As long as they don't have more serious heart disease such as CHF, most horses do well with intervention through pharmacologic or electrical cardioversion. Atrial fibrillation (AF), an electrical disorder of the heart rhythm, is the most common pathological arrhythmia in horses. With this condition, the atria fail to contract but instead quiver or fibrillate, and impulses are conducted intermittently through the atrioventricular (A-V) node to the ventricles. The resulting electrocardiogram (ECG) hasirregular R-to-R intervals, a lack of P waves and undulations in the baseline—known as F waves—that are caused by the fibrillating atria (see Figure 1, p. E7).
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