Introduction. Hypokalemia and hypomagnesemia have been reported to increase the frequency of ventricular arrhytmias in patients with heart diseases, including those under thiazide diuretic treatment. Gitelman disease(GD) is a well recognized form of hereditary renal tubular disorder associated with hypokalemia, hypomagnesemia and hypocalciuria and a genotype characterized by mutations in the protein codifying the thiazide-sensitive Na-Cl contransporter of the distal tubule. Aim. To define the role of chronic hypokalemia and hypomagnesemia on cardiac function in GD.Patients and Methods. We performed a cardiologic evaluation based on basal and 24 hours electrocardiographic (ECG) monitoring according to Holter, ecocardiography and ergometric tests in 10 children and adolescents (aged 6-16 years), with GD. All patients had hypokalemia, Ks 3.2 (SD 0.3 mmol/l); hypomagnesemia, Mgs 0.62 (0.10 mmol/l); metabolic alkalosis, HC03 31.6 (3.4 mmol/l); hypocalciuria, molar urinary calcium/creatinine 0.065 (0.046); hyperreninemia 13.6 (3.4 ng/ml/h) and normotension. molecular variants of the Na-Cl cotransporter gene were demonstrated in 6 patients.

Results. Basal ECG revealed a Qtc of 446.8 ms (24.4 ms); in 6 patients it was > 440 ms (maximum value, 479.7 ms). Holter monitoring revealed rare isolated premature ventricular contractions in 3 children. Echocardiography evaluation and ergometric tests were normal in all patients.

Conclusions. Chronic hypokalemia and hypomagnesemia do not induce significant adverse cardiac events in GD. In fact, no major ventricular or other heart arrhytmias were detected under resting or exercising conditions in our children and adolescents with GD. The only ECG alteration was a slight Qtc prolungation in 6 patients.