QUANTITATIVE MORPHOMETRIC ANALYSIS OF PROGRESSIVE INFUNDIBULAR OBSTRUCTION IN TETRALOGY OF FALLOT - A PROSPECTIVE LONGITUDINAL ECHOCARDIOGRAPHIC STUDY

Background The morphological hallmark of tetralogy of Fallot is contro versial, with much disagreement as to whether the subpulmonary infundi bulum in this lesion is hypoplastic. In addition, few quantitative dat a are available regarding the morphometry of the subpulmonary infundib ulum, what anatomic characteristics are acquired in the postnatal peri od, and at what rate they progress. We also sought to determine whethe r echocardiographic morphometric analysis of the infundibulum can pred ict clinical course in infants with tetralogy of Fallot.Methods and Re sults Twenty-one infants with tetralogy of Fallot (median age at initi al study, 1.6 months) were prospectively followed with serial echocard iograms until the time of first surgical intervention (median age at s urgery, 10 months). Selected video still frames were digitized off-lin e with a computerized system. Compared with age-matched normal control infants (n=37), the following indexed infundibular dimensions in pati ents with tetralogy of Fallot were significantly smaller: length (1.86 +/-0.54 versus 2.7+/-0.56 cm/BSA(0.5), P<.0001), cross-sectional area (1.6+/-0.49 versus 4.7+/-1.3 cm(2)/BSA, P<.0001), and volume (1.24+/-0 .62 versus 7.2+/-3 mL/BSA(1.5), P<.0001). The following measurements w ere increased in tetralogy patients: infundibular septal thickness (0. 83+/-0.21 versus 0.54+/-0.06 cm/BSA(0.5), P=.0002) and infundibular fr ee-wall thickness (0.62+/-0.13 versus 0.49+/-0.06 cm/BSA(0.5), P=.006) . The angle between infundibular septum and ventricular septum had a g reater degree of anterosuperior deviation in tetralogy patients, resul ting in a larger infundibuloventricular septal angle (77+/-8.2 degrees versus 31+/-6.5 degrees, P<.0001). During follow-up, infundibular vol ume in tetralogy patients decreased from 1.24+/-0.62 to 0.81+/-0.47 mL (BSA(1.5) (P=.002), correlating with infundibular septal thickness (r= -.63, P<.003). The mean rate of decrease of indexed infundibular volu me was 0.1+/-0.13 mL . BSA(-1.5) . mo(-1). Correlation analysis reveal ed a nonlinear correlation between the degree of infundibular septal m alalignment and indexed infundibular volume (r=.93, P<.0001). Tetralog y patients who required early surgical intervention (4.8+/-0.9 versus 10.7+/-1.7 months, P<.0001) had a smaller infundibulum at presentation (0.92+/-0.35 versus 1.41+/-0.67 mL/BSA(1.5), P=.04) and an accelerate d rate of infundibular narrowing (0.17+/-0.18 versus 0.06+/-0.08 mL . BSA(-15) . mo(-1), P=.04). Conclusions Compared with normal infants, t he subpulmonary infundibulum in tetralogy of Fallot is characterized b y a smaller volume, shorter and thicker infundibular septum, and anter osuperior deviation of the infundibular septum. Infundibular obstructi on in tetralogy patients is progressive, with an average rate of decre ase in indexed infundibular volume of 0.1+/-0.13 mL . BSA(-1.5) . mo(- 1). Infants who are likely to require early therapeutic intervention m ay be identified on their initial echocardiogram as having an infundib ular volume of <0.9 to 1.0 mL/BSA(1.5).