A 7-year-old boy with Down syndrome underwent surgery to rep…

A 7-year-old boy with Down syndrome underwent surgery to repair a congenital ventricular septal defect. During this procedure, iatrogenic injury to the coronary artery supplying the conduction system of the heart, including the sinuatrial (SA) and atrioventricular (AV) nodes, occurred, resulting in a heart block. What artery was most likely damaged by the surgeon?