Prolonged QT interval due to hypocalcemia

The QT interval in this case is quite prolonged (0.50 sec) at a heart rate of 55 beats/min. The rate corrected QT (QTc) interval can be calculated from: QT interval ÷ sqrt (RR interval). The RR interval is 1.05 sec leading to a QTc of 0.48 sec which is longer than the normal value of ≤0.44 sec. A long QT interval with a "stretched out" ST segment and normal T wave is most consistent with hypocalcemia. In contrast, hypercalcemia shortens the QT, hyponatremia usually has no effect on the ECG, and hypokalemia prolongs repolarization with flattened or broad T waves and prominent U waves.

Normal rhythm strip in lead II. The PR interval is 0.15 sec and the QRS duration is 0.08 sec. Both the P and T waves are upright.