Acute Coronary Syndrome: Diagnostic Evaluation CRAIG BARSTOW, MD, and MATTHEW RICE, MD, Womack Army Medical Center, Fort Bragg, North Carolina JONATHAN D
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Acute Coronary Syndrome: Diagnostic Evaluation CRAIG BARSTOW, MD, and MATTHEW RICE, MD, Womack Army Medical Center, Fort Bragg, North Carolina JONATHAN D. McDIVITT, MD, Naval Hospital, Jacksonville, Florida Myocardial infarction (MI), a subset of acute coronary syndrome, is damage to the cardiac muscle as evidenced by elevated cardiac troponin levels in the setting of acute ischemia. Coronary artery disease is the leading cause of mor- tality in the United States. Chest pain is a common presentation in patients with MI; however, there are multiple non- cardiac causes of chest pain, and the diagnosis cannot always be made based on initial presentation. The assessment of a possible MI includes evaluation of risk factors and presenting signs and symptoms, rapid electrocardiography, and serum cardiac troponin measurements. A validated risk score, such as the Thrombolysis in Myocardial Infarction score, may also be useful. Electrocardiography should be performed within 10 minutes of presentation. ST elevation MI is diagnosed with ST segment elevation in two contiguous leads on electrocardiography. In the absence of ST seg- ment elevation, non–ST elevation ACS can be diagnosed. An elevated cardiac troponin level is required for diagnosis, and an increase or decrease of at least 20% is consistent with MI. In some patients with negative electrocardiography findings and normal cardiac biomarkers, additional testing may further reduce the likelihood of coronary artery dis- ease. Cardiac catheterization is the standard method for diagnosing coronary artery disease, but exercise treadmill testing, a stress myocardial perfusion study, stress echocardiography, and computed tomography are noninvasive alternatives. (Am Fam Physician. 2017;95(3):170-177. Copyright © 2017 American Academy of Family Physicians.) CME This clinical content hest pain affects 20% to 40% of infarction (MI), which is damage to the car- conforms to AAFP criteria the general population during diac muscle caused by ischemia (Table 1).3 for continuing medical their lifetime. Each year, approxi- This can be caused by a thrombotic occlu- education (CME). See CME Quiz Questions on mately 1.5% of the population sion of a coronary vessel (type 1) or by the page 149. Cconsults a primary care physician for symp- myocardial oxygen demand surpassing the 3 Author disclosure: No rel- toms of chest pain. The rate is even higher in oxygen supply (type 2). evant financial affiliation. the emergency department, where more than In the United States, coronary artery dis- 5% of visits and up to 40% of admissions ease is the leading cause of mortality, with are because of chest pain.1,2 Chest pain is more than 300,000 deaths annually. Each often the presenting symptom of myocardial year, more than 600,000 persons will have their first MI, and nearly 300,000 patients with known coronary artery disease will 4 BEST PRACTICES IN CARDIOLOGY: RECOMMENDATIONS FROM have recurrence. MI is a subset of acute cor- THE CHOOSING WISELY CAMPAIGN onary syndrome (ACS), which is a spectrum of clinical presentations.5 ACS is divided Sponsoring into ST elevation MI (STEMI) and non– Recommendation organization ST elevation ACS, which includes unstable Do not test for myoglobin or creatine kinase MB American Society angina and non–ST elevation MI (NSTEMI) in the diagnosis of acute myocardial infarction. for Clinical because the two entities are often indistin- Instead, use troponin I or T measurements. Pathology guishable at presentation. STEMI is defined Do not use coronary computed tomography Society of as symptoms characteristic of cardiac isch- angiography in high-risk emergency department Cardiovascular CT patients presenting with acute chest pain. emia with persistent ST segment elevation or a new left bundle branch block on electro- Source: For more information on the Choosing Wisely Campaign, see http:// cardiography (ECG).6 NSTEMI is persistent www.choosingwisely.org. For supporting citations and to search Choosing symptoms with elevated cardiac troponin Wisely recommendations relevant to primary care, see http://www.aafp.org/afp/ recommendations/search.htm. levels but no ST segment elevation. Unstable angina produces symptoms suggestive of 170Downloaded American from the Family American Physician Family Physician website at www.aafp.org/afp.www.aafp.org/afp Copyright © 2017 American AcademyVolume of Family 95, Physicians. Number For3 ◆the February private, noncom 1, 2017- mercial use of one individual user of the website. All other rights reserved. Contact [email protected] for copyright questions and/or permission requests. Acute Coronary Syndrome Table 1. Definition of Myocardial Infarction Detection of a rise or fall of cardiac biomarker values (preferably cardiac troponin) with at least one value above the 99th percentile of the cardiac ischemia without elevated cardiac normal reference range, and at least one of the following: troponin levels. Symptoms of ischemia New or presumed new significant ST segment T wave changes, or new Initial Approach to the Patient or presumed new left bundle branch block with Chest Pain Development of pathologic Q waves on electrocardiography* Most patients with chest pain do not have Imaging evidence of new loss of viable myocardium or new regional wall motion abnormality MI, and a systematic approach can usually Identification of an intracoronary thrombus by angiography or autopsy rule it out (Figure 1).5-7 The assessment begins with rapid 12-lead ECG within 10 minutes of *—Pathologic Q waves are a Q wave in leads V2 to V3 that are ≥ 0.02 seconds, or a presentation. If there is evidence of STEMI, QS complex in leads V2 and V3 or a Q wave that is ≥ 0.03 seconds and ≥ 0.1 mV deep the patient should be emergently referred for in any two contiguous leads. reperfusion therapy with primary percuta- Information from reference 3. neous coronary intervention (preferred) or fibrinolytic therapy.6 If there is no evidence of STEMI, the patient’s risk of ACS should be categorized as low, intermediate, or high Evaluation of Patients with Chest Pain (Table 2).8 This is based on an assessment of Patient presents with chest pain; obtain risk factors, presenting signs and symptoms, ECG within 10 minutes of presentation and serial cardiac troponin measurements. Cardiac troponin levels should be measured ST segment elevation? at presentation and again three to six hours after symptom onset.5 Patients with elevated levels consistent with non–ST elevation ACS Yes No should be hospitalized and treated accord- STEMI: Admit Measure cardiac troponin levels ing to the American College of Cardiology/ and manage and perform a history, physical American Heart Association guidelines with according to examination, and risk assessment ACC/AHA an early invasive strategy (diagnostic angi- guidelines6 ography with revascularization as indicated) Cardiac troponins positive? for higher risk groups.5 In patients with negative cardiac troponin levels, additional No confirmatory testing may be performed to Yes further lower the risk of undiagnosed ACS; NSTE-ACS: Admit and Repeat cardiac troponin manage according to measurement three to six this may be done in a chest pain unit, as an 5 5 ACC/AHA guidelines hours after symptom onset; inpatient, or as an outpatient. consider observation with serial ECG and cardiac Clinical Diagnosis and Risk Assessment troponin measurements Risk factors for MI include increasing age, male sex, chronic renal insufficiency, diabetes Positive cardiac troponin levels or mellitus, known atherosclerotic disease (cor- ECG changes suggesting ischemia? onary or peripheral), and early family history of coronary artery disease (first-degree male Yes No relative with first event before 55 years of age or first-degree female relative with first event NSTE-ACS: Admit and Consider exercise treadmill 5 manage according to testing, a stress myocardial before 65 years of age). A calculator from the ACC/AHA guidelines5 perfusion study, or stress American College of Cardiology and Ameri- echocardiography can Heart Association estimates 10-year risk of atherosclerotic cardiovascular disease Figure 1. Algorithm for the evaluation of patients with chest pain. and assists with primary prevention (http:// (ACC = American College of Cardiology; AHA = American Heart Associ- my.americanheart.org/cvriskcalculator). ation; ECG = electrocardiography; NSTE-ACS = non–ST elevation acute Although determining risk factors pro- coronary syndrome; STEMI = ST elevation myocardial infarction.) vides helpful background information, Information from references 5 through 7. February 1, 2017 ◆ Volume 95, Number 3 www.aafp.org/afp American Family Physician 171 Acute Coronary Syndrome Table 2. Likelihood That Signs and Symptoms Represent an ACS Secondary to CAD Intermediate likelihood Low likelihood Absence of high-likelihood Absence of high- or High likelihood features and presence of any intermediate-likelihood Feature Any of the following: of the following: features but may have: History Chest or left arm pain or discomfort Chest or left arm pain or Probable ischemic symptoms as chief symptom reproducing prior discomfort as chief symptom in absence of any of the documented angina Age greater than 70 years intermediate-likelihood Known history of CAD, including MI Male sex characteristics Diabetes mellitus Recent cocaine use Examination Transient MR murmur, hypotension, Extracardiac vascular disease Chest discomfort reproduced diaphoresis, pulmonary edema, or rales by palpation ECG New, or presumably new, transient