Andersons pediatric cardiology 1111

Infundibular Stenosis Pure narrowing of the muscular subpulmonary infundibulum is rare in the setting of an intact ventricular septum Probably many of the cases described as having isolated infundibular stenosis also had a ventricular septal defect, which then closed spontaneously Combined Valvar and Infundibular Stenosis Hypertrophy of the subpulmonary infundibulum occurs along with hypertrophy of the rest of the right ventricle in response to valvar stenosis This reduces the infundibular diameter Endocardial fibroelastosis may also be seen along with the hypertrophy Such reactive stenosis is an important component to be noted when the results of balloon valvoplasty are judged, since time is needed for its regression Other Types of Stenosis Occurring Within the Right Ventricle Other types of stenosis within the right ventricle are rare when the ventricular septum is intact Hypertrophy of the body of the septomarginal trabeculation, which in its severest form produces the typical two-chambered right ventricle, is usually found with a ventricular septal defect.7 It can occur with an intact septum In other patients the valves of the embryonic venous sinus can persist and become so expanded and aneurysmal that they pass through the tricuspid valve and obstruct the pulmonary outflow tract This is called spinnaker syndrome.8 Aneurysmal dilation of the membranous septum can also produce subpulmonary stenosis,9 as can cardiac tumors10 or aneurysm of the right coronary sinus of the aorta.11 Hypertrophic cardiomyopathy can also afflict the right ventricle, particularly in the setting of lentiginosis, although left ventricular obstruction usually dominates Pulmonary Arterial Stenoses Stenoses of the pulmonary arterial tree are frequent in association with complex malformations such as tetralogy of Fallot or transposition They can also complicate more simple lesions, such as pulmonary valvar stenosis or ventricular septal defect Stenoses in the pulmonary arteries can also occur in isolation and can be found in various parts of the pulmonary arterial tree.12 Thus the stenosis may be localized and central within the pulmonary trunk, involve the intrapericardial part of the right and left pulmonary arteries, or be localized and peripheral at the sites of branching of major intrapulmonary arteries It can also be more extensive, producing hypoplastic arterial segments commencing either at the end of the right or left pulmonary artery or at a major intrapulmonary branch point When found, the changes are often not limited to the pulmonary arteries but also involve the systemic vessels.13 Developmental Considerations As described in Chapter 3, the heart develops as a tubular structure, initially with a solitary lumen Remodeling of the lumen of the outflow tract to produce the aortic and pulmonary channels, each with its own arterial valve, involves tissues derived from several sources The walls of the outflow tract are derived from the second heart field, with the walls initially being myocardial to the margins of the pericardial cavity Additional contributions from the second heart field then produce the nonmyocardial walls of the intrapericardial arterial trunks and the arterial valvar sinuses.14 Septation then involves components developed within the outflow tract itself but also an extrapericardial component growing from the dorsal wall of the aortic sac Both sources contain tissues initially derived by migration from the neural crest.15 The protrusion growing from the dorsal wall of the aortic sac divides the distal part of the outflow tract into the intrapericardial components of the arterial trunks The cushions developing throughout the outflow tract, in contrast, separate the components of the developing arterial roots and, similarly, separate the ventricular outflow tracts These cushions, packed with cells derived from the neural crest, fuse with each other in a distal-to-proximal direction However, only the central parts of the distal cushions fuse together The peripheral parts, which occupy the intermediate part of the overall length of the outflow tract, remain unfused Together with the intercalated cushions, which are also developed in the intermediate part of the outflow tract, they produce the primordia of the developing aortic and pulmonary valves At the beginning of these changes, which will eventually lead to formation of the arterial roots, the cushions themselves remain encased in a turret of myocardium Already, however, the most distal part of the outflow tract has separated into the intrapericardial components of the aorta and the pulmonary trunk, with each trunk developing its own discrete walls (Fig 42.10) The distal ends of the outflow cushions themselves then excavate to produce the valvar leaflets and their semilunar hinges (Fig 42.11).16 FIG 42.10 Images taken from an episcopic dataset prepared from a developing mouse sacrificed at embryonic day 12.5 These show how the primordia of the developing arterial roots are derived from the distal ends of the outflow cushions, which are separating the intermediate part of the outflow tract (A) A cut replicating the oblique subcostal echocardiographic plane (B) A cross section across the ventricular mass as viewed from the aspect of the ventricular apex