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Topics for study:
Intrinsic myocardial disease (e.g., myocarditis, ischemia, infarction, infiltrative or myopathic processes)
Drugs (e.g., digoxin, quinidine, tricyclics, and many others)
Electrolyte abnormalities of potassium, magnesium, calcium
Neurogenic factors (e.g., stroke, hemorrhage, trauma, tumor, etc.)
Metabolic factors (e.g., hypoglycemia, hyperventilation)
Atrial repolarization (e.g., at fast heart rates the atrial T wave may pull down the beginning of the ST segment)
Ventricular conduction abnormalities and rhythms originating in the ventricles
ST-T changes seen in bundle branch blocks (generally the ST-T polarity is opposite to the major or terminal deflection of the QRS)
ST-T changes seen in fascicular block
ST-T changes seen in nonspecific IVCD
ST-T changes seen in WPW preexcitation
ST-T changes in PVCs, ventricular arrhythmias, and ventricular paced beats
Drug effects (e.g., digoxin, quinidine, etc)
Electrolyte abnormalities (e.g., hypokalemia)
Ischemia, infarction, inflammation, etc
Neurogenic effects (e.g., subarrachnoid hemorrhage causing long QT)
Example #1: "Early Repolarization": note high take off of the ST segment in leads V4-6; the ST elevation in V2-3 is generally seen in most normal ECG's; the ST elevation in V2-6 is concave upwards, another characteristic of this normal variant.
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Acute transmural injury - as in this acute anterior MI
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Persistent ST elevation after acute MI suggests ventricular aneurysm
ST elevation may also be seen as a manifestation of Prinzmetal's (variant) angina (coronary artery spasm)
ST elevation during exercise testing suggests extremely tight coronary artery stenosis or spasm (transmural ischemia)
Concave upwards ST elevation in most leads except aVR
No reciprocal ST segment depression (except in aVR)
Unlike "early repolarization", T waves are usually low amplitude, and heart rate is usually increased.
May see PR segment depression, a manifestation of atrial injury
Left ventricular hypertrophy (in right precordial leads with large S-waves)
Left bundle branch block (in right precordial leads with large S-waves)
Advanced hyperkalemia
Hypothermia (prominent J-waves or Osborne waves)
Pseudo-ST-depression (wandering baseline due to poor skin-electrode contact)
Physiologic J-junctional depression with sinus tachycardia (most likely due to atrial repolarization)
Hyperventilation-induced ST segment depression
Subendocardial ischemia (exercise induced or during angina attack - as illustrated below)
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Note: "horizontal" ST depression in lead V6
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Note: "Upsloping" ST depression is not an ischemic abnormality
Non Q-wave MI
Reciprocal changes in acute Q-wave MI (e.g., ST depression in leads I & aVL with acute inferior MI)
Nonischemic causes of ST depressionRVH (right precordial leads) or LVH (left precordial leads, I, aVL)
Digoxin effect on ECG
Hypokalemia
Mitral valve prolapse (some cases)
CNS disease
Secondary ST segment changes with IV conduction abnormalities (e.g., RBBB, LBBB, WPW, etc)