Page 149 - Problem-Based Feline Medicine

9 – THE CAT WITH ABNORMAL HEART SOUNDS AND/OR AN ENLARGED HEART 141

● Normally, shunting occurs from the left to Diagnosis
the right, unless right heart pressures rise above
Congenital systolic ejection murmur is heard over
systemic pressures causing reversal of shunting of
the right sternal border in a young cat.
blood flow.
VSD is the most common cause of a congenital mur-
In most cases, the defect is present in the perimembra-
mur in the cat.
nous area of the interventricular septum, immediately
below the aortic valve annulus.
● The right ventricular location of the defect is Radiographic findings
commonly situated below the septal leaflet of the Pulmonary over-circulation demonstrated by a promi-
tricuspid valve, but can also be located in other nent and enlarged vasculature of the lungs.
areas of the perimembranous septum.
Left atrium and ventricular dilation with variable degrees
● Primary muscular defects of the septum are rare.
of right ventricular enlargement can be seen.
With small defects, the amount of blood being
shunted is small and unlikely to create volume over-
Echocardiographic findings
load of the pulmonary circulation and the left heart.
● However, with large defects different degrees of Most defects are not visualized except for large ones.
volume overload can be expected, depending on the
Demonstration of shunting and direction of blood flow
shunt fraction.
across the interventricular septum is possible using
● In some cases chronic volume overload may lead to
Doppler technique.
the development of left-sided congestive heart fail-
ure. Left atrial and ventricular dilation may be present.
● In rare instances, chronic volume overload of the
High-velocity flow across the pulmonic valve may be
pulmonary circulation may result in increased pul-
found (relative stenosis due to high volume if large
monary vascular resistance with significant elevation
shunting fraction is present). Usually maximal blood
of right ventricular systolic pressures that may
flow velocity obtained with continuous flow Doppler is
result in reversal of the direction of shunting
higher than 1.8 m/s.
(Eisenmenger’s syndrome).
● Large defects can result in abnormal morphology In severe cases, right ventricular dilation is observed.
of the aortic valve annulus leading to aortic valve
If shunting from right to left, an injection of saline from
prolapse and variable degrees of aortic insuffi-
a peripheral systemic vein will demonstrate “bubbles”
ciency.
traveling from the right ventricle to the left ventricle
and/or aorta.
Clinical signs In large defects, aortic insufficiency is commonly found.
No sex or breed predilection is reported and it is seen
usually in cats less than 1 year old.
Cardiac catheterization
Systolic murmur is heard over the right sternal border
Left ventricular injection with angiographic contrast
(the louder the murmur the smaller the VSD).
shows shunting of blood from the left ventricle to right
In many cases, a thrill is felt over the right sternal border. ventricle.
Most cases are asymptomatic. If direction of shunting is right to left, a right ventric-
ular injection of contrast shows shunting to the left
Tachypnea and/or dyspnea may be a clinical complaint.
ventricle.
The femoral pulses are normal.
Increase in oxygen saturation equal to or above 5%
Bounding pulses occur in cases with significant aortic from the right atrium to the right ventricle is diagnostic
insufficiency (usually with large VSDs). for a left to right ventricular septal defect.