U Waves
Report:
Sinus rhythm
Non-specific T wave changes
Prominent U waves[!xe "U wave:hypokalæmia" \b!]
Comment:
The patient became hypokalæmic following hæmodialysis; she also had chronic hypocalcæmia. It is very difficult to measure the true QT interval in the presence of large U waves. Some suggest using the lead aVL, where U waves are usually isoelectric; this is obviously not the case here. The JT interval may be more appropriate one to measure190, but the technical difficulty remains.
The T waves can be discerned in anteroseptal leads only; elsewhere one could be forgiven for mistaking U waves for T waves with long QT interval.
It is likely that the large U waves have the same significance as the prolonged QT interval in most settings191.
Below Fig 259a) is a normalised trace, indicating that chronic hypocalcæmia did not have a large effect on her QT interval; it would very likely be shorter with normal calcium.
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