Ventricular septal defect
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Ventricular septal defects (VSD) represent a hole or pathway in the interventricular septum that allows for communication between the right and left ventricles. It typically results in a left-to-right shunt.
They represent one of the most common congenital cardiac anomalies and may be associated with up to 40% of such anomalies 1. They are considered the most common congenital cardiac abnormality diagnosed in children and the second most common diagnosis in adults 9. The estimated incidence is at ~1 in 400 births 6.
A VSD can occur on its own but frequently tends to occur with other cardiovascular associations:
Clinical presentation varies depending on the size and resultant severity of the VSD 10. Small lesions with minimal shunting may be asymptomatic, however, may have a loud harsh pansystolic murmur heard on precordial auscultation over the left sternal border 10. Larger lesions, in comparison, may cause signs of heart failure such as exertional dyspnea, raised jugular venous pressure, hepatomegaly, peripheral edema, or failure to thrive in pediatric patients, but may have a very soft murmur 10.
In addition to a pansystolic murmur, there may also be a mid/end-diastolic murmur mimicking mitral stenosis as well as an ejection systolic murmur mimicking aortic stenosis, each due to increased pulmonary circulation compared to systemic circulation resulting in more total blood passing through the left atrium and ventricle 10. Cyanosis is generally not seen in patients with VSDs 10 (unless Eisenmenger syndrome develops).
While small VSDs will remain electrocardiographically occult, larger defects will classically demonstrate some of the following features 12:
high left ventricular voltage (HLVV)
voltage criteria for left ventricular hypertrophy
prominent, biphasic RS complexes (V2-V4) with amplitudes >50 mm
referred to as the Katz-Wachtel phenomenon
An understanding of complex cardiac development is important in understanding the numerous possible abnormalities that can arise.
No consensus exists (c.2018) for the description/categorization of VSDs although they can be based on location (geography) from the right ventricle viewpoint and/or borders of the defect 14.
Quantitative severity of defect size
While the presence and degree of shunting is typically assessed by imaging (e.g. echocardiography), and more precisely but far less commonly with cardiac catheterization, the size of the defect is often semi-quantified relative to the patient's aortic annular diameter:
defects measuring <25% of the aortic annular diameter are considered small
those with a diameter >75% of the aortic annular diameter are considered large
defects size is referred to as medium if between the above-mentioned cutoffs
Sizing reference criteria has included severity estimation by absolute diameter measurements (e.g. <5 mm defining small, 10 mm or greater considered large); significance may vary, however, based on location/type of VSD and age. as well as dichotomous classification relative to a defined diameter relative to the body surface area (BSA) 13:
likelihood of spontaneous resolution less likely with defects with an area exceeding 0.5 cm2 per square meter of BSA compared to defects below this cutoff
A chest radiograph can be normal with a small VSD. Larger VSDs may show cardiomegaly (particularly left atrial enlargement although the right and left ventricle can also be enlarged). A large VSD may also show features of pulmonary arterial hypertension, pulmonary edema, pleural effusion, and increased pulmonary vascular markings.
Allows direct visualization of the septal defect; a transthoracic parasternal short axis at the level of the aortic valve is typically the view of choice for differentiation between supracristal and perimembranous defects, whereas apical and subcostal windows are preferred for muscular defects 11.
Specific features sought after include:
a perimembranous VSD can be seen as a septal dropout in the area adjacent to the tricuspid septal leaflet and below the right border of the aortic annulus
muscular VSDs are variably located along the septum
may be numerous
inlet VSDs involve the septal component of the right ventricular inflow tract, a modified apical 4 chamber view commonly allows identification
supracristal VSDs are visualized as dropout above the crista supraventricularis in the right ventricular outflow tract
often associated with aortic regurgitation
direction of VSD jet
a parasternal short axis at the aortic valve level will reveal aliased flow at the 10 o'clock position in a perimembranous defect
a supracristal VSD will demonstrate flow at the 2 o'clock position
restrictive VSDs have a more benign prognosis
tend to be smaller defects with a large attendant pressure gradient
rarely progress to cause structural or hemodynamic derangement
non-restrictive septal defects are larger and tend to transmit significant volume to the right-sided circulation
demonstrate low-velocity jets with a much lower pressure gradient
associated with dilation of the left ventricle and pulmonary hypertension
the pulmonary artery systolic pressure (sPAP) may be calculated using the doppler acquired velocity across the defect and the systolic blood pressure
sPAP = SBP - 4 x (jet velocity)2
CTA with ECG-gating allows direct visualization of the defect. Large VSDs may be seen in non-gated studies.
May also show added functional information (e.g. quantification/shunt severity) in addition to anatomy. Some muscular defects can give a "Swiss cheese" appearance owing to their complexity.
Treatment and prognosis
The prognosis is good for small VSDs which show a high spontaneous intrauterine or postnatal closure rate. VSDs usually do not cause any hemodynamic compromise in utero due to the right and left ventricular pressures being very similar during that period.
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