Distance Between the Anterior Papillary Muscle and Interventricular Septum Evaluated by Echocardiography to Diagnose Midventricular Obstruction in Hypertrophic Cardiomyopathy.

Abstract

Background: Left ventricular midventricular obstruction (MVO) is thought to be dynamic with hypertrophic cardiomyopathy (HCM). Therefore, the distance between the anterior papillary muscle (APM) and the interventricular septum (IVS) was used to assess MVO on rest echocardiography.

Methods: MVO was defined as a midventricular gradient of ≥30 mm Hg at rest or after being provoked. APM-IVS distance was analyzed in the apical three-chamber view at end-diastole.

Results: A total of 2,125 patients with HCM were enrolled in this study. Among these, data from 1,453 patients with measurable APM-IVS distances were analyzed. Of the 1,453 patients, 596 had MVO, while 857 did not exhibit MVO. Multivariate logistic regression analyses showed that APM-IVS distance was an independent indicator of MVO (adjusted odds ratio, 0.487; 95% CI, 0.448-0.529). APM-IVS distance demonstrated the highest diagnostic accuracy in identifying MVO, exhibiting an area under the receiver operating characteristic curve of 0.949 (95% CI, 0.937-0.960). The presence of a smaller APM-IVS distance was correlated with increased incidence of left ventricular apical aneurysm and MVO, elevated levels of N-terminal pro-brain natriuretic peptide, and higher New York Heart Association functional class. Among patients with MVO, 198 underwent surgical myectomy and were followed up after a median time of 12 months. APM-IVS distance increased from 7.6 ± 2.2 to 18.9 ± 4.9 mm, and the peak midventricular gradient decreased from 50 mm Hg (36-57 mm Hg) to 3 mm Hg (3-7 mm Hg) at follow-up.

Conclusions: A small APM-IVS distance was associated with MVO, which was alleviated after myectomy following an increase in APM-IVS distance.