Abstract 558: Clinical Significance of Papillary Muscle Abnormalities in Hypertrophic Cardiomyopathy Identified by Cardiovascular Magnetic Resonance
Background. Increased thickness of the left ventricular (LV) wall is the predominant feature of the hypertrophic cardiomyopathy (HCM) phenotype. However, the structural characteristics of the LV papillary muscles have received less attention. We applied cardiovascular magnetic resonance (CMR) to characterize and understand the clinical significance of papillary muscle morphology in a large HCM cohort.
Methods. Cine and delayed enhancement (DE) CMR images were obtained in 201 HCM patients and 43 control subjects.
Results. Papillary muscle number and mass index were greater in HCM patients compared to controls (2.5 vs. 2.1; p<0.001; 6 vs. 3 g/m2; p<0.001, respectively), including 109 (54%) with papillary muscle muscle mass ≥7 g/m2 (≥2 SD above the mean for controls). Greater LV wall mass index was associated with more substantial papillary muscle mass (r=0.09; p<0.001). Furthermore, 12 HCM patients (19%) had normal LV mass with localized wall thickness, but increased papillary muscles mass. In HCM patients with LV outflow obstruction at rest, compared to those without obstruction, papillary muscles were positioned closer to the ventricular septum (displaced anteriorly: 58% vs. 42%; p=0.02) with more marked hypertrophy (9.0±5 vs. 6.3±4 g/m2; p<0.001). Preoperative CMR identified 3 patients with an accessory, anteriorly displaced papillary muscle, judged to contribute to outflow obstruction, that was resected during septal myectomy. Thirteen (6%) HCM patients demonstrated DE of the papillary muscles, including 3 with DE confined to papillary muscles.
Conclusions. CMR demonstrates that the cardiomyopathic process in HCM extends to the LV papillary muscles with increased number and mass (often contributing substantially to overall chamber mass) and not uncommonly associated with remodeling and myocardial fibrosis. Identification of accessory papillary muscles may be useful in planning preoperative strategy.