The challenge for this quarter is the mysterious U wave. When Einthoven set about naming the waveforms of his electrocardiogram (ECG), he purposely chose letter designations within the alphabet, rather than the beginning or end, because he expected that additional waveforms might be discovered in the future. Indeed, the existence of the U wave following the T wave was confirmed within his lifetime.1  The U wave is mysterious, because, despite our knowing of its existence for more than 100 years, the mechanism for this ECG sign remains unknown to this day. Acute and critical care nurses who use continuous cardiac monitoring traditionally do not document the U wave because of the difficulty finding it on the surface ECG, but sometimes it is prominent or interferes with the measurement of the QT interval, so it has some clinical usefulness. This column addresses theories for the mechanism of the U wave,...

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