Page 39 - Small Animal Internal Medicine, 6th Edition

CHAPTER 1 Clinical Manifestations of Cardiac Disease 11

abnormalities (and also are called physiologic murmurs). can be almost 30%, the presence of a murmur alone is not a
Physiologic murmurs have been associated with anemia, highly sensitive predictor of cardiomyopathy. This is espe-
VetBooks.ir fever, high sympathetic tone, hyperthyroidism, marked cially true in young cats. The PMI of most feline murmurs
is near the sternal border. Many of these murmurs are associ-
bradycardia, peripheral arteriovenous fistulae, hypopro-
teinemia, and athletic hearts. Aortic dilation (for example,
tion. Congenital cardiac malformations are another potential
from hypertension) and dynamic RV outflow obstruction ated with dynamic left (or right) ventricular outflow obstruc-
are other conditions associated with systolic murmurs in cause of murmurs in cats. NT-proBNP measurement can
cats. Innocent puppy murmurs also are nonpathologic help with screening for structural disease in cats. However,
and generally disappear by the time the animal is about an echocardiogram performed by a veterinary cardiologist
6 months old. or other person with advanced echocardiography training is
The murmur of mitral insufficiency (regurgitation) most the most sensitive tool for detecting structural disease in cats
often is heard best at the left apex, in the area of the mitral with a murmur.
valve. It radiates well dorsally and often to the left base and Diastolic murmurs
right chest wall. Mitral insufficiency characteristically causes Diastolic murmurs are uncommon in dogs and cats. They
a plateau-shaped murmur (holosystolic timing), but in its are always pathologic. Aortic valve insufficiency from infec-
early stages the murmur may be protosystolic, tapering to tive endocarditis is the most common cause, although con-
a decrescendo configuration. Occasionally this murmur has genital malformation or degenerative aortic valve disease
a musical or “whoop-like” quality. With degenerative mitral occasionally occurs. Clinically relevant pulmonic valve
valve disease, murmur intensity usually relates to disease insufficiency is rare, but an audible pulmonic insufficiency
severity. murmur would be more likely in the face of pulmonary
Systolic ejection murmurs most often are heard at the left hypertension. These diastolic murmurs begin at the time of
base. Ventricular outflow obstruction, usually from a fixed S 2 and are heard best at the left base. They are decrescendo
narrowing (e.g., subaortic or pulmonic valve stenosis) or in configuration and extend a variable time into diastole,
dynamic muscular obstruction, is the typical cause. Ejection depending on the pressure difference between the associated
murmurs become louder as cardiac output or contractile great vessel and ventricle. Some aortic insufficiency murmurs
strength increases. The subaortic stenosis murmur is heard have a musical quality.
well at the low left base and also at the right base, because Continuous murmurs
the murmur radiates up the aortic arch, which curves As implied by the name, continuous (“machinery”)
toward the right. This murmur also radiates up the carotid murmurs occur throughout the cardiac cycle. They indicate
arteries and, when loud, occasionally can be heard on the that a substantial pressure gradient exists continuously
calvarium. Soft (grade 1-2/6), nonpathologic (functional) between two connecting vessels. The murmur is not inter-
systolic ejection murmurs are common in sighthounds, rupted at the time of S 2 ; rather, its intensity often is greater
Boxers, and certain other large breeds; these can be related at that time. The murmur becomes softer toward the end of
to a large stroke volume, as well as breed-related left ven- diastole, and at slow heart rates it may even become inau-
tricular (LV) outflow tract characteristics. The murmur of dible by mid- or late-diastole. Patent ductus arteriosus (PDA)
pulmonic stenosis is best heard at the cranial left base. Rela- is by far the most common cause of a continuous murmur.
tive pulmonic stenosis occurs when flow volume through a The PDA murmur is loudest high at the left base, dorsal to
structurally normal valve is abnormally increased (as with the pulmonic valve area; it tends to radiate cranially, ven-
a large left-to-right shunting atrial or ventricular septal trally, and to the right. The systolic component usually is
defect). louder and heard well all over the chest. The diastolic com-
Most murmurs heard on the right chest wall are holosys- ponent often is more localized to the left base. The diastolic
tolic, plateau-shaped murmurs, except for the subaortic ste- component (and the correct diagnosis) may be missed if only
nosis murmur (discussed earlier). The tricuspid insufficiency the cardiac apical area is auscultated.
murmur is loudest at the right apex over the tricuspid valve. Continuous murmurs can be confused with concurrent
Its pitch or quality may be noticeably different from a con- systolic ejection and diastolic decrescendo murmurs (the
current mitral insufficiency murmur. Moderate to severe so-called to-and-fro murmur). However, with to-and-fro
tricuspid insufficiency often is accompanied by jugular pul- murmurs, the ejection (systolic) component tapers in late
sations. Ventricular septal defects also cause holosystolic systole, and the S 2 usually can be heard as a distinct sound.
murmurs. The PMI usually is at the right sternal border, The most common cause of a to-and-fro murmur is the
reflecting the direction of the intracardiac shunt. A large combination of subaortic stenosis and aortic valve insuffi-
ventricular septal defect can also cause the murmur of rela- ciency (usually as a result of aortic valve endocarditis).
tive pulmonic stenosis. Rarely, stenosis and insufficiency of the pulmonic valve cause
In the general population of apparently healthy cats, the this type of murmur. Likewise, both a holosystolic and a
prevalence of systolic murmurs is estimated at up to 40%, diastolic decrescendo murmur can occur together occasion-
and is even higher in older cats. Although a systolic murmur ally (such as with a ventricular septal defect and aortic insuf-
can accompany subclinical structural cardiac disease, espe- ficiency from loss of aortic root support); this also is not
cially in older cats where the prevalence of cardiomyopathy considered a true continuous murmur.