Left ventricle accessory antero-septal papillary muscle: an echocardiography and cardiac MRI case-series report.

Background. We studied by means of echocardiography and cardiac MRI (CMR) the occurrence of an accessory papillary muscle that unites mostly the left ventricle (LV) apex with the basal antero-septum in the immediate vicinity of left ventricle outflow tract (LVOT) in patients with and without hypertrophic cardiomyopathy (HOCM). Methods. We included all good quality echocardiography and CMR studies as reviewed by two cardiologists and assessed the occurrence of a contractile papillary muscle situated between the LV apex and antero-septum. Results. A contractile accessory papillary muscle situated between the LV apex and the anteroseptum was seen in 100% of HOCM patients and 62% of control patients (p=0.05) in the CMR images acquired from a total of 9 HOCM and 13 control patients. The same structure was observed in 241 patients representing 69.5% of all-comers echocardiography studies. The age was 69 ± 17 years on average in the echocardiography arm, patients harboring the antero-septal accessory muscle being older (71.6 + 15.7 years old vs 63.5 ± 18.1 for those without, p=0.0005). We exemplify this structure by parasternal long axis still echocardiography images and clips from 24 patients and CMR SSFP still images and a clip from two HOCM patients and one control. Conclusion. A contractile accessory papillary muscle was observed in more than half of the all-comer echocardiography studies, and in all HOCM patients in the CMR arm. Further research is needed to fully characterize the anatomical and physiological significance as well as the possible structural interventional consequences of this structure attaching in the immediate vicinity of the LVOT in HOCM and control patients.