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 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'.
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.