Page 262 - Feline Cardiology

Chapter 19: Congestive Heart Failure 269

roid receptors (Hadoke et al. 2009). Therefore, even in
• There is no clear relationship defined at this time linking the absence of significant mineralocorticoid activity,
diabetes mellitus and congestive heart failure in cats, methylprednisolone and triamcinolone may still
but studies are lacking.
promote sodium and water retention.
Diseases that increase circulating blood volume and
lead to a high output state, such as anemia, may precipi-
An antecedent event is common in cats with heart tate development of congestive heart failure in patients
failure. Recent fluid administration (intravenous or with underlying heart disease (Yaphe et al. 1993). Anemia
large volume [>100 ml] subcutaneous) is a common is a common comorbidity in humans with heart failure,
clinical scenario preceding the clinical presentation of but prevalence is not documented in cats with heart
congestive heart failure. Cats often have significant heart failure. Anemia is associated with a twofold increase in
disease without overt clinical abnormalities, but they 1-year mortality in people with systolic or diastolic heart
may be precariously “on the edge” of developing heart failure and was shown to be an independent predictor
failure by expansion of the blood volume. Standard of cardiovascular mortality in heart failure patients
volumes and rates of fluid resuscitation may not be tol- (Groenveld et al. 2008). Anemia is associated with a
erated in patients with noncompliant hearts due to con- high cardiac output when the hemoglobin is <7 g/dl.
centric hypertrophy or fibrosis. In a retrospective study Arteriolar vasodilation and hypoviscosity of the blood
of cats with HCM (Rush et al. 2002), half of the cats lead to low systemic vascular resistance. Tissue hypoxia
presenting with heart failure had an antecedent event, and enhanced tissue production of endothelium-derived
including in order of occurrence: intravenous fluid nitric oxide may be responsible for arteriolar vasodila-
administration (17/61), recent anesthesia or surgery tion in anemia. Elevated circulating catecholamine levels Congestive Heart Failure
(15/61, within a mean of 5 days), recent corticosteroid lead to tachycardia and increased myocardial contractil-
administration (13/61), trauma (7/61), upper respira- ity. Chronic increases in blood volume from anemia lead
tory tract infection (3/61), or miscellaneous causes. to eccentric hypertrophy of the ventricular myocardium
Methylprednisolone was the most common corticoste- (i.e., volume overload hypertrophy) and elevated dia-
roid administered (70%) followed by a parenteral form stolic filling pressure (since the ventricle is operating on
of triamcinolone (30%). Ketamine hydrochloride was the rightward aspect of the pressure volume curve).
the most common anesthetic agent administered (8/9 Increased plasma volume and increased diastolic filling
cats with known anesthetic protocol) followed by pressure in cats with significant systolic or diastolic dys-
tiletamine-zolazepam (1/9). Possible mechanisms of function may precipitate heart failure. The cardio-renal-
methylprednisolone contributing to heart failure were anemia syndrome has been recently described in people,
further studied in 12 normal cats (Ployngam et al. 2006). whereby heart failure precipitates renal failure because
Methylprednisolone was shown to increase plasma of poor cardiac output and renal perfusion. Renal failure
volume by 13.4 % (>40% in 25% of cats) and reduce red leads to decreased endogenous production of erythro-
blood cell count, hematocrit, hemoglobin concentra- poietin and subsequent development of anemia. Anemia
tion, as well as serum sodium and chloride concentra- increases the cardiac workload, which continues the
tions in normal cats (Ployngam et al. 2006). However, vicious circle. This syndrome has not been well charac-
echocardiographic variables and blood pressure did not terized in cats with heart failure.
change after methylprednisolone administration in Pregnancy may be associated with high output cardiac
these normal cats. In cats with marked diastolic or sys- disease and although rare, it may precipitate congestive
tolic dysfunction, the increased plasma volume may heart failure. CHF was described in a Himalayan queen,
further elevate diastolic filling pressures and lead to which resolved after cesarean section and did not recur
development of heart failure. In a subgroup analysis of for the life of the cat (Stoneham et al. 2006). Plasma
cats presenting for heart failure after methylprednisolone volume and cardiac output may increase up to 50% in
administration, 58% (7/12) of cats recovered without pregnancy, which may increase diastolic filling pressures
requirement of long-term medical therapy and lived and exacerbate heart failure in cats with underlying
for ≥1432 days without recurrence of heart failure diastolic dysfunction (i.e., compensated hypertrophic,
(Smith et al. 2009). In addition to the main effects of restrictive, or unclassified cardiomyopathies) (Schrier
regulation of carbohydrate and protein metabolism, et al. 1994).
negative feedback on the hypothalamic pituitary axis, Although diabetes mellitus is associated with a spe-
anti-inflammatory effects, and immunosuppressive cific cardiomyopathy, hypertension, and coronary
effects, glucocorticoids also mediate body water and artery disease in people, there is no clear evidence of
electrolyte balance through the low affinity corticoste- this relationship in cats. Diabetic cardiomyopathy in