Congenital Absence of the Left Circumflex Artery Presenting With Inferoposterior Wall Myocardial Infarction Due to Stenosis of the Super Dominant Right Coronary Artery: A Rare Case

The primary coronary arteries are the right coronary artery (RCA), the left main coronary artery (LMCA), which bifurcate into the left anterior descending artery (LAD), and the left circumflex artery (LCX), arising from the right coronary sinus and left coronary sinus, respectively. The congenital agenesis of LCX is a very unusual anomaly caused by the inability of LCX to form in the atrioventricular (AV) groove. This condition is usually accompanied by the presence of a large, dominant RCA that supplies its own territory and that of LCX, i.e., the inferior, posterior, and lateral walls. This anomaly is generally detected incidentally during coronary angiography. This condition usually does not manifest as a major cardiovascular event and mildly presents as chest pain upon exertion. The chest pain is vastly attributed to ischemia in the RCA territory, as this "super dominant" vessel majorly directs its supply to the LCX territory for compensation. This is known as the steal phenomenon. In this paper, we discuss a case of a 61-year-old female who came to the ED with the chief complaint of acutely radiating chest pain for five hours and was diagnosed as a case of acute myocardial infarction of the inferior and posterior walls. Coronary angiography revealed 90% stenosis of the RCA and a congenital absence of LCX, which has a significantly low prevalence.