Congenital malformations - Edocr

CHAPTER 28 CONOTRUNCAL HEART DEFECTS 189
the outlet ventricular septum and aortic and pulmonary
valves have formed. With incomplete
rotation, the arteries have a normal or near normal
relationship, but the aorta does not shift to commit
completely to the left ventricle. The outlet portion
of the ventricular septum is displaced anteriorly
and cephalad, creating the VSD and obstructing
flow to the main pulmonary artery. The earlier
and more severe the obstruction in fetal life, the
smaller the pulmonary valve annulus and the more
common distal areas of obstruction to pulmonary
flow become. The right ventricle pumps against
obstruction, and has volume overload due to shunting
at the VSD, both of which lead to ventricular
hypertrophy.
The clinical presentation is determined by
the relative resistance to blood flow to the pulmonary
arteries, compared to the resistance out
to the aorta. Cyanosis becomes more severe
when increasing resistance to the pulmonary arteries
limits the amount of blood that can go to
the lungs to be oxygenated. When systemic pressures
drop there is relative increased resistance
to flow to the pulmonary arteries; increasing aortic
outflow decreases pulmonary outflow.
EPIDEMIOLOGY
Tetralogy of Fallot is the most common cyanotic
heart defect. Prevalence of TOF has been reported
between 0.26 and 0.48 per 1000 live
births. 8 It represents between 3.5% and 9% of all
congenital heart defects. There is no predilection
toward either sex. 2,8 Infants of diabetic
mothers who had poor blood glucose control
have higher risk of TOF, as do infants of mothers
with phenylketonuria (PKU), and retinoic
acid or trimethadione exposure. 8
CLINICAL PRESENTATION
Although TOF is increasingly a fetal diagnosis,
the degree of pulmonary stenosis may not be
fully delineated. The infant always should be
reassessed after delivery. On physical examination
cyanosis and tachypnea are common. The
right ventricular impulse may be prominent.
Auscultation reveals a normal S1 and single S2. A
pulmonary outflow systolic ejection murmur is auscultated
along the left sternal boarder. Typically
there is no VSD murmur due to equal or near
equal right and left ventricular pressures. If present,
a PDA may be audible.
With critical pulmonary stenosis or pulmonary
atresia, the pulmonary blood flow is
dependent on the PDA and/or multiple aortopulmonary
collaterals (MAPCAS). A continuous
murmur in the infraclavicular areas and back
should be audible. Congestive heart failure may
develop in this setting.
ASSOCIATED MALFORMATIONS
AND SYNDROMES
Patients with TOF frequently have other associated
cardiac defects. Approximately 80% will
have an ASD. A right sided aortic arch is seen in
nearly 25%. 8 Left pulmonary artery atresia and
anomalous origins of the coronary arteries are
also frequently encountered. Complex tetralogy
of Fallot includes TOF with absent pulmonary
valve, and TOF with complete AV canal.
Trisomy and the 22q11 deletion syndrome are
frequent comorbidities with 11.9% of patients with
TOF having, in order of frequency, trisomy 21, 18,
or 13. 8 Population studies have concluded that
over 9% of patients are syndromic or have extra
cardiac anomalies. 2,8 From 8% to 23% of patients
with TOF, especially complex TOF, have the 22q11
deletion syndrome (Fig. 28-1). Alagille patients
typically have peripheral pulmonary stenosis;
however 10–15% of these patients will have
Tetralogy of Fallot. 8 Other common syndromes
associated with TOF are listed in Table 28-1.
EVALUATION
Once cyanotic heart disease is suspected, the
patient should be evaluated by chest x-ray, ECG,