Noninvasive assessment of left-to-right shunting in ventricular septal defects by the proximal isovelocity surface area method on Doppler colour flow mapping

Abstract

The proximal isovelocity surface area (PISA), which is the zone of flow convergence appearing on the left ventricular septal surface where flow approaching the defect accelerates, allows quantitative estimation of ventricular septal defect (VSD) flow and defect area on colour Doppler imaging. In the present study, the clinical applicability and reliability of the PISA method in assessing the amount of left-to-right shunting in patients with VSDs were evaluated. Fifty-eight patients aged 0.25 to 15 years (mean age 4.3+/-4.4 years) with VSDs were prospectively studied. Maximum PISA radius in peak systole (r), peak velocity (V(max)) and velocity time integral (VTI(VSD)) of flow through the VSD were measured. In addition, peak VSD flow (2pir(2) Nyquist limit [NL]), amount of left-to-right shunting (Qp-Qs = heart rate x [2pir(2) x NL x VTI(VSD)]/V(max)) and defect area ([2pir(2) x NL]/V(max)) were calculated. There were significant positive correlations between Qp-Qs values calculated by PISA and other spectral Doppler methods using the cross-sectional area, as well as the VTI of pulmonary-aortic (r=0.73, P<0.001) or mitral-tricuspid (r=0.58, P<0.001) flows and cardiac catheterization (20 patients, r=0.82, P<0.001). PISA-derived left-to-right-shunting discriminated moderate to large defects from small defects, which were classified according to the catheter-derived Qp/Qs ratio (2 or greater versus less than 2; P=0.001) or clinical evaluation (P<0.001). The present study demonstrated that the PISA method is a reliable semiquantitative method to determine the amount of left-to-right shunting of VSDs and to discriminate moderate to large defects from small defects. Consequently, this method may serve as a simple and useful adjunct to conventional spectral Doppler methods in the noninvasive assessment of patients with VSDs.