ST elevation on the electrocardiogram (ECG) is considered a criterion standard sign of myocardial injury. The American College of Cardiology and American Heart Association guidelines for diagnosis and management of ST-elevation myocardial infarction (MI) state that ST elevation of 1 mm or more in 2 contiguous leads is suspicious for MI.1 Before administering fibrinolytic therapy to a patient with ST elevation, it is important to rule out other causes of ST elevation that could indicate conditions in which administration of these drugs could be dangerous (Table 1). This article discusses some of the conditions that cause nonischemic ST elevation that can mimic MI.
|Table 1: Non-myocardial infarction causes of ST-segment elevations|
Inflammation of the pericardium often causes widespread ST elevation that can mimic MI.2-6 The ST elevation that results from pericarditis often differs from ST elevation due to MI in several ways. Pericarditis ST elevation is often concave in appearance (sometimes referred to as "smiley" ST elevation) as opposed to MI ST elevation, which tends to be more domed in appearance (Figure 1). Pericarditis ST elevation is usually very widespread and involves many leads, whereas MI ST elevation follows the distribution of the involved coronary artery (eg, inferior MI due to right coronary artery occlusion shows ST elevation in leads II, III, aVF). There is no reciprocal ST depression in pericarditis, whereas MI often presents with reciprocal ST depression in leads that do not directly face the infarcted area. PR-segment depression is common with pericarditis because the atria are often involved in the inflammatory process. Figure 2 is an ECG of a patient with pericarditis. Note widespread ST elevation in leads I, II, III, aVF, and V2 through V6 and PR-segment depression in several leads.
|Figure 2: Electrocardiogram showing widespread ST elevation in a patient with pericarditis.|
|Figure 1: Comparison of ST elevation in pericarditis with myocardial infarction.|
Printzmetal (Variant) Angina
Angina due to coronary artery obstruction typically presents with ST-segment depression and/or T-wave inversion, whereas angina due to coronary artery vasospasm (Printzmetal or variant angina) often presents with ST elevation.6,7 This ST elevation usually resolves with treatment with nitroglycerin or other therapy that relieves the spasm. Figure 3 is an ECG of a patient who had severe chest pain and huge ST elevations in the anterior and lateral leads with reciprocal depression in the inferior leads. Cardiac catheterization revealed coronary artery spasm but no significant stenosis. This is an example of Printzmetal angina due to coronary artery vasospasm, mimicking anterolateral MI.
|Figure 3: Electrocardiogram showing significant ST elevations in a patient with Printzmetal (vasospastic) angina.|
Acute Cholecystitis and Pancreatitis
Acute abdominal conditions can produce ST elevation that mimics MI.2,6Figure 4 is the admission ECG of a patient with chest pain, nausea, and diaphoresis. There is ST elevation in leads III and aVF, a Q wave in lead III, and widespread T-wave inversion. The initial diagnosis was acute inferior wall MI, but fortunately the patient went to the cardiac catheterization laboratory where her coronary arteries were found to be normal. Additional workup revealed that she had acute cholecystitis, a situation in which administration of a fibrinolytic drug could have been a disaster.
|Figure 4: Electrocardiogram showing slight ST elevation in leads II and III and widespread T-wave inversion in a patient with acute cholecystitis.|
As the potassium level rises, T waves become tall and peaked with a narrow base, the QRS complex widens, and the ST segment can become elevated.6,8-10 Because tall T waves and ST elevation can occur in acute MI, hyperkalemia can mimic MI. Figure 5 is an ECG from a patient with a serum K+ concentration of 6.8 mEq/L. The tall narrow-based T waves are typical of hyperkalemia but can also occur in early infarction, and there is ST elevation in many of the V leads that can look like anterior wall MI.
|Figure 5: Electrocardiogram showing ST elevations in several V leads in a patient with hyperkalemia.|
Early ventricular repolarization can be a normal variant in men and can cause ST elevation that can be mistaken for MI.2,5-7 Often there are little "barbs" at the beginning of the ST segment that resemble fishhooks as illustrated in Figure 6, which shows leads V4-V6 from a 38-year-old man with no coronary artery disease.
|Figure 6: Leads V|
Tako-Tsubo cardiomyopathy, also called left ventricular apical ballooning syndrome, is a stress-induced transient condition presenting with acute onset of chest pain, elevated cardiac biomarkers, and left ventricular wall motion abnormalities in which the left ventricle balloons out during systole.11-14 The ECG often shows ST elevation, especially in the V leads, that can mimic anterior wall MI; however, the coronary arteries are usually normal. This typically presents after severe physical or emotional stress in postmenopausal women, but occasionally occurs in younger women and in men.13Figure 7 is an ECG from a patient with Tako-Tsubo syndrome and shows ST elevation in leads V2-V5; coronary arteries were normal.
|Figure 7: Electrocardiogram showing ST elevation in leads V|