Page 94 - Feline Cardiology

92 Section C: Congenital Heart Disease

History and Chief Complaint would be expected to allow the ventricular pressures to
In many cases, the diagnosis is made after auscultation equilibrate more and a lower pressure gradient would be
of a murmur in an asymptomatic kitten or adult cat at observed.
the time of a routine evaluation. In other cases, the
diagnosis is made after a cat presents for signs consistent Treatment
with congestive heart failure including tachypnea, Some small, restricted ventricular septal defects are
Congenital Heart Disease Physical Examination defects is generally thought of as surgical or medical.
well-tolerated and the cat may remain asymptomatic
dyspnea, anorexia, or depression.
for years. Treatment for cats with large ventricular septal
Surgical therapy could include surgical closure of the
Physical examination findings should include the pres-
defect, which would require cardiopulmonary bypass,
ence of a heart murmur typically ausculted at the right
something that is technically possible in a full-sized cat
sternum or parasternal area (4th–5th intercostal space)
as blood shunts from the left ventricle to the right.
Interventional procedures that implant a device across the
Sometimes a murmur of mitral regurgitation may also
VSD by a catheter would be technically challenging in a cat
be heard at the left apex or the sternum because the left and very difficult in an immature cat with a large defect.
ventricle and atrium may be dilated with volume over- because of the small body size. Interventional or surgical
load and lead to valve regurgitation. options for a kitten with a large defect should be discussed
with a cardiologist or surgeon because new techniques and
Diagnostic Testing devices are becoming increasingly available.
However, because there are currently very limited surgi-
Electrocardiography
cal interventions feasible for cats with large defects (par-
Cats with a VSD may have a sinus rhythm and normal ticularly small cats), most animals that develop clinical
axis. In cases with larger defects, evidence of left ven- signs are simply managed with heart failure medication
tricular eccentric dilation may be noted based on the as described (see Chapter 19).
identification of a tall R wave (>0.9 mV) in lead II.

Prognosis
Radiography
The prognosis is largely dependent on the size of the
Depending on the severity of the defect and the age defect. Some cats with a small VSD will remain asymp-
of the cat, the radiographs may be normal or may
have evidence of left-sided or generalized cardiomegaly. tomatic for years and live a normal life; others with
larger defects and/or concurrent defects develop
Signs of left heart failure with pulmonary venous con-
gestion and patchy pulmonary edema may be observed. congestive heart failure very quickly. Finally, in a small
number of patients with small defects the ventricular
Cats with large defects that are developing pulmonary
hypertension secondary to their left-sided volume septal defect may become partially or completely
covered with a thin fibrous membrane; this outcome
overload may show evidence of pulmonary arterial
hypertension with dilated peripheral pulmonary arteries is thought to be most likely in the first year of life
(Thomas 2005).
as well.
Echocardiography AORTIC STENOSIS
Echocardiography with Doppler is the diagnostic test of Aortic stenosis is a narrowing or stenotic region that can
choice. Two-dimensional echocardiography should occur at the subvalvular, valvular, or supravalvular level
identify the septal defect, most commonly in the peri- (Liu 1977; Stepien and Bonagura 1991; Margiocco and
membranous region immediately below the aortic valve Zini 2005).
on a long-axis 5-chamber view or on a right parasternal
short-axis view. Doppler echocardiography should be Etiology and Pathophysiology
used to measure the pressure gradient across the defect.
If one assumes that the normal left ventricular systolic Etiology
pressure is 125 mm Hg and the right ventricle is 25 mm The etiology is unknown. A breed predisposition has not
Hg, the pressure gradient or difference between the ven- been noted, although one report described the malfor-
tricles should be approximately 80–100 mm Hg. With a mation in 2 Himalayans and 3 mixed-breed cats (Stepien
small ventricular septal defect that is “restricted” (a small and Bonagura 1991). Several early reports also described
shunt), the pressure gradient should remain in this subvalvular aortic stenosis in the Siamese cat (Liu 1977;
“normal” range (i.e., 80–100 mm Hg). Larger defects Stepien and Bonagura 1991).