|Classification and external resources|
It can be difficult to distinguish unstable angina from non–Q-wave myocardial infarction. Unstable angina (UA) and non-ST elevation (non-Q wave) myocardial infarction (NSTEMI) differ primarily in whether the ischemia is severe enough to cause sufficient myocardial damage to release detectable quantities of a marker of myocardial injury. Unstable angina is considered to be present in patients with ischemic symptoms suggestive of an ACS and no elevation in troponin, with or without ECG changes indicative of ischemia (e.g., ST segment depression or transient elevation or new T wave inversion). Since an elevation in troponin may not be detectable for up to 12 hours after presentation, UA and NSTEMI are frequently indistinguishable at initial evaluation.
Unstable angina is angina pectoris caused by disruption of an atherosclerotic plaque with partial thrombosis and possibly embolization or vasospasm. It is characterized by at least one of the following:
- Occurs at rest or minimal exertion and usually lasts more than 20 minutes (if nitroglycerin is not administered)
- Being severe (at least Canadian Cardiovascular Society Classification 3) and of new onset (i.e. within 1 month)
- Occurs with a crescendo pattern (brought on by less activity, more severe, more prolonged or increased frequency than previously).
Fifty percent of people with unstable angina will have evidence of myocardial necrosis based on elevated cardiac serum markers such as creatine kinase isoenzyme (CK)-MB and troponin T or I, and thus have a diagnosis of non-ST elevation myocardial infarction.
Nitroglycerin can be used immediately to widen the coronary arteries and help increase blood flow to the heart. In addition, nitroglycerin causes peripheral venous and artery dilation reducing cardiac preload and afterload. These reductions allow for decrease myocardial oxygen demand. Antiplatelet drugs such as aspirin and clopidogrel can help reduce the progression of plaque formation, as well as combining these with an anticoagulant such as a low molecular weight heparin.
- Yeghiazarians Y, Braunstein JB, Askari A, Stone PH (January 2000). "Unstable angina pectoris". N. Engl. J. Med. 342 (2): 101–14. doi:10.1056/NEJM200001133420207. PMID 10631280.
- "unstable angina" at Dorland's Medical Dictionary
- "Unstable Angina and Non-ST-Segment Elevation Myocardial Infarction: Part I. Initial Evaluation and Management, and Hospital Care - August 1, 2004 - American Family Physician".
- "Unstable Angina: Overview - eMedicine".
- Robbins. Pathologic basis of disease 7th edition.2005.
- Braunwald E, Antman EM, Beasley JW, et al: ACC/AHA guideline update for the management of patients with unstable angina and non-ST segment elevation myocardial infarction-2002: Summary Article: A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee on the Management of Patients with Unstable Angina). Circulation 2002; 106:1893-1900.
- Libby: Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine
- Markenvard J et al. The predictive value of CKMB mass concentration in unstable angina pectoris: preliminary report. Journal of Internal Medicine. 1992 Apr;231(4):433-6.