## Blood Supply of the SA Node **Key Point:** The SA node is supplied by the sinoatrial nodal artery (also called the SA nodal artery), which arises from the right coronary artery in approximately 60% of the population and from the left circumflex artery in about 40% of cases. ### Anatomical Basis The SA node is located at the junction of the superior vena cava and the right atrium. Its arterial supply follows a predictable pattern: | Feature | Details | | --- | --- | | **Primary source (60%)** | Right coronary artery (RCA) | | **Secondary source (40%)** | Left circumflex artery (LCx) | | **Location of node** | Sulcus terminalis, at SVC-RA junction | | **Clinical significance** | RCA occlusion → SA node ischemia → bradycardia, sinus arrest | **High-Yield:** In inferior wall MI (RCA occlusion), SA node dysfunction is common, presenting as sinus bradycardia or sinus arrest. This is a frequent NEET PG question association. **Clinical Pearl:** The dual blood supply (RCA dominance but LCx backup) explains why complete SA node infarction is relatively rare — collateral circulation often preserves function. ### Why RCA Dominance Matters The right coronary artery is dominant in ~70% of individuals and supplies not only the SA node but also the AV node and inferior wall of the left ventricle. This is why inferior MI often presents with bradyarrhythmias. 
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