Physiology of the AV node in AF

The atrioventricular (AV) node modulates the response between the atrium and the ventricle. In atrial fibrillation, the atrial rate is up to 600 beats per minute while the ventricular rate in response is 90 to 170 beats per minute; this difference in the rate results from several properties of the AV node that impede impulse conduction. The AV node generates a slow action potential (AP) that is mediated by calcium (Ca++) ion currents; the node is therefore slow response tissue. Parasympathetic innervation via the vagus nerve also slows conduction, while activation of the sympathetic nervous system speeds conduction.