ECG Challenge: Post-op Cramping and Spasms in Cancer Patient

Philip J. Podrid, MD


February 18, 2020

The correct diagnosis is normal sinus rhythm, hypocalcemia (Figure 2).

Figure 2. Courtesy of Dr Podrid.


The rhythm is regular at a rate of 66 beats/min. A P wave occurs before each QRS complex (+) with a stable PR interval (0.16 sec). The P wave is positive in leads I, II, aVF, and V4-V6. Hence, this is a normal sinus rhythm.

The QRS complex duration (0.08 sec) and morphology are normal. The axis is normal between 0° and +90° (positive QRS complex in leads I and aVF).

The QT/QTc intervals are prolonged (600/630 msec) (↔). There are two patterns of QT prolongation:

  • Delayed repolarization. The T-wave duration is normal but the onset of repolarization is delayed. The ECG in this case shows a long QT interval due to a long ST segment.

  • Prolonged repolarization. Depolarization occurs on time and the ST segment is normal, but there is a very broad T wave as the time for repolarization is prolonged.

In this case, there is a long ST segment (↑) due to delayed repolarization. The most common etiology for this is hypocalcemia (or hypomagnesemia).

Philip Podrid, MD, is an electrophysiologist, a professor of medicine and pharmacology at Boston University School of Medicine, and a lecturer in medicine at Harvard Medical School. Although retired from clinical practice, he continues to teach clinical cardiology and especially ECGs to medical students, house staff, and cardiology fellows at many major teaching hospitals in Massachusetts. In his limited free time he enjoys photography, music, and reading.

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