Heart Disease in Dogs

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The canine heart is a hard-working organ and is divided anatomically into left and right sides; valves allow for blood flow through the heart. The left atrium, the right atrium, the left ventricle, and the right ventricle comprise the four heart chambers. The external heart "sac" is designated the pericardium, and the myocardium is the actual muscle of the heart. The endocardium is the inner layer of cells in the heart. Heart disease, or cardiac disease, can affect any of these components.

"Dirty" blood (carrying carbon dioxide from organs, tissues, and cells) enters the right atrium through large vena cavae veins and flows to the right ventricle via the tricuspid valve. It travels through the pulmonary artery (via the pulmonary valve) to the lungs to collect oxygen and eliminate carbon dioxide and re-enters the left atrium through the pulmonary vein. The mitral valve ferries the oxygen-rich blood to the left ventricle, and the aorta (entering through the aortic valve) carries "clean," oxygen-rich blood to the remainder of the body.

Heart disease, or cardiac disease, can be a devastating clinical condition in companion animals. Early recognition and treatment can facilitate appropriate clinical management and a long life.

Types of Heart Disease in Dogs

Cardiac disease is classified as either congenital or acquired.

• Most congenital cardiac defects are present from birth or near birth and include conditions such as septal defects (atrial and ventricular), valve dysplasias, patent ductus arteriosus, tetralogy of fallot, vascular ring anomalies, aortic, pulmonic, and mitral valve stenosis, and cor triatriatum dexter. All involve some degree of structural heart component or valvular dysfunction.
• Although some breed-associated congenital conditions are detected early in life, others are not identified until adulthood. Cavalier King Charles spaniels, doberman pinschers, boxers, and Newfoundlands are among breeds frequently diagnosed with familial cardiac conditions.
• Acquired conditions can also affect any heart component but are not present at or near birth. They develop over time, and many are not pathologic or progressive. However, some may be associated with progressive heart and valve disease.
• Endocarditis, myocarditis, and pericarditis are structural inflammatory conditions that result from a variety of causes, including infectious, traumatic, and immune conditions.
• Pericardial effusion occurs when excessive fluid collects between the layers of the pericardial sac; causes are diverse and can include cancer.
• Valvular endocardiosis, valvular degeneration, and valvular regurgitation/insufficiency are frequently-identified valvular conditions.
• Heartworm disease is an important acquired heart disease.

What is a Heart Murmur?

A heart murmur is an extra sound in the heartbeat that is detected by the veterinarian during the physical examination; such murmurs usually develop secondary to turbulent blood flow. Heart murmurs are identified in patients with and without heart disease.

Many murmurs are innocent, or occur without any evidence of heart disease. These are especially common in young puppies. They are soft murmurs and usually disappear on their own. Other benign murmurs are seen secondary to anemia (decreased red blood cell count), pain, and intense excitement.

Pathologic murmurs (those that indicate the presence of heart disease) may have very characteristic sounds and locations and are associated with cardiac disease.

Clinical Signs and Complications of Heart Disease in Dogs

Clinical signs of heart disease in dogs include:

• Pale or lilac-colored mucous membranes
• Weak pulses
• Cold extremities
• Poor circulation
• Fainting
• Jugular vein pulses
• Breathing difficulties
• Coughing
• Exercise intolerance
• Heart murmurs
• Clots in the arteries
• Fluid collection in the abdomen
• Edema or swelling of the limbs
• Weight loss (cardiac cachexia)

Breathing difficulties are an extremely common cardiac complication in dogs because of fluid retention inside or outside of the lungs.

Diagnosis of Heart Disease in Dogs

Diagnosis of canine heart disease is usually facilitated by a combination of cardiac ultrasonography (ultrasound), chest x-rays, blood pressure measurement, blood work/cardiac enzyme level measurement, urinalysis, and electrocardiogram analysis. Veterinary cardiologists may perform more advanced diagnostics in necessary cases.

Treatment of Heart Disease in Dogs

Treatment of heart disease in dogs is dependent on the cause; its goal is to slow the progression of heart failure (the inability of the heart to keep up with its necessary functions).

Treatment may include any of the following therapies and drugs:

• Antibiotics: Antibiotics are used to treat infectious causes of cardiac disease.
• Angiotensin converting enzyme (ACE) inhibitors: This class of drugs can increase the blood output of the heart, increase sodium loss in the urine, and decrease blood pressure.
• Diuretics: Diuretics promote urine formation to assist in fluid removal from the body.
• Dietary modification/low salt diets
• Pimobendan: This drug is a calcium sensitizer and phosphodiesterase enzyme inhibitor. It is useful in specific clinical cases of canine heart disease.
• Positive inotropes: These drugs increase the ability of the heart muscle to contract, allowing it to be more efficient.
• Taurine/carnitine therapy: An amino acid important for heart health.
• Vasodilators: These drugs can assist in high blood pressure and congestive heart failure.
• Calcium-channel blockers: Can assist in high blood pressure and congestive heart failure.
• Anti-clotting agents: To prevent the formation of dangerous clots.
• Fluid removal from the pleural space or abdomen: This can be done periodically by a veterinarian as needed.
• Surgery may be required in certain cases, particularly in congenital, structural cardiac disease.

Prognosis of Heart Disease in Dogs

Prognosis is completely dependent on the etiology, or cause, of the heart disease.

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