Intrinsic atrioventricular conductive function in horses with a second degree atrioventricular block

The atrioventricular (AV) conductive functions were investigated before and after the pharmacological autonomic nervous blockade (PAB) through the electrophysiological study on six horses (AV block group) in which the dropped beats occurred more frequently (over 200 beats/24 hr) and on five horses (control group) in which the dropped beats occurred sporadically (under 200 beats/24 hr) or in which the arrhythmias were not recognized at all on the long-term electrocardiogram. As a result, AV conductivity, conduction time and refractoriness in the AV block group were lower, longer and higher, respectively, than those in the control group even after PAB. These results indicate the intrinsic AV conductive functions in the AV block group were withdrawing than in the control group.