Rebecca L. Stepien DVM, MS, DACVIM (Cardiology)
Thanks to the assistance of the Whippet Health Foundation and the many owners who participated in this cardiologic screening event, 65 dogs were screened during the AWC National Specialty in Greensboro, NC in April, 2004. Of these 65 dogs, 12 underwent auscultation only, and 53 had auscultation results, an electrocardiogram (ECG) and an echocardiogram recorded. This report is to summarize some of the early results of this testing. The results presented pertain to the 53 dogs that had both auscultation and echocardiogram recorded. These results are preliminary only and may change as more information is acquired and analyzed.
What was the purpose of the cardiac screening?
Many whippet owners are aware that their dogs have a heart murmur. In many cases, the dog is healthy and never shows any signs of cardiac disease. These murmurs may represent ejection murmurs (also called flow murmurs or athletic murmurs) and are the sound of blood rushing through a normal heart. Mitral valve (MV) insufficiency (a disorder of one of the left-sided valves in which the valve thickens and does not close properly, leading to MV leakage) has also been documented in whippets. MV insufficiency may cause a heart murmur that is difficult to differentiate from ejection murmurs. The purpose of this screening event was to examine a group of healthy dogs at a large show to determine how many of the dogs have harmless “ejection” murmurs and how many have MV murmurs, and whether simple auscultation is adequate to differentiate the two conditions.
Who were these dogs?
Twenty six dogs in the study were male and 27 dogs were female. Most dogs were described as being in “good” condition (53%), 26% were considered to be “pet-level” athletes, 17% were considered to be in “top athletic” condition and 4% were considered to be non-athletic. No dogs had overt signs of heart disease. The average weight was 14 kg (31 lbs), but ranged from 8.6 kg (19 lbs) to 19 kg (42 lbs). The average age was 4.5 years, but as could be expected in a show population, most were young (75% were under 6 years old).
In this narrow population, most dogs (>90%) had heart murmurs detected. More than half of the dogs had murmurs thought to be ejection murmurs, and about 1/3 had murmurs thought to be typical of mitral insufficiency.
Echocardiographic findings were categorized as mitral insufficiency, tricuspid insufficiency (leakage of the valve on the right side of the heart) and abnormalities of the MV apparatus (abnormal valve appearance). About 2/3 of the dogs were noted to have one or more MV abnormalities; most but not all MV anatomic abnormalities were associated with valvular insufficiency. A few dogs had only tricuspid insufficiency and many of the dogs with MV also had TV insufficiency noted by color-flow Doppler.
Auscultation was able to “pick up” mitral insufficiency much more reliably if the insufficiency jet was moderate to severe. Mild grades of insufficiency were more difficult to differentiate from ejection murmurs in these healthy and athletic dogs.
Overview of the heart conditions under discussion:
1. Ejection murmurs (also called “athletic” or “flow” murmurs) are the sound of blood passing through normal valves. Ejection murmurs are most commonly heard in thin, athletic animals with large hearts. They can be a normal finding in a healthy animal, but may be confused with murmurs caused by heart diseases such as aortic stenosis or mitral insufficiency. Ejection murmurs are characteristically heard best at the left heart base, and their intensity may vary with the heart rate. They can be heard at any age.
2. Mitral murmurs (also called mitral regurgitation or insufficiency murmurs) are the sound of blood leaking backward through a mitral valve that does not close properly. The changes seen on the valve include thickening and improper/incomplete closure and are due to age-related degeneration of the valve. Dogs may have mitral murmurs and mitral insufficiency for years before showing any signs of heart disease, so overall good health does not indicate whether a murmur is indicative of valve disease or an ejection murmur. Mitral insufficiency murmurs are characteristically heart best over the left apex of the heart.
Mitral insufficiency due to degenerative valvular changes is a common disease of middle-aged to older dogs and as such, may be a disease of aging in whippets much as it is in other breeds. In contrast, Cavalier King Charles Spaniels are subject to an earlier onset of valvular changes peculiar to the breed, and this tendency is thought to be inherited.
3. Ejection murmurs may be detected in animals with other cardiac diseases including mitral insufficiency. Therefore, an animal diagnosed with an ejection murmur at one auscultation may also have or develop mitral disease.
4. Small amounts of valvular insufficiency may be noted by Doppler examination on both mitral and tricuspid valve. If trace insufficiency is not associated with overt anatomic abnormalities of the valve, it may indicate very early disease or be a normal variation in healthy dogs. Other factors used to decide the importance of small amounts of valvular insufficiency include cardiac chamber size, the presence of changes in heart rhythm and presence of clinical signs of heart disease (including exercise intolerance, easy fatigue, cough, difficulty breathing or fainting). In healthy dogs, the importance of small amounts of valvular insufficiency remains unclear and the presence of these findings should not be overemphasized.
A few words about the population:
The population screened this year was a young and healthy population of dogs, many of which were involved in some level of athletic competition. The high proportion of dogs with murmurs may be due to the prime body condition and athletic training of these animals and the proportion of whippets in the general population with ejection murmurs or mitral insufficiency cannot be deduced from this year’s information. In addition, the young age of most of these dogs may have an effect on the findings of a disease (MV insufficiency) commonly thought to be associated with aging.
Importance of this year’s findings:
This year’s findings indicate that many whippets have heart murmurs, and that many of these heart murmurs are not associated with echocardiographic abnormalities of the mitral or tricuspid valve. However, some healthy dogs do have evidence of moderate to severe MV insufficiency, and it is unclear from a study performed at a single point in time whether the MV disease noted is a disease of aging or may have an inherited component.
It is too early in the information-gathering process to make any recommendations regarding breeding in animals noted to have valvular abnormalities in this study. In many cases, it is unclear whether mild changes noted represent a developing process or normal variation in the population.
Our research group continues to work with the Whippet Health Foundation to develop screening programs and acquire more information regarding the cardiac status of whippets as a breed. Watch for future events – we look forward to having you and your dog included in future studies.