Abnormal papillary muscle morphology is independently associated with increased left ventricular outflow tract obstruction in hypertrophic cardiomyopathy

Background: Abnormal papillary muscles (PM) are often found in hypertrophic cardiomyopathy (HCM). Objective: To assess the relationship between morphological alterations of PM in patients with HCM and left ventricular outflow tract (LVOT) obstruction, using magnetic resonance imaging (MRI) and echocardiography. Methods: Fifty-six patients with HCM (mean age 42 years (interquartile range 27, 51), 70% male) and 30 controls (mean age (42 (30, 53) years, 80% male) underwent MRI on a 1.5 T scanner (Siemens, Erlangen, Germany). Standard cine images were obtained in short-axis (base to apex), along with two-, three-and four-chamber views. The presence of bifid PM (none, one or both) and anteroapical displacement of anterolateral PM was recorded by MRI and correlated with resting LVOT gradients obtained by echocardiography. Results: Double bifid PM (70% vs 17%) and anteroapical displacement of anterolateral PM (77% vs 17%) were more prevalent in patients with HCM than in controls (p<0.001). Subjects with anteroapically displaced PM and double bifid PM had higher resting LVOT gradients than controls (45 (6, 81) vs 12 (0, 12) mm Hg (p<0.01) and 42 (6, 64) vs 11 (0, 17) mm Hg (p= 0.02), respectively. In patients with HCM, the odds ratio of having significant (>= 30 mm Hg) peak resting gradient was 7.1 (95% Cl 1.4 to 36.7) for anteroapically displaced anterolateral PM and 10.4 (95% Cl 1.2 to 91.2) for double bifid PM (both p= 0.005), independent of septal thickness, use of beta-blockers and/or calcium blockers and resting heart rate. Conclusions: Patients with HCM with abnormal PM have a higher degree of resting LVOT gradient, which is independent of septal thickness.