Muscle magnesium content and cardiac arrhythmias during treatment of congestive heart failure due to chronic chagasic cardiomyopathy.

Magnesium (Mg2+) plays a significant role in the electrical stability of the heart and hypomagnesemia may predispose patients to arrhythmias and digitalis toxicity. We measured the serum and skeletal muscle Mg2+ content of patients with chronic Chagasic cardiomyopathy (CCC) during treatment for congestive heart failure and compared it to 15 normal patients who were used to establish the normal values of our population. There is a high frequency of muscle Mg2+ deficiency (66%) in patients with CCC during treatment for heart failure. However, serum Mg2+ is not a sensitive index of deficiency, since hypomagnesemia occurred in only 50% of the patients whose muscle Mg2+ was low. Digitalis toxicity was observed in all muscle Mg2+-deficient patients (100%) and in 25% of patients with normal Mg2+ levels (P less than or equal to 0.05). Ventricular tachycardia (VT) occurred in 75% of muscle Mg2+-deficient patients and in none of the patients with normal magnesium levels (P less than or equal to 0.05). The frequency and severity of premature ventricular contractions (PVC) were higher in muscle Mg2+-deficient patients. We conclude that muscle Mg2+ deficiency is very common in patients with CCC being treated for congestive heart failure and that muscle Mg2+ deficiency defines a higher risk CCC group in terms of digitalis toxicity and severe ventricular arrhythmias such as ventricular tachycardia.