Page 150 - Problem-Based Feline Medicine

142 PART 3 CAT WITH SIGNS OF HEART DISEASE

Differential diagnosis Pathogenesis

Cardiomyopathy is uncommon in young cats. Cardiom- The ductus arteriosus should normally close within the
yopathy murmurs are usually not as loud. Cardio- first 72 hours of life. Failure of the ductus arteriosus
myopathy murmurs may sound different with serial to close will maintain a patent ductus and allow for
auscultations. shunting between the aorta and pulmonary artery and is
called a patent ductus arteriosus (PDA).
In pulmonic or aortic stenosis, the murmur is usually
louder on the left cranial thorax and its character is The most common direction of shunting is left to right
harsher than a VSD murmur. (aorta to pulmonary artery).

In tricuspid valve dysplasia, the murmur is usually The amount of blood being shunted is proportional to
lower frequency and a thrill is uncommon. the size of the ductus.
In tetralogy of Fallot, peripheral cyanosis may be pres- Volume overload of the pulmonary circulation and
ent; the murmur is similar to the murmur of pulmonic the left heart may be present and ultimately lead to the
stenosis. development of congestive heart failure.
Chronic overload of the left atrium and ventricle results
Treatment in progressive dilatation of these chambers, and
increased left ventricular filling pressures.
Treatment is not required in most cases.
Ventricular dilatation causes changes in geometry of the
Pulmonary arterial banding should be considered in
left ventricle and results in functional mitral regurgitation.
cases where severe volume overload of the left heart is
evident. Typically, systolic arterial pressures are increased
due to the increased stroke volume and diastolic pres-
If signs of congestive heart failure are present refer to
sures are lower than normal explaining the bounding
hypertrophic cardiomyopathy section for treatment
pulse.
detail (page 130).
In some cases, it is believed that chronic volume overload
of the pulmonary circulation results in vascular changes,
Prognosis which increase pulmonary vascular resistance.
The prognosis is good in most cases, unless congestive If pulmonary vascular resistance is elevated above sys-
heart failure is present at the time of presentation. temic vascular resistance, the direction of shunting of
Most cats have a normal lifespan. blood is right to left (pulmonary artery to aorta) resulting
in lower arterial oxygen content and an increase in red
blood cell numbers (polycythemia).
Systemic hypoxemia results in signs of dyspnea, panting
PATENT DUCTUS ARTERIOSUS
and decreased energy, which may be followed by collapse.
Classical signs Right to left shunting is uncommon.
● Continuous murmur is heard loudest over
the left cranial thorax. Clinical signs
● Palpable thrill, which may be present
bilaterally. No breed or sex predilection is seen. Cats at presenta-
● Bounding arterial pulses. tion are usually less than 1 year of age.
● Strong precordial impulse.
No symptoms are present in 1/3 of the cases at initial
● Signs of left-sided heart failure may be
presentation.
present (respiratory distress, tachypnea,
crackles). Cats are usually presented for abnormal respiration
(29%), lethargy (24%) and stunted growth (14%).