The architecture of the infundibulum: more than a simple tubular structure with relevance for ablation of idiopathic tachycardia of the right ventricular outflow tract

Abstract

The most common site of origin for right ventricular outflow tract (RVOT) tachycardias is the left septal side of the infundibulum just underneath the pulmonary valve (PV). Detailed anatomic information of this ventricular structure may be useful to perform the ablation techniques more efficiently and safely. Twenty-five structurally normal human hearts (18 m, 47±5 years) were carefully dissected. The RVOT tract region was defined superiorly by the PV and inferiorly by the superior margin of the RV inflow tract. The interventricular septum and the RV free wall constitute its medial and lateral aspects, respectively. We distinguished 3 morphological areas within the RVOT: 1) the septal part that contacts with the outflow of the left ventricle, 2) the left septo-parietal (LSP) and 3) the right septoparietal (RSP) parts which extend from the septal portion to the anterior wall of the infundibulum. The septomarginal trabeculation (SMT), is a muscle strap plastered onto the septal part. The septo-parietal trabeculations take origin from the anterior margin of the SMT and run round the parietal quadrant of the endocardial infundibulum. These trabeculations showed a variable extension (between 5 to 22 trabeculations) and thickness (range 2-10 mm) along the right and left septo-parietal wall of the RVOT. The more prominent and thicker trabeculations were found in the LSP part. We found in 80% of the hearts a deep muscular depression (cleft) between the septal and the LSP parts. This cleft is crossed by thick trabeculations forming holes or pits of variable depth (5-10 mm). In conclusion, the variable arrangement and thickness of the septoparietal trabeculations of the infundibulum are anatomic features of clinical relevance during endocardial ablation of the RVOT.