Cardiovascular Critical Care I
other cardiac enzymes assays are available for clinical use, cardiac troponins are usually used as sensitive
markers indicative of myocardial necrosis, with a negative troponin conferring a greater than 95% negative
predictive value for MI. Troponin is eliminated renally, so patients with end-stage renal disease often have
elevations in cardiac troponin without other evidence of myocardial ischemia. Therefore, other clinical signs
and symptoms of acute coronary syndromes as well as the rate of troponin increase should be assessed.
Unstable Angina
NSTEMI
STEMI
Acute Myocardial Infarction
Cardiac Enzymes
Negative
Cardiac Enzymes
Positive
12-Lead ECG (Positive)
| • | ST-segment elevation in two or more |
|---|
contiguous leads
| • | New Left Bundle Branch Block |
|---|
Clinical suspicion of ACS based upon signs and symptoms
| • | Non-traumatic origin of chest pain/discomfort radiating to neck, jaws |
|---|
or shoulders; or anginal equivalents of persistent shortness of breath,
nausea/vomiting, indigestion, or new weakness/malaise
| • | Higher suspicion should be given to those with a history of CAD, MI, |
|---|
CABG or PCI
| • | Women, elderly, and those with diabetes tend to present with atypical |
|---|
symptoms (i.e., epigastric pain or back pain)
Cardiac Enzymes
Positive
12-Lead ECG (Negative)
| • | Minimal change up to ischemic changes that may include |
|---|
T-wave inversion or ST-segment depression
Box 2. Causes of Troponin Elevation (Heart 2006;92:987-93)
Acute decompensated heart failure
Early post-cardiac surgery
Acute MI
Heart transplantation
Acute pulmonary embolism
Myocarditis
Aortic stenosis
Pericarditis
Cardiac amyloidosis
Post-PCI
Cardiotoxic chemotherapy
Rhabdomyolysis
Chest compressions
Sepsis
Chest wall trauma or compressions
Severe strenuous exercise
Chronic heart failure
Tachyarrhythmia
Direct current cardioversion/defibrillation
Type A aortic dissection
PCI = percutaneous coronary intervention.