[Transient mitral regurgitation induced by vagal stimulation in rabbits: a Doppler echocardiographic study]

Cervical vagal stimulation in rabbits frequently causes systolic murmur with bigeminy due to premature ventricular contractions. The bigeminy disappears in a few minutes, but the systolic murmur persists for a few days. The present study used Doppler echocardiography to examine whether or not this systolic murmur is due to mitral regurgitation. Electrocardiographic monitoring was performed on anesthetized rabbits forced into the supine position. Doppler echocardiography was performed in the animals which showed systolic murmur 6 hours, 3 days, and 1, 2, 3 and 4 weeks after vagal stimulation. Six hours after vagal stimulation, phonocardiography detected systolic click and late systolic murmur, and Doppler echocardiography detected marked mitral regurgitation. The systolic murmur and mitral regurgitation were attenuated and the papillary muscle was swollen 3 days after vagal stimulation. The mitral regurgitation disappeared within a week and swelling of the papillary muscle improved 3 weeks after vagal stimulation. Doppler echocardiography confirmed that the systolic murmur observed in rabbits after vagal stimulation is due to transient mitral regurgitation.