PRENATAL DIAGNOSIS

With the advent of ultrasound and its application to the human fetal heart,prenatal diagnosis and management of structural heart disease and cardiacdysrhythmia is possible (Figure 16.1). Congenital heart disease is relatively uncommonin the general population, and not every pregnancy can or should be examined with fetal echocardiography. Only those pregnancies with recognized risk factors for cardiac disease and those with an abnormal four-chamberview on level I obstetrical sonograms should be evaluated.

TECHNIQUE OF FETAL ECHOCARDIOGRAPHY

The fetal heart is most easily examined by ultrasound transabdominally at 18-24 weeks gestation, when a nonfixed fetal position, incompletely calcifiedbones, and abundant amniotic fluid make cardiac imaging easier (Table 16.1). Transvaginal images show excellent cardiac detail as early as 14 weeks gestation. Transvaginal imaging is invasive, however, and carries a small potential risk, it should be used when transabdominal imaging is inadequate. Transabdominal ultrasound uses a relatively high-frequency transducer to examine the heart and great vessels segmentally. It uses M-mode, two-dimensional, pulsewave, and color flow Doppler to delineate the cardiac anatomy, fetal hemodynamics, and patency of the fetal circulatory pathways. Anormal fetal echocardiogram does not eliminate the potential for congenital heart disease. Lesions that may not be identified prenatally include mild semilunar valve obstruction, atrial septal defect, small ventricular defect, and partial anomalous venous return. In addition, coarctation of the aorta is a significant lesion that is difficult to diagnose.

The early fetal heart can be dissected under a dissecting microscope in the same manner as the heart of anolder fetus or a newborn (illustrated in Chapter 3).