Ventricular hypertrophy and the electrical axis of the QRS complex in infancy.

The recognition of ventricular hypertrophy is of paramount importance in the differential diagnosis of congenital anomalies of the cardiovascular system. In infancy the distinction between right and left ventricular hypertrophy may be impossible on clinical grounds, and the information contributed by radiological examination may be indecisive. In such circumstances considerable reliance is placed on the electrocardiographic appearances and especially on those in the unipolar precordial leads. Even so the recognition of mild hypertrophy may prove difficult largely because of the physiological preponderance of the right ventricle in early infancy and the gradual transition to left ventricular preponderance which follows (Massie and Walsh, 1960). The electrical axis of the QRS complex, sometimes described as the mean manifest electrical axis of the QRS complex, is the frontal mean QRS vector or mean direction of the electrical forces associated with ventricular depolarization as projected in the frontal plane. Deviation of this axis or vector beyond the normal range is still regarded by some as a sign of diagnostic value in childhood (Nadas, 1957). Its validity as a measure of ventricular hypertrophy can be criticized, however, not only because the electrodes of the extremity leads from which the electrical axis is calculated are distant from the heart, but also because the axis is affected by the electrical position of the heart within the thorax. For this reason more reliable information regarding ventricular hypertrophy is expected from an analysis of the unipolar precordial leads to which these criticisms apply with less force. Nevertheless, just as the electrical axis reflects only the frontal projection of the cardiac vector, the precordial leads reflect electrical forces only in the horizontal plane (Massie and Walsh, 1960). In an attempt to determine whether in infancy the electrical axis of the QRS complex is of any value in the diagnosis of right and left ventricular hypertrophy an analysis was made of the electrical axes of 100 healthy infants and of a group of patients subsequently shown to have preponderant right or left ventricular hypertrophy at autopsy.