Determination of the anatomical size of ventricular septal defects on the basis of hemodynamic data and noninvasive assessment of pulmonary to systemic vascular resistance ratio Rp/Rs by Doppler-echocardiography.

The pulmonary and systemic flow (Qp/Qs) and resistance ratios (RP/Rs) were determined in children with isolated ventricular septal defects (VSD) to derive an "effective defect resistance" (Rd/Rs) representing the ratios of the resistance of the defect to the systemic vascular resistance. The defect size (expressed as the ratio of the area of the defect to the cross-sectional area of the ascending aorta) was related to the calculated "effective defect resistance," where a significant (non-linear) correlation was found. The effective resistance of the defect is a useful aid for estimation of the anatomical size of a ventricular septal defect. The close correlation between anatomical size and the hemodynamic parameter Rd/Rs allows one to calculate the ratio Rp/Rs with this concept using noninvasive Doppler-ultrasound and echocardiography. This was performed in 21 children with VSD who underwent cardiac catheterisation. The noninvasive calculated flow ratio Qp/Qs and the resistance ratio Rp/Rs showed a close correlation to the values measured at cardiac catheterisation.