WBR0460

Author	[[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Yazan Daaboul, M.D.)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Anatomy
Sub Category	SubCategory::Cardiology
Prompt	[[Prompt::A 56-year-old man presents to the emergency department (ED) with complaints of chest pain and shortness of breath. On arrival, and ECG demonstrates ST-segment elevation in 2 consecutive leads, and blood work-up reveals elevated serum troponin level. The diagnosis of STEMI is made, and the patient is sent to the cardiac catheterization lab for an emergent percutaneous coronary intervention (PCI). Cardiac catheterization reveals a total occlusion of the right coronary artery (RCA). Which of the following anatomical locations of the heart is most likely affected as a result of this patient’s STEMI?]]
Answer A	AnswerA::Anterior interventricular septum
Answer A Explanation	AnswerAExp::The LAD usually provides the blood supply to the anterior interventricular septum.
Answer B	AnswerB::Left atrium
Answer B Explanation	AnswerBExp::The left main coronary artery usually provides the blood supply to the left atrium.
Answer C	AnswerC::Anterolateral papillary muscle
Answer C Explanation	AnswerCExp::The anterior papillary muscle most commonly receives a dual blood supply from the LAD and the LCx.
Answer D	AnswerD::Sinoatrial (SA) node
Answer D Explanation	AnswerDExp::The RCA usually provides the blood supply to the SA node.
Answer E	AnswerE::Apex
Answer E Explanation	AnswerEExp::The apex of the heart receives a dual blood supply from the LAD and the PDA. The LDA provides the majority of the blood supply to the apex.
Right Answer	RightAnswer::D
Explanation	[[Explanation::There are two primary arteries supplying the heart, the left coronary artery (LCA) and the right coronary artery (RCA). The heart is supplied by these two arteries and their branches in such a way that the LCA supplies mainly the left ventricle, whereas the RCA supplies the right atria and ventricle, the SA node, the inferior wall, posterior interventricular septum, and posteromedial papillary muscle in 85 % of the cases. The RCA originates above the right cusp of the aortic valve. It travels down the right atrioventricular groove, towards the crux of the heart. In addition to supplying blood to the right ventricle (RV), the RCA supplies 25% to 35% of the left ventricle (LV). The LCA normally arises from the aortic sinus above the left cusp of the aortic valve. This artery supplies the majority of the blood flow to the left ventricle. In fact, the LCA supplies the posterolateral side of the LV as well as the anterior part of the LV, which includes the anterolateral myocardium, the apex, the anterior interventricular septum, and the anterolateral papillary muscle. The origin of the left coronary artery is called the left main coronary artery, and it bifurcates into the following two main branches: Left anterior descending (LAD) artery and Left circumflex artery (LCx). The dominance of coronary circulation is determined by the type of arteries that supply the posterior and inferior wall of the left ventricle. The artery that supplies the posterior descending artery (PDA) and the posterolateral artery (PLA) determines the coronary dominance. Approximately 60 - 70% of the general population are right-dominant, 25% are co-dominant, and 15% are left-dominant. Educational Objective: The heart is supplied by these two arteries and their branches in such a way that the LCA supplies mainly the left ventricle, whereas the RCA supplies the right atria and ventricle, the SA node, the inferior wall, posterior interventricular septum, and posteromedial papillary muscle in 85 % of the cases. References: First Aid 2014 page 266]]
Approved	Approved::Yes
Keyword	WBRKeyword::Coronary artery, WBRKeyword::Sinoatrial node, WBRKeyword::SA, WBRKeyword::blood supply, WBRKeyword::cardiovascular system, WBRKeyword::cardiology
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