Page 17 - Feline Cardiology

Chapter 1: Heart Murmurs and Gallop Heart Sounds 7

Box 1.2. Websites with libraries of digital heart and respira- Box 1.3. Grading of murmurs (6 grade scale)
tory sounds
Grade 1: a very soft, localized murmur detected only in a
Veterinary quiet room after intense listening
http://cal.vet.upenn.edu/projects/newsmcardiac/default.htm Grade 2: a soft murmur, heard immediately, localized to a
http://www.vetgo.com/cardio/index.php single area Clinical Entities
Grade 3: a moderate-intensity murmur that is evident at
Human
more than one location
http://depts.washington.edu/physdx/heart/demo.html Grade 4: a moderate-intensity to loud murmur that radiates
http://www.dundee.ac.uk/medther/Cardiology/hsmur.html
well, but a consistent precordial thrill is not present
http://www.med.umich.edu/lrc/coursepages/M1/anatomy/ Grade 5: a loud murmur accompanied by a palpable
html/surface/thorax/hsounds.html
precordial thrill
http://www.blaufuss.org/ Grade 6: a loud murmur with a precordial thrill, audible
http://www.bioscience.org/atlases/heart/sound/sound.htm
when the stethoscope is removed from the thorax
http://www.med.ucla.edu/wilkes/intro.html
http://www.medstudents.com.br/cardio/heartsounds/
heartsou.htm vessel with rapid flow, or when blood viscosity is
http://www.csulb.edu/org/college/bme/respiratory_sounds/ decreased (with anemia), there is a tendency toward tur-
medic.htm bulence. Rapid changes in vessel diameter such as occurs
http://www.cvmbs.colostate.edu/clinsci/callan/breath_ with stenotic lesions may also lead to turbulent flow.
sounds.htm
http://www.rale.ca/ Classification of Heart Murmurs
Murmurs are classified in several ways:
Timing in the cardiac cycle (systolic, diastolic, continu-
murmur along the right or left parasternum (Rishniw
and Thomas 2002; Allen 2010). There are several good ous). While most common cardiovascular diseases in the
websites, which include libraries of normal and abnor- cat result in systolic murmurs, occasionally feline patients
mal heart and respiratory sounds, that are excellent for will present with diseases such as mitral stenosis (which
educational purposes. See Box 1.2 for a list of these sites. results in a diastolic murmur) or patent ductus arteriosus
(which results in a continuous cardiac murmur).
Intensity is the loudness of the murmur most often
HEART MURMURS
graded using a 6-tier scale. See Box 1.3 for definitions in
Cardiac murmurs are most often caused by the vibra- this classification scheme. The intensity of the murmur
tions associated with high-velocity, disturbed, and tur- does not necessarily correlate with the severity of the
bulent blood flow. Such disturbances may be caused by underlying heart disease, as some well tolerated abnormali-
valvular insufficiency (regurgitation), valvular stenosis, ties (such as restrictive/resistive ventricular septal defects)
or the presence of a shunt. Disturbed flow that is low produce very loud murmurs, while some severe lesions may
velocity, such as pulmonic valve regurgitation/ produce soft murmurs (i.e., large unrestrictive/unresistive
insufficiency, may not be auscultable. Low-velocity ventricular septal defect or severe tricuspid regurgitation).
abnormal flow often is of no consequence (e.g., pul- Point of maximal intensity is the area at which the
monic valve regurgitation) but in some instances may murmur is loudest, and it generally relates closely to the
exist with a severe cardiac lesion (e.g., low-velocity flow underlying source of turbulent flow. For example, a left-
through a large atrial septal defect). Murmurs can also to-right patent ductus arteriosus murmur is usually
be created by other physiologic or pathological processes. heard loudest over the left heart base at the pulmonary
For example, murmurs are often heard with changes in artery, because high-velocity flow from the aorta is
the viscosity of blood (anemia), and high-output dis- shunting through the duct into the pulmonary artery at
eases such as hyperthyroidism can be associated with the this location.
development of murmurs due to increased velocity of Radiation of a murmur refers to how widely the
ejected blood. The Reynolds number is used for predict- murmur can be heard from the point of maximal inten-
ing whether a flow pattern is likely to be laminar or sity. Generally, the wider the radiation of the murmur,
turbulent. Typically it is defined as v s L/v, where v s is the the greater the amount of turbulence being generated.
−1
mean fluid velocity in ms , L is the characteristic length Pitch and quality are subjective descriptions of the
of the blood vessel in meters, and v is the kinematic fluid character of a murmur (i.e., coarse, musical, etc.). These
2
viscosity in m /s. Simplified, the relationship is inertial descriptors are not precise and do not have the same
forces/viscous forces. Therefore, in a large-diameter objectivity as timing and point of maximal intensity.