Presented at the ANTA fall Festival, Oct 15, 2005 by Lori Pelletier and Carol Falk

Transcription

1 Mitral Valve Disease in Norfolk Terriers Presented at the ANTA fall Festival, Oct 15, 2005 by Lori Pelletier and Carol Falk What is Mitral Valve Disease (MVD) The heart has two chambers. The upper middle chambers are the atria and the lower chambers are ventricles. The heart is also divided into right and left sides. Blood flows from the body into the right atrium. It is stored there briefly then pumped into the right ventricle. The right ventricle pumps blood into the lungs where it receives oxygen. It flows from the lungs into the left atrium where it is held a few seconds before going to the left ventricle. The left ventricle is surrounded by the largest and strongest of the heart muscles. This large muscle is necessary to pump blood to all parts of the body (pethealthcare, 2005) Each side of the heart has a valve to keep blood from going backward from the ventricles to the atria. The valve between the left atrium and left ventricle is called the mitral valve. Because of the very large pressure created when the left ventricle contacts, the mitral valve wears out in many dogs. This wearing out process begins with a small leak that gradually gets more severe. How common is Mitral Valve Disease? MVD is the most common cause of heart failure in small dogs. 1 / 5

2 What are the earliest signs of MVD? The earliest sign of a leaking heart is a heart murmur. A murmur is produced by the turbulence created when some of the blood goes backward through th leaking valve and into the left atrium. Most dogs will have a murmur by age ten. 1 Diagnosing MVD 1. Auscultation locating the murmur with a stethoscope 2. Chest x-rays viewing the size and shape of the heart 3. EKG (electrocardiogram) assesses the electrical activity of the heart 4. Ultrasound (Doppler) gives the best look at the size of each heart chamber, and permits visualization of the heart valves 2 As breeders, what are we doing? Research characterizing Mitral Valve Disease in the Norfolk Terrier is being conducted at Washington State University by Sunshine M. Lahmers, DVM. Although breeders, owners and veterinarians who work with Norfolk terriers are suspicious that an early onset form of MVD exists in this breed there have been no published studies to characterize MVD in the Norfolk terrier. The goal of the proposed study is to investigate the incidence, pattern of inheritance, progression, pathology and potentially the genetic basis of MVD in the Norfolk Terrier. This information will benefit the breeder,, veterinarian and pet owner by providing the information necessary to make informed medical and breeding decisions. In addition, this study proposes the development of a canine cardiac gene array. This array has the potential to increase our understanding about a variety of cardiac disorders by providing a screening tool for expression of a subset of cardiac genes. 2 / 5

3 3. Data Collected MVD Clinic Test Group (Nofolks) 24 dogs tested 15 had mitral valve degeneration, 9 were normal, average age of dogs tested 7.5 yr. Control Group (Cairn, mix, Norwich) 3 dogs tested, 3 were normal, average age 1 year Results - 15/24 (62%) Norfolks had evidence of mitral valve degeneration - 11/12 (92%) Norfolks with mitral valve degeneration had an audible murmur - 1/3 (33%) Norfolks with mitral valve prolapse had a click - none of the dogs were severely affected, approximate age of affected dogs 8 years, approximate age of unaffected dogs 3.6 years, 6/15 (40%) were less than 5 years 4. The Good News a. The disease callusing the leaky mitral valve is due to valve degeneration, which is common and usually slowly progressive in many small breed, older dogs b. The vast majority of the Norfolk s with the disease have heart murmurs and can be 3 / 5

4 identified by a skilled veterinarian. c. None of the dogs tested were severely affected yet (at age of 8 yrs.). 5 The Not So Good News a. In general, this is a late-onset (average 8 years) and breeders cannot screen for the late onset form of the disease during the breeding age. b. There was a subset of young Norfolks (less than 5 years of age) that were affected by the disease c. The very early stages are very hard to detect by routine methods. d. 60% of the Norfolks were affected by mitral valve degeneration 6. Where do we go from here? a. 60% of the Norfolk Terriers examined so far in this study have degeneration of the mitral valve; of those 40% were less than five years of age. 4 / 5

5 b. There appears to be two affected populations 1. Early onset (less than five years of age severe form) 2. Late onset (over five years of age less aggressive form) 7 Recommendations a. Annual OFA (cardiac) screening is recommended during each year the dog is used for breeding. Keep in mind that Norfolks with late onset disease will be missed. b. Annual physical exams of breeding stock Once a murmur is detected, then a cardiac ultrasound should be performed by a cardiologist to confirm diagnosis 5 / 5