Physiology of the right heart
Neglected for many years and even referred to as ‘the forgotten chamber’, the right ventricle (RV) has proven to be the dominant ventricle in utero 21 . Doppler interrogation has revealed the fetal right ventricular stroke volume to be one-third higher than that of the LV22. There is compelling evidence that right ventricular dysfunction is the major contributor to perinatal mortality even in the setting of left-sided lesions23. Recent studies have consistently demonstrated a central role for RV dysfunction in the prognosis and outcomes for a wide variety of acquired and congenital cardiac conditions24. In adulthood, the RV differs from the left ventricle in terms of its contraction characteristics at significantly lower myocardial energy costs due to lower impedance of the pulmonary vascular bed accompanied by a unique pressure-volume relationship. In contrast, in the fetus, cardiovascular physiology is characterized by a high-resistance pulmonary circulation; a low-resistance systemic circulation; a large, nonrestrictive ductus arteriosus; right-to-left flow across the foramen ovale; equal pulmonary arterial and aortic pressure; and hypoxemia25.
Sonographic imaging of the right ventricle as the most anteriorly situated cardiac cavity in its entirety might be challenging because of the very particular crescentic shape of the right ventricle that wraps around the side26. Nevertheless, the apical trabecular architecture including the moderator band that is morphologically maintained in all hearts allows anatomic distinction between right and left ventricles irrespective of the location of the chamber within the ventricular mass. From a physiological perspective, the right and left ventricular free wall thickness and force development are equal throughout fetal life and increase up to 20-fold with advancing pregnancy27. The interventricular septum is located on the midline between the ventricular chambers and is flat throughout the cardiac cycle28. For comprehensive analysis of congenitally malformed hearts, a tripartite concept of the RV has been established; it is divided into the inlet, apical trabecular and outlet (conus) components29. In right-sided CHDs, one or more of these components may be affected, and this will be discussed below.