Page 210 - Clinical Small Animal Internal Medicine

178 Section 3 Cardiovascular Disease

Stage A identifies patients at high risk for developing (e.g., exercise intolerance, lethargy, coughing, tachypnea)
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VetBooks.ir heart disease but that currently have no identifiable at rest or with minimal activity.
structural disorder of the heart (e.g., every Cavalier
King Charles spaniel without a heart murmur, boxers
without evidence of arrhythmia or myocardial Phase 1 – Initial Insult
Cardiovascular disease is encountered commonly in
dysfunction). daily veterinary practice. Patent ductus arteriosus, sub-
Stage B identifies patients with structural heart disease aortic stenosis, and pulmonic valve stenosis are common
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but that have never developed clinical signs caused by congenital conditions in dogs while ventricular septal
heart failure. This stage is further subdivided. defect and atrioventricular valve dysplasia are more
– Stage B1 refers to asymptomatic patients that have common in cats. Chronic degenerative valvular disease
no radiographic or echocardiographic evidence of (CDVD) and dilated cardiomyopathy (DCM) are the
cardiac remodeling. most common acquired cardiac diseases in dogs while
– Stage B2 refers to asymptomatic patients that have hypertrophic cardiomyopathy (HCM) is the most com-
hemodynamically significant cardiac disease as evi- mon acquired cardiac disease in cats. Although identifi-
denced by radiographic or echocardiographic find- cation of disease at its exact onset is next to impossible,
ings of heart enlargement. it is useful to highlight some of the available data on dis-
Stage C denotes patients with past or current clinical ease prevalence.
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signs of heart failure associated with structural heart Congenital cardiac malformations are uncommon,
disease. with data from several veterinary schools suggesting a
Stage D refers to patients with end‐stage disease with prevalence of 0.46–0.85%. Feline congenital heart dis-
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clinical signs that are refractory to “standard therapy.” ease is even less common with a reported prevalence of
0.2%. Although these data are several decades old, they
The ABCD system is useful because it enables veterinar- still highlight that even at large referral centers, the prev-
ians to educate owners that their animal is at risk for alence of congenital heart disease is low.
developing heart disease even in the absence of an audi- However, identification of acquired cardiovascular dis-
ble murmur, gallop or arrhythmia. This system is also ease is much more common and represents the majority
useful because treatment and subsequent resolution of of dogs and cats that ultimately develop heart failure.
signs attributable to heart failure alters patient classifica- Dilated cardiomyopathy is encountered most often in
tion with the modified NYHA model whereas animals large‐ and giant‐breed dogs with a reported prevalence
that have previously displayed heart failure always of 0.16–1.1%, depending on the study cited and the pop-
remain a Stage C or D with the newer system.
ulation investigated. In some breeds and age groups, the
prevalence of DCM is much higher. For example, a study
of Doberman pinschers in Europe found that only 3.3%
Phases of Heart Failure
of Dobermans 1 to <2 years of age were affected while
Discussion of heart failure can center around three dis- 43.6% aged 6 to <8 years of age were affected. The preva-
tinct phases. Phase 1 constitutes the initial cardiac injury lence of CDVD is also dependent on the breed and age of
and in most veterinary patients, this phase passes silently, the dog, but it also varies based on the method of disease
without detectable clinical signs, because the disease is detection (e.g., auscultation, echocardiography, nec-
mild and slowly progressive (e.g., valvular disease, feline ropsy). While these variables cloud clear documentation
cardiomyopathies). However, some conditions (e.g., of disease prevalence, there is little debate that CDVD is
development of cardiac tamponade subsequent to bleed- the most common acquired cardiac condition in dogs
ing of right atrial hemangiosarcoma or pulmonary throm- and represents the most common etiology for develop-
boembolism) can produce severe life‐threatening signs ment of heart failure. Hypertrophic cardiomyopathy is
commensurate with the initial cardiac injury. Phase 2 is the most common myocardial disease in cats although
the stage wherein short‐term and ultimately long‐term various other forms of cardiomyopathy (CM), including
compensatory mechanisms are activated for stabilization restrictive CM, arrhythmogenic right ventricular CM,
of cardiac output and normalization of afterload. dilated CM, and unclassified CM, may also contribute to
Unfortunately, cardiac disease is often progressive and heart failure.
the heart’s ability to hypertrophy may ultimately be Primary cardiomyopathies are a diagnosis of exclusion
overwhelmed. A heart murmur, gallop rhythm, cardiac and true disease confirmation would require necropsy.
arrhythmia, or cardiomegaly is more likely to be identi- Because of this limitation, echocardiography is most
fied in this second phase despite the absence of signifi- often considered the gold standard for diagnosis of CM in
cant or activity‐limiting clinical signs. The hallmarks of cats. A study in an apparently healthy, nonreferred popu-
phase 3 of heart failure are the emergence of clinical signs lation of 103 cats found echocardiographic alterations