Reduced heart rate variability following repair of tetralogy of Fallot

Objective-To examine autonomic function as assessed by heart rate variabili ty in patients 10 or more years after repair of tetralogy of Fallot, and to relate this to cardiac structure, function, and electrocardiographic indic es. Methods-Heart rate variability was measured by standard time domain techniq ues on a 24 hour Holter ECG in 28 patients, aged 12 to 34 years (mean 19.5) , who had undergone repair of tetralogy of Fallot at least 10 years previou sly. Echocardiography was performed to assess left ventricular size and fun ction, right ventricular size and pressure, and any proximal pulmonary arte rial stenosis. Right ventricular function was evaluated by radionuclide sca n. QRS duration, QT interval, and QT dispersion were measured on a standard 12 lead EGG. Measurements of heart rate variability were compared with val ues from 28 age matched healthy controls (mean age 19.9 years). Interrelati ons between variables were assessed using Pearson correlation coefficients and stepwise regression analysis. Results-Heart rate variability was reduced, compared with values for age ma tched normal controls, in 12 of the 28 patients. Reduced heart rate variabi lity was associated with increased age, increased right ventricular size an d pressure, and widening of the QRS complex. Conclusions-Reduced heart rate variability is a feature following repair of tetralogy of Fallot. It is associated with increasing age, impaired right ventricular haemodynamics, and widening of the QRS complex. Under these cir cumstances, reduced heart rate variability may be a marker for deterioratin g right ventricular function. Increased QRS duration has been identified as a risk factor for sudden death following repair of tetralogy of Fallot, an d impaired cardiac autonomic control may be one of the mechanisms involved.