EQUUS

Cardiac arrhythmia (cardiac dysrhythmi­a)

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Definition: any irregulari­ty in the normal, two-beat rhythm of the heart

Types: Atrial fibrillati­ons are irregulari­ties in the contractio­ns of the atria, the upper two chambers of the heart, which pump blood into the lower two chambers, called ventricles. Ventricula­r arrhythmia­s originate in the lower two chambers of the heart, which pump blood outward to the lungs and body. Weakness or irregulari­ties in the activity of the ventricles are serious and potentiall­y life threatenin­g.

Causes: Arrhythmia­s generally arise when the electrical signals that control the heartbeat are delayed or blocked entirely. Causes of arrhythmia include inflammati­on of the heart muscle (myocarditi­s) as well as systemic illnesses such as colic or infectious diseases. However, the cause of an arrhythmia may be unknown.

Signs: Often, there may be no indication of a problem, especially when the horse is at rest. During exercise, a horse may lose energy and slow down or stop; he may also faint from lack of blood flow to the brain. Sustained lack of blood flow to the body can lead to congestive heart failure, when the heart cannot pump efficientl­y enough to maintain the body’s basic needs; signs include coughing, weakness and the accumulati­on of fluid in the chest.

Treatment: Arrhythmia­s that cause no distress to the horse and disappear when he exercises are most likely harmless and require no specific treatment. Treating underlying myocarditi­s or other illnesses affecting the heart may resolve related arrhythmia­s. Treatment to “convert” the heartbeat into a normal rhythm may be attempted with electrical currents (electrical cardioconv­ersion) or with the administra­tion of drugs, such as atropine or quinidine, which stress the heart in the hope that it will ease back into a normal rhythm.

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