The Hypertrophic Septal Papillary Muscle




Ntekim, Nedeke
Nazzal, Alex
Oad, Shayrin
Palapati, Tarun
Fisher, Cara L.


0000-0003-0257-3614 (Fisher, Cara L.)

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Background: The septal papillary muscle (SPM) is one of three papillary muscles found in the right ventricle of the heart (the others are the anterior and posterior papillary muscles). Typically, the SPM arises from the interventricular septum and attaches to the chordae tendineae of the anterior and septal cusps of the tricuspid valve, although it can differ greatly in its location and morphology. The SPM has been found anterior to the septum, posterior to the septum, and laying centrally in the septum. One study also showed that a typical SPM originates from the upper one-third of the ventricle (81.25%) and attaches to chordae tendineae. In another study, it was found that the SPM was absent in around 22% of the hearts that were examined. The SPM has also been found to come off the top third of the wall of the ventricle and has a shape that resembles a cone. The average SPM in the aforementioned study had a mean measurement of 0.95 cm in length and 0.59 cm in width. Along with the other papillary muscles, the SPM functions to keep the tricuspid valve in position and closes the tricuspid valve to prevent the regurgitation of blood from the right ventricle back into the right atrium. In surgeries designed to correct ventricular septal defects, the SPM serves as a landmark for the right bundle branch within the right ventricle. Case Information: During a cadaver dissection in the anatomy lab for first-year medical students, a hypertrophic SPM was found in the right ventricle of a 67-year-old male. The SPM arose from the interventricular septum, attaching to the chordae tendineae and atypically to the anterior wall of the right ventricle. Using digital calipers, the width of the donor's SPM was measured to be 0.456 cm, while the length was measured to be 3.246 cm. Conclusion: Although the morphology of the SPM is quite variable, the one found in our donor is a unique variant because of its length and location. One study found the mean length of the SPM to be 0.51, 0.65, and 0.81 cm in three groups of adults at progressively older ages, adding to the conclusion that the SPM enlarges with age. The length of the donor's SPM in this case is approximately 340% longer than the average SPM. The attachment of the SPM to the anterior ventricular wall in this case is also unusual, even among common variants. Information on these variants of the SPM could prove useful in the identification of diseases and surgical operation within the right ventricle.