USMLE® Step 1 style questions USMLE
A 70 year old man was brought to the hospital by ambulance subsequent to chest pain that lasted 40 minutes. In order to assess the degree of stenosis of his coronary arteries, he underwent coronary angiography, a procedure during which a contrast dye was injected in his coronary vessels. To which phase of the ventricular action potential does visualization of the stenotic lesion correspond?
Content Reviewers:Yifan Xiao, MD
With coronary circulation, coronary comes from the Latin word “coronarius,” meaning "crown." This is because the coronary blood vessels surrounding the heart resembles a little crown! And circulation refers to “the flow of blood.” So, coronary circulation is the movement of blood throughout the vessels that supply the myocardium also known as the heart muscle.
Now, the heart is a pump, primarily made up of cardiac muscle cells known as cardiomyocytes. And like any other cell, they require a steady supply of oxygen, nutrients, and a way to eliminate wastes. And although the heart is continually pumping blood throughout its chambers, the myocardium is too thick for the diffusion of blood to happen effectively. So, instead, the coronary circulation provides an efficient way for the exchange of substances to occur.
Okay, the coronary circulation system is mainly made up of arteries and veins. To begin, the arterial supply of the heart starts with the branching out of the left and right coronary arteries from the base of the aorta. It’s like a superhighway that carries oxygenated blood from the heart to the rest of the body.
Now, the left coronary artery heads along the left coronary sulcus, a groove on the outer surface of the heart that marks the point of division between the ventricles and the atria. Not too far along the sulcus, the left coronary artery divides into two major branches. The first is the left anterior descending artery or LAD. It travels down the anterior interventricular sulcus, and it supplies the anterior 2/3 of the interventricular septum, the anterolateral papillary muscle, and the anterior surface of the left ventricle. The second branch is the left circumflex artery or LCX. It goes along the coronary sulcus, around the left side of the heart and supplies the left atrium and the posterior walls of the left ventricle.
Alternatively, the right coronary artery heads in the opposite direction, following the coronary sulcus, and along the way it supplies the SA node It later divides into two branches. The first is the right marginal artery, which stretches along the margins of the bottom right side of the heart, supplying the right ventricle. The second branch is the posterior descending artery or PDA, sometimes called the posterior interventricular artery. It goes down the posterior interventricular sulcus towards the heart’s apex while supplying the posterior 1/3 of the interventricular septum the posterior 2/3 of the ventricular walls, and the posteromedial papillary muscle. At the apex, the posterior descending artery merges with its anterior counterpart, through interconnected arterial branches called anastomoses. Together, they supply the right atrium and nearly all of the right ventricle.