Acute Coronary Syndromes: NSTE-ACS (Unstable Angina and NSTEMI)

Descriptive text is not available for this image BASICS

DESCRIPTION

  • Unstable angina (UA) and non–ST-segment elevation myocardial infarction (NSTEMI) are acute coronary syndromes without ST-segment elevation (NSTE-ACS) that are differentiated from one another based on the absence of cardiac damage in UA (no elevation in cardiac biomarkers) that is present in NSTEMI.
  • UA and NSTEMI are difficult to distinguish initially because elevation in cardiac biomarkers levels may not be detectable until several hours after presentation. Initial management for both syndromes is similar.
  • Patient history alone is not sufficient to make a diagnosis of ACS and the clinical dilemma of distinguishing between cardiac and noncardiac chest pain involves a combination of patient history, ECG, and cardiac biomarkers.

EPIDEMIOLOGY

Incidence

  • The estimated annual incidence of new and recurrent MI is 605,000 and 200,000, respectively.
  • In the United States, the average age at first MI is 65.6 years for males and 72.0 years for females, and males outnumber females at a 3:2 ratio.

ETIOLOGY AND PATHOPHYSIOLOGY

  • NSTE-ACS is due to a sudden decrease in myocardial blood flow, resulting in an imbalance between myocardial oxygen consumption and demand. This can be due to acute plaque rupture or plaque erosion and leads to a partially occluding thrombus in the coronary artery, rather than a total or complete occlusion as seen in STEMI.
  • Other mechanisms of NSTE-ACS include:
    • Prinzmetal angina or coronary vasospasm induced by tobacco use, hyperventilation, magnesium deficiency, cocaine, or methamphetamines.
    • Increased myocardial oxygen demand resulting in supply-demand mismatch (type 2 NSTEMI) due to underlying causes such as pulmonary embolism, sepsis, shock, and arrhythmias/tachycardia
    • Myocardial Infarction with No Obstructive Coronary Artery (MINOCA)
    • Less commonly: coronary arterial aneurysm, spontaneous coronary artery dissection, and thromboembolism

Genetics

Genetic polymorphisms of MMP-3 5A/6A and ACE I/D along with conventional ischemic heart disease risk factors can increase the risk of occurrence of STEMI, while having no influence on the pathogenesis of NSTEMI or UA.

RISK FACTORS

  • Traditional/classic: age, male sex, prior MI, hypertension (HTN), tobacco use, diabetes mellitus (DM), dyslipidemia, and family history of premature CAD (defined as age of onset prior to 55 years in males and 65 years in females)
  • Novel/emerging risk factors: sedentary lifestyle, overweight/obesity (metabolic syndrome), inflammation (psoriasis, rheumatoid arthritis), cigarette or smoking, psychosocial factors (anxiety/depression/stress), chronic kidney disease (CKD), obstructive sleep apnea, environmental pollutants

GENERAL PREVENTION

Smoking cessation, normal body mass index, stress management, regular physical activity, glycemic control for patients with DM and blood pressure control in patients with HTN, risk-based lipid control, aspirin in those with documented CAD

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