Author Joan Davenport replies: I appreciate the careful critique and interest these readers express. Hypercalcemia causes several alterations in the patient's EKG pattern, including progressive widening of the QRS, and shortened QT interval and ST segment. Figure 6 doesn't demonstrate the widening of the QRS, only the shortening of the ST segment resulting in a short QT.
I agree that a common cause of hypercalcemia is bony metastatic disease, and this should have been listed as a cause of elevated serum calcium levels. However, there is also some evidence that "malignant neoplasms, especially those with bone metastases" may also produce hypocalcemia.
Hyperparathyroidism is a cause of elevated calcium levels, but hyperthyroidism and the associated increase in metabolic rate also causes hypercalcemia. Although the therapies listed in the article are often sufficient to normalize serum calcium levels, dialysis is a treatment for hypercalcemia.
Regarding the cause of hypomagnesemia, diabetic ketoacidosis is certainly a contributing factor, but "simple" hyperglycemia is responsible for intracellular shifting of magnesium and decreased serum magnesium levels. Assessing Babinski's sign is an additional way to help identify hypomagnesemia.
Since this article's focus was on causes of lethal arrhythmias of ventricular tachycardia, ventricular fibrillation, and complete heart block, hypermagnesemia was only briefly mentioned. Elevated magnesium levels are not known to contribute to these arrhythmic conditions. Treatment of hypermagnesemia would include saline and furosemide and possibly renal dialysis.