[The VCG in ventricular septal defect in the first two years of life. Qualitative and quantitative analyses (author's transl)].

A group of 37 patients, less than 2 years old, with a ventricular septal defect of variable degree, and a left to right shunt, were studied by vectorcardiography. The duration, the direction and the aspect of the QRS loop on the three orthogonal planes, the voltage of the 0.01; 0.02; 0.04 vectors, the right and the left maximum spatial vectors and their projection on the H and F planes were analyzed and correlated to the right ventricular systolic pressure and Qp/Qs. A clockwise or an eight-type loop on the frontal plane, regardless of RVSP, was observed; on the H plane the loop is, usually, counterclockwise when the pressure is low or medium, and can be of the eight-type but never clockwise when the pressure is systemic. Very interestingly, the quantitative analysis showed a consistent increase of the LMSV. A progressive relationship between the spatial vectors and the right ventricular pressure was noted. The diagnosis of combined ventricular hypertrophy depend upon the following findings: the majority of cases showed a large, counterclockwise and anterior QRS loop on the H with the maximum vector to the left and anteriorly; in all cases the 0.01; 0.02; 0.04 vectors were enlarged, thus warranting the diagnosis of combined ventricular hypertrophy in the first few months of life. 4 cases with low RVSP presented increased initial forces to the right and anteriorly directed, while the major portion of the loop was in the left posterior quadrant on the H plane, with a counterclockwise direction. In our view, the differential diagnosis between this type of aspect and that of diastolic overload of the left ventricle can rest only on the increased voltage of the 0,02 vector which means both systolic and diastolic overload of the right ventricle when accompanied by an increased 0.01 vector which indicates volume overload of left ventricle. Likewise only a quantitative analysis can help in differentiating a combined ventricular hypertrophy from a normal tracing in children under 6 months who show an eight-type loop on the H plane with initial and medium vectors directed anteriorly to the left and counterclockwise, and terminal vectors to the right, posteriorly and clockwise, or in those cases with an anterior clockwise loop on the H plane. Moreover, in the first month of life, the VCG of large VSD with increased pulmonary flux and pressure, can be differentiated from the normal by the QRS loop on the H plane which is clockwise, with initial vectors directed to the left and anteriorly with increased LMSV.