An abnormal U wave may be taller than normal or inverted.
Causes of a taller U waves (> 2 mm):
(1) ventricular arrhythmias
(2) myocaridal ischemia/infarction (especially left circumflex artery related)
(3) sodium channel blocking drugs (Class IA): quinidine, disopyramide, procainamide
(4) potassium channel blocking drugs (Class III): amiodarone, dofetilide, sotalol
(5) digitalis
(6) phenothiazines
(7) hypokalemia
(8) hypocalcemia
(9) hypomagnesemia
(10) hypophosphatemia (rare)
(11) hypothermia
(12) mitral valve prolapse
(13) cardiomyopathy
(14) acquired complete AV block
(15) congenital long QT syndrome
(16) bradycardia
(17) left ventricular enlargement
Causes of a negative (inverted) U wave:
(1) coronary artery disease
(2) hypertension
(3) valvular heart disease
(4) congenital heart disease
(5) hyperthyroidism
(6) primary cardiomyopathy
(7) normal finding for patient
