Detection and assessment of straddling and overriding atrioventricular valves by two dimensional echocardiography

Sixteen patients with a straddling tricuspid and two with a straddling mitral valve were identified by two dimensional echocardiography. In all but one the atrioventricular valves appeared at the same level, indicating absence of the ventriculoatrial septum. A straddling valve was diagnosed by identifying subvalvular apparatus from one atrioventricular valve in both chambers, independent of whether they were ventricles or rudimentary chambers. Further confirmation was obtained during real time study where the valve leaflets appeared to fly through the ventricular septal defect. Overriding of the valve annulus was greater than 50% in 12 and less than 50% in five, with one other patient having none detectable. The relation of the central fibrous body to the tip of the interventricular septum was reliable in assessing overriding of greater than 50%, but where it was less than 50% other views were necessary to detect its presence. The diagnosis of straddling with or without overriding of an atrioventricular valve can be reliably made by two dimensional echocardiography, and carries important implications relating to the type of surgical intervention possible, and in those with a straddling tricuspid valve, the position of the atrioventricular node.