Canine heart disease can be either
congenital, hereditary or acquired in much
the same way as it can be in humans.
Research has shown that some forms of heart disease is
much more prevalent in some breeds than in others.
For example, Persistent Right Aortic Arch (PRRA) is
twelve times more common in German Shepherd Dogs than it is in all other breeds
combined and Sub Aortic Stenosis (SAS) is well documented in
both the GSD and the Rottweiler. Cardiovascular disease in
older dogs is commonly found on post mortem
examination although most of these animals may never have shown symptoms of it in
their life time. Some of the most common forms of
the disease found in dogs is arterio sclerosis (hardening of the arteries) and
atheroma (fatty deposits laid down in the vessels of the circulatory
system) and valvular disease. In the case of valvular
disease, the Mitral valve between the left atria and ventricle) and the Aortic
valve (at the exit to the left ventricle) are the
valves most commonly affected and of greatest importance. A healthy and balanced
diet throughout the lifetime of the dog, combined with
exercise will positively contribute towards minimising the
risk of developing these forms of the disease in
older life as indeed, can informed selective breeding. Accurate and honest
recording of conditions and causes of death through systems such as Breed Data
Base Records, can be invaluable to the breeder of
pedigree animals when they are deciding upon which animals are
suitable to use in selective breeding programs
This article is written as an educational resource article
and is designed to give a broad overview of some of
the diverse and complex conditions which affect our
canine friends.
Basic Anatomy and functions of the Heart.
The heart is the body's major organ situated
in the chest cavity and upon which
all other body functions are dependant for the supply of oxygen to the
tissues which is essential to sustain life.
It is an integral part of a basic 'plumbing system' which,
once it's operational mechanism is understood, a
clearer insight can be gained into the problems that arise when the heart itself
malfunctions.
The heart, in simple terms, is a 4 chamber double pump
supplying both the systemic and pulmonary
circulation . The pressure within these chambers is
finely balanced in such a way that, in health, the out put and return of blood
to the chambers causes no congestion in either of
the 2 systems. One major
circulatory vessel enters or leaves each chamber. The flow
of blood throughout the heart is controlled by
means of a one way valve system. In a correctly
functioning organ, blood enters the Right Atria (the upper right chamber of
the heart) deprived of oxygen. From there, it is pumped to the Right Ventricle
(the lower right chamber) where upon it is pumped
to the lungs by way of the Pulmonary Artery. As it
travels, it collects oxygen essential for the function of all tissues. Blood
returns via the Pulmonary Vein to the Left Atria (the upper left
chamber of the heart) from where it is pumped passed the
mitral valve to the
Left Ventricle (the lower left chamber) in preparation for
distribution around the body. While the function of
the upper chambers of the heart are important, the
function of the lower chambers are more important with the function of the
left lower chamber outweighing the importance of the function of the lower right.
A mal function in any one chamber will in turn have
a knock-on effect on the other chambers to a
greater or lesser degree depending upon where and why.
Structurally, the heart consists of 3 layers - an inner
layer known as the endocardium, an outer layer
known as the pericardium, and a muscle layer or
myocardium. Any or all of these parts may be involved in heart disease, but it
is the effect that such disease has upon the myocardium which is of the utmost
importance. The muscle layer is the structure which
performs all the physical work necessary to
maintain the circulation of blood and therefore all
disease/defects must be regarded from the point of view of their effect upon
the myocardium.
All cardiac disease at some stage may present themselves
as disorders of the hearts rhythm, likewise, they
may ultimately terminate in chronic heart failure and death. It should be noted
that most forms of heart disease may be present for
many years before any evidence of failure develops.
Types of Structural Defects.
In normal foetal heart development, a direct
connection exists between the Aorta
(the major vessel leaving the heart) and the Pulmonary Artery (the major
vessel leading from the heart to the lungs). Prior to
birth, the oxygen supply to the tissues is provided
by the mother via the placenta, so there is no
requirement for the lungs to function. The connection which exists effectively
'cuts out' part of the circulatory system. At birth, the
lungs inflate and the connection disconnects thus completing the system and
allowing blood flow to the lungs for it's supply of
oxygen. In some cases this connection fails to
'disconnect' at birth this condition is known as Patent (Persistent) Ductus
Arteriosis (PDA) This condition has been identified in the
German Shepherd Dog although it is more common in other breeds such as Poodles
and Collies
and such gross congenital deformities are responsible for
many sudden deaths in pups within the first days of
life.
A similar connection can exist as part of a developmental
fault, in the division between the left and right
ventricles of the heart - Ventricular Septal Defect
-VSD ( more commonly known as a hole in the heart) The closure of this hole can
take a few days, weeks or even months and in some cases, . In the case of
very small holes resulting from incomplete closure, no
real symptoms may occur, and the system might
function adequately despite the defect. In cases
where the closure of the hole is less complete however, the symptoms
displayed will be greater or lesser depending on the size
of the hole. Such' holes' can be detected initially upon listening to the heart
sounds with a stethoscope. In a healthy heart there
are 2 basic heart sounds as blood is pumped firstly
from the atria, then secondly from the ventricles to either the
lungs or to the tissues. In the case of a septal defect, a
sound of "swishing" can be heard between the first
and second regular sound as blood is shunted from the left side of the heart
(where the pressure is greatest) across to the right side.
Once again, the degree of sound will depend upon the size
of the defect, and some sounds are so quiet they
are obscured by other background noise. This sound
is commonly heard in young pups and would only become an issue for concern if the
"swishing" continued to be heard associated with the display of
symptoms, or if the volume of the "swishing" sound
indicated a very large defect. In some severe cases
of VSD, the sound can even be heard by listening to
the chest wall of the dog without a stethoscope.
A similar "swishing" sound is also heard in the case of a
valve defect as blood back flows from one chamber
to another , back along a vessel, or fights to be expelled from the left
ventricle as is the case in Sub Aortic Stenosis - SAS (a
common condition in Rottweilers). Again the volume of
sound will depend upon the degree of function in
the affected valve.
A far more accurate method of defect detection would be to
view the circulation of the heart using
radiological techniques however, this would not generally be considered as
routine, and surgical repair of such structural defects is not well
developed in dogs or is often considered by some to be
inhumane.
Chronic (congestive) Heart Failure.
The symptoms of heart disease are almost
entirely due to the inability of the
heart muscle to maintain the normal circulation. Thus, as a puppy grows and
becomes more active, symptoms of congenital disease become
more apparent, or, in the case of older animals, they are no longer able to
sustain the degree of
activity they once did.
The term "Heart Failure" indicates the hearts failure to
perform its primary function and to its subsequent
ultimate demise. The inability of the heart to adequately perfuse other organs
creates a knock -on effect in that they too cease
to function adequately. In an attempt to rectify the situation, the heart
tries to compensate for the reduction in out put by
speeding up (tachycardia). It works on the premise
that 'little and often' is as good as 'regular and in
proportion'.
Structures affected
The heart soon becomes overworked and,
depending on the cause, either the
right side or the left side of the heart may start to fail first. Eventually
that failure will become general and involve both sides more or less equally.
The 'little and often' theory, reduces the over all
forward pressure of the out put rendering it as
ineffective. Due to the fall in systemic pressure, the kidneys fail to
maintain the pressure required within them to expel toxins
from the body, and urine out put is seen to
decrease. Renal failure quickly follows long term or repeated reduction in this
pressure .
The brain is also suffering from reduced perfusion -
reduced oxygen supply (hypoxia) and raised toxin
(urea) levels create an agitated, confused and restless
state, and in extreme situations can cause fitting. In
these situations dogs can display aggressive tendencies they have never before
displayed, and other
animals have been known to attack and kill a failing dog,
so it is often best to keep them separated.
A poorly per fused alimentary system will result in a
feeling of nausea (sickness) with vomiting. The
appetite and fluid intake desire will tail off and often eating or drinking is
made difficult due to shortness of breath. Weight loss which results
from this can make the dog prone to the developing of
sores on the skin especially where the dogs
mobility has decreased.
Peripheral circulation will shut down as a defence
mechanism to direct oxygenated blood to the vital
organs and this would be seen as pale maybe blue
tinged membranes in for example the mouth/ around the lips. The general feel of
the skin to touch would be clammy and fluid (oedema) will build up in the
tissues of the limbs abdomen and chest.
The over worked right and in particular, the left
ventricle of the heart become distended and back
logged with blood the pump can not deal with. This
situation creates a back log of pressure into the lungs and the vessels of
the lungs, creating a situation of breathing difficulties as the increased vessel
pressure forces fluid out into the tissue of the lung
spaces themselves where upon the sufferer feels as
if they are drowning. Breathing difficulties are often
noted to be worse at night or when the dog is trying to
rest. The inability to rest comfortably eventually
leads to a condition of exhaustion due to sleep
deprivation at a time when rest is essential. Drug therapy can be administered
to
'off load' this excess fluid and regulate the rhythm of the heart in an attempt
to raise the system pressure to improve cardiac
efficiency. Drugs therapy can bead ministered to reduce other symptoms such as
nausea - However, in many cases side effects and other associated problems which
they bring such as incontinence, out weigh the
benefits on a long term basis and the effects of
such repeated treatments, combined with repeated tissue stress and
continuing failure, eventually renders any such attempts to restore the status
quo as futile.
At some point in this sorry state of affairs we are forced
to make the decision of when to say we have done
all that we can ( in some cases more) and to decide when is the time to say
Good-bye to our friend . Such a decision is never going
to be easy to reach regardless of how much time we feel we
have given
ourselves to get used to the idea.
Decisions of exactly *when* to terminate life will vary
from person to person and from circumstance to
circumstance , but it is important to remember at this
emotional time, the effects such a condition is having
upon the quality of life of our animals. We should not allow our desperation for
a cure to over shadow the well being and dignity of
an animal who in most cases, will have devoted its
own lives to our service and companionship.
Alyson Lockwood SRN.RMN.AFET Cert. Cert.
Advanced Animal Health Care.