Correct Answer: C. It gives rise to circumflex coronary branch
The circumflex coronary artery (LCx) is a major branch of the left main coronary artery (LMCA), not the right coronary artery (RCA). This is the fundamental anatomical distinction that makes option C incorrect. The RCA arises from the right aortic sinus of Valsalva and courses along the right atrium and right ventricle, typically giving rise to the right conal artery (first branch), right ventricular branches, and the posterior descending artery (PDA) in most individuals. The circumflex artery, conversely, branches from the left main coronary artery and supplies the left atrium, left ventricle (lateral wall), and in some cases the AV nodal artery. This anatomical distinction is clinically critical in India where coronary artery disease (CAD) is increasingly prevalent—RCA occlusion presents with inferior wall MI, while LCx occlusion causes lateral wall MI. The question tests whether students can distinguish the branching patterns of the two main coronary systems, a fundamental concept in cardiac anatomy and essential for interpreting coronary angiography reports in clinical practice.
Why the other options are wrong
A. Right conal artery is its first branch — This is TRUE. The right conal artery (also called conus artery) is indeed the first branch of the RCA, arising just after the RCA emerges from the right aortic sinus. It supplies the right ventricular outflow tract and conus arteriosus. This is a well-established anatomical fact and a common teaching point in Indian medical curricula. B. It arises from the right aortic sinus — This is TRUE. The RCA originates from the right aortic sinus of Valsalva, one of the three sinuses of the aortic root. This is standard coronary anatomy taught in all Indian medical schools and is the basis for coronary angiography catheterization technique where the right coronary ostium is selectively cannulated. D. Its diameter is less than left coronary artery — This is TRUE. The RCA typically has a smaller diameter (2–3 mm) compared to the left main coronary artery (4–5 mm). This anatomical difference is clinically relevant in India where CAD prevalence is high—the larger LMCA diameter allows greater blood flow capacity, and LMCA stenosis is considered more critical than isolated RCA disease in risk stratification.
High-Yield Facts
- Circumflex artery is a branch of the left main coronary artery (LMCA), not the RCA—it supplies the lateral wall of the left ventricle and left atrium.
- Right conal artery is the first branch of the RCA, supplying the right ventricular outflow tract and conus arteriosus.
- RCA diameter is 2–3 mm while LMCA diameter is 4–5 mm—the larger LMCA makes its stenosis more hemodynamically significant in Indian CAD populations.
- RCA arises from the right aortic sinus and courses along the right atrium and right ventricle, typically terminating as the posterior descending artery (PDA) in 80% of individuals.
- RCA occlusion causes inferior wall MI, while LCx occlusion causes lateral wall MI—a critical distinction for ECG interpretation in Indian emergency departments.
Mnemonics
RCA vs LCx Origin Right Coronary from Right sinus; Left Circumflex from Left main. Use this to anchor: RCA = right sinus origin, LCx = left system branch. RCA First Branch = Conus Conus comes Cirst from RCA. The right conal artery is always the first RCA branch—remember 'C' for both Conus and Comes first.
NBE Trap
NBE pairs the RCA with circumflex to test whether students confuse the branching anatomy of the two coronary systems—a common error in students who memorize RCA branches without clearly distinguishing LMCA derivatives. The trap exploits the fact that both arteries are major coronary vessels, making superficial learners vulnerable to mixing their branches.
Clinical Pearl
In Indian CAD patients presenting with acute coronary syndrome, rapid ECG and angiography interpretation depends on knowing that RCA occlusion → inferior/posterior wall MI (ST elevation in II, III, aVF), while LCx occlusion → lateral wall MI (ST elevation in I, aVL, V5–V6). Confusing RCA with LCx branches can lead to misinterpretation of coronary anatomy on angiography and delayed intervention.
_Reference: Robbins & Cotran Pathologic Basis of Disease, Ch. 11 (Cardiovascular System); Gray's Anatomy (Indian edition), Ch. 3 (Thorax)_