Mitral Valve Disease In  Cavalier King Charles Spaniel

• What is mitral valve disease?
  
  This disease is known by many different names. The names used apply either to the heart valve affected (mitral valve disease), to the changes that are seen on the valves (endocardiosis) or to the time course of the disease (chronic valvular disease).
  
  Mitral valve disease is the most commonly diagnosed cause of a heart murmur and heart failure in all dogs in small animal veterinary practice. It is a degenerative disease of the heart valves) affecting mainly the mitral valve on the left side of the heart but can also affect the triscuspid valve on the right side of the heart. It causes distortion of the valves which results in leakage of the affected valves. This disease usually occurs in older dogs however it is seen in the Cavalier King Charles breed at a very young age and may result in premature death.

• What happens to the heart in mitral valve disease?
  
  Mitral valve leakage (insufficiency) leads to dilation of the left atrium and the left ventricle, the two chambers on the left side of the heart. If the changes occur slowly then the left atrium distends and accommodates the increased volume, however eventually
   

  the pressure within the left atrium increases and the drainage of fluid from the lungs is compromised resulting in left sided congestive heart failure. If a chordae tendinae (chords which hold the heart valves in place) ruptures then left atrial pressures increase suddenly and acute severe pulmonary congestion results. Tricuspid valve leakage leads to right atrial and right ventricular dilation If right atrial pressure increases then drainage of the liver and abdomen is compromised resulting in right-sided congestive heart failure. If not enough blood is being pumped forward because of valve leakage then the kidneys sense this change and retain fluid making matters worse. The heart muscle will eventually fail due to the chronic presence of excess fluid

• Which breeds are affected?
  
  Any breed may be affected however the following breeds are more commonly affected: Cavalier King Charles Spaniel, Cocker Spaniels, Poodles, Terriers, Dachshunds, Irish Setters.

• Males are predisposed.

• What are the typical presenting signs of mitral valve disease?
  
  Chronic coughing is a common presentation due to the large left atrium pressing on tile airways. Exercise intolerance is frequently noted, many dogs will tire easily or breath heavily during exercise. Some dogs will present at annual vaccination and the murmur is an incidental finding. Other dogs will present in acute congestive heart failure with evidence of severe difficulty breathing (dyspnoea) and fluid retention in the abdomen (ascites). Fainting (syncope) is seen in some dogs in the later stages of the disease, this is due to poor forward flow of blood.

• How is mitral valve disease diagnosed?

• Clinical examination
  
  A murmur is heard by auscultation using the stethescope over the mitral +/- tricuspid valves. The murmur starts off as a low-grade murmur at the apex of the heart on the left side of the chest. Murmurs are graded on a scale 0-6. As the disease progresses the murmur grade increases and the murmur duration lengthens. The mitral murmur radiates to the right side and it can be impossible to distinguish a murmur of mitral insufficiency radiating to the right from a separate tricuspid murmur. In the early stages of the disease, the gums will be pink and the pulse, which is felt inside the hindleg over the femoral artery, will be strong. As the disease progresses the gums may be pale and the pulse weak. If congestive failure is present then dyspnoea may be noted or fluid in the abdomen.

• Thoracic radiography
  
  Thoracic radiographs are useful to assess chamber enlargement and lung congestion. Radiographs of the chest will show left atrial/left ventricular enlargement with significant mitral insufficiency or in the case of tricuspid insufficiency right atrial/right ventricular enlargement. Generalised cardiac enlargement (cardiomegaly) will occur with long standing disease. Thoracic radiography is the most useful method of determining pulmonary congestion. The pulmonary veins may be congested and fluid may be seen in the lung fields (oedema). Radiographic changes may occur before there is clinical evidence of left sided congestive heart failure.

• Electrocardiography (ECG)
  
  The ECG will again show if the heart chambers are enlarged, however it will also show if arrhythmias are present. Arrhythmias are seen due to dilation and stretch of the chamber walls and due to poor oxygen supply of the heart muscle. It is not unusual to get fast rhythm disturbances (tachycardia) with mitral valve disease which may require medication.

• Echiocardiography
  
  Echocardiography is very useful to show the thickened valves and also to see if chamber dilation is present. The ability of the heart to contract and pump blood forward can also be assessed. Doppler echocardiography is a specialised form of echocardiography which allows confirmation and quantification of valvular insufficiency.
  
  
                   

• What treatments are available for mitral valve disease?

• Treatment
  
  This very much depends on the class of failure on presentation. There are three main classes of heart failure with two subsections leading to a total of five classes. In the early stages of disease many dogs are not treated and a murmur is monitored, by listening to the heart regularly or sometimes by chest radiographs. As the disease gets worse arid coughing or exercise intolerance is noted then the majority of dogs are treated with diuretics and angiotensin converting enzyme inhibitors (ACE inhibitors). There are different types of diuretics and two types may be used together if excessive fluid is present in the lungs or in the abdomen. The diuretics help to reduce the excessive fluid in the lungs and elsewhere in the body.
  
  There are several different types of ACE inhibitors now available and they all seem to be equally effective. ACE inhibitors help to decrease the excess fluid in the body however they also dilate the blood vessels making it easier for the heart to pump blood forward. Advanced cases may require drugs that make the heart pump better (positive inotropes) e.g. digoxin, pirnobendan. If the heart rate is very fast then drugs may be needed to decrease the rate (negative inotropes) e.g. digoxin.
  
  In the presence of severe congestive heart failure then hospitalization with cage rest is advisable. Oxygen may need to be administered by a tube into the nose or by putting the dog into a special oxygen chamber. The diuretics may need to be given into the veins rather than by mouth and a special cream may have be applied to the skin inside the ear to dilate the veins and decrease some of the fluid in the lungs.
  
  The following table gives some classification of heart failure;
  (guidelines to therapy based on the ISACHC)

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