This section is on canine cardiac topics. These are all questions that have been submitted or that I have been inspired to talk about because of a question submitted. If you have any topics that you would like to have discussed please feel free to email me with the topic or question.
In the mammalian heart there are two sides -- a left and and a right -- and each side has two chambers -- the atrium and the ventricle. The right atrium takes returning blood from the veins of the body that is low in oxygen. This blood them flow into the right ventricle which contracts and sends the blood to the lungs to get oxygen. The blood leaves the lungs and goes to the left atrium which then sends the blood to the left ventricle. The left ventricle contracts and sends the blood out into the arteries to take oxygen and nutrients to the rest of the body. To keep blood from going back into the atrium when the ventricles contract and to force blood to go out of the heart, there are one-way valves between the atrium and the ventricle on both sides of the heart. The valve between the left atrium and left ventricle is called the mitral valve. The valve between the right atrium and right ventricle is called the tricuspid valve. The proper functioning of these valves are critical to maintaining adequate heart function. If they mess up then less blood leaves the heart (some blood goes into the atrium when the ventricle contracts instead of leaving the heart) and, thus, more blood remains in the heart. The body responds to receiving less blood by demanding the heart increase it function. The heart does so but as the valves get worse and worse, less and less blood leaves the heart for the body. Eventually, the heart can no longer properly deliver blood to the rest of the boy and the animal dies.
TVD is a congenital (that is, it is present at birth as a result of genetic or developmental problems) defect that occurs in Labrador Retrievers and some other breeds. In this condition, the tricuspid valve (the valve between the right atrium and right ventricle) is not properly formed. TVD ranges in severity from very mild to very severe. The very mild to moderate cases may not ever show any clinical signs of disease and, thus, no one knows they have this problem. They live happy, healthy, active lives. The problem arises with these individuals not because of any problems to themselves but because if this problem is inheritable, their offspring might have the problem and, if so, often have a more severe form of the disease. Indivuduals affected by a more severe form of the disease are unable to have a properly functioning right side of the heart and usually develop right-sided congestive heart failure. With medical manangement these individuals can survive for a period of time (few month to couple of years). Many breeders of Labradors are working to eliminate this problem from breeding stock with the hope that it will then no longer be a problem.
Anything that causes the heart to not be able to adequately maintain blood flow can cause congestive heart failure (CHF) over a period of time. Typically, CHF is divided into left-sided and right-sided to denote which side of the heart has the problem. If both sides do then it is called bilateral CHF. Left sided CHF is characterized by a failing left side of the heart. Since the left side of the heart takes blood returning from the lungs and sends it to the body, the first place affected by a failing left heart are the lungs. Blood backs up in the veins of the lungs causing fluid to leak out into the lung. This leads to respiratory problems and is typically characterized by coughing in the dog. As it progresses the dog suffers worse and worse respiratory distress, and if untreated, often dies from the respiratory complications. This is very common in older, small breed dogs in particular Cavalier King Charles Spaniels. In right-sided CHF the blood backs out in the veins returning blood from the body. Thus, the fluid leaks out into the rest of the cody causing limb and abdomen swelling. Because fluid accumulation is a component of both types of CHF, a diuretic is given to encourage removal of this fluid. Other drugs are given to reduce the amount of work the heart has to do and to aid the heart in pumping the blood better. Typically, dogs can live months to years with CHF given proper medical, nutritional (low salt), and management (low exercise) treatment.
Dilated means expanding and Cardiomyopathy means abnormal and bad change in the heart muscle. DCM is characterized by a heart that gets larger and larger without increasing adequately the size of the heart muscle. Thus, the heart actually holds more blood but is unable to contract with enough force to get the blood out of the heart. Imagine a balloon being blown up -- the sides get thinner and thinner. That is how the heart changes in DCM. Once again, this is a basic heart muscle disease -- that is, it is an inherent problem with the heart muscle. Dobermans as a breed are HIGHLY susceptible to this condition. Any Doberman over the age of 3-5 years should be checked annually for this problem. It seems to be a part of the genetic makeup of the breed. Boxers are another breed highly prone to this condition. And there are certain lines of Giant breed dogs like Irish Wolfhounds and Great Danes that are also predisposed. DCM signs are primarily the result of the inability of the heart to contract with enough force to deliver blood to the body. Lethargy, weakness, exercise intolerance, fainting, and sudden death are all signs of DCM.
Cardiomegaly is simply the enlargement of the heart. In dogs, there are two distinct varieties. One is the result of an underlying disease with the heart muscle itself resulting in malformation of the heart. An example of this is Dilated Cardiomyopathy that is present in very high numbers among Dobermans is also seen in Boxers and giant breed dogs. The other variety of cardiomegaly is secondary to another disease. Any disease that puts added stress on the heart by making it harder to pump the blood out or by reducing the amount of blood pumped each time the heart beats will cause the heart to enlarge. This is often seen in chronic valve dysfunction such as occurs in most small breed dogs with mitral valve disease or in congenital heart defects. Basically, in these conditions when the heart pumps blood out but because of defective valves blood leaks back in making the next "load" more than it should be and this compounds with each heart beat. Initally, the heart increases muscle mass so that is can contract more strongly and pump more blood out. This causes an increase in the thickness of the heart wall with a slight increase in heart size. After a while, the load on the heart becomes so much that the heart cannot continue to increase muscle mass to compensate and, thus, the chambers of the heart dilate in order to hold more blood. This serves to compensate for a while but like the increased muscle mass can only compensate for so long. Once it can no longer compensate, then the animal goes into heart failure with the concurrent signs of shortness of breath, exercise intolerance, etc. Chronic hypertension (high blood pressure) and heartworm disease can also result in an enlarged heart from a similar mechanism only in these causes the primary cause is increased difficulty of pumping blood out rather than blood leaking back in once it has been pumped out.
In the case of this Westie, the most likely cause is cardiomegaly secondary to a valve defect but it is possible for there it to be a primary cardiomegaly. It is certainly possible that the ECG is normal if the heart is still in the compensatory stage of the disease. I would expect a slightly abnormally high wave complex on the ECG if there is significant cardiomegaly but the overall wave form on the ECG as well as the contraction of the heart would be normal. Treatment will be to address the cause -- ie hypertension, heartworm, valvular dysfunction -- and to treat the symptoms if there are any.
Aortic Stenosis is a condition in which the valve that allows blood to flow out of the heart to the body is abnormally narrow. Because it is narrow the blood has to flow faster and with more force. This creates two problems: (a) the left ventricle (the chamber of the heart that pumps the blood out to the body) has to work harder and can become larger than normal; if the stenosis (or narrowing) is extreme the left ventricle may not be able to pump blood hard enough to deliver enough to the body resulting in fainting, exercise intolerance, left-sided heart failure, and possibly death and (b) dilation of the aorta (the vessel into which the blood flows from the valve).
It is proven that this condition is a genetic one in Newfoundlands. Since the Labrador's foundation includes the Newfoundland it is supposed that it is also genetic condition in the Labrador although this has not been proven. Recommendations are to definitely NOT breed the affected dog and consider strongly not breeding the parents to one another again. The incidence in Labradors is not high enough to warrant recommendation to never breed the parents to any other dog or to not breed siblings.
Severity of clinical disease is entirely dependent on the degree of stenosis. Severe stenosis will lead to failure of the heart to deliver blood and oxygen to the body resulting in fainting, exercise intolerance, organ disease, and eventually death. Mild to moderate stenosis is often not associated with any clinical disease and the dog can live a relatively normal life although intense exercise is not recommended for these dogs. Thus, if this pup has only mild to moderate stenosis which is probable if it is healthy, well-growing puppy without any clinical disease and the stenosis was detected via auscultation with a murmur the only sign, then it can very well go on to live a normal albeit exercise limited life without any treatment. Owners of this pup should be advised, though, that the heart is predisposed to developing dysfunction and possible failure later in life due to the abnormal stress placed upon it. There are surgical prcedures being done at several of the vet schools. These range from actual heart surgery to alter the anatomy to doing balloon dilation via the aorta to enlarge the aortic valve.
The heart is divided into four compartments. Two on the left side and two on the right side. Each side has a ventricle which is responsible for pumping the blood out and an atrium that is responsible for collecting the blood as it flows back to the heart. Between the ventricle and the atrium on either side is a valve called a atrioventricular valve. Basically, this valve prevents blood from flowing back into the atrium when the ventricle contracts. The atrioventricular valve on the left side is called the mitral valve. Dysplasia means improper formation. Thus, mitral valve dysplasia is improper formation of the valve that separates the atrium and the ventricle on the left side of the heart. This improper formation prevents the valve from properly doing its job to keep blood from backtracking into the atrium when the ventricle contracts. A G1 (which I am assuming to mean a grade one -- I could not find that abbreviation listed in any of the cardiology books I looked in) would be the mildest form of this condition. Any dysfunction of the mitral valve allows blood to flow back into the atrium when the ventricle contracts creating turbulence in the bloodflow and, thus, a murmur. If the dysfunction is mild it may never present a clinical problem or if it does it will be as the animal ages and the hearts starts wearing down. At that time a dog with the mitral valve dysplasia would be more prone than a normal dog to develop congestive heart failure. If the condition is not currently causing any clinical signs than I would just have an annual heart checkup done on the affected dog to monitor progression of the condition so that any necessary therapy can be initiated as soon as a problem starts to develop.
In Labradors and Goldens valvular dysplasia seems to hereditary. Thus, affected dogs should not be bred. How strong of a genetic component is present is still unclear, thus it is hard to recommend whether or not parents and siblings should be bred.
About your dog (the affected dog's sister ) -- at the heart clinic there was definitely a murmur? And the cardiologist did not think it was mitral valvular dysplasia? Honestly, any heart abnormality or blood abnormality that cause alterations in bloodflow can lead to turbulence and thus a murmur. Without knowing location, intensity, and timing of the murmur it is very difficult to decide probable cause of the murmur. If she is showing any clinical signs of exercise intolerance or difficulty breathing that I would highly recommend a thorough workup of the heart murmur. If, however, she is not having any problems I wouldn't necessarily consider it warranted to do a full cardiology workup. If wouldn't hurt and might assauge any worries you are having but her condition does not mandate it. If you do not do a full cardiology workup on her now I would monitor her closely for signs of difficulty breathing, exercise intolerance, etc and if they develop pursue it then.
I have researched and answered these questions to the best of my ability. But I am human and make mistakes. If there is any part of my answer that you feel is incorrect, please let me know. The last thing I want is to disseminate false or incorrect information.