Page 157 - Problem-Based Feline Medicine

9 – THE CAT WITH ABNORMAL HEART SOUNDS AND/OR AN ENLARGED HEART 149

● The murmur of pulmonic stenosis may be similar to Pathogenesis
the murmur heard in tetralogy of Fallot.
Tetralogy of Fallot implies four separate anatomic
● Cyanosis or brick-red mucus membranes are not
abnormalities:
seen with pulmonic stenosis.
● Large ventricular septal defect (VSD).
Cardiomyopathies. ● Pulmonic valvular stenosis.
● The murmur is usually not as loud and may vary in ● Overriding aorta (dextroposition of the aorta)
intensity. results from the cranial displacement of the aorta
relative to the interventricular septum. This leads to
the abnormal alignment of the aorta and the left
Treatment ventricular outflow tract. A portion of the aorta is
positioned over the right ventricular outflow tract.
Use furosemide if congestive heart failure is present
● Right ventricular hypertrophy.
and treat arrhythmias (see page 160 The Cat With
Tachycardia, Bradycardia or an Irregular Rhythm). These abnormalities have a common morphogenetic
cause and result from anterior deviation of the inter-
Surgical options are available but rarely performed.
ventricular septum during development.
● Blalock–Taussig shunt can be recommended (artifi-
cial shunt from the left subclavian artery to the pul- It is a rare congenital disease in the cat and is inherited
monary artery). This increases blood flow through as a simple autosomal recessive trait.
the pulmonary circulation.
The increased resistance to blood flow across the pul-
● Other modified techniques have been described.
monary valve stenosis results in elevation of right ventric-
Consult with an experienced surgeon.
ular systolic pressures above left ventricular systolic
Catheter balloon valvuloplasty can be very success- pressures. These hemodynamic alterations cause the shunt-
ful in reducing the gradient across the stenotic valve. ing of blood through the large ventricular septal defect.
The catheter is positioned through the valve and the
The cranial displacement of the aortic root allows for
balloon inflated to dilate the stenosis.
direct ejection of blood from the right ventricle into the
aorta.
Prognosis
The degree of shunting is relative to the amount of pul-
Most cats reach middle age and some even have a monary stenosis and dextroposition of the aorta. In
normal lifespan. some patients, minimal shunting occurs at rest, and
symptoms are only present during exercise.
Long-term prognosis depends on the severity of
obstruction to blood flow. Chronic hypoxia results in polycythemia (PCV >
65%).
TETRALOGY OF FALLOT
Clinical signs
Classical signs Many cats are asymptomatic at rest and present for
evaluation of a heart murmur.
● Systolic murmur over the cranial ventral
thorax. The age of presentation varies from the first few
● Cyanosis or brick-red mucus membranes months of life until middle age.
may be present.
Cats with symptoms may show open-mouth breathing
● Signs of increased respiratory rate (with
and/or cyanosis after mild to moderate exercise. In
open-mouth breathing), dyspnea or collapse
some cats, syncope is seen.
may be seen while playing.
● Many cats are asymptomatic on The mucus membranes may be pink or cyanotic
presentation. depending on the degree of the polycythemia and
shunting.