INTERPRETATION of ABNORMAL ECGs
ABNORMAL COMPONENT
POSSIBLE CAUSES
P waves (abnormal)
Left or right atrial hypertrophy, atrial escape (ectopic) beats

P waves (absent)
Atrial fibrillation, sinus node exit block, hyperkalemia (severe)

P-P interval (varying)
Sinus arrhythmia

PR interval (long)
First-degree atrioventricular block, Mobitz type I atrioventricular block, multifocal atrial tachycardia

QRS complex (wide)
Right or left bundle branch block, ventricular flutter or fibrillation, hyperkalemia

QT interval (long)
MI, myocarditis, hypocalcemia, hypokalemia, hypomagnesemia, hypothyroidism, subarachnoid or intracerebral hemorrhage, stroke, antiarrhythmics (eg, sotalol Some Trade Names BETAPACE , amiodarone Some Trade Names CORDARONE ), tricyclic antidepressants, other drugs

QT interval (short)
Hypercalcemia, hypermagnesemia, Graves' disease, digoxin Some Trade Names DIGITEK LANOXIN

ST segment (depression)
Myocardial ischemia; acute posterior MI; digoxin Some Trade Names DIGITEK LANOXIN ; ventricular hypertrophy; pulmonary embolism; left bundle branch block; right bundle branch block in leads V1 −V3 +/− II, III, and aVF; hyperventilation; hypokalemia

ST segment (elevation)
Myocardial ischemia, acute MI, left bundle branch block, acute pericarditis, left ventricular hypertrophy, hyperkalemia, pulmonary embolism, digoxin Some Trade Names DIGITEK LANOXIN , normal variation (eg, athletic heart syndrome), hypothermia

T wave (tall)
Hyperkalemia, acute MI, left bundle branch block, stroke, ventricular hypertrophy

T wave (small, flattened, or inverted)
Myocardial ischemia, age, race, hyperventilation, anxiety, drinking hot or cold beverages, left ventricular hypertrophy, certain drugs (eg, digoxin Some Trade Names DIGITEK LANOXIN , pericarditis, pulmonary embolism, conduction disturbances (eg, right bundle branch block), electrolyte disturbances (eg, hypokalemia)

U wave (prominent)
Hypokalemia, hypomagnesemia, ischemia

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