CARDIOLOGY CORNER

Congenital Cardiac Defects in Dogs
Bonnie K. Lefbom, DVM

Spring approaches, and with it a new batch of puppies. This may be a good time to review our top five list of congenital defects in dogs and discuss our therapeutic options. Auscultation in puppies can be a challenge. It is important, however, to obtain a clear evaluation at all valve sites as well as in front of the heart at the base of the carotids.

The easiest defect to recognize is a PDA (Patent Ductus Arteriosus) with its continuous, machinery quality murmur. The diastolic component of this murmur can be difficult to hear in the face of a loud systolic murmur from mitral regurgitation. The key to picking up the diastolic component is to listen cranially in front of the left shoulder at the base of the carotids. Of all defects, PDA provides the best prognosis with repair. We are able to perform surgical ligation of the ductus and most often provide a normal lifespan for these puppies. Of course there are several caveats. Risk of death is moderate (although our practice success rate is >95% survival). If the defect is large and the volume overload on the heart dramatic, life long post-operative medications may be required. An alternative therapy we offer for PDA repair is coil occlusion. This procedure is performed transvenously and is therefore much less invasive. The coil is placed under fluoroscopic guidance and can successfully occlude the smaller diameter ductus. Puppies with larger vessels are not candidates for this procedure and there is a higher risk of incomplete occlusion or unsuccessful repair. As with all defects, complete echocardiographic examination is mandatory prior to any interventional procedure to rule out the presence of additional defects.

Another defect we see routinely is SAS (subaortic stenosis). The popularity of some commonly affected breeds - Golden Retrievers, Newfoundlands, and Boxers - has brought this defect a lot of attention over the past few years. The murmurs in these puppies are typically harsh, systolic murmurs heard best over the Aortic region at the left heart base (high in the left axillae). Many dogs can be mildly affected with SAS and live normal lives. We categorize their defect into mild, moderate, and severe based on the Doppler derived pressure gradient through the left ventricular outflow tract. Gradients less than 50 mm Hg are considered mild and generally allow a normal lifespan. Gradients of 50-80 mm Hg are moderate and can shorten the lifespan to some degree. We may prescribe beta blockers in these dogs to lower the dynamic component of their gradients. Dogs with gradients over 80 mm Hg are considered severely affected and candidates for intervention. The intervention consists of transvenous balloon dilation of the subaortic region. We perform this technique under fluoroscopic guidance. The risk associated with this procedure is low but can result in sudden death due to rupture of the coronary arteries or ventricular tachyarrhythmias. Colorado State University offers surgical repair of these defects using cardiac bypass technology. We offer our clients referral to CSU if desired.

Pulmonic stenosis can be difficult to distinguish from subaortic stenosis based on auscultation. The breed predisposition is different which can be a helpful clue. Bulldogs, Westies, Beagles, and Schnauzers are representative breeds. The interventional technique is essentially the same as for SAS-fluoroscopic guided balloon dilation of the affected region. 80% of severely affected dogs achieve a 50% reduction in their transvalvular gradients with this technique.

Septal defects are more readily diagnosed based on auscultation. These murmurs generally are systolic and loudest on the right side of the chest (due to the most common left to right flow). Most dogs with these defects live normal lives with no restrictions. The uncommon very large or unrestrictive defect can cause a volume overload on the heart and predispose to heart failure.

Finally, probably the worst defect we see in our young, larger breed of dogs - Labrador retrievers most commonly - is tricuspid dysplasia. These puppies can present in fulminant right heart failure including ascites and exercise intolerance. Their murmurs generally are systolic and right-sided as well. They can be missed early because of their softness. Unfortunately, we do not have an intervention for this problem. The best we can offer is medical management of the right heart failure which is typically unrewarding long term. Tricuspid dysplasia does have variable degrees of severity, however, and mildly affected dogs can live on medication for several years.

As with all congenital abnormalities, we strive to identify these animals as early as possible. Our ultimate goal is to minimize these defects in the dog population and encourage owners to prevent affected animals from breeding, regardless of the severity of the defect. Our combined efforts with you along with local breeders will continue to move us all towards this goal.