Following postnatal repair, the 20-year survival rates exceed 95 percent (Knott-Craig, 1998). However, cases with pulmonay atresia have a more complicated course. There is also a variant in which the pulmonary valve is absent. These afected fetuses are at risk for hydrops and for tracheomalacia from compression of the trachea by an enlarged pulmonary artery.
Cardiac Rhabdomyoma. his is the most common cardiac tumor. Approximately 50 percent of cases are associated with tuberous sclerosis, an autosomal dominant disease with multiorgan system manifestations. Tuberous sclerosis is caused by mutations in the hamartin (TSCl) and tuberin (TSC2) genes.
Cardiac rhabdomyomas appear as well-circumscribed echo genic masses, pler depicts flow from the right atrium to the right ventricle only, and left ventricular filling is usually within the ventricles or out not visible. C. The left ventricular outflow tract view demonstrates marked narrowing of the aorta (Ao). RV = right ventricle; LA = low tracts. They may be single or is the hypoplastic aortic root. (Used with permission from Rafael Levy, ROMS.) multiple; may grow in size during gestation; and occasionally, may lead to inlow or outflow obstruction. In cases without obstruction or large tumor size, the prognosis is relatively good from a cardiac standpoint, because the tumors tend to regress after the neonatal period. Because extracardiac findings of tuberous sclerosis may not be apparent with prenatal sonography, MR imaging may be considered to evaluate fetal CNS anatomy (p. 217).
Motion-mode or M-mode imaging is a linear display of cardiac cycle events, with time on the x-axis and motion on the y-axis. It is often used to measure embryonic or fetal heart rate (Fig. 10-33). If an abnormality of heart rate or rhythm is identiied, M-mode imaging permits separate evaluation of atrial and ventricular waveforms. Thus, it is particularly useful for characterizing arrhythmias and their response to treatment (Chap. 16, p. 316). M-mode can also be used to assess ventricular function and atrial and ventricular outputs.
Premature Atrial Contractions. Also called atrial extrasystoles, these are the most common fetal arrhythmia and a frequent
FIGURE 10-31 Hypoplastic left heart syndrome. A. In this 4-chamber view at 16 weeks, the let ventricle (L) appears "filled in" and is Significantly smaller than the right ventricle (R). The tricuspid valve () is open, whereas the mitral valve appears closed (asterisk). B. Color Dop let atrium. D. The tiny circle (arrow) in this short axis view
FIGURE 10-32 Tetralogy of Fallot. This image shows a ventricular septal defect with an overriding aorta in a fetus with tetralogy of Fallot. The arrow points to the aortic valve. The left ventricle (LV)and right ventricle (R) are labeled.
FIGURE 10-33 M-mode, or motion mode, is a linear display of the events of the cardiac cycle, with time on the x-axis and motion on the y-axis. M-mode is used commonly to measure the fetal heart rate, as in this 12-week fetus.
finding. They represent cardiac conduction system immaturity and typically resolve later in gestation or in the neonatal period. Premature atrial contractions (PACs) may be conducted and thus sound like an extra beat. However, they are more commonly blocked, and with handheld Doppler they sound like a dropped beat. As shown in Figure 10-34, the dropped beat may be demonstrated with M-mode evaluation as a compensatory