Page 137 - Problem-Based Feline Medicine

9 – THE CAT WITH ABNORMAL HEART SOUNDS AND/OR AN ENLARGED HEART 129

The obstructive form is caused by anterior motion of Most cats with aortic saddle thrombosis present for
the mitral valve during systole, which obstructs the acute onset of hindlimb paralysis, hypothermia, pain,
left ventricular outflow tract. This results in decreased absent femoral pulses, cool extremities and cyanosis of
cardiac output at faster heart rates, in addition to the nail bed. In some cases a history of episodic lame-
abnormal diastolic function. ness is given.
The outflow obstruction may contribute to the presence
of ventricular concentric hypertrophy. Diagnosis
Histologically there is myocardial fiber disarray Clinically, cats with hypertrophic cardiomyopathy
and diffuse myocardial fibrosis. HCM is usually lim- present with a history of a heart murmur, arrhythmia,
ited to the left ventricle but in some cases, concur- collapse or respiratory distress. Radiographic and elec-
rent right ventricular hypertrophy is present. trocardiographic findings may support the diagnosis,
but echocardiography is required for a definitive diag-
The development of left ventricular hypertrophy is
nosis.
associated with altered intracellular calcium regulatory
mechanisms. This results in the development of relax-
Radiographic findings
ation abnormalities during diastole.
The cardiac image varies from normal to obvious left
The chronic diastolic dysfunction ultimately results in ventricular and atrial enlargement.
left atrial dilatation, elevation of left atrial pressures
and finally congestive heart failure. Enlargement of the pulmonary veins may be seen, rep-
resenting venous congestion.
Clinical signs Areas of focal alveolar densities representing pul-
monary edema may be found. In some cases, pleural
Hypertrophic cardiomyopathy most commonly occurs effusion may be present.
in middle-aged male cats.
A heart murmur is usually present, but in some cases Electrocardiographic findings
may not be present. When present, the murmur is sys- Tachycardia (HR > 220 bpm), left anterior fascicular
tolic and varies in location and intensity. block (evidenced as left axis deviation with a mean
electrical axis (MEA) from 0 to –60 degrees, a QRS
A gallop rhythm is commonly heard. It is identified
in lead I and aVL with a QR pattern, and large
when more than two heart sounds are present on auscul-
S waves in leads II, III, aVF), tall R waves on lead II
tation. The extra sound is classified as S or S
3 4. (>0.9 mV), and notched QRS in any lead may be seen.
The fast heart rate in cats makes it often impossible to
Ventricular arrhythmias are more common than
distinguish between a S and S sound.
3 4 supraventricular arrhythmias.
Arrhythmias are occasionally heard as premature
Atrial fibrillation is rare but if present is always asso-
heart beats with pulse deficits. Ventricular arrhythmias
ciated with extreme dilatation of the left and/or right
are most common.
atria.
Dyspnea is seen in symptomatic cases together with
an increased respiratory rate (greater than 30 Echocardiographic findings
breaths/min) at rest or with open-mouth breathing in Left ventricular hypertrophy (diastolic dimension of
extreme cases. the interventricular septum and/or LV posterior wall
greater than 6 mm), which may be global or focal (see
Collapse may result from impaired cardiac output
Pathogenesis), and left atrial enlargement (dimension
associated with either ventricular tachycardia or the
greater than 13 mm) can be seen.
obstructive form of hypertrophic cardiomyopathy.
● Elongated mitral valve leaflets with systolic ante-
Sudden onset of lameness, paralysis or paresis may rior motion (anterior displacement into the left ven-
occur and is usually the result of systemic thromboem- tricular outflow of the anterior mitral valve leaflet)
bolism. causing secondary left ventricular outflow obstruc-