Ventricular septal defects
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| Fig.12 |
The interventricular septum is a highly complex, three-dimensional
structure formed from a number of morphologically distinct subunits.
It can be divided into subarterial, perimembranous and muscular
components, the subarterial and perimembranous septa being tiny
in comparison to the vast bulk of the muscular septum (Fig.
12). As with atrial septal defects, it is important to note
the precise location of these defects as each may have a different
clinical prognosis for ultimate spontaneous closure and each may
require a different surgical approach when operative intervention
is indicated.
When shunting is significant, the right ventricle invariable
enlarges depending on the degree of excess flow into the right
side. If the defect is large and the shunt unrestricted, the pressures
within the right heart will be identical to those in the left.
In this case the right- sided pressures are referred to as "systemic".
On occasion of long-standing high flow into the lungs, right-sided
pressures may become "suprasystemic".
Compared to atrial septal defects, where it is common for the
anomaly to be restricted to one or the other portion of the atrial
septum, there is frequent crossover between ventricular septal
defects. For example, those in the muscular septum may extend
into the perimembranous septum. Any combination is possible.
Two-dimensional echocardiography is highly rewarding in identifying
the presence of moderate-to-large ventricular septal defects,
particularly in small children. When the defects are small, they
may be quite difficult to visualize. Doppler methods are very
helpful in identifying the defects, whether large or small. Contrast
injection is less helpful, except when right ventricular pressures
are in excess of those in the left ventricle and result in right-to-left
shunting. In most cases where right ventricular pressures are
lower than on the left side, a negative "wash-out" of uncontrasted
blood must be identified. Such approaches are only rarely helpful.
Using two-dimensional echocardiography, each type of ventricular
septal defect can be identified and classified on the basis of
a specific echocardiographic pattern. Each view must be used for
proper spatial orientation of the defect.
 |
| Fig.13 |
Classic muscular defects are those bound entirely by areas of
the muscular septum. Fig.
13 demonstrates ventricular short axes from two patients with
very large midmuscular ventricular septal defects with virtually
free communication between the ventricles.
 |
| Fig.14 |
Fig.
14 shows a parasternal long axis from a patient with a somewhat
smaller ventricular septal defect in the midmuscular septum. Such
ventricular septal defects, when located toward the apex in the
trabecular septum may be difficult to identify by echo alone.
In these cases, Doppler methods are required.
 |
| Fig.15 |
Outlet (or subarterial) defects are noted in subarterial regions.
Fig.
15 demonstrates a notably large subarterial defect from the
parasternal long axis. The right ventricle is dilated indicating
significant shunting.
 |
| Fig.16 |
Any ventricular septal defect, regardless of its location, may
be covered by an aneurysm, as seen in Fig.
16. Such aneurysms are thought to occur as a result of a spontaneous
attempt of closure and are quite variable in size.
Experienced examiners are usually able to image almost all hemodynamically
significant ventricular septal defects in infants, children, and
adults (the exception being those with small, multiple trabecular
defects). Precise location of these defects is very important,
as their location gives some indication as to the likelihood for
spontaneous closure. For example, small perimembranous and muscular
defects may spontaneously close, and in the proper clinical setting
may be followed by echocardiography and Doppler.
It is also important to note the precise location of the defects
when surgical intervention is indicated. Muscular defects may
be multiple, and depending on their size, may be quite difficult
to see through the tricuspid valve as they may be obscured by
the multiple trabeculations of the right ventricle. Such multiple
muscular defects are referred to as a "Swiss cheese" septum.
 |
| Fig.17 |
Similarly, the position of the defects guide the surgeon's approach.
Fig.
17 (left) shows a short-axis view of a subarterial outlet
defect entering the right ventricle just below the pulmonic valve.
Such a defect would be very difficult to approach through the
tricuspid valve as it is a great distance away and requires a
ventriculotomy for proper closure. In addition, these types of
defects may, over time, allow for prolapse of the right coronary
cusp of the aortic valve into the defect resulting in aortic insufficiency.
Fig. 17 (right), in contrast, shows a short axis view of a
perimembranous defect. Its proximity just under the tricuspid
valve indicates its easy surgical closure through the tricuspid
valve and obviates an unwarranted ventriculotomy.
2004