Diagnostic ultrasound ( PDFDrive )

1280 PART IV Obstetric and Fetal Sonography
A
1.0 sec
RV
Open
AL
Closed
1 cm
AO
LA
PL
F F
TV
IVS
MV
B
C
FIG. 37.14 M-Mode Echocardiography. (A) M-mode tracing through the right atrium (RA) and the left ventricle (LV) showing normal atrial
contractions followed by normal ventricular contractions. LA, Left atrium; RV, right ventricle. (B) M-mode tracing through the aortic root shows the
aortic valve opening and closing. The foraminal lap (F) can be seen opening into the left atrium (LA). AL, Anterior lealet of aortic valve; AO, aorta;
PL, posterior lealet of aortic valve; RV, right ventricle. (C) M-mode tracing shows opening and closing of the mitral valve (MV) and tricuspid valve
(TV). IVS, Interventricular septum.
he sinus venosus ASD is a rare defect that can be divided
into two types: (1) sinus venosus ASD of the SVC, with the
defect adjacent to the SVC, and (2) sinus venosus ASD of the
IVC, with the defect adjacent to the IVC. he irst type is oten
associated with anomalous pulmonary venous return (APVR)
(Fig. 37.20C). Coronary sinus ASDs, located at the ostium of
the coronary sinus in the right atrium, may also occur but are
exceedingly rare.
he prenatal sonographic diagnosis of ASD is diicult because
the normal patent foramen ovale, which allows blood to low
from the right to the let atrium in utero, itself represents an
ASD. It can be diicult to distinguish a small, pathologic ASD
from the normal patent foramen ovale. he foraminal lap, or
septum primum, is clearly visualized on the four-chamber view.
It has a “loose pocket” coniguration, appearing either circular
or linear in shape as it opens into the let atrium 52,53 (Fig. 37.21).
he septum secundum, which is thick and relatively stationary,
makes up the majority of the atrial septum. he foramen ovale
is an opening in the septum secundum. he septum secundum
and foramen ovale are well visualized in the four-chamber
views. he maximal size of the normal foramen ovale difers
by 1 mm or less from the aortic root diameter at all gestational
ages. 54 An ostium secundum ASD appears as a larger than
expected defect in the central portion of the atrial septum near
the foramen ovale. Alternatively, it can appear as a deicient
foraminal lap.
If the lowest portion of the atrial septum (just adjacent to the
A-V valves) is deicient, an ostium primum defect should be
suspected (Fig. 37.22). Color Doppler ultrasound may be helpful
in the diagnosis of larger ASDs. However, small ASDs are commonly
obscured by the normal low through the patent foramen
ovale. 55,56
A large right-to-let shunt is physiologic in utero, and thus
an ASD usually does not compromise the fetus hemodynamically.
Ater birth, the shunt may cause right ventricular overload and
pulmonary hypertension. Spontaneous closure of an ASD will
occur in approximately two-thirds of patients. 57 Patients with
small ASDs may remain asymptomatic into their 50s. 58