William R. Pritchard Veterinary Medical Teaching Hospital

Frequently Asked Questions

What are Acquired Heart Diseases?

Degenerative Mitral Valve Disease (DMVD) - This is a degenerative process of uncertain cause which affects the mitral valve (the valve between the receiving and pumping chambers on the left side of the heart). Currently, there is no way to predict when or even if a dog with DMVD will develop congestive heart failure. Thus, many dogs diagnosed with DMVD live their entire lives without ever requiring treatment. With of this knowledge, and due to the risks associated with open heart surgery, we currently only recommend surgery for dogs after they have had evidence of congestive heart failure. Once congestive heart failure develops, the average life expectancy is much more predictable (usually around 6-18 months) and as such, the risks versus benefit of surgery become more reasonable. Two main surgical options exist to correct the disease, mitral valve repair or mitral valve replacement. The option for which procedure to perform depends on stage of the disease, size of the dog, and findings at the time of the surgery. In either case, surgery is undertaken with curative intent, and this goal is achieved in approximately 75% of dogs which survive the procedure. Currently, dogs are alive up to four years after surgery and no longer require diuretic therapy to control their disease.

Valvular Endocarditis - This is a disease where one of the cardiac valves (usually the aortic or mitral valve) has become infected. Due to the risks of operating in an infected environment, coupled with the unpredictable outcome associated with valve replacement in dogs, surgery for valvular endocarditis is currently not recommended.

Cardiac Tumors - Several different types of cardiac tumor are reported in dogs. Open heart surgery has application in addressing some of these tumors, particularly when the tumor is located within one of the cardiac chambers. The intent of surgery in these cases is usually curative, however this implies complete removal of the mass which is not always possible. Palliative removal may still have benefit in such patients, as removal of the mass may alleviate clinical signs and heart failure associated with the mass. However, when palliative surgery is performed, it is expected that the mass will regrow over time, and eventually the clinical problem will recur.    

What are Congenital Heart Diseases?

Atrial Septal Defect (ASD) - The atria of the heart are the receiving chambers for blood. There are two atria (right and left), which are usually separated from one another by the interatrial septum. Failure of the interatrial septum to form normally in-utero leads to the presence of an ASD at birth. If your dog has been diagnosed with an atrial septal defect, the good news is that this lesion alone, rarely requires surgery. Even relatively large ASD's are usually well tolerated by the patient with relatively normal quality and quantity of life.

In cases where an ASD is considered to be significant, then open heart surgical repair of the lesion should be considered. Surgery for uncomplicated ASD's is carried out with curative intent. ASD is occasionally found in combination with other lesions, and in this situation, are always closed during surgery for the primary lesion.

Ventricular Septal Defect (VSD) - This is more commonly known as a "hole in the heart". The ventricles are the pumping chambers of the heart. There are two ventricles (right and left) which are usually separated from one another by the interventricular septum. Abnormal development of the interventricular septum in-utero leads to the presence of a VSD at birth. Presence of a VSD does not necessarily mean that the patient will ever suffer any detrimental effects from the lesion. In assessing patients with VSD, your cardiologist will determine if the VSD is having a significant effect on heart function. This determination is related to the amount of blood which leaks through the VSD as the ventricles contract. The more blood which leaks, the more significant the VSD becomes. Insignificant VSD's are well tolerated and are unlikely to ever effect your dog's quality or quantity of life. Consequently, only significant VSD's require treatment.

Where possible, the preferred method for VSD closure is by a catheter based procedure. However, this is not applicable to all cases of VSD at this time, and surgery remains an option for difficult cases. Using cardiopulmonary bypass, closure of VSD is performed with curative intent.

Double Chamber Right Ventricle (DCRV) - This is a congenital malformation which may also be termed subvalvular pulmonic stenosis or primary infundibular stenosis. The lesion is usually a fibromuscular obstruction which separates the right ventricular inflow and outflow portions. This lesion causes an obstruction to blood flow out of the inflow portion of the right ventricle, leading to increased muscle formation in the inflow portion of the right ventricle. The name double chamber right ventricle refers to the inflow portion of the right ventricle becoming highly muscular, while the outflow portion remains normal.

Currently, only open heart surgical correction is capable of correcting this problem. Surgery is performed with curative intent, as the lesion is removed during the procedure and the area of constriction relieved by placement of a synthetic patch of material on the outside of the heart.

Pulmonic Stenosis (PS) - The most common form of pulmonic stenosis is a lesion which affects the pulmonary valve itself (valvular pulmonic stenosis). Commonly, this lesion is well treated with a catheter based procedure (balloon dilation) and as surgical options are usually reserved for patients who have failed previous balloon dilation attempts. The surgical procedure can be performed either with the use of cardiopulmonary bypass (Open heart) or by use of a technique called inflow occlusion (where blood flow is temporarily stopped completely while the procedure is rapidly performed). The advantage of performing the procedure with the use of cardiopulmonary bypass is that the lesion can be deliberately removed/relieved and outcome is very predictable. The procedure leaves the patient with significant leak of the pulmonary valve, but this leak is usually well tolerated by the patient, and as such the surgery is essentially curative.

Tetralogy of Fallot (TOF) - This is a complex congenital abnormality, which has 4 components (Pulmonic stenosis, Ventricular Septal Defect, Over-riding Aorta and Right Ventricular Hypertrophy). The disease leads to clinical signs due to blood from the right side of the circulation being able to enter the systemic circulation, without ever passing through the lungs. This leads to deoxygenated blood (right sided circulation) entering the systemic circulation and thus muscles, brain etc receive less oxygen than normal. Common clinical signs of this are collapse, weakness and gasping for breath (as the body interprets the lack of oxygen as inadequate breathing). Two categories of surgery can be contemplated for dogs with TOF.

The first type of surgery does not require Cardiopulmonary Bypass and is undertaken with palliative intent. This type of surgery involves creating another route for blood to get from the systemic circulation to the lungs. This increases the proportion of blood which enters the lung vasculature and thus improves the amount of oxygen in the systemic blood. This surgery is purely aimed at reducing clinical signs, and does nothing to correct the original physical heart abnormalities. Open heart surgery for TOF is undertaken with essentially curative intent. The surgery consists of correcting the VSD (which simultaneously corrects the over-riding aorta), and correcting the pulmonic stenosis. This surgery is thus, essentially curative.

Tricuspid Valve Dysplasia (TVD) - This occurs due to a malformation of the Tricuspid Valve. The malformation leads to leak of blood into the right atrium (receiving chamber for blood on the right side of the heat) as the right ventricle contracts. For unknown reasons, prediction of outcome for dogs with TVD is very inaccurate, especially on a single examination. Some dogs will have what appears to be a large amount of leak on echocardiogram, but will cope with the leak and never develop heart failure, while other dogs with relatively moderate leak will develop progressive failure of the right heart. Having said that, the good news is that a large proportion of these dogs seem able to cope with the leak and live their entire lives without ever needing any treatment.

Due to the difficulty of predicting whether dogs with TVD will ever require treatment, we suggest serial (multiple time point) radiographs as a method for assessing whether the right heart is progressively dilating with time (a finding which is presumed to be associated with high risk of developing right sided heart failure). Ideally, surgical candidates should be operated upon before right sided heart failure actually occurs. The valve is usually not able to be repaired, and thus replacement is the only feasible option.

The surgery is aimed at curative intent, however this is rarely achieved, due to the risks of replacement valves in dogs, and the finding that the right heart is rarely able to fully recover from the huge pre-operative enlargement. Due to these problems, surgery for TVD is currently best thought of a palliative only. Even with a successful surgery, the right heart may continue to degenerate in function and patients can develop heart failure once more years after the initial surgery.

Mitral Valve Dysplasia (MVD) - This occurs due to a malformation of the Mitral Valve. The malformation can lead either to leak of blood into the left atrium (receiving chamber for blood on the left side of the heart) as the left ventricle contracts (Mitral Insufficiency), or to obstruction of blood flow into the left ventricle from the left atrium during the filling phase of the heart beat (Mitral Stenosis).

In the case of Mitral Insufficiency, the amount of leak is usually well correlated to whether the heart can cope with the lesion or not. Many dogs have trivial mitral dysplasia, which has no effect on quality or duration of life. However, more severe mitral dysplasia can lead to left sided congestive heart failure. Only dogs with the more severe form of the disease should be considered for surgery, and coupled with our inability to predict when or even if congestive heart failure will occur in the future, we only advise operation once the dog has experienced a bout of failure. Unlike tricuspid valve dysplasia, repair of mitral dysplasia is commonly possible at surgery. The surgery is thus undertaken with curative intent, although valve replacement is always reserved as an option for cases where repair is found to be impossible at the time of the surgery.

In the case of mitral valve stenosis, the severity of the lesion again determines whether the dog can cope with the lesion or not. In dogs which develop left sided congestive heart failure, surgery is indicated. Repair of the valve is the primary aim of the surgery, although valve replacement is always reserved as an option.