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.