## Arterial Supply of the SA Node ### Blood Supply Pattern **Key Point:** The right coronary artery (RCA) supplies the SA node in approximately **60% of the population**, making it the most common source. ### Distribution of SA Nodal Artery Origin | Artery | Frequency | Notes | |--------|-----------|-------| | Right coronary artery (RCA) | ~60% | Most common; arises as first branch of RCA | | Left circumflex artery (LCx) | ~40% | Second most common | | Left anterior descending (LAD) | <5% | Rare | | Left main coronary | <1% | Extremely rare | **High-Yield:** The SA nodal artery typically arises as the **first branch of the RCA**, just after the RCA originates from the right coronary ostium. It courses posteriorly around the SVC-RA junction to reach the SA node. ### Clinical Significance **Clinical Pearl:** In RCA dominance (most common), RCA occlusion can lead to: - SA node ischemia - Sinus bradycardia - Sinus arrest - AV nodal dysfunction (AV node also supplied by RCA in ~90% of cases) **Warning:** Inferior wall MI (typically RCA territory) frequently presents with bradycardia and heart block because both the SA and AV nodes are compromised. **Mnemonic:** **"RCA Rule 60"** — RCA supplies SA node in 60% of people; remember this as the "dominant" source. ### Anatomical Course 1. SA nodal artery arises from proximal RCA (or LCx in 40%) 2. Travels posteriorly around the junction of SVC and right atrium 3. Penetrates the SA nodal tissue 4. Forms an arterial plexus within the node [cite:Gray's Anatomy 42e Ch 8; Robbins 10e Ch 12] 
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