## Blood Supply to the Sinoatrial Node ### Primary Arterial Supply **Key Point:** The sinoatrial (SA) node is supplied by the SA nodal artery, which arises from the right coronary artery (RCA) in approximately 60% of the population. In the remaining 40%, it may arise from the left circumflex artery. ### Coronary Arterial Supply to Conduction System | Conduction Structure | Primary Supply | Alternative Supply | Frequency | | --- | --- | --- | --- | | SA node | Right coronary artery | Left circumflex artery | 60% RCA, 40% LCx | | AV node | Right coronary artery | Left circumflex artery | ~90% RCA | | Bundle of His | Left anterior descending artery | Right coronary artery | Variable | | Right bundle branch | Right coronary artery | — | ~100% | | Left bundle branch | Left anterior descending artery | — | ~100% | ### Anatomical Course of SA Nodal Artery **High-Yield:** The SA nodal artery: 1. Arises from the proximal RCA (or LCx in minority) 2. Courses posteriorly around the SVC–RA junction 3. Penetrates the SA node at the junction of the SVC and right atrium 4. Supplies the nodal tissue and surrounding atrial myocardium ### Clinical Significance **Clinical Pearl:** Occlusion of the RCA proximal to the SA nodal artery takeoff can cause: - Sinus bradycardia - Sinus arrest - Sinoatrial exit block - These arrhythmias are common in inferior wall myocardial infarction **Warning:** Do not assume the SA node is always supplied by the RCA — in ~40% of cases, the LCx provides the blood supply. However, RCA dominance (60%) makes it the "majority" answer. 
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