Types of heart disease in dogs

Myxomatous Mitral Valve Disease (MMVD)

MMVD actually stands for Myxomatous Mitral Valve Disease and diseases are also known under names such as Mitral Valve Insufficiency, Mitral Valve Disease (MVD) or Endocardiosis.

MMVD is a frequently occurring heart disease in both dogs and humans – in dogs it is seen especially in cavalier king charles spaniels and dachshunds.

The Cavalier King Charles Spaniel has a breeding program against MMVD, where the breeding animals are heart examined several times in their lives.

During the heart examination, the vet will listen to the dog's heart with a stethoscope and then scan the dog's heart. The vet listens for heart murmurs.

If the dog has a noise, it is assessed on a scale from 1-6, where 1 is the mildest degree, and grade 0 means no noise.

The heart scan is recorded on a disc and sent to KU/SUND, where professor and veterinarian Lisbeth Høier Olsen takes measurements of the heart valve to assess whether the dog has a malformed mitral valve - what is also called mitral prolapse.

The degree of mitral prolapse is indicated on a scale of 1-3, where 1 is the lowest degree and degree 0 will mean no prolapse.

         Symptoms of Mitral Valve Insufficiency

The typical symptoms of MMVD are fatigue, shortness of breath and possibly cough. In many dogs, the heart disease MMVD will develop gradually, and the dogs can live for many years with a small leak in the heart without symptoms or discomfort. In other dogs, however, the disease develops quickly, and it may end up with the dog having to be euthanized. The inheritance of MMVD is very likely polygenic, which means that several genes are important for the development of the disease.

Ultimately, the disease will result in a leak in the heart valve, called the mitral valve.
The mitral valve is the name for the valve that sits between the left atrium and the left ventricle.

Normally, the oxygenated blood from the lungs enters the left atrium, from where it flows down into the left ventricle. When the heart contracts, the blood is sent from the left ventricle into the large main artery - the aorta. If the valve between the left atrium and heart chamber is not tight, part of the oxygenated blood flows back into the left atrium instead of flowing into the main artery (aorta). The leak makes it harder for the heart to pump blood out into the body, and the heart becomes overloaded and enlarged.

Dilated Cardiomyopathy (DKM)

In cardiomyopathy, it is the heart muscle itself that is changed. A distinction is made between dilated cardiomyopathy, where the heart muscle becomes large and flaccid - and hypertrophic cardiomyopathy, where the heart muscle is enlarged/thickened. The latter is not so frequently seen in dogs, but more often in cats, e.g. of the Maine Coon breed.

DKM particularly affects large dog breeds such as Irish Wolfhound, Doberman and Great Dane. Males are also more exposed than bitches. The disease reduces the heart's ability to contract because there is a breakdown of the heart muscle.

Inheritance is most likely autosomal dominant with reduced penetrance

        Symptoms of Dilated Cardiomyopathy

The symptoms of DKM include fatigue and fast heart rate. The diagnosis is made by ultrasound scan or X-ray combined with EKG. The walls of the heart will here appear thin and flabby.

Subaortic stenosis (SAS) and Pulmonary stenosis (PS)

Stenosis is the term for a narrowing – here in the form of a ring of connective tissue. With SAS, the narrowing is located in the large main artery - the aorta, with PS, the narrowing is in the blood vessel that sends blood from the heart to the lungs. Both diseases are seen in large dog breeds, e.g. boxer, newfoundland and dogue de bordeaux.

When the blood cannot pass freely into the aorta, the pressure inside the heart increases. The heart also has to work overtime, because more effort must be used to push the blood past the narrowing.

The mode of inheritance has not been determined in detail, but probably several genes are involved – i.e. polygenic inheritance. The disorder is congenital, so the diagnosis can be made already in small puppies. Registration of results for SAS/PS scans has been introduced in several breeds.

An SAS examination uses a clinical examination in which the vet listens to the heart (auscultation), supplemented with ECG recordings and ultrasound scanning with the special technique called Doppler. The Doppler technique is used to measure how fast the blood flows out of the aorta - the faster it flows, the worse the narrowing. It is a bit like squeezing a garden hose with pressure on it.

        SAS is divided into grades 0 – 4 depending on the outflow velocity of the blood.

• Grade 0:
  Discharge speed below 2 m/s (equivalent to 7.2 km/h): Normal
• Grade 1:
  >2 and ≤ 2.25 m/s, Gray zone cases. It is not possible to make a final diagnosis – some of these dogs may have aortic stenosis in the process
• Grade 2:
  >2.25 and ≤ 3.5 m/s, Mild aortic stenosis. Dogs with mild aortic stenosis often live a normal life without symptoms of disease, but it cannot be ruled out that they die earlier than healthy dogs.
• Grade 3:
  > 3.5 and ≤ 4.5 m/s, Moderate aortic stenosis. Dogs with moderate aortic stenosis may be symptom-free, or show the same symptoms as described for severe aortic stenosis
• Grade 4:
  > 4.5 m/s Severe aortic stenosis. Dogs with severe aortic stenosis often develop symptoms such as tightness, reduced fitness and fainting spells in the first years of life. Sudden death can also occur. Many of these dogs die before they are 3-4 years old.

For boxers, the limit values ​​for the 4 degrees deviate slightly from the stated general values.

（This article is adapted from an article by DANSK KENNEL KLUB. If there is infringement, please contact us to delete)