Surgical anatomy of the atrioventricular conduction bundle in tetralogy of Fallot. New findings relevant to the position of the sutures.

To avoid three of the causes of right ventricular end-diastolic pressure elevation, complete heart block, residual leakage, and fixing of tricuspid septal leaflet, we studied detailed anatomy of the posteroinferior corner of the ventricular septal defect of tetralogy of Fallot in 81 specimens. A new stitching method was applied in 79 patients with tetralogy of Fallot. Sixty-eight specimens (84%) had perimembranous outlet ventricular septal defect with a membranous flap 4.5 +/- 2.6 mm long. Thirteen (16%) had a muscle bar separating the defect from the central fibrous body area. The width was 5.8 +/- 1.7 mm. Microscopic study revealed that the membranous flap is a safe structure for suturing because of the thick posterior extension of the trabecular septomarginalis. In the clinical application of a new stitching method that uses the membranous flap, all patients showed sinus rhythm and no patient had complete heart block. We conclude that a membranous flap can be used safely as a suture line to avoid conduction tissue damage without using the tricuspid septal leaflet.