Table 7.4 Summary: Treatment of atrial fibrillation

Selection of cases


Signs of underlying heart disease, e.g. murmurs, tachycardia

Duration of arrhythmia

Type of work required from horse



Good prognosis:

No pathological cardiac murmurs

Normal heart rate

Duration of AF <4 months Moderate prognosis:

Murmur of Al, TR and MR but no volume overload on echocardiography Duration unknown or suspected to be >4 months

Poor prognosis:

Pathological murmur (especially MR) with volume overload

Previous unsuccessful treatment

Heart rate >55 bpm


Dose with 20 mg/kg every 2 hours up to total dose of 6080 g per 500kg horse

Monitor heart rate, ECG if possible

Monitor for side-effects

Monitor plasma levels if possible, to titrate drug level into therapeutic range of 2.5-5.0 mg/I

Do not move horse during course of treatment

If fail to convert after 60-80 g, or reaches upper end of therapeutic range, switch to 20 mg/kg every 6 hours. If uncertain, take a blood sample 2 hours after last dose and assay to see if therapeutic levels were reached

If still in AF after 24 hours, consider addition of digoxin at dose of 0.002 mg/kg IN

If sufficiently severe side-effects develop, stop treatment and consider administration of balanced electrolyte solution, bicarbonate (1 mEq/kg IV), or if life threatening

phenylephrine (10 mg in 500 ml of normal saline to effect)

If unsuccessful, and levels were therapeutic, consider repeating treatment a few days later after starting on a maintenance level of digoxin

If converts, can return to light work after 3-5 days, full training 7-10 days

If reverts to AF later, can repeat treatment

If unsuccessful, consider if animal is capable of a reduced level of athletic work