Acute Coronary Syndromes: Unstable Angina and Non–ST-Segment Elevation Myocardial Infarction

Cardiovascular disease is the most common cause of death for both men and women, with more than half of all deaths attributed to coronary artery disease in individuals under the age of 75 years. Of interest is that the rate of people dying from a heart attack each year in the United States has decreased from 1 in 2 to 1 in 8 individuals.1 Some of this reduction can be attributed to the decrease in percentage of adults who smoke (approximately 11% currently) compared with the more than 40% of adults who smoked in the 1960s.1Acute coronary syndromes (ACS) refer to a spectrum of pathophysiologic substrates at the myocardial cellular level resulting in a series of pathophysiological responses that contribute to a reduction in coronary blood flow. The end result is myocardial ischemia, injury, and/or infarction.2 Acute coronary syndromes encompasses 3 distinct diagnoses: (1) unstable angina, (2) non–ST-segment elevation myocardial infarction (NSTEMI), and (3) ST-segment elevation myocardial infarction (STEMI).3 All 3 are associated with onset of chest pain that drives the patient to seek medical attention. Along with a thorough history, the electrocardiogram (ECG) and cardiac biomarkers contribute to the decision-making process to differentiate among the 3 diagnoses.The American Heart Association (AHA) identified an important evolution in the management of ACS in 2012 to further differentiate the 3 diagnoses. The presence of persistent ST-segment elevation on the ECG, indicating the need for timely reperfusion therapy, led to a different pathway when compared with unstable angina and NSTEMI.4 Since it is often difficult to distinguish between unstable angina and NSTEMI at the onset of chest pain, a focused updated guideline was published in 2012 combining both under one title, Management of Patients with Unstable Angina/NSTEMI,4 followed by the publication of a separate guideline for STEMI in 2013.5 In 2014 the AHA published a new guideline, Management of Patients with Non-ST-Elevation Acute Coronary Syndromes, which encompasses both unstable angina and NSTEMI.3 The previous column addressed STEMI and its associated ECG changes.6 This column will address unstable angina and NSTEMI, focusing on ECG changes along with other clinical data that aid the differentiation between the 2 clinical syndromes.Patients with unstable angina and NSTEMI usually present with similar chest pain symptoms. Patients may describe their pain as pressure, tightness, burning, sharp, or general discomfort and potentially radiating to one or both jaws. Women may experience nausea and vomiting accompanying their chest pain. Patients may also complain of shortness of breath and lightheadedness.7 If the administration of nitroglycerin results in the relief of the patient’s chest pain, this does not confirm the presence of ACS.7 The differentiation of their symptoms at this point is whether the ischemia is severe enough to cause damage to the myocardium.A 12-lead ECG should be obtained within 10 minutes of the patient’s arrival to the emergency department (ED) with chest pain. Initially, the ECG may remain relatively normal or have subtle changes that are nondiagnostic. An initial normal ECG does not exclude ACS.3 Serial ECGs should be obtained at 15-to 30-minute intervals during the first hour to continue to look for ischemic changes even in the absence of chest pain.3,7 Electrocardiogram changes that are commonly seen in NSTEMI patients include ST-segment depression, transient ST elevation, or new T-wave inversion.3 Other changes that may be present include hyperacute, biphasic, or flat T waves.8 However, the ECG may be normal even with NSTEMI and unstable angina. Figure 1 is a diagram of the possible ST-T wave changes.As stated previously, reliance on the 12-lead ECG in this group of patients can be challenging. Therefore, the patient’s high-sensitivity troponin level should be assessed to assist with the differentiation between unstable angina and NSTEMI. The measurement of high-sensitivity troponin has been found to be much more sensitive than the original test. The reference range for the troponin level for women is 0 to 10 ng/L and for men, 0 to 14 ng/L. If the patient’s troponin level is elevated, they are presumed to have NSTEMI. If the troponin level is not elevated, unstable angina is the working diagnosis. In some cases, an echocardiogram can detect regional wall motion abnormalities.4 However, continued monitoring with serial ECGs and serial troponin level measurements should be implemented based on the patient’s clinical condition.Both groups should have continuous ECG and ST-segment monitoring.9 Guidelines recommend that the patient with NSTEMI undergo an interventional procedure (cardiac catheterization with a possible percutaneous coronary intervention) within 24 hours of admission or sooner if the patient’s condition is determined to be unstable.3A 55-year-old man with a prior history of coronary artery bypass surgery, hyperlipidemia, and hypertension was admitted to the outpatient unit for an elective coronary angiography because he had been having intermittent chest pain at home for the past 3 weeks. The pain was relieved either with rest or 1 sublingual nitroglycerin. A stress test showed anterolateral ischemia. While awaiting his procedure, he developed 7/10 substernal chest discomfort. An ECG was obtained (Figure 2). Note the ST depression and T-wave inversion (see Figure 1C) in the anterolateral leads (V3 through V6). He was given 1 sublingual nitroglycerin tablet resulting in relief of his chest pain. A second ECG (Figure 3) was recorded after he was pain free. Note the ST segments and T waves returned to normal. His high-sensitivity troponin level was assessed and found to be within normal limits. This case is an example of unstable angina.A 61-year-old man with a history of hypertension, hyperlipidemia, type 2 diabetes, and nonobstructive coronary artery disease diagnosed 3 years ago by coronary angiography was admitted to the ED with 2 hours of chest discomfort and shortness of breath. An ECG was obtained (Figure 4). The clinicians compared it to the ECG recorded during his last routine visit with his cardiologist (Figure 5). He now had ST depression and T-wave inversion in both his inferior and anterior lateral leads. Two repeated tests to assess his high-sensitivity troponin level were conducted, the first showing a result of 22 ng/mL and the second showing a result of 63 ng/mL. The diagnosis was NSTEMI.A 72-year-old woman was admitted to the ED with chest pain. Her past medical history included type 2 diabetes and hypertension. She quit smoking 1 year ago. She admitted that over the past 2 weeks she had been having chest pain lasting a few minutes; however, what brought her to the ED was chest pain lasting over an hour. An ECG was obtained (Figure 6). There was T-wave inversion in leads V2 through V6, with ST-segment depression in leads V3 through V6. She was given 1 sublingual nitroglycerin, which gave her relief. Her high-sensitivity troponin level was within the normal range. A second ECG (Figure 7) was recorded when she was pain-free. The T waves in leads V2 through V6, II, and aVF remained inverted but not as deep as they were when she had chest pain. She still has ST depression in leads V3 through V5 (maybe V6 as well). Although she is pain-free, this ECG represents silent ischemia. She should undergo a coronary angiogram within 24 hours of being hospitalized if there are no contraindications.Patients admitted with chest pain should undergo a 12-lead ECG within 10 minutes of arrival to determine if there is ST elevation in 2 out of 3 contiguous leads. If so, a STEMI alert should be called. If not, whether the ECG is normal or not, serial ECGs and tests to determine the patient’s troponin level should be done to determine if the patient is experiencing a non–ST-segment acute coronary syndrome (unstable angina or NSTEMI). If the troponin level is elevated and the ECG is suggestive of ST-T wave abnormalities, the working diagnosis should be NSTEMI. If the troponin level is within the normal range, the working diagnosis should be unstable angina. There are many causes of chest pain besides STEMI, NSTEMI, and unstable angina, but these 3 conditions must be seriously considered when a patient with chest pain arrives in the ED or reports chest pain when in the hospital.