Atrial fibrillation is characterized by rapid, irregular activation of the atria. Causes can include reentry and abnormal automaticity. In veterinary practice, atrial fibrillation is one of the most commonly seen supraventricular arrhythmias. AF sometimes is paroxysmal; however, it is usually chronic in dogs and cats AF and is associated with advanced stages of chronic AV valve insufficiency or cardiomyopathy. Chronic AF often causes a markedly elevated ventricular response rate and thereby contributes to the clinical signs of heart failure. AF also can occur in the absence of overt structural heart disease as lone AF, which can feature a normal of mildly elevated ventricular response rate.
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