CARDIOLOGY
murmur is loudest along the right sternal border (fig.
2). A very large shunt volume will result in a functional flow murmur across the pulmonic valve and
a left heart base ejection murmur. Unlike other murmurs, a small defect results in higher velocities into
the right ventricle producing more intense (louder)
murmurs. Conversely very large defects may produce a barely audible sound.
4. Mitral and tricuspid valve dysplasia
They are most common in the larger dog breeds,
and are not uncommon in cats. Auscultatory findings are similar to endocardiosis (see below) with
PMIs over the affected valve area (figs. 2,3).
5. Patent ductus arteriosus (PDA)
Female dogs are about 3 times more frequently affected. Smaller breeds (eg poodles, collies, pomeranians, and Maltese) are more predisposed. It is occasionally encountered in cats.
CATS
Cats frequently present with murmurs. It is sometimes stated that 30% of all cats presented to clinics
will have a detectable murmur. In a recent investigation of 57 apparently healthy cats with murmurs, cardiac pathology was found in over 80%. (Dirven 2010)
Atrioventricular valve dysplasia, aortic stenosis, and
VSD are common congenital defects encountered.
Unlike dogs, the PMI of many murmurs is along the
right and left sternal area due to the sternum acting as
an acoustic enhancer
Cats frequently present with an ejection murmur that
is `dynamic` in nature i.e. it increases with the heart
rate and is due to certain forms of hypertrophic cardiomyopathy (HCM) called hypertrophic obstructive
cardiomyopathy (HOCM) and also systolic anterior
motion (SAM) of the mitral septal leaflet that leads to
both aortic outflow stenosis and mitral valve regurgitation (fig. 5).
The murmur is loudest high in the left heart base (fig.
2), and is easily overlooked if the stethoscope is not
correctly placed. A palpable thrill is often detected.
The murmur is described as `continuous/machinery`, but will wax and wane with its peak at the end
of systole and early diastole. It frequently radiates
widely over the left and right heart base areas. In
cats the PMI is typically more caudoventral, and the
diastolic component is often more difficult to detect.
ACQUIRED CARDIAC LESIONS
1. Mitral and tricuspid regurgitation
Myxomatous degeneration of the mitral valve (endocardiosis) accounts for most murmurs encountered
in middle-age and older small breed dogs. Approximately 30% will have accompanying tricuspid valve
involvement. It is unusual for the tricuspid valve to
be solely affected. Occasionally a loud (4/6) murmur
with a high frequency is heard and is described as
having a whooping, musical or seagull character;
this murmur can be alarming but usually represents a
small orifice with a high velocity regurgitant jet and a
minimal volume overload response; high frequency
vibrations of the chordae tendinae are involved in the
generation of this murmur. Dogs with dilated cardiomyopathy will often present with a soft low-grade
murmur over the mitral valve area due to stretching
and distortion of the valve annulus.
2. Endocarditis
Infectious endocarditis is recognised in both dogs
and cats, mostly involving the aortic valve, mitral
valve or both, with large breed male dogs more affected. A high index of suspicion is required for diagnoses, the murmur will be recent and often changes
in character and even position over a short period
of time. PMIs will be over the affected valve(s). Predisposing factors include pre-existing endocardiosis
and congenital defects including SAS and MD.
Fig 5. Echocardiographic image of a feline heart, from right parasternal long-axis. Colour Doppler shows turbulent flows into
aorta and left atrium due to SAM.
These dynamic murmurs do require an index of suspicion necessitating a protracted period of auscultation
waiting for the cat to relax upon which the murmur
may disappear completely, it is then confirmed by
gentle stimulation/stress such as shaking H