CARDIOLOGY
Intensity of murmur
Grade 1
Very soft and localized, and is initially inaudible.
Grade 2
Soft, but heard immediately and is localized.
Grade 3
Soft and radiates to more than one location.
Grade 4
Moderate-intensity to loud that radiates,
but has no precordial thrill (a palpable
`buzzing` sensation on the hand)
Grade 5
Loud and accompanied by a precordial
thrill.
Grade 6
Loud with a precordial thrill and is still
audible when the stethoscope is lifted
off the chest wall.
As a rule low grade murmurs (< 2/6) are mild and
probably not haemodynamically important. There
are exceptions to this, notably a ventral septal defect
(VSD) – see below.
Again, as a general rule, an increasing murmur grade
correlates with increasing cardiac pathology.
CAUSES
1. High velocity blood flow
These murmurs have normal valves, with no
cardiac disease and are known as physiological,
functional or flow murmurs. Examples include
exercise, fever, hypotension and hyperthyroidism.
Anaemia also produces increased flow velocity
with audible murmurs (haemic) when the haematocrit is less than 25% in dogs and 20% in cats;
conversely, polcythaemia may mask a murmur.
Young animals often present with low grade (<
3/6) soft systolic ”innocent” flow murmurs that
usually disappear by 6 months of age. Lower
haematocrit and faster heart rates are causes.
They are often intermittent, even during the
course of auscultation.
Bradycardias result in increased stroke volume, as
will an `athletic` heart. These murmurs are usually soft, early systolic and <3/6. Certain breeds,
notably boxers, are often ascribed as having a
normal but relatively narrow aortic outflow tract
which results in increased velocity. These murmurs are often more readily detectable in the thoracic inlet area.
2. Congenital cardiac defects.
Ventricular outflow obstruction (ejection) murmurs are systolic, harsh, and described as having
a crescendo-decrescendo configuration with a
PMI in the heart base area. Causes include pulmonic stenosis, sub-aortic stenosis and bacterial
endocarditis.
• Regurgitant murmurs from abnormal (dysplastic) mitral and tricuspid valves are systolic
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with PMIs over the relative valve area, and described as having a plateau configuration.
Abnormal congenital conduits between c \