Pediatric emergency medicine trisk 1707 1707
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murmur at all, since left ventricle (LV) and right ventricle (RV) pressures are
equal. Small VSDs produce louder murmurs due to the pressure gradient from LV
to RV. The murmur of a small VSD may become louder as PVR falls.
Hepatomegaly and tachypnea are prominent features of large left-to-right shunts
(Table 86.2 ).
Right-to-Left Shunts
Right-to-left shunts include defects that allow deoxygenated blood to pass from
the right side of the heart into the systemic circulation resulting in cyanosis.
Defects such as TOF are examples of this group. The physiology of TOF is
defined by the large, nonrestrictive VSD and pulmonary stenosis. Even though
the tetrad also describes an overriding aorta and right ventricular hypertrophy,
these components do not define the physiology or presentation. The stenotic
pulmonary outflow tract offers higher resistance to blood flow than SVR and
blood preferentially shunts right-to-left through the VSD. The degree of
pulmonary stenosis determines the volume of right-to-left shunting and thus the
degree of cyanosis. The murmur is determined by the degree of pulmonary
stenosis, not the VSD. These infants present with normal feeding, weight gain,
and vital signs but they are cyanotic. Dehydration may worsen cyanosis.
Right-to-Left and Left-to-Right Shunts (Total Mixing Lesions)
Total mixing lesions such as atrioventricular septal defects (AVSDs) may present
with mild cyanosis and pulmonary overcirculation. These patients have right-toleft and left-to-right shunting causing both cyanosis and pulmonary
overcirculation. Presentation will also be affected by associated defects such as
pulmonary stenosis, unbalanced ventricles (one ventricle larger than the other),
and so forth. If either of these associated defects is present with AVSD, they will
present as a ductal dependent lesion, rather than as pulmonary overcirculation.
Triage. Age, vital signs, weight, color, oxygen saturation, and respiratory status
will indicate acuity of most congenital heart lesions ( e-Table 86.1 , Table 86.3
).
Initial Assessment/H&P. Newborn infants with significant congenital heart
malformations may be completely asymptomatic until the DA closes or PVR
drops. Large population studies have shown that screening newborns using pulse
oximetry combined with physical examination prior to hospital discharge can
detect up to 82.8% of all cardiac defects. The most likely defects to be missed in
the newborn nursery are left ventricular (LV) obstructive lesions. This is
