The sinoatrial (SA) node receives its blood supply from which artery in approximately 60% of individuals?

Explanation

## Blood Supply to the SA Node **Key Point:** The right coronary artery (RCA) supplies the SA node in approximately 60% of individuals, making it the most common source of SA nodal blood supply. ### Arterial Supply Patterns | Artery | Frequency | Clinical Significance | |--------|-----------|----------------------| | Right coronary artery | ~60% | Most common; SA nodal artery typically arises as first major branch | | Left circumflex artery | ~40% | Alternative supply; increases in left-dominant systems | | Left anterior descending | Rare | Occasionally contributes in anomalous patterns | | Left main coronary | Rare | Only in unusual anatomical variants | ### Anatomical Basis The SA nodal artery typically arises as the **first major branch of the right coronary artery** near the junction of the superior vena cava and right atrium. This artery penetrates the atrial wall and supplies the nodal tissue. **High-Yield:** While RCA dominance is more common overall (~70% of hearts), the SA node receives RCA supply in ~60% of cases. This slight discrepancy occurs because the left circumflex can supply the SA node even in RCA-dominant systems. **Mnemonic:** **SA = RCA (in 60%)** — Remember that the SA node's primary blood supply is the Right Coronary Artery in the majority of cases. ### Clinical Correlations **Clinical Pearl:** Occlusion of the RCA can lead to: - Sinus bradycardia - Sinus pause or arrest - Sinoatrial block - Junctional rhythms These arrhythmias are particularly common in inferior wall myocardial infarction (IWMI), where RCA occlusion is typical. ## Embryological Basis The SA node develops from the sinus venosus, which is supplied by branches of the RCA. This explains why RCA dominance in SA nodal supply is preserved through development. [cite:Gray's Anatomy 42e Ch 3; Robbins 10e Ch 12]