Morphological three-dimensional analysis of papillary muscles in borderline left ventricles

Mitral valve anatomy has a significant impact on potential surgical options for patients with hypoplastic or borderline left ventricle. Papillary muscle morphology is a major component regarding this aspect. The purpose of this study was to use cardiac magnetic resonance to describe the differences in papillary muscle anatomy between normal, borderline, and hypoplastic left ventricles.

We carried out a retrospective, observational cardiac magnetic resonance study of children (median age 5.36 years) with normal (n=30), borderline (n=22), or hypoplastic (n=13) left ventricles. Borderline and hypoplastic cases had undergone an initial hybrid procedure. Morphological features of the papillary muscles, location, and arrangement were analysed and compared across groups.

All normal ventricles had two papillary muscles with narrow pedicles; however, 18% of borderline and 46% of hypoplastic cases had a single papillary muscle, usually the inferomedial type. In addition, in borderline or hypoplastic ventricles, the supporting pedicle occasionally displayed a wide insertion along the ventricular wall. The length ratio of the superolateral support was significantly different between groups (normal: 0.46±0.08; borderline: 0.39±0.07; hypoplastic: 0.36±0.1; p=0.009). No significant difference, however, was found when analysing the inferomedial type (0.42±0.09; 0.38±0.07; 0.39±0.22, p=0.39). The angle subtended between supports was also similar among groups (113°±17°; 111°±51° and 114°±57°; p=0.99). A total of eight children with borderline left ventricle underwent biventricular repair. There were no significant differentiating features for papillary muscle morphology in this subgroup.

The superolateral support can be shorter or absent in borderline or hypoplastic left ventricle cases. The papillary muscle pedicles in these patients often show a broad insertion. These changes have important implications on surgical options and should be described routinely.