ANOMALIES OF THE VENTRICULAR SEPTUM
Ventricular Septal Defects (“MEMBRANOUS”)
Of the anomalies involving ventricular septal defects, those located beneath the aortic valve, the membranous ventricular septal defects, are by far the most common. Not only are these defects frequently seen in association with other cardiac anomalies, but even when occurring as isolated lesions, the membranous VSDs constitute the most important and also the most common type of congenital heart disease. This is not surprising considering the complex embryologic history of the subaortic portion of the ventricular septum. This is the last part of the septum to close, a closure effected by the fusion of components from the embryonic muscular septum, endocardial cushions, and conal swellings. Anomalous development of any one or several of these contributors will lead to a defect of the ventricular septum. There fore, although located in the same general area, membranous VSDs may vary considerably in position and size. Some are found immediately beneath the right and posterior aortic valve cusps; these probably are caused mainly by deficiency of the conus septum and, because of a lack of support for the aortic valve cusps, may lead to prolapse of one or both cusps, causing aortic regurgitation. Other membranous VSDs mainly caused by deficiency of the right limb of the endocardial cushions, or failure of otherwise normally developed endocardial cushions to fuse with the ventricular septum and conus septum, are located a few millimeters away from the aortic valve, leaving a rim of muscular or fibrous tissue. All these defects are located in the general area where the membranous septum is found in the normal heart, and thus are usually rather loosely referred to as “membranous septal defects.”
The clinical features vary, as might
be expected in an anomaly with a diverse pathologic anatomy. Children who have small
defects and shunts are well developed and asymptomatic, and the ECG is normal. Chest
radiographs also are generally normal, although occasionally the vascular pattern
may be slightly increased, with evidence of some left atrial enlargement. Such cases
are referred to as having “maladie de Roger.” A harsh systolic murmur, often well
localized and, at times, quite loud, is heard best over the lower left parasternal
area or (sometimes) somewhat higher up. A thrill may be palpable. Treatment is
generally not indicated unless the anomaly is complicated by endocarditis, which,
fortunately, occurs only rarely.
Large VSDs may cause symptoms in early
infancy. Growth failure is usual in such cases; weight gain may be distressingly
slow, and the children are pale, delicate-looking, and scrawny. Feeding difficulties,
respiratory infections, and congestive failure are common, and the infants may spend
more time in the hospital than at home. There is cardiomegaly, and a loud, harsh,
holo- systolic murmur audible over the left lower sternum, accompanied by a thrill,
is almost invariably present. An apical diastolic rumble, ascribed to torrential
blood flow across the mitral valve, is often also heard.
The chest radiograph shows cardiomegaly,
mainly caused by biventricular and left atrial enlargement; marked
hypervascularity of the lungs, with a prominent pulmonary
trunk and main pulmonary arteries; and a relatively small aorta. ECG generally reveals
right-axis deviation and evidence of biventricular enlargement. This often takes
the form of large, biphasic QRS complexes in the midprecordial leads (Katz-Wachtel
phenomenon). Cardiac ultrasound and MRI easily confirm the diagnosis of VSD and
can define its anatomic pathology and location.
Cardiac catheterization readily demonstrates
a marked increase in the oxygen content of the RV blood samples, and the catheter
may enter the left ventricle or aorta through
the VSD, especially when the catheter is advanced from the superior vena cava. Catheters
advanced from the inferior vena cava generally do not cross the VSD. The RV and
pulmonary artery pressures are elevated and may reach systemic levels. The pulmonary
hypertension is caused in part by some increase in pulmonary vascular resistance,
but mostly by the greatly increased pulmonary blood flow, which may be several times
that of the systemic blood flow. The injection of a radiopaque medium selectively
into the pulmonary trunk, after passage through the lungs, demonstrates the interventricular shunt. A selective left ventricular
angiogram will give even clearer pictures of the shunt.
Therapeutically, infants with large VSDs
may present a serious problem. Every effort should be made to carry them through
the first year, after which many improve greatly, probably because of the relative
decrease in size of the VSD. If medical treatment is unsuccessful, a pulmonary banding
procedure may be done, or in some cases a percutaneous approach may be used to close
the VSD with a device. With banding, a plasticlike band is placed around the pulmonary
trunk, just above the valve, and tightened until the diameter of the vessel is reduced
by about two thirds, and the pressure distally has dropped closer to normal. Usually,
there is a con-comitant rise in aortic pressure, indicating a more favorable pulmonary/systemic
blood flow ratio. The surgical results may be excellent, although many failures
occur as well. In any case, banding is a temporary procedure followed by closure
of the defect later, at which time the band is removed.
Fortunately, most children with moderately
sized VSDs do not have the stormy infancy previously described, although respiratory
infections are prevalent and many patients are small for their age. Dyspnea on exertion
is also common. Congestive heart failure occurs rarely in older children, however,
and the physician should always consider the possibility of a complicating
lesion, such as prolapse of an aortic valve cusp causing aortic regurgitation,
or bacterial endocarditis. A harsh, rather loud, holosystolic murmur accompanied
by a thrill is generally best heard along the lower left sternal border. An apical
diastolic murmur of moderate intensity (mitral flow murmur) is usually audible at
the apex.
Clinical examination and chest radiography
usually show moderate cardiomegaly; the pulmonary vasculature is distinctly increased,
and the left atrium is enlarged. The ECG typically shows a normal or right-axis
deviation with a pattern of so-called left ventricular diastolic overloading, consisting
of deep Q waves, very tall R waves, and often tall, peaked T waves in the left precordial
leads. Evidence for biventricular enlargement is also common. Cardiac ultrasound
and MRI can define the size and position of the VSD. Cardiac-catheterization findings
are similar to those described above; however, the right ventricular and pulmonary-artery
pressures are generally only slightly or moderately elevated and show little tendency
to rise during childhood. A left ventricular angiogram is easily done in
this age group, and it will clearly demonstrate the size and position of the defect.
 |
| TRANSATRIAL REPAIR OF VENTRICULAR SEPTAL DEFECT |
Treatment of patients with moderate-sized
VSDs is surgical and consists of closure of the defect transatrially, using direct
suture or a prosthesis and cardiopulmonary bypass (see Plate 5-17). The surgical
risk is low, but heart block caused by injury to the atrioventricular bundle can
occur infrequently.
Some patients with VSDs either always have had, or
develop as young adults, marked pulmonary hypertension because of vascular
changes in the lungs. The pulmonary vascular resistance equals or exceeds systemic
vascular resistance, and the shunt across the defect is (or becomes) bidirectional
or mainly from right to left, causing cyanosis and digital clubbing. In some patientsa
murmur is barely audible, an expression of the presence of equal pressures in the
two ventricles and minimal net shunt. P2 is loud and snapping, and the
pulmonary valve may become incompetent, resulting in a diastolic murmur at the left
upper sternal border.
Chest radiography reveals little or no
cardiomegaly. The pulmonary artery and the branches are usually dilated and the
lung fields are clear. ECG reveals right axis deviation and RV hypertrophy.
Prostaglandins, endothelin receptor antagonists,
phosphodiesterase type 5 inhibitors, and activators of soluble guanylate cyclase
are used to decrease pulmonary artery pressure in many VSD patients with
hypertension, especially those with some evidence of pulmonary artery constriction.
Surgical closure of the defect carries a prohibitive mortality (~100%) and is
contraindicated. Lung transplant may be the only surgical procedure to reduce
symptoms and prolong life.
Aneurysms of the membranous septum are
being diagnosed with increasing frequency as selective left ventricular angiocardiography,
echocardiography, CT, and MRI are increasingly done. The aneurysm may be intact
or may contain one or more perforations (see Plate 5-15). The aneurysm itself produces
no symptoms, unless large enough to cause RV outflow obstruction, or unless an
aortic cusp prolapses into it; both are rare complications.
Muscular Interventricular Septal Defects
Defects of the muscular interventricular
septum may occur anywhere in the septum (see Plate 5-16). These defects may be single
or multiple and any size. If located in the trabeculated apical part of the septum,
the defect may go undetected. Some defects have a “Swiss cheese” appearance. In
the adult population without CHD, ventricular septal rupture secondary to acute
myocardial infarction can produce comparable signs and symptoms as the congenital
variety, and the prognosis is poor. The symptoms and signs depend on the combined
size of the defects as well as the degree of ventricular dysfunction. Treatment
is surgical or with a percutaneous closure device.
A special form of muscular interventricular
septal defect is located beneath the two arterial valves and is caused by malalignment
of the truncus and conus septa, which do not meet each other and therefore cannot
fuse. The truncus septum is deviated to the left, and the pulmonary artery overrides
the anteriorly located defect. The murmur tends to be located somewhat higher than
usual and may sound superficial.
In a common ventricle the entire septum
is absent except for a low muscular ridge, usually present along the posteroinferior
ventricular wall (see Plate 5-16). Both atrioventricular valves enter the common
chamber, and both structurally resemble the normal mitral valve. The two posterior
papillary muscles, together with the low muscular ridge, may form a single muscle
mass. The two great arteries are transposed, and both may originate from the common
chamber, or one (usually the aorta) may spring from a small outflow chamber separated
from the main ventricular body by a muscular septum like ridge. Associated pulmonary stenosis often occurs
and, if not too severe, generally improves the prognosis. Ventricular inversion
is common and is present in the specimen illustrated here.
The clinical features depend largely
on the presence of pulmonary stenosis; patients with stenosis present similar to
those with tetralogy of Fallot (see Plate 5-18). If there is no stenosis, the symptoms
and signs are those of a large VSD, except that the thrill and the loud systolic
murmur are not present. A systolic murmur at the base is probably caused by a large
pulmonary blood flow across the normal pulmonary valve. As in VSD, an apical diastolic
rumble may be heard. Vascular changes in the lung develop early, resulting in a
high resistance to blood flow and pulmonary hypertension.
On chest radiography the heart is normal
in size if pulmonary stenosis is present, and the pulmonary vasculature is diminished.
In patients without pulmonary stenosis, cardiomegaly
may be present, associated with an increase in the pulmonary vasculature. In patients
with severe pulmonary hypertension as a result of the intrapulmonary vascular changes,
cardiomegaly is mild or absent; the hilar vessels are large, but peripherally the
markings are diminished. There is no characteristic ECG findings associated with
the common ventricle, and the QRS axis and precordial lead patterns vary greatly.
Selective angiocardiography establishes the diagnosis, as does the cardiac echocardiography,
MRI, or CTA.
At present, treatment of common ventricle can be only palliative; correction is not possible for anatomic and hemodynamic reasons. Patients with mild to moderate pulmonary stenosis require no surgical treatment and may do well for many years. Patients with severe pulmonary stenosis may have a Blalock-Taussig shunt or an anastomosis from vena cava to pulmonary artery. In young children without stenosis, a pulmonary artery banding procedure may be considered.
