Morphological spectrum of the septal papillary muscle complex and chordal support in the human tricuspid valve: a quantitative anatomical study

The tricuspid valve is anatomically variable. The septal/medial papillary muscle complex (SPM) contains two elements. The papillary muscle of the conus arteriosus (MCA) is always present. The septal papillary muscles (MPS) vary in number and form. We asked where their chordae tendineae actually attach. We dissected 111 structurally normal human hearts from donors aged 49–97 years. Every chorda arising from the MCA and MPS was assigned to one predefined region: the anterior leaflet (CA), the posterior leaflet (CP), the anteroseptal commissure (Com a), the posteroseptal commissure (Com p), or the anterior (CSa), middle (CSm) or posterior (CSp) zone of the septal leaflet. Counts were compared with the Friedman test, followed by Wilcoxon signed-rank tests with Holm–Bonferroni correction. We traced 385 MCA-derived chordae. Most ended in CA (85.97%). Far fewer ended in Com a (7.28%) or CSa (6.75%). The 934 MPS-derived chordae behaved differently. They clustered in the septal leaflet (CSa 33.94%, CSm 26.55%, CSp 12.10%), in Com a (18.31%) and in CA (8.46%). Com p received only 0.64%, and CP received none. Regional differences were significant ( p < 0.001). MCA chordae dominated CA. MPS chordae dominated Com a and the septal leaflet ( p < 0.001). MCA and MPS act as one functional unit. Together they brace the anteroseptal region of the tricuspid valve. These numbers sharpen the anatomical picture of septal papillary support and give a reference point for surgical repair and imaging.