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Background: In patients with the tetralogy of Fallot, QRS prolongation predicts malignant ventricular arrhythmias. QRS prolongation may result from right ventricular dilatation. The relation of ECG markers to biventricular wall mass and volumes has not been assessed.Objective: To investigate the relations of surface ECG markers of depolarisation and repolarisation to right and left ventricular volume and biventricular wall mass.Methods: 37 Fallot patients (mean (SD) age 17 (9) years) were studied 14 (8) years after surgical repair; 34 had important pulmonary regurgitation. Left and right ventricular size was assessed from tomographic magnetic resonance imaging (MRI), and the amount of pulmonary regurgitation by velocity mapping MRI. QT, QRS, and JT duration and interlead dispersion markers were derived from a standard 12 lead ECG.Results: Mean QRS duration was significantly prolonged (133 (31) v 91 (11) ms in controls), as were dispersion of QRS (36 (17) v 20 (6) ms), QT interval (87 (48) v 42 (20) ms), and JT interval (93 (48) v 42 (19) ms). Biventricular volumes were increased (right ventricular end diastolic volume, 129 (41) v 70 (9) ml/m(2); left ventricular end diastolic volume, 83 (16) v 69 (10) ml/m(2)), as was right ventricular wall mass (24 (7) v 17 (2) g/m(2)). QRS duration correlated best with right ventricular mass (r = 0.55, p < 0.01).Conclusions: In patients operated on for tetralogy of Fallot and with pulmonary regurgitation, ECG predictors of ventricular arrhythmias are influenced by several mechanical factors that may occur simultaneously. These include increased right ventricular volume, but also increases in left ventricular volume and in right and left ventricular wall mass. [ABSTRACT FROM AUTHOR]