[Echocardiography and therapy of atrial fibrillation in horses]

Echocardiographic evaluation of 45 horses (43 warm-blooded horses, one Thoroughbred and one Standardbred) with atrial fibrillation was performed, using M-mode, B-mode and pulsed-wave Doppler echocardiography. Seventeen (38%) of these horses had a history of poor performance. An increase of left ventricular shortening fraction was found in 25 horses (56%). Atrial dilatation was seen in 37 horses (82%). Eight horses (18%) had normal atrial dimensions. In nine horses only left atrium and in six horses only right atrium was enlarged. In the other 22 horses both atria were dilated. Correlation was found between atrial and ventricular dilatation. M-mode echocardiogram of septal leaflet of mitral valve revealed the lack of A-peak and showed diastolic undulation. Additionally, pulsewave Doppler spectral tracings of atrial outflow tract showed absence of A-peak which is associated with atrial in healthy horses. Quinidine sulfate was used for treatment in 19 horses. Nine horses converted to sinus rhythm, eight of them had normal atrial dimensions. Treatment was not successful in nine horses with severe atrial dilatation and in one horse with normal atrial dimensions but with mitral valve insufficiency. Echocardiographic evaluation of atrial diameters seems to be a reliable method to predict therapeutic success in horses with atrial fibrillation.