Other associated lesions include atrial septal defects, and
additional ventricular septal defects, the latter usually
being muscular. Straddling and overriding of the tricuspid
valve may also occur, which will complicate the closure of
the ventricular septal defect. An important finding when
there is overriding of the orifice of the tricuspid valve is
the anomalous location of the atrioventricular conduction
tissues [18]. A right aortic arch, which is of no haemodynamic
consequence, is present in one-quarter of
patients with tetralogy of Fallot.