Page 710 - Small Animal Clinical Nutrition 5th Edition

Cardiovascular Disease 737

total, free and esterified carnitine concentrations in plasma activity and aldosterone measurements are available through
VetBooks.ir based on measurements from a small number of healthy dogs several reference laboratories.
and cats fed a standard dry commercial food (Jacobs et al,
Risk Factors
1990, 1990a; Keene, 1992; Shelton, 1995). Total carnitine
concentrations in plasma are influenced by intake of carnitine Risk factors for causing or complicating cardiovascular disease
in food. Plasma concentrations will be elevated in animals include breed, gender, obesity, renal disease, drug therapy,
that eat foods high in carnitine (e.g., raw meat or moist foods endocrinopathies and heartworm infection. Breed and gender
high in skeletal muscle content). To measure carnitine con- appear to be the most important risk factors for cardiovascular
centration, approximately 1 ml of heparinized plasma should disease in dogs. A number of breeds are at increased risk for
be immediately separated, frozen and submitted to an appro- several different congenital cardiovascular malformations,
priate laboratory. b including patent ductus arteriosus, portacaval shunts, aortic
Carnitine concentrations can also be measured in cardiac stenosis, pulmonic stenosis, ventricular septal defects, tricuspid
muscle, skeletal muscle and liver (Jacobs et al, 1990, 1990a; dysplasia and persistent aortic arch and related vascular abnor-
Keene, 1992; Shelton, 1995). Cardiac tissue is obtained by malities. Estimated relative risks (odds ratios) are listed else-
using a modified transvenous endomyocardial biopsy tech- where by breed for many of these congenital abnormalities
nique (Keene et al, 1990). Skeletal muscle and liver tissue are (Buchanan, 1992). Chronic valvular heart disease occurs with
obtained using standard biopsy techniques. Tissue specimens relatively greater frequency in small dogs, whereas large dogs,
are blotted dry, immediately frozen in liquid nitrogen and especially males, are predisposed to dilated cardiomyopathy.
º
º
stored at –70 C (–94 F) until the carnitine concentration is Certain canine breeds also have characteristic cardiac dysrhyth-
b
measured at an appropriate laboratory. Tissues for carnitine mias that may occur with or without significant cardiomegaly
assay should not be placed in formalin. Dogs with confirmed or signs of CHF. Finally, an increased risk of pericardial effu-
lipid storage myopathy should have plasma and tissue carni- sion is noted in golden retrievers, Labrador retrievers, German
tine assays performed in the hope of identifying a potentially shepherd dogs, German shorthaired pointers and Akitas
treatable cause of an otherwise difficult to manage disease (Buchanan, 1992).
(Shelton, 1995). c Obesity occurs frequently in dogs and cats with cardiovascu-
lar disease. Obesity not only produces clinical signs that mimic
BLOOD CONSTITUENTS ASSOCIATED WITH those of early heart failure (i.e., exercise intolerance, tachypnea,
NEUROHUMORAL ACTIVATION weakness),but also causes cardiovascular changes that can exac-
It is well established that activity of several neurohumoral erbate underlying cardiovascular disease.
systems is increased in many patients with chronic CHF. Chronic progressive kidney disease and failure often occur in
Elevated levels of renin, angiotensin, aldosterone and arginine dogs and cats with cardiovascular disease, especially in older
vasopressin (AVP; antidiuretic hormone [ADH]) occur in patients. Cardiac disease often exacerbates underlying renal
both spontaneous and experimental canine models of CHF disease because a large proportion of the cardiac output is nor-
(Watkins et al, 1976; Riegger and Liebau, 1982; Riegger et al, mally destined for the kidneys. Renal disease influences the
1988; Maher et al, 1989; Villarreal et al, 1990; Himura et al, types and dosages of medications that are used to treat patients
1994). Increased concentrations of renin, aldosterone, norep- with cardiovascular disease. Chronic kidney disease is also a risk
inephrine and brain or atrial natriuretic peptide or atrial natri- factor for secondary hypertension in dogs and cats.
uretic factor (BNP, ANP or ANF) occur in dogs with spon- Therapy for CHF often includes: 1) diuretics and salt restric-
taneous heart disease and failure (Knowlen et al, 1983; Ware tion to reduce preload and venous congestion, 2) pimobendan
et al, 1990; Takemura et al, 1991; Vollmar et al, 1991; Buoro to increase contractility and dilate veins and arteries to increase
et al, 1992; Haggstrom et al, 1994; Pederson et al, 1995). contractility and decrease preload and afterload and 3) ACE
Aldosterone, norepinephrine and ANP concentrations also inhibitors, which also act as arterial and venous dilators to
increase with the severity of heart failure (Knowlen et al, reduce venous congestion, preload and afterload, but more
1983; Ware et al, 1990; Haggstrom et al, 1994). Aldosterone importantly appear to have long-term survival benefits from
concentrations may offer some prognostic information about inhibiting the activity of the renin-angiotensin-aldosterone
the severity of heart failure (Knowlen et al, 1983). (RAA) system. Dehydration, systemic hypotension, renal
Measurement of n-terminal BNP or troponin-I (a calcium insufficiency, electrolyte abnormalities, acid-base disturbances,
regulatory protein that leaks from myocytes in many heart arrhythmias and loss of appetite are all potential complications
diseases) in the serum of dogs or cats shows significant prom- of combined pharmacologic and nutritional therapy for
ise as a means of identifying patients with either clinical or patients with CHF.
subclinical heart disease; however, the optimal application of Hyperthyroidism is a risk factor for hypertrophic cardiomy-
these techniques awaits the availability of a reliable point-of- opathy and secondary hypertension in older cats. Hyper-
care test with proven positive predictive value in a variety of adrenocorticism is a risk factor for pulmonary thromboem-
clinical settings (Prosek et al, 2007; Oyama et al, 2007). bolism. Heartworm infection is a risk factor for pulmonary vas-
Norepinephrine, angiotensin, ANP and AVP analyses are cular disease, cor pulmonale, right-sided CHF and pulmonary
only available through research laboratories. Plasma renin thromboembolism.