Electrocardiogram with prolonged QT interval in Gitelman disease.

BACKGROUND: Potassium and magnesium deficiency prolong the QT interval on a standard electrocardiogram and predispose the patient to dangerous cardiac arrhythmias. No information is available on QT interval in patients diagnosed with Gitelman disease. METHODS: The QT interval was assessed on lead II in 27 patients with biochemically and genetically defined Gitelman disease, who had discontinued medical treatment for at least four weeks. They included 15 female and 12 male subjects, aged 6.7 to 40 years old, median 20 years old. The corrected QT interval was calculated from the measured QT interval and heart rate using the Bazett formula. RESULTS: The corrected QT interval was normal (between 391 and 433 msec) in 16 and prolonged in the remaining 11 patients (between 444 and 504 msec). Patients with prolonged and patients with normal QT interval did not significantly differ with respect to female to male ratio, plasma potassium, plasma total magnesium, and plasma ionized calcium. Plasma sodium and chloride values were slightly but significantly lower and bicarbonate levels higher in patients with a prolonged than in those with a normal QT interval. CONCLUSIONS: The corrected QT interval is often pathologically prolonged in patients with Gitelman disease, suggesting that there is an increased risk for development of dangerous arrhythmias. Further investigations are required in patients with a prolonged QT interval to assess the true hazard of dangerous arrhythmias.

Cardiac work up in primary renal hypokalaemia-hypomagnesaemia (Gitelman syndrome).

BACKGROUND: Potassium and magnesium depletion prolongs the duration of the action potential of the cardiomyocyte, which predisposes to ventricular arrhythmias. In addition, potassium or magnesium depletion might impair cardiac performance and facilitate coronary artery thrombosis. METHODS: Continuous 24-h ambulatory electrocardiographic monitoring, treadmill exercise testing and echocardiography were assessed in 21 patients (11 female and 10 male subjects, aged 5.9-39, median 19 years) with primary renal hypokalaemia-hypomagnesaemia. RESULTS: The QT interval corrected for heart rate was normal (between 379 and 430 ms) in 10 and slightly to moderately prolonged in the remaining 11 patients (between 446 and 509 ms). Plasma potassium, magnesium and bicarbonate were similar in patients with normal and in those with prolonged QT interval. Continuous ambulatory electrocardiography over 24 h and exercise testing did not detect significant abnormalities of cardiac rhythm or features suggestive of myocardial ischaemia. Finally, echocardiographic and Doppler assessment failed to reveal any abnormalities in myocardial morphology and function. CONCLUSION: The QT interval is often prolonged in primary renal hypokalaemia-hypomagnesaemia, confirming that potassium and magnesium depletion tends to prolong the duration of the action potential of the cardiomyocyte. The results of continuous ambulatory electrocardiography, exercise testing and echocardiography are reassuring. Nonetheless, we assume that dangerous cardiac arrhythmias may occur in patients with very severe hypokalaemia, during medication with drugs that prolong the QT interval or in the context of short-term non-adherence to the recommended regimen of care.