Commentary: Tricuspid regurgitation in hypoplastic left heart syndrome: Getting beyond a finger in the dyke.

Reconstructed tricuspid valve image in HLHS: Hope for better surgical planning.

Tricuspid regurgitation is significantly morbid in hypoplastic left heart syndrome. Advanced image reconstruction may facilitate development of better surgical techniques to yield a durable repair.

See Article page 324.

In this issue of JTCVS Open, Ross and coworkers examined the mechanics of the tricuspid valve annulus in 8 infants with hypoplastic left heart syndrome (HLHS) and compared it with that of 4 normal newborns. Among other findings, annular circumference in patients with HLHS was 20% to 30% larger and anteroposterior diameter 35% to 45% greater than in normal hearts. Normal annuli remained elliptical throughout the cardiac cycle, with major axis in the septal–lateral direction. In HLHS, the major axis was instead in the anteroposterior direction and decreased during isovolumic contraction, ie, the annulus became more circular. The annulus was flatter in mid-diastole and more “bent” (off-plane) at valve closure.

Significant tricuspid regurgitation (TR) develops in approximately 30% of HLHS. Using conventional imaging, the most common reported preoperative pathology is anterior leaflet prolapse, followed by septal leaflet tethering, septal leaflet prolapse, annular dilation, and cleft anterior leaflet., Effective repair has been challenging. Combining the results from 3 studies published within the past year, the unadjusted incidence of moderate-to-severe TR after valvuloplasty was 52 of 96 patients (54%).2, 3, 4 At 10 years, transplant-free survival is lowest (38%) when valvuloplasty is performed at stage 1 for single-ventricle defects.

The pathophysiologic pathway to TR likely begins in utero, because some babies with HLHS are born with TR. In utero, the right ventricle (RV) already has a 50% excess volume load that lasts for months. After birth, when pulmonary vascular resistance drops, the volume load is 2 to 3 times normal. After the stage 1 operation, several more months pass with the volume and pressure load. (The pressure load likely contributes but not dominantly, ie, patients with tetralogy normally don't get progressive TR). TR itself adds more to the volume load; so does RV dysfunction. The volume load deforms the RV geometry, dilates the annulus, changes its shape, and alters papillary muscle orientations. While biological adaptation has been shown to occur in the mitral valve, it is unclear whether the tricuspid valve in HLHS does so and does so sufficiently. While the stage II operation removes much of the volume load, by then “the cat's out of the bag,” ie, some of the changes are permanent. Simplistic procedures such as posterior annuloplasty and commissuroplasty often do not yield a lasting result.

The current work by Ross and coworkers adds important information to the behavior of the tricuspid apparatus in infants with HLHS. For image acquisition, they used “4-dimensional” echocardiography, then performed manual segmentation at 5 time points to reconstruct the time-related shape of the annulus. Similar studies had been performed in the past, but at only 1 or 2 time points. The current study effectively shows us how the annulus behaves throughout the cardiac cycle. The process is time-intensive and was limited to the annulus. As mentioned by the authors, a study published just months ago accelerates the workflow using a deep learning technique (fully convolutional network) and reconstructs individual leaflet anatomy (Figure 1). Once this technique is improved and extended to analyzing the subvalvar apparatus and RV, one may hope to use the findings to design surgical techniques to intelligently refashion the tricuspid valve in HLHS, rather than just putting a finger in the dyke.

Figure 1

Three-dimensional model of a tricuspid valve segmented using the fully convoluted network, a machine-learning technique, modified to illustrate areas of regurgitation. Small heart image shows view direction. L, Apical; A, anterior, P, posterior, C, commissure; S, septal. Adapted from Figure 1D of Herz and colleagues. Used with permission.