Abstract 16994: Left Ventricle Accessory Antero-Septal Papillary Muscle Detected in the LVOT Vicinity by Means of Cardiac MRI and Echocardiography in HOCM and Control Patients

Abstract

Background: We studied by means of echocardiography (echo) and cardiac MRI the occurrence of an accessory papillary muscle that unites mostly the left ventricle (LV) apex with the basal or mid antero-septum. Methods: We included all good quality 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 antero-septum was seen in 100% of HOCM patients and 62% of control patients (p=0.05, panels 1-6 HOCM patients and 7-9 controls; panels 1, 4 and 7 - diastole; 2,5 and 8 - early-systole; 3, 6 and 9 - end-systole) in the cardiac MRI images acquired from a total of 22 HOCM (9) and control (13) patients. The same structure was observed in 241 patients representing 69.5% of all-comers echo studies. The age was 69 ± 17 years on average in the echo 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 echo images from 24 patients (panel 14) as well as more detailed images from 4 patients in the same group (panels 10-13). Red arrows point out the accessory antero-septal papillary muscle and white arrows the antero-septum. Pink and yellow dots neighbor the regular antero-lateral and postero-medial pap muscles and the white dots the mitral valve. Conclusion: A contractile accessory papillary muscle was observed in slightly more than half of the all-comer echo studies, and in all HOCM patients in the cardiac MRI arm. Further research is needed to fully characterize the anatomical and physiological significance of this structure attaching in the immediate vicinity of the LVOT in HOCM and control patients.