Snapshot A 70-year-old man presents to the emergency room with chest pain for the past hour. He has a medical history of coronary artery disease, hyperlipidemia, and type 2 diabetes mellitus. He has a 30-pack-year smoking history and drinks alcohol regularly. His electrocardiogram reveals ST-segment elevations in leads V3 and V4. Aspirin is given and he is rushed for an angioplasty. (Myocardial infarction with left main coronary artery involvement) Anatomy Coronary arteries include right coronary artery (RCA) arises from right aortic sinus supplies right ventricle and His bundle branches sinoatrial nodal artery supplies the sino-atrial (SA) node right marginal artery supplies the right ventricle posterior descending artery (PDA) supplies AV node (supplied by atrioventricular nodal artery) posterior portion of interventricular septum and ventricles posteromedial papillary muscle left main coronary artery (LCA) arises from left aortic sinus branches left circumflex coronary artery (LCX) supplies lateral and posterior wall of left ventricle anterolateral papillary muscle supplies some blood flow to SA node and AV node left anterior descending artery (LAD) supplies anterior portion of the interventricular septum left ventricular sinus anterolateral papillary muscle anterior surface of the left ventricle most common artery to be involved in myocardial infarction Coronary arterial system dominance defined by which artery supplies the PDA right dominance 85% of cases RCA gives rise to PDA left dominance 8% of cases LCX gives rise to PDA codominance 7% of cases both LCX and RCA give rise to PDA Coronary sinus the endpoint of coronary flow and is continuous with the right atrium in chronic pulmonary hypertension, coronary sinus becomes dilated blood in the coronary sinus has the lowest oxygen content in the body oxygen saturation levels 30% Left atrium most posterior part of the heart enlargement can compress the esophagus, causing dysphagia the left recurrent laryngeal nerve, causing hoarseness Localization of Myocardial Infarctions (MI) Leads with ST-Segment Elevation Location of MI Vessel(s) Affected V1-V2 Septal LAD V3-V4 Anterior LAD V5-V6 Apical LAD, LCX, or RCA I and aVL Lateral LCX V7-V9 Posterior RCA and LCX II, III, and aVF Inferior RCA and LCX Pathology Coronary steal phenomenon myocardial ischemia narrowed coronary arteries are dilated maximally to increase blood flow to ischemic tissues when a vasodilator is used, coronary arteries that are not narrowed vasodilate narrowed coronary arteries cannot further dilate thus, blood flow is stolen from the narrowed arteries classically, dipyridamole is associated with this also used for cardiac stress testing