Page 143 - Problem-Based Feline Medicine

9 – THE CAT WITH ABNORMAL HEART SOUNDS AND/OR AN ENLARGED HEART 135

Hypertension caused by other diseases requires Abnormal chamber compliance results in inadequate
long-term life-long management. ventricular filling. The non-compliant ventricle rapidly
reaches end-diastolic filling pressure typically during
the first half of the diastolic phase.
RESTRICTIVE AND UNCLASSIFIED
CARDIOMYOPATHIES** Chronic diastolic dysfunction leads to the progressive
development of increased left atrial size and second-
ary increase in left atrial pressures resulting in pul-
Classical signs
monary venous congestion, pulmonary edema and in
● Heart murmur (in some cases may not be advanced cases pulmonary artery hypertension.
present).
Chronic pulmonary artery hypertension will result in
● Gallop rhythm.
right-sided congestive heart failure.
● Arrhythmia.
● Dyspnea. Classification of these forms of cardiomyopathies is
● Hypothermia. poorly defined.
● Collapse.
Clinically it is difficult to distinguish between restric-
● Lameness, paralysis or paresis from
tive and unclassified forms of cardiomyopathy.
systemic thromboembolism.
Clinical signs
Pathogenesis There is no age or sex predilection.
Endocardial, subendocardial and myocardial fibro- Burmese cats seem to have a higher incidence of
sis are the primary pathologic characteristics of restrictive cardiomyopathy.
restrictive cardiomyopathy. Myocardial fibrosis is also
Heart murmur is often present but in some cases may
present in intermediate/unclassified cardiomyopathy.
not be present. When present, a systolic murmur
Geometrically the left ventricle may be normal or mis-
varies in location and intensity with variations in heart
shapen.
rate.
Histopathologically, myocardial infarction is reported
Gallop rhythm is commonly heard. It is identified when
to be a feature of intermediate/ unclassified car-
more than two heart sounds are present on auscultation.
diomyopathy, but it can also be seen in cases with
restrictive cardiomyopathy. Arrhythmias are frequently heard as premature heart
beats with pulse deficits. Ventricular arrhythmias are
Adhesions of papillary muscle and chordae tendinae
most common.
may interfere with normal ventricular blood flow during
systole, causing mid-ventricular obstruction. Mono- Dyspnea is seen in symptomatic cats with an increased
nuclear infiltration of the myocardium suggests an respiratory rate (greater than 30 breaths/min) at rest or
inflammatory process, resulting in endomyocarditis. with open-mouth breathing in extreme cases.
Left atrial (echocardiographic dimension > 13 mm), In symptomatic cats, hypothermia is common.
biatrial and right ventricular enlargement (maximal
Collapse may result from impaired cardiac output (ven-
internal diameter > 7 mm) are often found. Intracardiac
tricular tachycardia).
thrombi are frequently observed. Infiltrative myocar-
dial disease may be present. Lameness, paralysis or paresis is usually the result of
systemic thromboembolism. Aortic saddle thrombosis
Hemodynamically this disease is characterized by
resulting in hindlimb paralysis may be seen. In some
pure diastolic dysfunction due to abnormally low
cases, embolism may only cause lameness.
compliance of the ventricular chambers. Systolic
function is usually preserved or just slightly Most cats with aortic saddle thrombosis present for
decreased. acute onset of hindlimb paralysis, pain, absent femoral