Dual anterior interventricular artery type IV: a rare anatomical variation.

Type IV dual anterior interventricular artery (AIVA) is a rare variant that involves bilateral connection of this vessel to the left main coronary artery and right coronary artery or right aortic sinus. We present a case of such a variant where the ectopic branch traveled an intraseptal course, i.e., through the superior aspect of the crista supraventricularis in a subendocardial position and then intramyocardially inside the upper interventricular septum to reach the anterior interventricular sulcus and descend toward the apex. In a left anterior oblique view, this course lacked the typical caudal anterior loop but it was recognized by virtue of emergence of a septal branch as the first branch of the ectopic AIVA. Recognition of this variant and differentiation among the possible courses of the ectopic branch is important for patient management.