Atrio-His bundle tracts.
The atrio-His bundle tracts are very rare; only two have been found in 687 hearts studied histologically. These tracts have a similar appearance to those of the atrioventricular bundle and form a complete bypass of the atrioventricular node. In their presence the electrocardiogram may show a short or normal PR interval. They may be responsible for some cases of very rapid ventricular response to supraventricular arrhythmias.
D001283:Atrioventricular Node / Q000033:anatomy & histology; D002036:Bundle of His / Q000033:anatomy & histology*; D006325:Heart Atria / Q000033:anatomy & histology; D006329:Heart Conduction System / Q000033:anatomy & histology*; D006801:Humans; D008875:Middle Aged