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414 Heart Murmurs

PROGNOSIS & OUTCOME Technician Tips disease, can still develop acquired heart disease
When auscultating murmurs in anxious in the future.
VetBooks.ir directly. If the murmur is caused by fever, calm. Because stress increases cardiac output and SUGGESTED READING
patients, it helps to wait until the patient is
Physiologic murmurs do not affect health
this can be a reason for physiologic murmurs, a
anemia, or other systemic illness, prognosis
Belanger MC: Innocent heart murmurs. In Ettinger
decrease in the intensity of the murmur as the
depends on the underlying condition.
patient settles is often noticed with physiologic SJ, et al, editors: Textbook of veterinary internal
medicine, ed 7, St. Louis, 2010, Saunders.
PEARLS & CONSIDERATIONS murmurs. AUTHOR: Ivan Sosa, DVM, DACVIM
Comments Client Education EDITOR: Meg M. Sleeper, VMD, DACVIM
Murmurs that change significantly in character It is important to reiterate to owners that
with changes in heart rate are more likely to patients with physiologic heart murmurs,
be physiologic. although they may be currently free of heart

Heart Murmurs Client Education
Sheet

BASIC INFORMATION RISK FACTORS • Heart murmurs may be noted in patients
• Heart murmurs may occur secondary to with overt signs compatible with heart disease
Definition various noncardiac entities such as fever, (e.g., dyspnea, exercise intolerance, collapse,
Normal blood flow in the circulatory system anemia, hyperthyroidism, extreme thinness signs of thromboembolism). The murmur is
is laminar in nature and very quiet. When or obesity, and pregnancy. a clue that these generalized signs may be
laminar flow through the heart is altered, • Some breeds of dogs and cats are more prone caused by a heart problem and that cardiac
turbulence develops, causing a sound that to physiologic murmurs, especially under diagnostic testing is indicated.
can be heard: a heart murmur. This can be stress circumstances, and diseases of the heart
likened to a slow-flowing, wide river undulat- (myocardium, heart valves, endothelial lining PHYSICAL EXAM FINDINGS
ing quietly back and forth; if suddenly an of the heart) and the great vessels. • Murmurs should be identified during the
obstruction such as a large boulder is placed • Heart murmurs develop with congenital and physical exam process. Using the stethoscope,
in the river, the quiet river becomes a noisy one acquired heart defects. the dog’s or cat’s thorax is thoroughly
as the water flows around the rock, creating • Physiologic murmurs are unusual in adult auscultated using the diaphragm and then
turbulence. dogs; this is a murmur present in the absence using the bell of the instrument. All four
of any cardiac or systemic abnormalities. valve areas—mitral, tricuspid, pulmonic, and
Epidemiology Dynamic right ventricular outflow turbulence aortic regions—are ausculted, listening for
SPECIES, AGE, SEX (dRVOT) has been described in cats and is abnormalities of the heart rate and rhythm,
A heart murmur is a clinical sign that may associated with obstruction to flow in the for alterations in the heart sounds, and most
develop in any animal. Pathologic murmurs ventricle; clinical consequences may develop commonly, for a heart murmur. If a murmur
caused by structural heart lesions generally over time. exists, it must be identified with respect to
increase in intensity with age and disease • Murmurs also may be identified in the timing, intensity, and musical tonality, as
progression. Characteristics of functional or veins and arteries under circumstances that well as where it is heard loudest on the
physiologic heart murmurs (p. 413) in young, cause nonlaminar flow, such as arteriovenous thorax (point of maximal intensity) and if
growing dogs and cats: fistulas or extravascular partial obstructions. the sounds spread to other parts of the thorax
• Soft (grade II/VI or less) • Systemic infection may cause bacterial or into the jugular region of the neck. This
• Systolic endocarditis (p. 294). is radiation of the murmur to another part
• Point of maximal intensity: left hemithorax Clinical Presentation of the thorax. Some stethoscopes are single
or left parasternal region in kittens head only. When gently placed on the thorax,
• Abolished with an increase in heart rate or HISTORY, CHIEF COMPLAINT they intensify the low frequency sounds, and
change in body position • Heart murmurs may be detected during a when pressed more firmly, they bring out
• Usually disappear around 4 months of age routine exam in a patient that is otherwise the entire range of heart sounds.
• Often eliminated by reduction in pressure well. The goal is to identify the cause of the • Murmurs are described by their intensity.
of the stethoscope on the thoracic wall murmur (may be highly suggestive based on Using a grading system with a maximum
signalment, history, and exam findings or of VI, I/VI is the least intense and barely
GENETICS, BREED PREDISPOSITION may require diagnostic testing). heard; II/VI is soft but unmistakably heard;
Many breeds are predisposed to specific • Heart murmurs may be noted in a patient III/VI is easily distinguished; IV/VI is intense
congenital heart malformations that are associ- that is systemically ill (e.g., anemic). Ascer- but without a palpable thrill; V/VI is loud,
ated with heart murmurs (e.g., patent ductus tain whether the murmur can be explained intense, and associated with a precordial
arteriosus [PDA], subaortic stenosis, pulmonic by the systemic illness alone (see Risk Factors vibration (thrill) on the thorax where it is
stenosis, ventricular septal defect, tricuspid above) or an underlying heart problem is auscultated; and VI/VI is so loud that it is
dysplasia) and to adult-onset disorders, some of coexistent (e.g., endocarditis). heard with the stethoscope off the thorax and
which have a heritable basis (e.g., myxomatous • Differentiate murmurs that are present but so intense that a thoracic thrill is present.
mitral valve disease, dilated cardiomyopathy). not causing a problem from those related • The murmur is identified by when it
See specific chapters on the individual diseases to the clinical signs for which the animal is occurs—in systole, diastole, or seamlessly
for lists of at-risk breeds. presented. through both of these physiologic periods

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