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Evaluating and Managing Low-Risk Chest Pain in the ED

Evaluating and Managing Low-Risk Chest Pain in the ED

Testing of Low-risk Patients Presenting to the Emergency Department with Chest Pain: A Scientific Statement From the American Heart Association. Amsterdam EA, Kirk JD, Bluemke DA, Diercks D, Farkouh ME, Garvey JL, Kontos MC, McCord J, Miller TD, Morise A, Newby LK, Ruberg FL, Scordo KA, Thompson PD. Circulation. 2010; 122: 1756-1776.

The American Heart Association (AHA) published a statement regarding the evaluation of low-risk chest pain in the ED ranging from assessing clinical symptoms to outpatient testing. There are over 8 million visits to the ED for chest pain every year in the United States with only a small percentage actually having a life-threatening condition. At the same time, about 2% of patients with acute coronary syndrome (ACS) are inadvertently discharged from the ED. The ED clinician must be able to determine when urgent therapy, admission and further testing, or direct discharge from the ED is warranted.

Initial Assessment

Initial risk stratification is made by the ED clinician based on the history and physical, ECG, and cardiac injury markers. When symptoms are suggestive of ACS, patients may be deemed low-risk if they are hemodynamically stable, have no arrhythmias noted on telemetry, the ECG is normal, and the initial cardiac injury markers are negative.

Due to the wide differential of chest pain, the history should include questions to help determine the likelihood of ACS versus other causes of chest pain. The information obtained concerning the patient's pain should include its location, onset, character, time course, severity, whether it radiates, any alleviating and/or exacerbating factors, history of similar episodes, and presence of any associated symptoms (e.g., diaphoresis, dyspnea, dizziness, palpitations, or nausea). Symptoms of myocardial ischemia are classically described as diffuse chest heaviness, pressure, or tightness that may radiate to the arm, neck, or jaw. However, careful attention should be made for atypical presentations known as "anginal equivalents" in certain populations such as the elderly, women and diabetic patients. These anginal equivalents include jaw, neck, or arm discomfort without chest pain; dyspnea; nausea; vomiting; diaphoresis; or fatigue. Sharp or stabbing pain may allude to pain that is musculoskeletal in nature. However, keep in mind that the Multicenter Chest Pain Study found that 22% of patients with sharp or stabbing chest pain were eventually diagnosed with ACS.

A normal physical exam is found in the majority of chest pain cases. The exam can help identify higher-risk patients who might have signs of heart failure or peripheral arterial disease. The exam may also help suggest non-ACS causes of chest pain such as unequal extremity pulses (aortic dissection), prominent murmurs (endocarditis), friction rubs (pericarditis), fevers and abnormal lung sounds (pneumonia), or chest wall pain (musculoskeletal). However, any of these findings can be seen in a patient with ACS.

An initial ECG should be obtained within 10 minutes of presentation, as it is crucial in early risk stratification. In patients with a nonischemic ECG and no history of CAD, the frequency of MI was found to be 2% and 4% in those with a history of CAD. With a normal initial ECG, repeat ECGs have been recommended to assess for evolving ischemia. ST-segment depression (≥0.05mV) in contiguous leads, in the absence of LVH, is associated with an increased risk of ischemia. ECGs with posterior leads (V7-V9) or right-sided leads (V4R-V6R) may be done when suspicion of posterior or right-sided infarction is present.

Most patients with uncomplicated ACS have normal chest radiographs. Findings indicative of other diagnosis maybe noted on radiographs including widened mediastinum, enlarged cardiac silhouette, pleural effusion, pneumonia and pneumothorax.

Cardiac injury markers (highly sensitive and specific cardiac troponin) should be measured in all patients suspected of myocardial ischemia. In patients who present within 6 hours of symptom onset and with negative initial cardiac markers, the markers should be re-measured 6 to 8 hours after symptoms onset. Current troponin assays can identify most MIs within 3 hours of ED arrival. Because there are numerous non-ischemic causes of elevated troponins, confirmation of MI is based on the clinical setting and pattern of troponins. However, though a positive troponin can be diagnostic for myocardial ischemia, negative troponins do not equate to no ACS or myocardial ischemia.

Risk-scoring systems may help in risk stratification of chest pain. One simple criterion can be obtained with one set of cardiac markers, an ECG, and a history of CAD. If all three are negative, the patient can be considered low risk with a probability of MI <6%. The Thrombolysis in Myocardial Infarction (TIMI) score is widely used in high-risk patients but has shown mixed results when applied to low-risk patients. The Global Registry of Acute Coronary Events (GRACE) scoring system has been reported to be accurate in predicting risk, but is more complex than the TIMI score and many variables are not available in the ED. Scoring systems are recommended as adjuncts to clinical judgment in the evaluation of chest pain.

Chest Pain Units and Accelerated Diagnostic Protocols

Chest pain units (CPU) provide short-term observation of low-risk patients. They were created to carry out accelerated diagnostic protocols (ADP). ADPs provide cost-effective rapid assessment and exclusion of ACS in low-risk patients in order to prevent admissions and prolonged hospital stays. CPUs use ADPs to further stratify low-risk patients with serial ECGs and cardiac markers. If negative, further confirmatory testing is done to exclude inducible ischemia.

Confirmatory Test Selection in ADPs

The purpose of CPU observation and confirmatory testing in an ADP is to further minimize the likelihood of ACS low enough to warrant a safe discharge. Exercise treadmill testing (ETT) is the cornerstone of confirmatory testing in an ADP The patient must be able to exercise and must have a normal baseline ECG. If the patient does not fit these criteria, an imaging test (myocardial perfusion imaging, echocardiogram, coronary angiography, or computed tomography coronary angiography (CTCA)) may be considered. Historically, ETTs were done 48 hours after clinical stability but the AHA changed the recommendations in 2002 stating that ETTs should be done 6 to 8 hours after an evaluation that revealed no evidence of ischemia. Studies have shown the cost benefit of ETT in an ADP One study of 421 patients showed no difference in cardiac events in 6 months in those managed with an ADP versus usual care, but the cost was 61% higher in the latter group.

Since many institutions are not able to provide confirmatory testing at all times, the American College of Cardiology (ACC)/AHA guidelines approve outpatient ETT in selected low-risk chest pain patients after a negative evaluation. The criteria include no further chest pain, non-diagnostic initial and follow-up ECGs, and normal cardiac injury marker measurements. A prospective study of 900 patients who underwent outpatient ETT had 3 nonfatal MIs and no deaths during follow up. This outpatient ETT should be obtained within 72 hours of their ED evaluation.

When ETT is not an option, the two most common stress imaging tests performed in CPUs are myocardial perfusion imaging (MPI) and echocardiography. They are both more accurate in detecting CAD than ETT, and they also provide information on left ventricular function as well as the location and extent of ischemia, if present. Stress imaging can be done with treadmill exercise as well as with pharmacologic agents such as dobutamine. MPIs can use coronary vasodilators such as dipyridamole or adenosine. Rest MPIs involve the injection of technetium 99m butilfenin radiopharmaceuticals. The technetium is taken up by the myocardium in direct relation to tissue perfusion and its redistribution is negligible, which makes it a good agent in the resting state. Because rest MPIs detect perfusion defects, old infarctions may also be seen on imaging. The rest MPI is beneficial because normal perfusion is associated with a very low clinical risk of ACS. Multiple studies have shown that rest MPIs can identify low and high-risk patients. Although MPI is associated with significant radiation exposure, they are a Class I indication in current guidelines for evaluation of patients with chest pain and non-ischemic ECGs.

Coronary artery calcification is considered a marker for CAD due to its relation with atherosclerosis. The coronary artery calcium (CAC) score is a quantitative index of the extent of calcification measured by either electronic beam or multidetector computed tomography (CT). Studies have shown that a high CAC score is associated with an increased risk for coronary events and that a zero CAC score indicates a very low risk. A zero CAC score also has a negative predictive value close to 100% for early adverse events.

CTCA provides anatomic, rather than functional, information regarding coronary patency. With the advent of 64-slice multidetector CT scanners, major coronary arteries and branch vessels can be visualized. In a study of 368 patients, CTCA was found to have a sensitivity of 100% and a negative predictive value of 100% for ACS after 6 months of follow up. Compared with standard care, CTCA has been reported to decrease time to diagnosis (15 versus 3.4 hrs), the number of repeat evaluations for chest pain, and cost. However, several limitations do exist. About 25% to 50% of patients presenting to the ED with chest pain may not be candidates due to obesity, contrast allergy, intolerance to beta blockade, arrhythmia, renal insufficiency, or a history of CAD. Despite the limitations, CTCA has the potential for major clinical utility in the evaluation of low-risk patients in the ED due to its high negative predictive value (NPV).

Follow-up of Patients With Negative CPU Evaluations

Most cases of chest pain with negative evaluations are non-cardiac in nature and require further evaluation for identification of the cause and management of their symptoms. Common causes of non-cardiac chest pain include pulmonary, gastrointestinal, musculoskeletal, or psychological causes. Panic attack or somatoform disorders may be causative factors in up to 40% of these patients. Finding a cause and managing symptoms will prevent unnecessary returns to the ED and improve quality of life. For patients with persistent concern even after negative noninvasive cardiac evaluation, coronary angiography or CTCA may be considered.

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