Importance of isthmus structure in the right atrium

Being the chamber receiving systemic venous return, the right atrium is a structure of morphological mosaic, comprising the smooth vestibule, the septum, the trabeculated appendage and junctional crista terminalis, the Eustachian ridge, the fanning pectinate muscle, and the tendon of Todaro. The mosaic milieu by itself predisposes to the formation of reentrant atrial tachyarrhythmias. Meanwhile, the right atrium is also common with secondary isthmus structures resulting from surgical iatrogenic scars or stretch-related spontaneous scars. Inside the heterogenous scars, between adjacent scars, and between natural structural barriers and the scars, there are also facilitated opportunities of creating clinical microreentrant (focal) and macroreentrant atrial tachyarrhythmias.