In the normal heart the sinoatrial (SA) node serves as the principal pacemaker and determines the heart rate. The SA node consists of groups of pacemaker cells marked by their ability to spontaneously depolarize and are located at the junction of the right atrium and the superior vena cava. The blood supply to the SA node is variable with the sinus nodal artery arising from the right coronary artery in 60% percent of cases and from the left circumflex artery in 40% of cases. Following depolarization of the SA nodal cells, the signal traverses the atrium before arriving at the atrioventricular (AV) node. The AV node is marked by its ability to delay impulse propagation, which allows for coordinated contraction of the atria and ventricles. The AV nodal artery arises from the right coronary artery in 90% of cases and from the left circumflex artery in 10% of cases. After exiting the AV node, the impulse is transmitted through the bundle of His, the right and left bundle branches, and ultimately exits the terminal Purkinje fibers of the conduction system into the myocardium near the apex of the heart.
Coronary artery conundrum: A single coronary artery with origin of the right coronary artery from the distal left circumflex artery