Abstract P116: The Physiological Ventricular Growth Signal Can Be Determined Using Infants with Congenital Heart Disease as Models

Abstract

Objectives The signal for ventricular growth has not been defined. This basic developmental question was studied using infants with congenital heart lesions as models. Our first hypothesis was that clinical ventricular hypoplasia is a developmental rather than a primarily genetic defect and, therefore, catch-up growth can be induced. Our clinical observations also led to the hypothesis that forward flow across the atrioventricular (AV) valve (mitral or tricuspid) is what generates the growth signal. To test these hypotheses we analyzed clinical data from infants with a variety of congenital defects including three groups of patients with a hypoplastic ventricle in whom a procedure was carried out to increase flow across the AV valve.

Methods Infants with one of several congenital heart problems had right and left ventricular volumes (RV, LV) assessed by biplane echo and indexed to body surface area (m²). The degree of hypoplasia was calculated using nomograms to determine the number of standard errors of the mean (SEM) below the expected volume (Table 1). Hypoplasia was considered significant when the SEM < −2.0. The three groups were studied before and after (3–6 months) procedures which increased AV flow.

Results Other possible growth mechanisms were assessed. (1) High wall stress with systemic or supra-systemic pressures produced no net cavitary growth unless AV valve flow was increased. (2) Significant retrograde flow from semilunar valve regurgitation did not increase ventricular size until failure developed. Therefore, no evidence was found for other growth mechanisms.

Conclusions 1) Patients with congenital heart disease have a variety of defects, some of which can serve as models to answer basic developmental questions. 2) Increased AV valve flow provides the signal which induces ventricular growth. 3) Operations which increased AV valve flow induced catch-up growth of hypoplastic ventricles and allowed beneficial two-ventricle repairs in these patients.