Hemodynamics before and after conversion of atrial fibrillation to normal sinus rhythm in horses.

Hemodynamic measurements were obtained from 17 horses with atrial fibrillation or flutter. Eight horses had atrial fibrillation of unknown duration. In 7 horses, atrial fibrillation developed during anesthesia. Atrial flutter developed during recovery from anesthesia in 2 horses. Hemodynamic measurements were considered normal in 7 of 8 conscious horses with atrial fibrillation. Cardiac output was decreased and pulmonary arterial blood pressure and right atrial pressure were increased in 1 conscious horse which had signs of congestive heart failure. Arterial blood pressure decreased in 5 of 7 horses in which atrial fibrillation developed during anesthesia. Heart rate and arterial blood pressure were increased in 2 horses in which atrial flutter developed during recovery from anesthesia. Conversion of atrial fibrillation to normal sinus rhythm with quinidine given orally generally decreased pulmonary arterial and right atrial blood pressures. Heart rate decreased and cardiac output increased in 1 horse after conversion of atrial fibrillation to normal sinus rhythm. It was concluded that the development of atrial fibrillation in conscious resting horses is not necessarily associated with a deterioration of hemodynamics, particularly if there is no other cardiac disease. Intravenous quinidine therapy was a safe and effective means of converting the acute onset of atrial fibrillation to normal sinus rhythm in anesthetized horses.