Page 214 - Small Animal Internal Medicine, 6th Edition

186 PART I Cardiovascular System Disorders

Mesothelioma occurs sporadically but may be more prev- into the lumen of a cardiac chamber or great vessel can
alent in some geographic regions. There appears to be no physically obstruct blood inflow or outflow and lead to low
VetBooks.ir gender or breed predisposition in dogs, although in Golden cardiac output signs. Myocardial tumor infiltration or sec-
ondary ischemia can disrupt the cardiac rhythm and impair
Retrievers with mesothelioma, chronic inflammation associ-
ated with prior idiopathic pericardial disease is a postulated
one or a combination of these disturbances. If the tumor is
predisposing factor. Mesothelioma is rare in cats. This neo- contractility. Ultimately, the patient’s clinical signs relate to
plasm can appear in variable forms and can be difficult to small or has not yet markedly impaired cardiac function,
identify echocardiographically. Other primary tumors clinical signs may be absent.
involving the heart are rare in dogs but include myxoma,
various types of sarcoma, and other neoplasms. Most cases Clinical Features
involve right-heart structures. Metastatic or systemic tumors, Dogs with cardiac tumors tend to be middle-aged and older.
especially lymphoma, but also other sarcomas (including More than 85% of affected dogs are between 7 and 15 years
HSA), malignant histiocytosis, and various carcinomas, may of age; however, very old dogs (>15 years) have a surprisingly
involve the heart or pericardium as well. Most breeds affected low prevalence. Reproductive status influences the relative
with malignant histiocytosis are Golden Retrievers, Labra- risk for cardiac tumors in dogs, despite a similar frequency
dor Retrievers, Rottweilers, or Greyhounds; mild pericardial of occurrence in males and females overall. Gonadectomized
effusion, without overt signs of cardiac tamponade, coexists dogs have a greater relative risk, especially spayed females,
with pleural and abdominal effusion. Rarely, nonneoplastic which have a risk that is four to five times greater compared
mass lesions can affect the heart or pericardium, including with that of intact females. Intact and neutered males also
fungal granuloma or pyogranuloma (as with coccidioidomy- have greater risk than intact females. Certain breeds of dog
cosis or blastomycosis), other granulomatous or cystic have a higher prevalence of cardiac tumor compared with
inflammatory lesions, and auricular aneurysm. the general population (Table 9.1). The age distribution of
Lymphoma is the most common cardiac tumor in cats. cats with cardiac tumors is different from that of dogs; about
Various (mostly metastatic) carcinomas occur less frequently. 28% are 7 years old or younger. It is unknown whether repro-
HSA is rare; other tumors (such as aortic body tumor, fibro- ductive status affects relative risk for cardiac tumors in cats.
sarcoma, rhabdomyosarcoma) also have been reported spo- Signs of right-sided CHF result from cardiac tamponade
radically in cats. or from blood flow obstruction within the RA or RV. Syncope,
Cardiac tumors can cause several pathophysiologic weakness associated with exertion, and other low output
abnormalities, depending on their location and size. Many signs also result from cardiac tamponade, blood flow obstruc-
tumors impede cardiac filling by causing pericardial effusion tion, arrhythmias, or impaired myocardial function second-
and cardiac tamponade (discussed earlier). An intrapericar- ary to cardiac tumors. Tachyarrhythmias of any type can also
dial mass can itself externally compress the heart, as well as occur; intracardiac conduction disturbances sometimes
cause pericardial effusion. Alternatively, a tumor that grows result from tumor infiltration. Lethargy or collapse might

TABLE 9.1

Dog Breeds with High Prevalence of Cardiac Tumors
BREED # WITH TUMOR # IN DATABASE RELATIVE RISK 95% CI

Saluki 6 401 7.75 3.92-15.38
French Bulldog 3 215 7.19 2.72-19.23
Irish Water Spaniel 2 168 6.13 1.81-20.83
Flat-Coated Retriever 4 534 3.85 1.54-9.62
Golden Retriever 215 32,940 3.73 3.26-4.27
Boxer 52 8496 3.22 2.47-4.18
Afghan Hound 12 2080 2.97 1.72-5.10
English Setter 21 3796 2.86 1.89-4.31
Scottish Terrier 16 3290 2.50 1.55-4.03
Boston Terrier 25 5225 2.47 1.68-3.62
Bulldog 24 5580 2.22 1.49-3.29
German Shepherd 129 37,872 1.81 1.52-2.17

CI, Confidence interval.
Modified from WA, Hopper DL: Cardiac tumors in dogs: 1982-1995, J Vet Intern Med 13:95, 1999.