Results suggested that frequency of EIPH-related epistaxis in racehorses is associated with the horse's age and sex, the type of race, and the distance raced. The higher frequency in shorter races suggests that higher intensity exercise of shorter duration may increase the probability of EIPH.

Results suggest that the likelihood of AF among racehorses that finish slowly is related to age and racing surface.

ABSTRACT. To determine a safe and efficacious dose of flecainide acetate for treating equine atrial fibrillation (Af), the safe dosage level was determined by injecting 1, 2, or 3 mg/kg i.v. of 1% flecainide acetate solution at a rate of 0.2 mg/kg/min to five clinically healthy horses. Clinical signs and the ECG were monitored (HR, PR, QRS, and QT intervals) and blood was taken to measure the plasma flecainide concentration pre-and post-administration. No abnormal signs were observed in the 1-or 2-mg/kg groups, while agitation was observed in three of five horses in the 3-mg/kg group. The QRS, and QT intervals for the 3-mg/kg group increased significantly. The peak plasma flecainide concentrations were 1,316 ± 358 (SD) ng/ml, 1,904 ± 314 ng/ml, and 2,251 ± 387 ng/ml for the 1-, 2-, and 3-mg/kg groups, respectively. To evaluate the efficacy of flecainide, Af was induced by right atrial pacing in six clinically healthy horses, and 1% flecainide acetate solution was then administered until they converted to sinus rhythm. All horses with induced Af converted. For the conversion, a total dose of 1.40 ± 0.63 mg/kg flecainide was required, the duration of administration was 7.00 ± 3.15 min and plasma flecainide concentration at conversion was 1,303 ± 566 ng/ml. In conclusion, flecainide acetate is a safe and effective antiarrhythmic agent for equine Af, and the clinically effective dosage is 1 to 2 mg/kg. Atrial fibrillation (Af) is one of the most common arrhythmias encountered in horses. It is thought that treatment is necessary for Af that does not recover spontaneously [1,4]. There have been a number of reports on Af in horses. Most of these studies used quinidine for treatment [1,11,14]. However, quinidine is known to have a number of side effects, including nasal mucosal edema, dyspnea, diarrhea, colic, tachycardia and laminitis [6,9]. Successful treatment has not been reported using any drug other than quinidine [10]. It would be highly desirable to convert equine Af, using an antiarrhythmic agent with less severe side effects than quinidine.In humans, a wide variety of antiarrhythmic agents have been developed and clinically applied to Af. Flecainide is an antiarrhythmic agent of Vaughan-Williams class Ic, a different class than quinidine [7]. In humans, flecainide has been shown to be effective in treating both supraventricular and ventricular arrhythmias. The rate of cardioversion of paroxysmal Af exceeds 90%, which is higher than that for other antiarrhythmic agents [2,8]. With side effects seldom involving organs other than the heart, flecainide is a relatively safe drug [5]. Nonetheless, flecainide has not been tried in horses, nor has its ability to convert equine Af been evaluated.In this study, we examined the safety and effectiveness of flecainide acetate in treating induced Af in horses. The efficacious dosage and rate of administration of flecainide was determined using clinical observations, ECG, and measurement plasma flecainide concentrations as indicators of side effects. MATERIALS AND METHODSStu...

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HR is influenced by different sympathovagal mechanisms during stall rest, compared with during road transportation; HRV may be a sensitive indicator of stress in transported horses.