cardiovascular disorders
Overview of Acute Coronary Syndromes (ACS)
Etiology of Acute Coronary Syndromes
Themost common causeof acute coronary syndromes is An acute thrombus in an Atherosclerosis None Atheromatous plaque sometimes becomes unstable or inflamed, causing it to rupture or split, exposing thrombogenic material, which activates platelets and the coagulation cascade and produces an acute thrombus. Platelet activation involves a conformational change in membrane glycoprotein (GP) IIb/IIIa receptors, allowing cross-linking (and thus aggregation) of platelets. Even atheromas causing minimal obstruction can rupture and result in thrombosis; in>50% of cases, pre-event stenosis is<40%. Thus, although the severity of stenosis helps predict symptoms, it does not always predict acute thrombotic events. The resultant thrombus abruptly interferes with blood flow to parts of the myocardium. Spontaneous thrombolysis occurs in about two thirds of patients; 24 hours later, thrombotic obstruction is found in only about 30%. However, in virtually all cases, obstruction lasts long enough to cause varying degrees of tissue necrosis. Rarer causesof acute coronary syndromes are Coronary artery embolism Coronary spasm Spontaneous coronary artery dissection Coronary arterial embolism can occur in Mitral Stenosis , use and other causes of Variant Angina can sometimes result in myocardial infarction. Spasm-induced MI may occur in normal or atherosclerotic coronary arteries. Spontaneous coronary artery dissection is a non-traumatic tear in the coronary intima with creation of a false lumen. Blood flowing through the false lumen expands it, which restricts blood flow through the true lumen sometimes causing coronary ischemia or infarction. Dissection may occur in atherosclerotic or non-atherosclerotic coronary arteries. Non-atherosclerotic dissection is more likely in pregnant or postpartum women and/or patients with fibromuscular dysplasia or other connective tissue disorders. Myocardial infarction in the absence of obstructive coronary artery disease (MINOCA) is found in about 5% to 6% of patients with acute MI who undergo coronary angiography ( Etiology reference ). Patients with MINOCA tend to be younger, women, and without dyslipidemia, and they have myocardial necrosis without significant coronary atherosclerosis. Plaque disruption and coronary vasospasm are common in MINOCA. Coronary thrombosis or embolism and spontaneous coronary artery dissection are causes of MINOCA. 1.Tamis-Holland JE, Jneid H, Reynolds HR, et al: Contemporary diagnosis and management of patients with myocardial infarction in the absence of obstructive coronary artery disease: A scientific statement from the American Heart Association.Circulation139:e891–e908, 2019. doi: 10.1161/CIR.0000000000000670 