[Vectorcardiographic manifestations of right ventricular enlargement]

The basic criteria for the vectorcardiographic diagnosis of right ventricular enlargement are discussed, in context with the course of myocardial activation. Right ventricular dilatation, secondary to isolated diastolic overloading (atrial septal defect) shows basically different degrees of dextrorotation. The ventricular curve starts to the left on the frontal and horizontal planes, and forward on the last one. Cases with right ventricular hypertrophy, produced by sustained systolic overload, are also evaluated. When the hypertrophy is generalized (pulmonary valvular stenosis), there is an increase in the manifestation of all the resulting vectors of activation of this ventricle: IIs, IIr, and IIIr. As a resultant of these changes, the ventricular curve presents a clockwise rotation in the three planes, and is oriented to the right and forward, with its terminal portions generally located above the E point. When the right ventricular hypertrophy is of the segmentary type, there is an increase of the manifestation of only some of the resulting vectors of the activation of this ventricle. For example, the vector IIr will be increased in cases of tetralogy of Fallot, while the IIIr will be increased in some cases of obstructive chronic pulmonary hypertensive cardiopathy. The T loop, of secondary type, generally opposes the vector IIr on the horizontal plane, and the IIIr on the frontal plane. When an important right ventricular dilatation is associated to a right bundle branch block of intermediate degree, owing to their proximity, the manifestation of the electromotive parietal forces is increased at the expense of the septal ones. This phenomenon produces a characteristic appearance of the SH loop, narrow and with a clockwise rotation.