Ebstein’s anomaly of the tricuspid valve

Heart failure in the adult Ebstein patient

Ebstein anomaly comprises approximately 1% of all congenital heart diseases. It occurs when the tricuspid valve fails to properly delaminate from the right ventricle, resulting in a clinical spectrum of abnormal tricuspid valve morphology and right ventricular dysfunction. Due to the anatomy of the tricuspid valve and right ventricle, as well as associated right- and left-sided pathology, patients are at risk for both right and left ventricular failure and the associated symptoms of each. Ebstein patients are also at risk for atrial arrhythmias, due to the atrial enlargement intrinsic to the anatomy, as well as the presence of potential accessory pathways. Arrhythmias are generally poorly tolerated, particularly in the setting of ventricular dysfunction. Cyanosis may also be present in Ebstein patients, due to the common occurrence of atrial communications, which can exacerbate other symptoms of heart failure. Treatment of heart failure can be through pharmacologic and procedural interventions, depending on the underlying cause of heart failure. While early heart failure symptoms may be treated with medical management, most Ebstein patients will require surgery. Various surgical and catheter-based interventions targeting the tricuspid valve and the atrialized right ventricular tissue have been developed to help treat the underlying cause of the heart failure. The optimal timing of transcatheter and surgical intervention in the Ebstein patient to prevent or treat heart failure needs further study.

Molecular effects of lithium exposure during mouse and chick gastrulation and subsequent valve dysmorphogenesis

BACKGROUND

Lithium (Li) has been associated with cardiac teratogenicity in the developing fetus. We took advantage of the association of therapeutic administration of Li with an increase in heart defects to gain insight into both normal and pathological heart and valve development with GSK-3 inhibition. The objective of this study was to define whether Li mimicry of canonical Wnt/beta-catenin signaling induces cardiac valve defects.

METHODS

Li was administered by a single intraperitoneal injection to the pregnant mouse on embryonic day E6.75, much earlier than heretofore analyzed. On E15.5 developing heart defects were defined by Doppler ultrasound. The embryonic hearts were analyzed for changes in patterning of active canonical Wnt expression and nuclear factor of the activated T cells-c1 (NFATc1), both key regulators of valve development. Li-exposed chick embryos were used to define the early cell populations during gastrulation that are susceptible to GSK-3 inhibition and may relate to valve formation.

RESULTS

Li exposure during gastrulation decreased the number of prechordal plate (PP) cells that reached the anterior intestinal portal, a region associated with valve development. Li decreased expression of Hex, an endoderm cardiac inducing molecule, normally also expressed by the PP cells, and of Sox 4 at the anterior intestinal portal and NFAT, critical factors in valvulogenesis.

CONCLUSIONS

Cells existing already during gastrulation are associated with valve formation days later. The Wnt/beta-catenin signaling in PP cells is normally repressed by Wnt antagonists and Hex is up-regulated. The antagonism occurring at the receptor level is bypassed by Li exposure by its intracellular inactivation of GSK-3 directly to augment Wnt signaling.