Sinoatrial Nodal Artery Arising from the Right Posterolateral Artery: A Rare Anatomical Variant

A 66-year-old male with no prior cardiac history presented to the hospital with persistent hiccups, causing shortness of breath. A nuclear stress test showed a fixed perfusion defect involving the inferior wall, possibly due to diaphragmatic attenuation artifact with no evidence of stress-induced myocardial ischemia, and a mildly decreased left ventricular ejection fraction of 44% (Figure 1). Coronary angiography revealed two-vessel coronary artery disease, 80% stenosis of the middle right coronary artery (RCA), diffuse heavy calcification of the left anterior descending artery (LAD) involving the proximal and mid-portions with 80% maximal stenosis, a small caliber left marginal, and a sinoatrial (SA) nodal branch originating from the right posterolateral artery (RPLA) (Figure 2 A, B).

Figure 1

Figure 2

The SA nodal artery, a branch of the main coronary arteries, supplies blood to the SA node. The SA node is also known as the natural pacemaker of the heart. In 60% to 70% of cases, its blood supply originates from the RCA, and in 20% to 30% from the LAD and left circumflex coronary artery (LCX). The SA nodal artery provides vital oxygen and nutrients to the SA node, which is a key component in heart contraction that originates the initial electrical signal for atrial contraction.¹ When originating from the RCA, the SA nodal artery most frequently arises at a mean distance of 1.2 cm (range 0.2–2.2 cm) from its beginning.² In less than 1% of cases, the artery originates from the distal RCA.³ The posterolateral artery, also known as the posterior left ventricular artery, arises from the RCA in a typical dominant circulation. It is a terminal branch that supplies the inferior portion of the heart along with the posterior descending artery (PDA). It can also arise from the LAD or LCX.⁴ Based on available data, this the first documented case of an SA nodal artery originating from the RPLA.