ECG Quiz 56 – Discussion

ECG Quiz 56 – Discussion

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QT interval is prolonged with a QTc of around 500 ms. T waves are flat in inferior and lateral leads. The speciality of QT prolongation is that ST segment is more prolonged (blue arrows) compared to width of QRS and T wave. Such ST prolongation should alert us about hypocalcemia because the effect of calcium is mainly in the plateau phase (phase 2) of the cardiac action potential and corresponds to the ST segment. In hypokalemia T wave amplitudes are reduced and U waves become prominent, causing an apparent QT prolongation.  Here prominent U waves are not seen, though T wave amplitude is reduced in inferior and lateral leads. ST segment depression (red arrow) is noted in inferior and lateral leads, with minimal ST elevation in aVR. This could be due associated ischemic heart disease or even due to hypokalemia. When a combination of findings of hypocalcemia and hypokalemia are seen, a common cause should be considered. Hypomagnesemia is a condition which can cause both hypokalemia and hypocalcemia as the enzyme needed for renal transport of these electrolytes has magnesium as  cofactor. Hence correction of magnesium levels could rectify both hypokalemia and hypocalcemia. As a corollary, it is often difficult to correct hypokalemia when there is associated hypomagnesemia, which is considered as a cause for refractory hypokalemia. These type of ECGs are often seen elderly with multiple comorbidities when it is difficult to delineate whether it is solely due to ischemia or electrolyte abnormality as they may have both!

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