Page 93 - Feline Cardiology

Chapter 10: Congenital Heart Malformations 91

of the leaflets during diastole may occur. The diagnosis Etiology, Pathophysiology, and
is established via Doppler echocardiography, which Gross Pathology
demonstrates increased mitral valve inflow velocities Etiology
demonstrating the existence of a pressure gradient
across the mitral valve during diastole (normal E wave The VSD is not known to be a familial trait in the cat
velocity = 0.7 ± 0.1 m/s in the cat; see the inside covers although extensive etiology studies have not been per-
of this book), with mitral valve E wave velocities typi- formed. There are no known breed predispositions.
cally >1 m/s unless severe diastolic dysfunction is also
present. In most cases (4/5), mitral valve insufficiency is Pathophysiology
also noted. In the case of supravalvular stenosis, a ste- Due to the pressure difference between the left and right
notic membrane is observed proximal to the mitral valve ventricles, blood typically shunts across the septal defect Congenital Heart Disease
on 2D echocardiography. from the left ventricle to the right. Most of the blood is
immediately pushed out of the right ventricle into the
Treatment pulmonary artery, to the lungs via the peripheral pul-
monary arteries, and returns to the left atrium again via
Depending on the location and severity of stenosis, the pulmonary veins. The pulmonary arteries, veins and
balloon valvuloplasty may possibly be beneficial. This left side of the heart (atrium and ventricle) experience
should be considered after careful consultation with a the majority of the volume load. Left heart failure with
cardiologist. Medical therapy to control signs of heart pulmonary artery and venous congestion may result
failure if present are warranted (see Chapter 19). depending on the size of the defect. In some cases, the
Additionally, cats with significant atrial enlargement are septal defect is so large that the right and left ventricular
at risk of developing an atrial thrombus, and antithrom- pressure may almost equilibrate with the two ventricles
botic therapy may be considered as described for tricus- largely openly connected.
pid dysplasia.
Some patients develop elevated pulmonary artery
pressure, likely due to the impact of the increased blood
Outcome and Prognosis volume on pulmonary vasculature (Eisenmenger’s phys-
Reported cats have presented at very advanced stages of iology). The elevated pulmonary pressures result in
disease and have lived between a few hours (critical elevated right ventricular pressures and may become
dyspnea at presentation) to 7 months (good response to high enough to cause a reversal of the direction of the
treatment) (Stamoulis and Fox 1993) after diagnosis. shunt, now becoming right to left. These patients may
Presumably a stenotic defect that is detected before a cat develop polycythemia and cyanosis as the deoxygenated
shows overt clinical signs carries a better prognosis, blood from the right ventricle is shunted to the left and
although physical exam limitations make such early out the aorta. Irreversible changes in the pulmonary
detection difficult as discussed above. vasculature may develop.
Because the defect is most commonly located at the
perimembranous region, directly under the aortic valve,
VENTRICULAR SEPTAL DEFECT the defect may weaken the support structure of the
aortic valve and result in aortic valve insufficiency.
A ventricular septal defect (VSD) is a common feline Finally, in a small number of patients, the ventricular
congenital malformation. It is characterized by an septal defect may become partially or completely covered
opening in the ventricular septum that occurs due to with a thin fibrous membrane, in essence closing itself
failure of the ventricular septum to complete formation. (Thomas 2005).
During ventricular septal development, the septum
develops by growing upward from the apical area of Gross Pathology
the ventricle. Defects that result from incomplete
development of the ventricular septum are called ven- The defect is generally observed just apical to the aortic
tricular septal defects. The most common location valve within the membranous part of the basal (upper)
for a ventricular septal defect in the cat is the perimem- ventricular septum (Liu 1977). Left ventricular and
branous area. On a long-axis, two-dimensional echocar- atrial dilation may be observed.
diographic view, this area is located immediately
apical to the aortic valve in the left ventricle and adjacent Signalment
to the region of the septal tricuspid valve leaflet in the A specific breed or gender predisposition has not been
right ventricle. noted.