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Proceeding of the NAVC
North American Veterinary Conference
Jan. 8-12, 2005, Orlando, Florida
Reprinted in the IVIS website with the permission of the NAVC
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Published in IVIS with the permission of the NAVC
Small Animal - Cardiology
HOW WORRIED SHOULD I BE ABOUT THIS
HEART MURMUR?
Rebecca L. Stepien DVM, MS, DACVIM
School of Veterinary Medicine
University of Wisconsin, Madison, WI
Heart murmurs are common findings in routine veterinary
physical examinations, but it may be difficult to discern the
underlying cause and severity of the heart disease
responsible for the murmur by auscultation alone. Common
questions owners may ask include:
1. Why does my pet have a heart murmur?
2. How will the murmur affect his/her life?
3. What diagnostic tests are necessary and why?
4. Does he/she need medication/lifestyle changes?
WHY DOES MY PET HAVE A HEART MURMUR?
The importance of age and breed cannot be overstated
when formulating a differential diagnosis list for causes of
cardiac murmurs. With rare exception, cats or dogs with
audible heart murmurs prior to 3 years of age are affected by
congenital heart disease (CHD); the specific abnormality can
often be suspected based on the characteristics (timing, point
of maximal intensity [PMI]) of the murmur. The most
common congenital heart murmur timings/PMI and their
differential diagnoses are listed in Table 1.
The auscultatory characteristics of the murmur are used to
develop a differential diagnosis list. In dogs, many congenital
diseases have specific breed predilections; knowledge of
these breed-associated abnormalities can narrow the
differential list. Although most CHD show some breed
predilection1, it is important to remember that some
abnormalities occur frequently in many breeds (e.g. PDA),
and that any animal can have any abnormality, regardless of
the breed. Cats show less breed predilection for specific
CHD, but mitral valve dysplasia and ventricular septal defects
are the most common abnormalities in all cats.
Discovery of a “new” murmur in an older animal usually
occurs as the animal develops degenerative valvular disease
(primarily dogs) or myocardial disease (cats, dogs). Other
causes of acquired murmurs include vegetative endocarditis,
anemia, and systemic hypertension (Table 2). In cases of
endocarditis or anemia, systemic derangements are often
evident on physical examination. A high index of suspicion
must be maintained to diagnose systemic hypertension in
many patients as this disease is often clinically ambiguous
(see diagnostic work-up, below). A special case of an
acquired murmur is the systolic murmur frequently heard in
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thin, athletic dogs (PMI: left base). Many athletic dogs
belong to breeds that have been associated with aortic or
subaortic stenosis and differentiation of an “athletic” murmur
and a murmur of CHD can be problematic.
This
differentiation frequently requires use of Dopplerechocardiographic studies. In cases involving breeding
animals, consider referral to a cardiologist experienced in
diagnosis of congenital heart disease.
Note: “New” murmurs may represent previously
undiagnosed congenital disease; this situation may occur in
patients new to your practice or very active or uncooperative
animals that are difficult to auscult with confidence. In
addition, some congenital murmurs increase in intensity as
the animal grows, and the murmurs may not attain their full
intensity until the animal is an adult.
HOW WILL THE MURMUR AFFECT HIS/HER LIFE?
Congenital Murmurs
Reliable indicators of moderate to severe congenital
malformations include lethargy (may be interpreted as a
“quiet” animal), poor growth (as compared to littermates) or
cyanosis or signs of congestive heart failure accompanying a
consistent murmur. More problematic are the outwardly
“normal” pediatric patients with easily audible murmurs. In
these animals, differentiation of an innocent murmur from a
significant murmur may be based on several criteria (Table
3).
Acquired Murmurs
Acquired murmurs in dogs that are thought to be due to
endocardiosis and are not associated with noticeable clinical
or physical examination abnormalities may not affect the
animal’s lifestyle a great deal at the time of diagnosis.
Endocardiosis is a slowly progressive disease, however, and
congestive heart failure is a likely outcome over the months
to years following first auscultation of the murmur.
Myocardial diseases tend to progress faster than valvular
disease, and most animals with DCM are not diagnosed
before the onset of clinical signs. Acquired heart murmurs in
cats may be identified early in the course of cardiomyopathic
disease (esp. HCM) and may not be associated with clinical
signs for several years. In other cases, a murmur is detected
when the animal is examined for a clinical sign of heart
disease (e.g. lethargy, congestive signs or signs of
thromboembolic disease) or of the underlying condition
responsible for 2o heart diseases (e.g. hypertension,
thyrotoxicosis). In some cases, the owners may not be
aware of the cat’s clinical abnormalities (e.g. lethargy) until
improvement occurs in response to appropriate medications.
Table 1: Murmur characteristics of common congenital heart diseases
Systolic Murmur
Left apex: MD
Left base: [S]AS, PS, ASD, VSD*
Right apex: TD, PS*
Right base/right sternal border: VSD, [S]AS*
Systolic/Diastolic Murmur
Left apex: bi-directional VSD
Left base: [S]AS/AI, PS/PI
Continuous Murmur#
Left base: PDA
#
other systolic/diastolic murmurs may sound continuous and be heard over left or right heart structures
*murmur listed is the secondary murmur, differential diagnosis applies if other appropriate murmurs are present
[S]AS: [sub]aortic stenosis, AI: aortic insufficiency, ASD: atrial septal defect, MD: mitral dysplasia, PDA: patent ductus
arteriosus, PS: pulmonic stenosis, PI: pulmonic insufficiency, TD: tricuspid dysplasia, VSD: ventricular septal defect
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Table 2: Differential diagnosis of acquired heart disease based on murmur characteristics
SYSTOLIC MURMUR
Left apex: mitral insufficiency
• mitral endocardiosis, mitral endocarditis (look for systemic
signs)
• myocardial disease with 2o mitral involvement
• Dogs: dilated cardiomyopathy
• Cats: cardiomyopathies
• idiopathic HCM, RCM or DCM
• secondary to systemic conditions
• hypertrophic: hyperthyroidism, hypertension, growth
hormone excess
• dilated myocardial disease (rare): taurine deficiency
• myocardial infiltration (usually neoplastic) in either species
SYSTOLIC/DIASTOLIC MURMUR
Left base:
•
aortic valve endocarditis
(with insufficiency)
•
pulmonic valve endocarditis
(with insufficiency)
Right apex: tricuspid insufficiency
•
tricuspid endocardiosis, tricuspid endocarditis (look for
systemic signs)
• myocardial disease/ 2o tricuspid involvement
• as above for dogs
• rare murmur in cats
Left base: “flow murmurs” e.g. anemia, “athletic” murmurs
Table 3: Characteristics of innocent murmurs and murmurs associated with congenital heart disease
Innocent Murmur
Grade usually < III/VI
Characteristics change with position of animal and heart rate
Systolic only
PMI: usually left base
Decreased intensity with age up to 16 wks of age
Inaudible after ~16 wks of age
WHAT DIAGNOSTIC TESTS ARE NECESSARY, AND
WHAT INFORMATION WILL WE GAIN BY SPENDING THE
MONEY?
Congenital Murmurs
A complete cardiac assessment including radiographs,
electrocardiography
and
Doppler-echocardiographic
examination is recommended for animals suspected of
having CHD. In some cases, the work-up will confirm the
mild nature of the abnormality, and the owner can be
informed of the relatively minor risk of development of serious
complications. Confident identification and diagnosis of
apparently mild congenital abnormalities is especially
important in animals under consideration for breeding
programs. In animals with more severe CHD, a complete
diagnostic work-up allows accurate prognostication of
survival and complications, based on clinical experience with
animals with similar disease severity. The high expectations
of many owners of potential breeding animals makes clear
understanding of the known prevalence, suspected
inheritance pattern and typical clinical course of CHD
important, and cardiologic referral should be considered
when a clinician experienced in CHD is not available in the
primary practice.
Possible Congenital Heart Disease
Grade >/= III/VI
Similar characteristics in all positions and
heart rates
Any timing possible
PMI: any possible
Same or increasing intensity up to and
beyond 16 wks of age
Persists after ~ 16 wks of age
Acquired Murmurs
The purpose of the diagnostic work-up in animals with
acquired heart disease is to diagnose the disease, judge the
severity of cardiac dysfunction and evaluate the animal for
signs of heart failure or complications of disease. A thorough
physical examination delineates cardiovascular signs, may
help to rule out systemic disease and is followed by more
focused diagnostic testing of the heart and cardiovascular
systems:
1. Baseline renal function and electrolyte balance should be
established in all animals that will be receiving cardiacrelated medication
2. Thoracic radiographs: Aid diagnosis of disease (“changes
compatible with...”) and establish diagnosis of congestive
heart failure
3. Electrocardiography:
Aid diagnosis of disease and
establish complications (e.g. conduction abnormalities,
dysrhythmias)
4. Echocardiography: recommended in all cases to delineate
disease, but required in canine cases if DCM is suspected
in atypical breed or signs are confusing in a “typical”
breed, and in all cats when definitive diagnosis is
required, since forms of myocardial disease cannot be
reliably differentiated based on ancillary testing. In both
species, echocardiography is required if presenting signs
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Small Animal - Cardiology
are confusing or complications (e.g. dysrhythmias)
develop, if the animal does not respond as expected to
therapy, or previous response is not sustained or when
more than one cardiac abnormality is suspected (e.g.
mitral endocardiosis with myocardial failure).
5. Resting serum T4 measurement is recommended in cats
with heart murmurs who are >6 years old or have a
palpable cervical nodule or compatible clinical signs, but
T4 levels may be abnormal even if cat not showing
“typical” thyrotoxic signs.
6. Resting blood pressure and retinal examination is
recommended for all cats with acquired heart murmurs,
but is especially important if renal dysfunction (but not
necessarily failure) is present, or if retinal detachment is
suspected.
DOES HE/SHE NEED MEDICATION/LIFESTYLE
CHANGES?
Congenital Murmurs
Animals with CHD that have signs of congestive failure
require palliative or curative procedures or aggressive
medical therapy to maintain reasonable quality of life.
Therapy of asymptomatic animals is more controversial.
Animals with known hypertrophic diseases (e.g. [S]AS, PS)
may be treated with therapies to slow heart rate or increase
diastolic function (e.g. beta-blockers or calcium channel
blockers). To date, little published information is available
regarding the risk/benefits of long-term therapy with these
drugs in asymptomatic animals with normal sinus rhythm. In
many cases of CHD, no therapy is used unless the animal
has clinical signs of inadequate cardiac function or
dysrhythmias are present.
Acquired Murmurs
There is little argument that animals with signs of low
output or congestive heart failure require specific cardiac
therapy. More controversial is the therapy of asymptomatic
(or perhaps “pre-symptomatic”) animals. It is generally
accepted (although proof of long-term benefit in
asymptomatic animals is lacking) that use of calcium channel
blockers to promote diastolic function in cats with
asymptomatic HCM is reasonable2. Whether similar or other
theoretic benefits could be obtained with beta-blocker therapy
is unknown3, and ultimately, client dedication and compliance
may be the deciding factor in treating any cat without easily
discernible clinical signs. Many people would agree that
dogs with known DCM but no clinical signs may benefit from
early therapy with ACE inhibitors with or without digoxin, but
no proof of such benefit in dogs has been published.
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In the case of asymptomatic mitral or tricuspid
insufficiency, some evidence suggests that early activation of
the renin-angiotensin-aldosterone system (RAAS) may be a
desirable intervention point for pre-symptomatic disease, but
some research has shown that intervention itself (with
diuretics or non-ACE inhibitor vasodilators) may lead to
activation of the RAAS4. It is still unclear which arm of the
neuroendocrine response to cardiac disease or what
imbalance in the response is the most likely cause of
development of signs,5 thus therapy of nonsymptomatic
endocardiosis cases remains controversial.
REFERENCES
1. Buchanan JW.
Causes and prevalence of
cardiovascular disease. In: Kirk’s Current Veterinary
Therapy XI: Small Animal Practice. Kirk RW, Bonagura
JD (eds). Philadelphia: W.B. Saunders Company.
1992, pp.647-655.
2. Bright J, Golden AL, Gompf RE, Walker MA, Toal RL.
Evaluation of the calcium channel-blocking agents
diltiazem and verapamil for treatment of feline
hypertrophic cardiomyopathy. J Vet Int Med 1991;5:272282.
3. Fox PR. Evidence for or against efficacy of betablockers and aspirin for management of feline
cardiomyopathies. Vet Clin N America: Small An Prac
1991;21(5):1011-1022.
4. Haggstom J, Hansson K, Karlberg BE, Kvart C, Madej A,
Olsson K. Effects of long-term treatment with enalapril of
hydralazine on the renin-angiotensin-aldosterone system
and fluid balance in dogs with naturally acquired mitral
valve regurgitation. Am J Vet Res 1996;57(11):16451652.
5. Haggstom J, Hansson K, Kvart C, Karlberg BE,
Vuolteenaho O, Olsson K. Effects of naturally acquired
decompensated mitral valve regurgitation on the reninangiotensin-aldosterone system and atrial natriuretic
peptide concentration in dogs.
Am J Vet Res
1997;58(1)77-82.
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