Heart Testing
Tricuspid Valve Dysplasia and Labrador Retrievers
What is tricuspid valve dysplasia?
It is a defect of a valve within the right side of the heart. Valves help blood flow in the correct direction in the heart. The tricuspid valve controls blood flow by the opening and closing of small flaps, leaflets, inside the valve. When the flaps are deformed, dysplastic, some blood can flow back in the wrong direction as the heart pumps. The defect is congenital, meaning present from birth.
Depending on how poorly formed the valve is, dogs with tricuspid valve dysplasia (TVD) may progress to congestive heart failure. Arrhythmia, or irregular heart rhythm, can also be associated with tricuspid valve dysplasia and cause sudden death. Some dogs have normal lifespans if their TVD is mild enough, but shortened lifespan is to be expected for severely affected dogs.
How is TVD found?
Sometimes TVD will produce a murmur, an abnormal heart sound, that can be heard with a stethoscope. Listening with a stethoscope is called auscultation. Generally, the worse the murmur; the worse the TVD. However, some veterinarians can and have missed even significant murmurs in dogs with TVD, mine included. Don’t assume that because a dog has had a basic vet check that it is clear of TVD. Of course, murmurs are not specific to TVD, several other murmur causing conditions, and even “innocent” murmurs are possible.
If a murmur is heard, then an ultrasound of the heart, called an echocardiogram, can be performed to show the cause of the murmur and severity of the heart condition. Auscultations and echocardiograms are best performed by qualified cardiologists because they have the most training, experience and equipment in finding and grading heart conditions.
Mild TVD may not produce an audible murmur at all. I know of several affected dogs that were only discovered because an echo was done for breeding screening purposes. It is likely that there are many Labs with “silent” TVD that generates no murmur.
Is TVD curable?
Practically speaking, no. Most dogs will only receive medication to treat and attempt to delay the symptoms of heart failure.
Is tricuspid valve dysplasia genetic?
Scientists believe so. In a study of a service dog breeding stock population, heritability of TVD was estimated to be 0.71.1 If so, then TVD is more heritable than hip dysplasia. Several estimates of the heritability of hip dysplasia have been done in Labradors in the UK with none higher than 0.37.2 However, no one knows exactly which gene or genes control the defect. Genetic research is ongoing. Currently scientists do not know the mode of inheritance (recessive, dominant, etc.), although the general opinion is that it is likely to be autosomal dominant with incomplete penetrance, but this has not been proven.
Why are we only now hearing about TVD?
TVD has not been considered an issue in Labrador Retrievers in Australia until approximately the last ten years. It has long been an issue in the US, however breeders in the UK do not regard it as a problem. It is not confined to particular bloodlines nor working bred vs. show bred Labradors.
Breeders who say it isn’t a problem in their lines can’t know that unless they are checking for it; mild TVD may go unnoticed without an echocardiogram.
Even if their foundation dogs seemed trouble free, each generation usually incorporates some outside dogs that a breeder simply cannot know everything about. No one is so experienced or smart that they can substitute their educated guesses for actual health screening.
What can be done to reduce TVD in the breed?
This starts with not breeding from affected dogs. Much as with hip and elbow dysplasia, there is no definitive DNA test for TVD. Thus, the only thing that can be done is to screen breeding stock to weed out obviously affected dogs. Radiographs, x-rays, are used for hip and elbow screening, but hearts need an echocardiogram. Auscultation does not catch “silent” TVD affected dogs. Although these silent TVD dogs may never have obvious problems themselves, they can pass on any genetic predisposition to TVD to future generations. Just as with hip dysplasia, their offspring may be more severely affected than them.
Dogs with normal echocardiogram results can still produce TVD affected puppies, just as dogs with 0:0 hips can still produce puppies with hip dysplasia. However, statistics indicate that dogs with normal hips produce fewer puppies with hip dysplasia than dogs with abnormal hips. One would expect, and hope, the same is true of TVD and dogs with normal hearts produce fewer TVD affected puppies than dogs with abnormal hearts.
In short, echo all breeding stock. We have moved from few and random breeders xraying hips and then elbows to now, where it is a requirement for registration of the litter that both parents be xrayed. The best we can do currently with TVD is to test breeding stock so we know where there are problems and hope that DNA research will soon provide a more definitive test. Knowledge is power.
Sylvia Power
July 2022
With sincere thanks to Laurel McCord for permission to use sections of her excellent article:
BE(heart a)WARE: Questions You Should be Asking About Tricuspid Valve Dysplasia and Labrador Retrievers
References:
- T Famula, L Siemens, A Davidson, M Packard. Am J Vet Res. 2002 Jun;63(6):816-20. Evaluation of the genetic basis of tricuspid valve dysplasia in Labrador Retrievers.
- BJ Wilson, FW Nicholas, JW James, et al. Heritability and phenotypic variation of canine hip dysplasia radiographic traits in a cohort of Australian German shepherd dogs. PLoS One. 2012;7(6):e39620. doi:10.1371/journal.pone.003962