Straddling tricuspid valve as a sign of ventriculoatrial malalignment: A morphometric study of 19 postmortem cases

Background Straddling tricuspid valve, despite extensive investigation, rem ains an incompletely understood form of complex congenital heart disease. Methods A morphometric study of 19 postmortem cases of straddling tricuspid valve was performed, and the results were compared with 32 normal control heart specimens. Results In straddling tricuspid valve, marked malalignment of the ventricle s was always found relative to the atria. The angle between the ventricular septum and the atrial septum in the short-axis projection averaged 61 degr ees +/- 24 degrees, the normal ventriculoatrial septal angle averaging 5 de grees +/- 2 degrees (P < .001). The right ventricular sinus (inflow tract) was significantly smaller than the left (P < .01). A ventricular septal def ect was present in 79%: atrioventricular canal type in 42%, atrioventricula r canal type confluent with a conoventricular defect in 26%, and a conovent ricular defect in 11%. When the straddling tricuspid valve adhered to the c rest of the muscular ventricular septum (n = 4 cases, 21%), the 2 salient f indings were (1) an intact ventricular septum and (2) double-outlet right a trium. The nonstraddling part of the tricuspid valve opened into the small right ventricle. The straddling part of the tricuspid valve opened into the larger left ventricle. The mitral valve also opened into the left ventricl e. Hence hearts with double-outlet right atrium had 3 atrioventricular valv es. Congenital mitral stenosis was present in 26% of this series. Conclusion Straddling tricuspid valve was always characterized by marked ve ntriculoatrial malalignment indicated by an abnormally large ventriculoatri al septal angle, best seen in the short-axis projection.