Spontaneous Coronary Artery Dissection

Spontaneous coronary artery dissection (SCAD) is a tear in one of the epicardial coronary arteries. The spectrum ranges from the intimal rupture to intramural hematoma and false lumen formation without preceding events like atherosclerotic plaque rupture, trauma, or coronary artery interventions. It is the leading cause of ACS in young women, including peripartum women, without any cardiovascular risk factors.  The clinical presentation varies from ST-elevation myocardial infarction (STEMI) to non-ST-elevation ACS, ventricular tachyarrhythmias, congestive heart failure, and sudden cardiac death. The most common cause of ACS in the general population is rupture of atherosclerotic coronary plaque leading to superimposed thrombosis, obstruction to the distal coronary flow, and coronary ischemia. SCAD leads to the formation of an intramural hematoma, compression of the true lumen, and obstruction to the distal coronary flow, resulting in ACS. Human coronary circulation is comprised of three epicardial coronary arteries. The left coronary artery (LCA) divides into the left anterior descending (LAD) and the left circumflex arteries (LCx). LAD branches into diagonal and septal branches and supplies the anterior wall, anterior and apical septum, and apical cap. LCx divides into obtuse marginal branches and supplies left ventricular anterolateral and posterolateral walls. Sometimes a separate branch arises from the left main between LAD and LCx and is called ramus intermedius. The right coronary artery (RCA), which is dominant in 80% of patients, arises from the right sinus of Valsalva and supplies the right atrium, the sinoatrial node, right ventricle, and posterior two-thirds of the interventricular septum (in the right dominant circulation), and inferior wall and posterior left ventricular segments. The branches of the right coronary artery are the conus artery, the sinoatrial branch, the right ventricular branch, the acute marginal, the right posterior descending, and the right posterolateral branches. The cross-section of the coronary arteries comprises three concentric histologic layers, tunica intima, media, and adventitia. Tunica intima is the primary site for atherosclerosis and consists of endothelial cells, smooth muscle cells, and connective tissue. Tunica intima is separated from tunica media by internal elastic lamina. The tunica media consists of smooth muscle cells separated from tunica adventitia by the external elastic lamina. Tunica adventitia is made up of collagen and elastic fibers and consists of vasa vasorum, which supplies oxygen to the vessels, lymphatics, and nerve fibers. Coronary dissection occurs when there is an accumulation of blood in the tunica media leading to the formation of an intramural hematoma. The source of blood in intramural hematoma is either injury to the vasa vasorum or an intimal tear. Intramural hematoma separates tunica intima from the outer layer creating the false lumen that compresses the true lumen obstructing blood flow and causing ACS. The left anterior descending artery is the most affected by spontaneous coronary dissection. The involvement of the coronary arteries and their branches in order of decreasing frequency are the LAD with its branches (about 50%); circumflex, ramus, and obtuse marginals (about 30%); RCA and its branches (25%), multivessel (about 15%) and LCA (about 4%). Distal vessels are more commonly affected than the proximal vessels. There are three angiographic types of spontaneous coronary artery dissection. Type 1:  Multiple radiolucent lumens or contrast staining of the wall. Type 2:  Diffuse stenosis with the abrupt change in vessels caliber. Type 3:  Focal or tubular stenosis (usually less than 20 mm) mimics atherosclerosis; intramural hematoma should be investigated by intracoronary imaging.