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For the last decade I have been involved in Saluki heart research. Our original goal was to examine the incidence of cardiomyopathy. When characterizing Saluki hearts through physical examinations, electrocardiograms and ultrasonography, we discovered that there were differences from what was accepted as "normal" in mixed-breed populations. To know if these changes were significant or were just unique to Salukis we had to continue to examine these dogs as they aged and after death to see if any of these changes resulted in heart disease.
Saluki fanciers want to know what heart diseases occur and if any of the conditions could be inherited or genetic. Our pathology study is documenting what heart conditions occur in Salukis. But determining if these are significant diseases that could be inherited or genetic is very difficult. Some heart conditions are thought to be inherited in certain breeds because the condition occurs at a greater incidence than in mixed breed populations. And some conditions seem to be prevalent in certain families. However, is it fair to generalize from what is found in other breeds to salukis? Pedigree studies need to be done on affected dogs and their relatives to determine the possible inheritance.
Heart conditions can be classified in two major groups, congenital or acquired. Congenital conditions, or defects that the dog was born with, are abnormalities in the structure of the heart, heart valves, or the major vessels. These might or might not be genetic. They typically cause problems or symptoms early in the dog's life, such as inactivity or poor growth and a heart murmur. Congenital heart diseases that are known to have a polygenic mode of inheritance in the following breeds are: Patent ductus arteriosis (PDA) in poodles, Aortic stenosis (AS) or narrowing of the valve in Newfoundlands, and Pulmonic stenosis (PS) in beagles.
Acquired heart conditions develop due to disease states or degenerative conditions that occur as the dog ages. The dog is born with a normal functioning heart, but changes occur with time and affect either the fibrous sac enclosing the heart, the pericardium (PERICARDIAL DISEASE) or the heart muscle itself, (PRIMARY MYOCARDIAL DISEASE) or the heart valves (VALVULAR DISEASE).
PERICARDIAL DISEASE is the least commonly encountered. It generally involves the accumulation of fluid in the sac around the heart. Heart sounds are often muffled due to the fluid accumulation. The heart looks huge on a radiograph and an echocardiogram is needed to determine of it is fluid around the heart or if the heart is enlarged. This fluid or pericardial effusion impairs the ability of the heart to fill properly with blood. As a result fluid builds up in the lungs or abdominal cavity causing signs of heart failure since the heart can't pump the blood through the body properly. Usually a mass on the surface of the heart or, much less commonly, thickening in the pericardium due to infection causes the fluid build up. In older dogs, cancer (usually hemangiosarcoma) in the heart is the most common cause and rupture of the mass causes bleeding into the sac and the dog collapses.
PRIMARY MYOCARDIAL DISEASE occurs when the heart muscle weakens and fails as a pump. Early on there are no symptoms as the heart compensates for its loss of contractility by enlarging. But eventually, the failure of the heart to pump enough blood results in accumulation of fluid in the body and signs of heart failure. Dilated cardiomyopathy (DCM), where the heart muscle wall thins out, is more commonly seen than where the muscle wall thickens (hypertrophic cardiomyopathy). A hereditary nature is suspected since DCM affects certain, generally large breeds of dogs, and expresses itself differently in different breeds. Giant breeds most often show congestive heart failure signs with fluid accumulation in the lungs. While in Boxers, the major abnormality is in the electrical conduction system of the heart. This causes an irregular heart rhythm and can result in fainting or syncopal episodes which makes the dog prone to sudden death. The condition is diagnosed on an echocardiograph by finding enlargement of the chambers of the heart and poor contractility. HOWEVER, other heart conditions can cause some secondary enlargement of the chambers and alteration of contractility, but these are not primary diseases of the heart muscle like DCM.
VALVULAR DISEASE occurs when any of the four valves that regulate the direction and amount of blood flow through and out of the heart don't function properly. The AV valves separate the upper chambers (atri) from the lower pumping chanbers (ventricles) on the right (mitral) and left (tricuspid) sides of the heart. The pulmonary valve regulates the blood flowing in the artery to the lungs and the aortic valve, blood flowing to the body. Since the valve doesn't close completely, blood spills back (regurgitation) across the leaky (insufficient) valve and a murmur from turbulent blood flow is heard. Over time this back flow of blood causes the heart muscle to have to work harder to move the same volume of blood. The muscle thickens and the heart enlarges. Eventually, signs of heart failure will develop as fluid builds up in the lungs or body (volume overload). This is the most common group of heart conditions and can occur from a variety of causes.
Valvular disease can be a congenital condition, generally termed dysplasia, because there is some defect that makes the valves not fit and close properly. There can be infectious causes where bacteria colonize on the valve causing vegetations or nodules to form (termed 'itis'). With age, degeneration (termed 'osis') of the valves can also occur where the leaflets thicken and develop nodular swellings that coalesce. With time this results in more leakage which causes more changes in the valves. In some dogs, this volume overload is well tolerated, whereas in other dogs there is a rapid progression to congestive heart failure.
Bacterial infections usually affect the aortic and mitral valves causing valvular endocarditis. Degenerative changes commonly affect the AV valves causing valvular endocardiosis. The left AV or mitral valve is more frequently involved and as the insufficiency progresses, eventually fluid will build up in the lungs. Less commonly, regurgitation of the tricuspid or right AV valve will result in fluid building up in the abdomen (ascites).
Early on, dogs with valvular endocardiosis have no outward signs, but a murmur can be heard by a veterinarian. The point of maximum intensity (PMI) or location of the murmur can indicate what valve is leaking. The loudness of the murmur (graded on a scale of I to VI) doesn't necessarily indicate the severity of the leak of blood across the valve. The definitive identification of valvular conditions requires a cardiac ultrasound with a Doppler exam to quantify the direction, volume, and velocity or severity of the regurgitant blood flow.
Mitral degeneration, or valvular endocardiosis (also termed verrucous or myxomatous degeneration of the valvular endocardium) is common in small breeds of dogs as they age. It is not thought to routinely occur in large breeds. However, a large number of the Salukis examined had varying degrees of mitral valve disease. In some dogs, this insufficiency was well tolerated. In others, it progressed to congestive heart failure. Pedigree analyses of affected and related dogs need to be conducted to help determine if this could have a heritable component.
Congenital heart defects generally cause clinical signs in young dogs. However acquired heart conditions develop as a dog ages. Without routine physical examinations, these will not be detected unless the dog has progressed to a severity of disease where signs of heart failure become apparent. Murmurs detected on physical examination are often early indicators of heart problems and necessitate further evaluation. Often, this requires repeated examinations as the dog ages to see if the heart condition progresses.
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