Source:http://linkedlifedata.com/resource/umls/id/C0242514
MSH: Abnormally rapid heartbeats caused by reentrant conduction over the accessory pathways between the HEART ATRIA and the HEART VENTRICLES. The impulse can also travel in the reverse direction, as in some cases, atrial impulses travel to the ventricles over the accessory pathways and back to the atria over the BUNDLE OF HIS and the ATRIOVENTRICULAR NODE.