| Interpretation of Abnormal ECGs |
Abnormal Component | Description | Possible Causes |
P waves | Abnormal | Left or right atrial hypertrophy, atrial escape (ectopic) beats |
P waves | Absent | Atrial fibrillation, sinus node arrest or exit block, hyperkalemia (severe) |
P-P interval | Varying | Sinus arrhythmia |
PR interval | Long | First-degree atrioventricular block |
PR interval | Varying | 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, congenital long QT syndrome, antiarrhythmics (eg, sotalol, amiodarone,quinidine), tricyclic antidepressants, phenothiazines, other drugs |
QT interval | Short | Hypercalcemia, hypermagnesemia, Graves disease,digoxin |
ST segment | Depression | Myocardial ischemia; acute posterior MI; digoxin; ventricular hypertrophy; pulmonary embolism; left bundle branch block; right bundle branch block in leads V1 −V3and possibly in 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, normal variation (eg, athlete's heart), hypothermia |
T wave | Tall | Hyperkalemia, acute MI, left bundle branch block, stroke, ventricular hypertrophy |
T wave | Small, flattened, or inverted | Myocardial ischemia, myocarditis, age, race, hyperventilation, anxiety, drinking hot or cold beverages, left ventricular hypertrophy, certain drugs (eg, digoxin), pericarditis, pulmonary embolism, conduction disturbances (eg, right bundle branch block), electrolyte disturbances (eg, hypokalemia) |
U wave | Prominent | Hypokalemia, hypomagnesemia, ischemia
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