U wave

TdP is characterized by long QT intervals or prominent U waves on the surface ECG. 

Cardiovascular manifestations include hypertension and cardiac arrhythmias (e.g., heart block, atrial flutter, paroxysmal atrial tachycardia, ventricular fibrillation, and digitalis-induced arrhythmias). In severe hypokalemia (serum concentration <2.5 mEq/L), ECG effects include ST-segment depression or flattening, T-wave inversion, and U-wave elevation. 

Measurement of QT interval Definition of the end of the T wave. Changes in T wave morphology and occurrence of U waves (these may be important warning signs and precede the occurrence of TdP) Errors in manual measurement in QT interval Variability in the heart rate (need to correct the QT value for heart rate) Lack of reliable correlation between readings from Holter recordings and standard ECG Lack of standardization of automated ECG readings (computerized methods are often unreliable) Need for a central core laboratory to analyze data... 

Amiodarone s predominant electrocardiographic changes include prolongation of the PR and QT intervals, development of U waves, and changes in T-wave contour. 

Electrocardiographic ST depression, T wave flattening and inversion, U waves and a prolonged Q-T interval are common but transient occurrences after acute ischemic, and particularly after acute hemorrhagic, stroke. They seldom cause clinical problems. Some abnormalities may have preceded the stroke (Oppenheimer et al. 1990). It is not known... 

An important predictor of arrhythmia is changes in the duration of the QT trace, the time for ventricular repolarization, displacement of the ST-segment, and changes in the pattern of T-waves that may sometimes be seen as a T and U wave (Roden, 2004, 2008). It can be linked to ventricular tachycardia, including TdP. Lengthened QT increases the time available for intracellular calcium accumulation, enabling early after-depolarization (BAD) in the Purkinje fibers, and activates calmodulin (CaM) and calmodulin kinase (CaMK). CaMK is believed to enhance after-... 

Little, R.E., Kay, G.N., Cavender, J.B., Epstein, A.E., Plumb, V.J. (1990). Torsade de pointes and T-U wave altemans associated with arsenic poisoning. Pacing Clin. Electrophysiol. 13 164-70. 

Fig. 19.8 Torsade de pointes The QT interval represents the phase of myocardial spread of stimulus and repolarization. Excessive QT lengthening may be caused by certain drugs or electrolyte imbalance. In addition, a U wave can occur, whereby its amplitude exceeds the T wave in V4-Vg. Subsequently, a potential life-threatening arrhythmia of type torsade de pointes may develop. Clinical symptoms include vertigo and syncopes. This arrhythmia can spontaneously disappear, but also pass into ventricular fibrillation and thus end fatally...

Figure 3.12 Male, 42 years old, with severe but not long-standing aortic regurgitation. Note the evident q wave in V5, the intrinsic deflection time (IDT) >0.07 s, the height of the R wave is >30 mm and the T wave is tall and peaked (14 mm). There is also a negative U wave.

On the other hand, an evident U wave (Figures 3.24 and 3.25) or even a less obvious one (Figure 3.26) in the presence of a positive T wave is equivalent to subepicardial ischaemia (Reinig, Harizi and Spodick, 2005). 

Figure 3.24 A patient with unstable angina who presents slight ST-segment depression in various leads, especially in II, III, V4-V6 and significantly marked negative U wave in V2-V3. This patient presents an important LAD occlusion.

Figure 3.25 (A) Basal ECG (V1-V6) with ECG pattern of important subepicardial ischaemia in a 65-year-old patient with daily crisis of variant angina that always appeared at the same hour. During a crisis (B,C), there is pseudonormalisation of the ST segment with an evident negative U wave. A few seconds later, the ECG returns to...

Figure 3.26 A 46-year-old patient with dubious precordial pain. The ECG (B) presented very discrete changes in V2-V3 leads (slightly negative U wave with somehow positive T wave). These small changes are significant when compared...

Also, a positive T wave, which has evidently increased its positivity with respect to the baseline T wave, maybe considered abnormal (Jacobsen et al., 2001). Furthermore, the presence of a negative U wave, ora positive U wave when the T wave is negative in leads with a dominant R wave, is considered abnormal (Figures 3.24 and 3.26). 

The existen ce of a negative U wave in I, VL and/or V2-V6 in a patient with coronary artery disease with or without prior infarction in the ECG is very... 

Correale E, Sattista R, Ricciardiello V, Martone A. The negative U wave apathogenetic enigma but a useful, often overlooked bedside diagnostic and prognostic clue in ischemic heart disease. Clin Cardiol 2004 27 674. 

Reinig MG, Harizi R, Spodick OH. Electrocardiographic T-and u-wave discordance. Ann Noninvasive Electrocardiol 2005 10 41. 

Always reported are the RR, PR, QRS, and QT intervals and the duration, magnitude, and configuration of the P waves, QRS complexes, ST segments, T waves, and U waves. Computer interpretation of the ECG provides a standardized reading and records and calculates basic rhythm patterns, heart rate, and intervals but does not interpret arrhythmias. Independent review of the ECG is necessary for accurate translation of findings. ... 

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