Atrioventricular Block, Third Degree
Total dissociation between the atrial (P waves) and ventricular (QRS complexes) rhythm because there is no conduction through the atrioventricular (AV) node. The ventricles depend on their own (slow) escape rhythm.
Physical Exam Findings
• Progressive filling of the jugular vein during long diastolic pauses with visible pulsation secondary to right atrial contractions.
• Signs of congestive heart failure may be found.
• Intermittent syncope or presyncope caused by long diastolic pauses. Immediately before syncope, the horse briefly shows an increased respiratory effort. Horses usually fall backward, sideways, or both.
• Lifting the head of a bradycardic horse may induce syncope.
• Syncopal episodes are usually short (seconds) and, after a few moments, the horse is able to stand again and looks relatively normal.
Etiology and Pathophysiology
• Causes of fainting or collapse