Description

Horses seem to be able to compensate for a diseased heart for many months or years without signs of heart failure. In most cases, the heart muscle is weakened and begins to lose the ability to provide adequate circulation to meet the body's needs.

Although acquired heart disease is uncommon in horses, when it develops it is accompanied by a reduction in exercise capacity and shortness of breath and the horse may collapse with congestive heart failure.

Atrial fibrillation is an electrical disorder of the heart rhythm, also known as arrhythmia, and is often associated with diminished performance.

Pericarditis is a viral respiratory infection of the membrane lining the chest cavity. As the disease progresses, fluid builds up in the sac, pressing directly on the heart and interfering with filling of the chambers. When the volume of blood entering the heart is restricted, congestive heart failure occurs.

Myocardial disease is often suspected when an arrhythmia develops after an infectious disease, such as strangles or influenza. When the heart muscle becomes inflamed, it loses strength and contracts less forcefully. The bacteria Streptococcus equi is the chief cause of myocarditis.

Thrombophlebitis of the jugular veins is the only common condition affecting the veins of horses. Unlike humans, horses are usually not prone to suffering heart attacks, strokes, and other peripheral arterial diseases.

Valvular heart disease is the most commonly recognized structural heart disorder. As the valve leaflets thicken and become deformed, usually with age, a valve leak can develop, leading to edema and cardiac insufficiency.

Symptoms

• Loss of condition
• Fatigue during exertion
• Weakness, occasionally resulting in collapse or fainting
• Shortness of breath
• Increased rate or effort of breathing
• Rapid, weak, and irregular pulse
• Signs of fluid accumulation in the abdomen or beneath the skin of the lower thorax
• Heart murmurs, indicating erratic blood flow
• Unexplained lameness
• Gait disturbances
• Stumbling or collapsing
• Weak digital pulses
• Tender, swollen cord in the neck, accompanied by heat, redness, and swelling (in the case of thrombophlebitis)

Causes

Congenital defects, bacterial and viral infections, long-term use of anabolic steroids, and age are common causes of heart disease in horses. Horses with chronic heart disease often suffer collapse, in association with arrhythmia and congestive heart failure.

Equine influenza, viral arteritis, and infectious anemia are among the viruses that may attack the equine heart. Cardiomyopathy is a form of myocarditis in which the heart enlarges rapidly. The enlarged, flabby heart fails quickly and the horse often dies.

Increasing evidence shows that genetic background may play a major role in a horse's susceptibility to developing heart disease. Heart muscle disorders have been shown to have a major genetic component and familial or breed tendencies strongly suggest that genetics play a role in these conditions.

Septal defects are the most common congenital heart defects in horses. A ventricular septal defect is a hole in the septum (wall), which separates the two ventricles. Blood flows from the right to the left side of the heart without going through the pulmonary circulation and receiving oxygen. This leads to fatigue and loss of condition.

Patent ductus arteriosus is a persistent fetal artery, joining the pulmonary artery to the aorta. Normally, the ductus closes shortly after birth. If the ductus does not close, aortic blood shunting through the pulmonary system leads to development of pulmonary hypertension, heart failure, and death.

Diet and exercise have not been shown to be factors in equine heart disease.

Prevention

Preventative strategies to reduce the likelihood of heart disease are, so far, limited to avoiding in-breeding, not breeding animals with known congenital defects of any kind, and not breeding horses that have acquired a heart disorder relatively early in life, as this may indicate a strong genetic component (with increased susceptibility in offspring).

Treatment

For any kind of heart disease, the services of a veterinarian skilled in treating heart conditions should be initiated. An accurate diagnosis that determines the type and extent of heart disease is essential before treatment can begin.

X-rays, EKG's, and echocardiograms should be done to determine the areas of the heart affected and the extent of the damage. Activities should be restricted to those within the horse's exercise tolerance, without bringing on symptoms of distress or discomfort.

Many of the same drugs used for heart conditions in humans are used for the same purposes with horses. Digitalis, lidocaine, atropine, magnesium sulfate, and propranolol are used to control arrhythmia and heart failure. These drugs require close monitoring and are usually used for short-term effect.

Searching for and correcting any underlying electrolyte or metabolic problems is also important in arriving at the best therapy for treating arrhythmia. In the case of bacterial pericarditis, antibiotics are usually prescribed for at least two months. If fluid build-up is present in the chest or body cavity, pericardiocentesis (drawing off fluid with a long needle inserted into the pericardial sac) may be used to improve cardiac functions.

In some cases, intensive and prolonged antibiotic therapy is required when bacterial infections are causing the heart disease. For treatment of myocarditis, rest and the use of corticosteroids to reduce heart muscle inflammation, has been recommended, although steroids are known to lower the body's immune response to viruses.

In the case of jugular vein thrombophlebitis, application of hot packs and topical DMSO (Dimethyl sulfoxide) to the neck three times a day until the swelling subsides is the recommended treatment, along with administration of anticoagulants, such as aspirin or low-dose heparin. In uncomplicated cases, the clot dissolves and the vein returns to normal.