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Heart Valve Malformation in Dogs

What Is Heart Valve Malformation in Dogs?

Heart valve malformation, known as atrioventricular valve dysplasia (AVD) in dogs, is a condition where the mitral or tricuspid valve develops abnormally, leading to improper closure and blood flow obstruction. This condition stems from developmental issues and results in narrowed valves. Symptoms vary based on the severity of valve narrowing and the specific location of the malformation.

Anatomy of a Dog’s Heart

A dog’s heart consists of four chambers: two atria on top and two ventricles on the bottom. These chambers are separated by atrioventricular (AV) valves, which open and close using leaflets to regulate the flow of blood from the atria to the ventricles during each heartbeat.

The mitral valve, with two leaflets, is situated on the left side of the heart, while the tricuspid valve, with three leaflets, is located on the right side. Deoxygenated blood from the body enters the right atrium, passes through the tricuspid valve to the right ventricle, and then travels to the lungs to receive oxygen. Oxygen-rich blood returns to the left atrium, passes through the mitral valve to the left ventricle, and is pumped out to the body.

This continuous cycle is essential for sustaining life. The AV valves play a crucial role in preventing the backward flow of blood from the ventricles to the atria while the heart contracts. Dysfunction of these valves can lead to blood backflow and ultimately result in congestive heart failure (CHF).

AV Malformations in Dogs

AV malformations are congenital defects, meaning they are present at birth and typically diagnosed within the first few years of a dog’s life, though they may be identified later if they are mild. There are two primary types of AV malformations:

Mitral valve dysplasia (MVD): This condition involves narrowing of the mitral valve, which allows blood to flow back from the left ventricle to the left atrium, impacting the flow of oxygen-rich blood to the lungs from the heart. Breeds predisposed to MVD include Bull Terriers, Dalmatians, German Shepherds, Golden Retrievers, Great Danes, Mastiffs, Newfoundlands, and Rottweilers.

Tricuspid valve dysplasia (TVD): In this condition, the tricuspid valve narrows, allowing blood to flow back from the right ventricle to the right atrium, affecting the flow of deoxygenated blood returning from the body to the heart. Breeds predisposed to TVD include Boxers, Dogue de Bordeaux, German Shepherds, Great Danes, Great Pyrenees, Irish Setters, Labrador Retrievers, Old English Sheepdogs, and Weimaraners.

AV malformations lead to enlargement (dilation) of the atria on the affected valve side, which in turn enlarges the ventricle. Eventually, this causes volume overload and affects blood flow, resulting in fluid accumulation in the lungs and/or abdomen, known as congestive heart failure (CHF).

Symptoms

Symptoms of AVD can vary greatly, ranging from nonexistent in the early stages to severe as the condition progresses. These indications typically manifest within the first 1 to 2 years of a dog’s life. One common sign is the presence of heart murmurs, characterized by an abnormal “whooshing” noise detected by a veterinarian when listening to the dog’s heart with a stethoscope.

Clinical signs differ based on which AV valve is affected. For MVD, symptoms may include:

  • Coughing
  • Fatigue during exercise
  • Increased respiratory rate or effort
  • Bluish or grayish discoloration of the gums
  • Episodes of collapse, weakness, or fainting

In contrast, clinical signs associated with TVD may include:

  • Stunted growth
  • Easily becoming fatigued during exercise
  • Abdominal distension due to fluid buildup
  • Episodes of collapse, weakness, or fainting

Causes

The exact cause of heart valve malformations in dogs remains unconfirmed, but they are believed to stem from genetic mutations, inadequate prenatal nutrition, infections during gestation, and certain medications administered during pregnancy. Veterinarians suspect that these AV defects may be hereditary, considering the predisposition of certain dog breeds.

Diagnosis

Diagnosis of heart valve malformation in dogs relies on a thorough examination of clinical symptoms and, at times, investigation into the dog’s lineage. Veterinarians also conduct blood tests, measure blood pressure, and perform radiographs to evaluate the heart’s size, blood vessels, and the presence of fluid in the lungs or abdomen.

For a definitive diagnosis of AVD and to assess fluid accumulation, veterinarians may recommend echocardiography, which involves ultrasounds of the heart. This procedure, considered the “gold standard,” aids in diagnosing the condition and monitoring its progression in dogs.

Additionally, an electrocardiogram (EKG or ECG) may be conducted to evaluate the heart’s electrical function and rule out any abnormal heart rhythms (arrhythmias). Analyzing heart rhythm often assists in determining the origin of the disease within the heart.

Treatment

Treatment of AVD focuses on managing the clinical symptoms since there is currently no cure for the condition. Typically, this involves addressing and controlling congestive heart failure (CHF). In severe cases, hospitalization may be necessary, along with oxygen therapy and diuretics to alleviate fluid buildup, especially in instances of right-sided CHF where removal of abdominal fluid may be required for relief.

Oral medications are commonly prescribed once changes in heart chambers are observed or CHF is diagnosed. These medications, often required for the rest of the dog’s life, include diuretics, ACE inhibitors, and Pimobendan. In some cases, anti-arrhythmic medications may also be necessary. Veterinarians often advise restrictions on exercise and reducing sodium intake in the dog’s diet.

While attempts have been made to perform artificial tricuspid valve replacements, they often fail due to complications. This surgical option is often not feasible due to its cost and limited availability.

Living and Management

Unfortunately, the long-term prognosis for dogs with AVD varies from unknown to poor, depending on the severity of the condition. Prognosis tends to worsen once a dog develops congestive heart failure.

Dogs diagnosed with AVD typically require lifelong cardiac medications and regular visits to the veterinarian or a board-certified cardiologist to monitor disease progression. Medications may need to be adjusted or added as the condition advances.

Managing dogs with AVD often involves reducing stress, limiting exercise, and modifying their diet to decrease sodium intake while ensuring they receive appropriate amino acids and nutrients. It’s crucial to avoid breeding dogs diagnosed with AVD, as veterinarians suspect these conditions may be hereditary.

Heart Valve Malformation in Dogs FAQs

What is the life expectancy of a dog with heart valve disease?

Dogs with mild heart valve disease can typically live normal lifespans. However, dogs with more severe valve disease may only survive for 1 to 2 years.

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