ANOMALIES OF
TRICUSPID VALVE
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| TRICUSPID ATRESIA |
Of the congenital tricuspid valve anomalies, only two tricuspid valve atresia and Ebstein’s anomaly are clinically significant. Tricuspid regurgitation and stenosis occurring as isolated lesions are extremely rare. Some forms of septal defects, such as endocardial cushion defects or ventricular septal defects, may involve the tricuspid valve’s medial cusp, rendering this cusp insufficient or allowing for a direct shunt from the left ventricle to the right atrium. Tricuspid valve stenosis usually accompanies pulmonary atresia or severe stenosis when the ventricular septum is intact. Actually, the tricuspid valve in these patients, although small and often with thickened cusps, is normally formed, and the stenosis is a secondary hypoplasia.
Although uncommon, tricuspid atresia
is seen often enough to have considerable clinical importance. Next to
transposition of the great arteries, tricuspid atresia is the most common cause
of pronounced cyanosis in the neonatal period, and the degree of cyanosis is usually
more marked than in cases of transposition. Only rarely is there a recognizable,
small tricuspid annulus, which then forms the rim of an imperforate membrane.
Usually there is only a dimple, or no indication of a tricuspid valve, in the floor
of the right atrium.
Several subtypes of tricuspid atresia
are distinguished based largely on whether there is an associated transposition
of the great vessels (with or without pulmonary stenosis) and whether the ventricular
septal defect (VSD), which is almost always present, is large or small. Of the various
types, tricuspid atresia without transposition and with a relatively small VSD is
by far the most common. Unfortunately, this type also carries one of the worst prognoses;
the great majority of infants die in the first year and usually in weeks or months
if not treated appropriately. The right atrium is dilated, and either the foramen
ovale is patulous or an ASD exists. If the atrial septum is minimally patent, balloon
atrial septostomy can be performed to widen a minimal patent foramen ovale or very
small ASD. This allows blood to flow into the left side of the heart and thus to
the systemic circulation. The mitral valve is large, as is the left ventricle. Usually
there is no trace of a right ventricular inflow portion, and the infundibulum generally
is present and thin walled. Although uncommon, pulmonary valve stenosis may be seen
in association with tricuspid atresia.
Characteristic clinical features include the early
appearance of moderate to marked cyanosis, progressing with time and increasing
with crying. Cerebral hypoxic spells, similar to those seen in tetralogy of
Fallot are occasionally seen, consisting of a sudden deepening of cyanosis, crying,
lethargy, and at times unconsciousness. The episodes usually last only a few
minutes but may lead to the death of the infant (see Plate
5-11).
Clubbing of the digits is never present
at birth and takes time to develop, generally not well marked until about 3 months
of age. The few children who live for any length of time usually have dyspnea on
exertion (or even at rest) and fatigability. Occasionally a child may squat, but
this is not a characteristic feature as in tetralogy of Fallot. Cardiomegaly is
typically absent in patients of tricuspid atresia, with no precordial bulge. A systolic
thrill is rare. The apical heart sounds are unremarkable; S2 at the base
is normal or slightly increased and single, with P2
greatly diminished or absent as a result of the reduced pulmonary blood flow.
Typically, there is a harsh systolic murmur of moderate intensity, best heard at
about the third left interspace parasternally.
On chest radiography the heart is either
normal in size or only very slightly enlarged. The right border of the heart is
prominent because of the enlarged right atrium; the left border may have a peculiar
angulated or squared-off appearance, and the pulmonary artery segment is reduced or absent. The vascularity of
the lung fields is diminished. The ECG is much more helpful in arriving at a diagnosis.
Left-axis deviation, left ventricular (LV) hypertrophy, and right atrial hypertrophy
are invariably present. These are so typical for tricuspid atresia and so unusual
in other types of cyanotic CHD that any cyanotic baby showing left-axis deviation
and LV hypertrophy on the ECG, and without cardiomegaly, should be considered to
have tricuspid atresia. The P waves are generally tall and peaked (often very tall),
indicating right atrial enlargement. Cardiac ultrasound and MRI can easily define
the anatomic pathology, including shunts, valve regurgitation, and ventricular function.
Cardiac catheterization to obtain hemodynamic
data generally should not be done; it contributes little to what is already known
or suspected on clinical grounds, merely adding another stressful procedure for
the very sick infant to undergo. If cardiac catheterization and angiography must
be done, a simple venous angiocardiogram or a selective right atrial angiocardiogram
confirms the diagnosis. Opacification of the right atrium is rapidly followed by
visualization of the left atrium, left ventricle, and great vessels. Generally,
there is a typical, more or less triangular filling defect between the opacified
right atrium and the left ventricle. Cardiac magnetic resonance angiography (MRA)
with contrast can confirm the anatomy as well. This area is normally occupied by
the inflow portion of the right ventricle. An LV injection in the lateral position
shows the diminutive right ventricular outflow portion to be filling by way of the
VSD.
Treatment is surgical and can be only
palliative. The surgery focuses on increasing pulmonary blood flow, which can also
be accomplished in the newborn using prostaglandin E1. PGE1
relaxes smooth muscle in the ductus arteriosus and keeps it patent to provide temporary
blood flow from the aorta to the pulmonary artery. This palliation allows time for
patients with tricuspid atresia to mature to the point where a surgical procedure
can be performed safely. Blalock-Taussig (subclavian to pulmonary artery anastomosis),
classic Glenn (right atrium to pulmonary artery), or a Fontan (variations of vena
cava to pulmonary artery) procedure provides flow to the pulmonary circulation in
these patients, who depend on pulmonary blood flow for survival. These surgical
procedures require the pulmonary artery pressure to be low in order for flow to
enter the pulmonary circulation from the vena cava or right atrium.
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| GLENN SURGERY FOR TRICUSPID ATRESIA |
A side-to-side anastomosis of the ascending
aorta to the pulmonary artery can substitute for the Blalock-Taussig shunt. In the
Glenn procedure, the proximal pulmonary artery is ligated, as is the superior vena
cava, between the anastomotic site and the right atrium (see Plate 5-12). This operation has the considerable advantage
of bringing blood directly from a large systemic
vein to the right lung, thus entirely bypassing the right side of the heart. Unfortunately,
it is not suitable in very small infants, who are at the highest risk and comprise
the majority of cases of tri- cuspid atresia, because the low-pressure shunt between
the small vessels has a strong tendency to thrombose, with disastrous results. This
is also characteristic, but to a lesser extent, of the Blalock-Taussig operation.
The Fontan procedure is another option to transfer venous blood directly into the pulmonary artery (see
Plate 5-11).
Of the other (much rarer) forms of tricuspid
atresia, those with a moderately large VSD and a normal to slightly increased
pulmonary vascular resistance carry a much better prognosis and may not require
surgery. A form that has a fairly good prognosis is that associated with transposition
of the great vessels and a mild to moderate
subpulmonic stenosis.
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| EBSTEIN’S ANOMALY |
As an isolated malformation, Ebstein’s
anomaly of the tricuspid valve is less common than tricuspid atresia. However, Ebstein’s
malformation is of considerable clinical importance because most patients reach
child-hood, adolescence, or even adulthood, and therefore it must be much better
tolerated than tricuspid atresia. In principle, Ebstein’s anomaly consists of a
downward displacement of the tricuspid valve “origin.” The valve cusps, except for
the medial two thirds of the anterior cusp, appear to originate from the right ventricular
(RV) wall, often as low as the junction of the inflow and outflow portions of the
right ventricle, instead of from the tricuspid annulus. The valve tissue is almost
always redundant and wrinkled, and the chordae tendineae are poorly developed or
absent (see Plate 5-13).
Embryologically, Ebstein’s malformation
can be considered an abnormality in the undermining process of the RV wall, which
normally leads to liberation of the inner layer of ventricular muscle. This process
should continue until the atrioventricular junction is reached. Much of the apical
portion of the valve “skirt” thus formed is normally resorbed, until only papillary
muscles and narrow strands remain. The latter become fibrous (chordae tendineae),
as do the valve cusps them-selves. In Ebstein’s
anomaly the process of undermining apparently is incomplete and does not reach the
annulus. Individual cases vary greatly in this respect, and instead of cusps, chordae
tendineae, and papillary muscles, there often are sheets of valve tissue with few
or no chordae tendineae incorporating the papillary muscles. The anterior cusp is
“liberated” very early in embryonic life, which may explain why this cusp always
originates normally. The actual valve opening, located close to the crista supraventricularis,
is usually much smaller than the normal tricuspid ostium, and the valve is almost
always incompetent.
The downward displacement of the
valve divides the right ventricle into two parts: (1) an “atrialized” part
between the normal annulus and the abnormal valve origin and (2) the normal outflow
portion of the right ventricle. The size of the “atrialized” portion of the right
ventricle varies greatly, and its wall may be fibrous and paper thin or
muscular and quite normally formed. Rarely, the valve is imperforate, or its free
portion is practically nonexistent. The pulmonary valve may be stenotic or rarely
atretic.
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| TYPES OF EBSTEIN’S ANOMALY |
The clinical features are highly diverse,
an expression of the considerable variability of the Ebstein’s pathology. In general,
the larger and thinner walled the atrialized RV part, the smaller will be the remaining
normally developed RV part. Also, the greater the insufficiency of the tricuspid
valve, the more serious will be the hemodynamic situation. In severe cases, symptoms
(cyanosis, dyspnea, feeding difficulty) may begin in the neonatal period (see Plate
5-14). The early occurrence of heart failure is an ominous sign and is usually followed
by death within weeks. In milder cases, symptoms may
not appear until later in childhood. Occasionally, the degree of malformation is
slight and is compatible with a fairly active and normal life. Cyanosis and clubbing
are usually present in older children, who tend to be underdeveloped and thin. Cyanosis
in infancy often subsides temporarily, only to reappear later. Fatigue is a prominent
symptom, along with exercise intolerance and dyspnea on effort. Cardiac arrhythmias
are very common, usually consisting of some form of supraventricular tachycardia.
The patient with Ebstein’s anomaly almost
always has considerable cardiomegaly on both the left and the right side, because
of enlargement of the right atrium and the “atrialized” right ventricle, and the
peripheral pulses are weak. The apical impulse is diffuse and poorly felt. A precordial
bulge and thrill are unusual. S1 is of normal intensity and often is
split, with the second component loud; S2 is generally normal. A loud,
early diastolic S3 is heard along the left lower sternal border, and
S4 may be present. A mild to moderate systolic murmur is usually present along the left lower sternal
border and may be accompanied by a diastolic murmur. The systolic murmur sometimes
may have a curious scratchy quality, resembling that of a pericardial friction rub.
Chest radiography shows moderate to marked
cardiomegaly, and the heart is often box or funnel shaped, mainly because of tremendous
right atrial enlargement and displacement and dilatation of the RV outflow tract.
The pulmonary vascular markings are decreased, and the main pulmonary artery segment
is small or absent. Left atrial enlargement is never seen in Ebstein’s anomaly.
Rarely, the heart may be almost normal in size and shape, indicating a mild degree
of malformation.
The characteristic ECG displays right-axis
deviation, low voltage, and widened QRS complexes in the limb leads and the right
precordial leads, and in the latter a right bundle branch-block pattern with “splintering”
of the complexes. A pattern of RV hypertrophy is rarely seen, and LV hypertrophy
is invariably absent. Tall, peaked P waves are usually seen in leads II, aVF,
and V1 to V3, and the PR interval is usually prolonged. Wolff-Parkinson-White
syndrome (see Plate 2-23) is relatively common in Ebstein’s anomaly.
Cardiac ultrasound or MRI can confirm
the diagnosis of Ebstein’s anomaly. With cardiac catheterization there is a distinct
tendency for arrhythmias to occur, but the procedure can be used to establish the
diagnosis and determine the degree of severity. The catheter tends to coil in the
right atrium and thus outlines its tremendous size. The pressure in the
atrialized portion of the right ventricle is low and in general resembles that measured
in the right atrium. RV pressures are normal, except in the rare case with associated
pulmo- nary stenosis and resulting elevated RV pressure. If an electrode catheter
is employed, pressure tracings and intracavitary ECGs can be recorded simultaneously.
Placement of the catheter in the distal portion of the right ventricle will show
typical RV pressure and ECG tracings. On pulling back into the atrialized part of
the right ventricle, the former do not change significantly, whereas the pressure
drops. On further withdrawal into the right atrium, the ECG complexes assume a right
atrial configuration with large P waves, and the pressure tracings show no further
change (see Plate 5-13).
On selective right atrial angiocardiography,
contrast successively opacifies the smooth walled right
atrium, the atrialized RV part, and often (after some delay) the trabeculated RV
outflow portion. The diaphragmatic right border of the heart may have a trilobed,
scalloped appearance. Injection into the RV outflow outlines the “incomplete” right
ventricle and regurgitation across the tricuspid valve.
Medical treatment is indicated mainly
in patients with Ebstein’s anomaly who have congestive heart failure or paroxysmal
supraventricular tachycardia. Therapy consists of the usual anticongestive measures:
digitalis, diuretics, oxygen, sedation, bed rest, and reduced salt intake. Angiotensin-converting enzyme
(ACE) inhibitors or angiotensin receptor blockers (ARBs) and beta-blocker therapy
should be considered in heart failure patients, as well as antiarrhythmics to
control the tachycardia.
Surgical treatment is complicated and usually palliative. The choice of procedure depends on whatever pathology is present. In general, surgery should be advised only for patients with Ebstein’s anomaly who are symptomatic and incapacitated. Rehabilitation of incapacitated patients has been achieved by prosthetic replacement of the anomalous valve and, in suitable cases, by resection or plication of the non-functioning atrialized part of the right ventricle. An ASD, if present, should probably be closed at the same time, to achieve the full benefit of the procedure. If the tricuspid valve is replaced, long-term anticoagulation must be achieved.
