Page 263 - Feline Cardiology

270 Section G: Congestive Heart Failure

people consists of diastolic and systolic dysfunction, vascular resistance and is typically mild in severity. The
and pathologic abnormalities include ventricular additive deleterious myocardial effects of concentric
hypertrophy, myocardial fibrosis, and small coronary hypertrophy and fibrosis in cats with concurrent
artery disease. Coexistence of hypertension and diabetes systemic hypertension and hypertrophic cardiomyopa-
mellitus accentuate myocardial fibrosis and diastolic thy may result in the development of diastolic heart
dysfunction. Hyperinsulinemia increases salt reabsorp- failure.
tion by the kidney and also exerts a direct growth- Bradycardia due to second- or third-degree atrioven-
stimulating effect on myocardial cells. There are few tricular block may contribute volume overload of the
studies evaluating cardiovascular effects of diabetes heart and development of congestive heart failure.
mellitus in cats. Unlike people, cats do not appear to Cardiac output is decreased from bradycardia and acti-
develop hypertension secondary to diabetes mellitus, vates RAAS to increase blood volume. Eccentric hyper-
as evidenced by the small clinical study demonstrating trophy of the ventricle develops in response to increased
that systemic hypertension was not present in 14 cats preload, which increases stroke volume and normalizes
with diabetes mellitus (Sennello et al. 2003). In a ret- cardiac output. Besides a slow ventricular rate, the
rospective case-control study of 20 cats with diabetes hemodynamic impact of third-degree AV block is wors-
mellitus and 57 matched controls, 30% (n = 6) of dia- ened by the asynchronous atrioventricular contraction,
where the atria intermittently contract against a closed
betic cats died of heart failure, with a relative risk
Congestive Heart Failure control cats (Little and Gettinby 2008). Of the cats left atrial pressures. In a study of 21 cats with third-
atrioventricular valve, which further elevates right and
of heart failure in diabetic cats 10.4 times that of
degree AV block, 38% had congestive heart failure, but
diagnosed with heart failure, echocardiography revealed
a majority (61%) had underlying primary cardiac
HCM as the underling disease in 3 of the 6 cats, 1 cat
disease (Kellum and Stepien 2006). Sinus bradycardia is
had left atrial dilation but normal ventricular size and
function (possibly unclassified or restrictive cardiomy-
heart failure in people (Alboni et al. 1999). Chronic
opathy), 1 cat had an incomplete echocardiogram with
no atrial measurements and normal ventricular size and rare in the cat but appears to be a factor facilitating overt
severe bradycardia leads to volume overload of the left
function, and 1 cat was not evaluated by an echocar- ventricle, compensatory eccentric hypertrophy, and ele-
diogram (Little et al. 2008). Therefore, it is unlikely vated filling pressures.
that diabetes mellitus caused heart disease in these cats,
but it may have precipitated or worsened underlying PHYSICAL EXAMINATION
heart disease.
Hyperthyroidism may contribute to development of
congestive heart failure in cats, but at present it is an Key Points
unusual primary cause of heart failure. The incidence of
congestive heart failure in hyperthyroid cats dramati- • Respiratory abnormalities including dyspnea, tachypnea,
cally fell from 20% in 1979–1982 to only 8% in 1992– adventitious lung sounds, or muffled lung sounds,
1993, likely due to early detection and more widespread are the most common abnormalities on physical
screening of cats (Fox et al. 1999). Like anemia, hyper- examination of cats with heart failure.
thyroidism causes high output heart disease, character- • A murmur, gallop, or arrhythmia is variably present
ized by increased plasma volume, cardiac filling pressures, in cats with heart failure. A systolic murmur is most
heart rate, contractility, and blood pressure. Concentric commonly ausculted in cats with HCM.
hypertrophy occurs due to direct stimulation of myo- • Clinical signs of low output heart failure include pale
cardial protein synthesis and may decrease myocardial mucous membranes with slow capillary refill time,
compliance. Hyperthyroid cats that develop heart failure weak femoral pulses, hypothermia, weakness, or
often have another underlying primary cardiac disease, collapse.
and the combination precipitates heart failure. Although • Jugular venous distension and pulsation, muffled lung
sounds, hepatomegaly, and abdominal distension are
rare, severe and chronic hyperthyroidism may lead to an commonly identified in cats with right heart failure.
end-stage dilated form of myocardial disease character-
ized by severe myocardial failure and congestive heart
failure (Jacobs et al. 1986).
Systemic hypertension is not associated with heart The most common physical examination findings in
failure unless significant underlying heart disease is cats with heart failure are respiratory abnormalities
present. Compensatory (secondary) concentric hyper- including dyspnea, tachypnea, and orthopnea. Cats with
trophy develops in response to increased systemic severe dyspnea may have open mouth breathing and