Low-K+ dependent QT prolongation and risk for ventricular arrhythmia in anorexia nervosa.

BACKGROUND: QT prolongation and ventricular arrhythmia have been proposed as the mechanism for sudden death in anorexia nervosa. The prevalence and the cause of QT prolongation remain controversial.

OBJECTIVES: 1) to evaluate ventricular repolarization in patients with anorexia; 2) to evaluate factors that may influence repolarization, with focus on electrolyte plasma levels and heart rate.

METHODS: 29 patients with anorexia, age 22 +/- 5 years, BMI 13.8 +/- 1.5 were compared to 14 control female subjects, age 23 +/- 2 years, BMI 20.7 +/- 1.1. QT interval and QT dispersion were measured. Whenever a low potassium (<3.5 mEq/l) was found, ECG was repeated after normalization of serum levels. Heart rate and its variability in the frequency domain (LF/HF ratio) were evaluated.

RESULTS: Three patients (10.3%) showed severe hypokalemia (K(+) levels <2.0 mEq/l). In 2 patients, QT was severely prolonged (QT(c) 600 and 670 msec) and in one case associated with ventricular arrhythmia. QT(c) after K(+) plasma levels normalization was 392 +/- 25 in anorexia vs. 407 +/- 19 msec in controls, p = 0.08. Heart rate was 55 +/- 11 in anorexia vs. 66 +/- 8 beats per minute (BPM) in controls, p = 0.002. The LF/HF ratio was 1.79 +/- 1.35 in anorexia and 3.66 +/- 2.64 in controls, p = 0.006.

CONCLUSIONS: QT interval is usually normal in patients with anorexia. QT prolongation and ventricular arrhythmia may develop in the setting of severe hypokalemia, exposing patients to high risk of sudden cardiac event. Resting heart rate is lower in anorexia than in controls with the spectral indices of sympatho-vagal balance indicating a prevalence of vagal activity.