Page 128 - Small Animal Internal Medicine, 6th Edition

100 PART I Cardiovascular System Disorders

CHAPTER 5
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Congenital Cardiac

Disease

GENERAL CONSIDERATIONS some patients. Congenital malformations vary widely in type
and severity. The patient’s prognosis and options for therapy
Common congenital cardiac malformations, as well as some depend on the definitive diagnosis and severity. Initial
that occur more sporadically, are described in this chapter. noninvasive testing usually includes thoracic radiographs,
Most congenital heart defects produce an audible murmur a complete echocardiogram (M-mode, two-dimensional
(Fig. 5.1), although some serious malformations do not. [2-D], and color and spectral Doppler), and sometimes an
Murmurs caused by congenital disease range in intensity electrocardiogram (ECG). A packed cell volume (PCV) is
from very loud to very soft depending on the type and indicated in cases of right-to-left shunting to document
severity of the defect and on hemodynamic factors. In addi- erythrocytosis. Cardiac catheterization with selective angio-
tion to murmurs of congenital disease, clinically irrelevant cardiography can be useful to define some structural abnor-
“innocent” murmurs are relatively common in puppies and malities and is used to guide transvascular interventional
kittens. The physiologic cause of these murmurs is incom- procedures. Surgical repair or palliation, balloon valvulo-
pletely understood but may involve mismatch in growth plasty, transcatheter shunt occlusion, or other interventional
rate between the heart and great vessels, relative anemia, or techniques may be helpful for some cases.
high sympathetic tone compared to adult animals. Innocent Patent ductus arteriosus (PDA), pulmonic stenosis (PS),
murmurs are usually soft systolic ejection–type murmurs and subaortic stenosis (SAS) have been identified in different
heard best at the left heart base; their intensity may vary surveys as the most common congenital cardiovascular
with heart rate or body position. Innocent murmurs tend anomalies in the dog. Persistent right aortic arch (a vascular
to get softer and usually disappear by about 4 months of ring anomaly), ventricular septal defect (VSD), malforma-
age. Murmurs caused by congenital disease usually persist tions (dysplasia) of the atrioventricular (AV) valves, atrial
beyond 6 months of age and may get louder with time, septal defect (ASD), and tetralogy of Fallot (T of F) occur
although this is not always the case. Careful examination less frequently but are not rare. The most common con-
and auscultation are important, not only in animals intended genital malformation in cats is VSD; other lesions include
for breeding but also in working dogs and pets. Puppies and AV valve dysplasias, stenotic lesions (SAS and PS), ASD, T
kittens with a soft left basilar systolic murmur and no other of F, and PDA. An AV septal (endocardial cushion) defect
clinical or radiographic signs can be auscultated repeatedly occurs more commonly in cats and consists of all or some of
as they grow to determine whether the murmur disappears. the following: a high VSD, a low ASD, and malformations of
Further diagnostic tests are indicated in puppies or kittens one or both AV valves. Endocardial fibroelastosis, mainly in
with a murmur that is loud (audible on both sides of the Burmese and Siamese cats, also has been reported. Con-
chest), is heard loudest on the right hemithorax, or has a dia- genital malformations are more prevalent in male than
stolic component, or with any murmur that persists beyond female cats. Congenital malformations in both species can
4 to 6 months of age. Additional reasons to pursue diag- occur as isolated defects, which is most often the case, or in
nostic testing early include patients with clinical signs and various combinations.
those for which economic or breeding-potential decisions The prevalence of congenital defects is higher in purebred
are pending. than in mixed-breed animals. In some studies, a polygenic
Congenital heart defects most often involve either a valve inheritance pattern has been suggested, although there is
(or valve region) or an abnormal communication between more recent focus on a single major gene effect influenced
the systemic and pulmonary circulations. Abnormally by other modifying genes. Recognized breed predispositions
formed valves can be insufficient, stenotic, or both. Other are listed in Table 5.1; animals of other breeds can be affected
malformations can exist, and multiple anomalies occur in with any of these defects as well.

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