A 68-year-old patient postoperative from thyroidectomy presents with muscle cramps; Chvostek's and Trousseau's signs are noted on examination.

Ans. (a) Prolonged QT interval.The rate is bradycardic at 54 beats/min. Ihe rhythm is regular with a narrow QRS and normal-appearing sinus P waves are seen. Axis is normal.The QT interval is very prolonged to more than 600 milliseconds with a long, isoelectric ST segment (best seen in lead V6) and T-wave inversions in leads I, aVL, and VI through V5.There are Q waves in leads VI through V3 consistent with anteroseptal myocardial infarction of indeterminate age. The clinical history coupled with ECG findings of a long QT and isoelectric ST segment are classic for hypocalcemia. If left untreated, hypocalcemia can progress to tetany and cardiovascular collapse. The long QT interval and sinus bradycardia predispose this patient to torsades de pointes.