than T-wave inversion alone or no ECG changes. The Global Use of Strategies to Open Occluded Coronary Arteries in Acute Coronary Syndromes (GUSTO-IIb) trial demonstrated that the 30-day incidence of death or MI was 10.5 % in those who had ST-segment depression versus 5.5 % in patients who had T-wave inversion, and a higher mortality also was seen at 6-month follow-up [1]. The sum of ST depression is a strong independent predictor of short-term mortality and the risk increases with the magnitude of depression [2].
Tropinins
Troponins play a central role in the diagnosis of NSTEMI and risk stratification. The joint statement of the European Society of Cardiology and the American College of Cardiology (ACC) defines myonecrosis as when the peak concentration of troponin T or I exceeds the decision limit (99th percentile for a reference group) on at least one occasion in a 24-h period [3]. This definition has increased the frequency of the diagnosis of NSTEMI in patients who have ACS by 30 %. The troponins are detectable approximately 6 h after myocardial injury and are measurable for up to 2 weeks. Mortality risk is directly proportional to troponin levels and the prognostic information is independent of other clinical and ECG risk factors [4].
Management of UA/NSTEMI
Risk Stratification
Risk stratification plays a central role in determining the treatment strategy of patients with NSTEMI. Two risk-assessment algorithms have been developed for determining whether a patient is at high risk or at relatively low risk for having an ischemic event. Patients with ≥3 TIMI variables are considered to be at high risk. Similarly patients with >110 Total Risk Score Points using the GRACE model have >5 % 6 month mortality.
Thrombolysis in Myocardial Infarction (TIMI) Risk Score [5]
age >65 years
≥3 risk factors for coronary artery disease
prior coronary stenosis of ≥50 %
ST segment deviation on electrocardiogram at presentation
at least two anginal events in prior 24 hRelated posts:
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