Author: Dima Quraini, MD
Editor: Ashley Davidoff, MD
Clinical considerations
Chest pain is a common emergency department complaint. Many benign diseases such as gastro esophageal reflux disease or costochondritis as well as life-threatening diseases such as myocardial infarction manifest themselves as chest pain. Therefore, it is important to extract pertinent clinical information from the patient that will help increase the likelihood of one etiology over another and direct further investigation.
Exertional substernal pressure radiating to the arms or throat that is associated with other symptoms such as shortness of breath, nausea or diaphoresis is the classical manifestation of an acute coronary syndrome. Patients presenting with such classical pain that is accompanied by a diagnostic 12 lead electrocardiogram for infarction are urgently treated with thrombolytics or directed to angioplasty as per current AHA/ACC guidelines. However, less than a third of patients presenting with chest pain have an acute myocardial infarct. The majority of the patients will need further imaging to help determine their risk of current and future cardiac events.
Imaging strategies
What study?
-Plain chest radiograph:
A plain chest radiograph is usually the first imaging modality used to evaluate chest pain in the emergency department. It is an inexpensive test that may yield important information on thoracic structures such as the lung, heart and the great vessels. It is highly sensitive to non-cardiac pathologies that are in the differential diagnosis of chest pain such as pneumonia and pneumothorax. Although one cannot diagnose an acute coronary syndrome from a chest radiograph, many indirect findings such as changes in cardiac silhouette, pulmonary edema, calcification of the myocardium or coronary arteries may suggest underlying coronary artery disease.
-Treadmill exercise electrocardiography (ECG):
A treadmill exercise ECG test is both safe and useful in patients thought to be at low to intermediate risk of having an acute coronary syndrome and who have a normal baseline 12 lead ECG. It is inexpensive, widely available and provides both diagnostic and prognostic information. Since prevalence of coronary artery disease in the selected population of patients is expected to be low, a negative treadmill exercise ECG has a high negative predictive value. A negative treadmill exercise ECG performed within 48 hours of presentation is associated with a 2 % cardiac event rate at 6 months, whereas that percentage rises to 15% in patients found to have a positive or equivocal treadmill exercise ECG.
– Resting myocardial perfusion imaging (MPI) and transthoracic echocardiography:
Both observational and prospective studies conclude that a resting myocardial perfusion imaging performed in the emergency department help reduce the rate of unnecessary hospitalizations in patients presenting with chest pain. A normal resting MPI has a negative predictive value that is equal or superior to 99% whereas a normal serum troponin level drawn at the same time has a negative predictive value of 39%. However, resting MPI is mostly useful in patients with no prior history of myocardial infarction.
A transthoracic echocardiography is most helpful during a patient?s episode of chest pain as wall motion abnormalities can be visualized within seconds of coronary artery occlusion. The echocardiography may also aid in patients in whom symptoms have resolved. Actually, a wall motion abnormality visualized with or without pain is associated with poor prognosis. The transthoracic echocardiography can help identify or rule out many causes of chest pain such as aortic dissection, pericarditis along with pericardial tamponade and pulmonary embolism. In brief, it is a highly sensitive exam for multiple pathologies and therefore not very specific.
– Stress echocardiography and radionuclide scans:
Stress echocardiography or radionuclide scans are preferred stress imaging modalities in patients with an abnormal baseline ECG or who have an inconclusive treadmill exercise ECG. Although these imaging modalities are more expensive and less available than a treadmill exercise ECG, they have a higher sensitivity to detect coronary artery disease. Also, they provide more information on extent and possible location of disease.
-Electron beam CT scan (EBCT):
The role of EBCT and its place in algorithms are still being determined. Electron beam CT scan has a promising role in patients deemed to be at low risk for an acute coronary syndrome. Coronary calcium noted on EBCT is associated with coronary artery disease with a sensitivity ranging between 88 to 100%. A coronary artery calcium score (CAC) can be determined. A low CAC score carries a high negative predictive value for future cardiac events.
Background to the disease
Myocardial ischemia occurs as a result of a mismatch between myocardial oxygen demand and delivery. Oxygen supply to the myocardium is most commonly limited by coronary atherosclerotic disease. An acute coronary syndrome is attributed to a ruptured atherosclerotic plaque or unstable plaque.
Myocardial oxygen supply may also be limited by coronary vasospasm either in normal coronary arteries or near atherosclerotic plaques in patients with coronary artery disease.
Less frequently encountered causes of decreased oxygen supply to the myocardium include aortic dissection, vasculitis, emboli, congenital abnormalities and myocardial bridges.
When?
A resting MPI can be obtained early on in the emergency department in a patient with ongoing symptoms or in whom symptoms have resolved less than 3 hours prior to injection of isotopes.
A stress exercise electrocardiogram test can be performed on a patient who has had two sets of negative cardiac enzymes, is asymptomatic and who has a interpretable baseline 12 lead electrocardiogram.
A stress echo or radionuclide imaging stress test can be obtained in patients who are unable to exercise, who have an abnormal 12 lead electrocardiogram once they have had two sets of negative cardiac enzymes.
All stress tests can also be performed electively in an outpatient setting.
How to order?
To order a stress test, specify the type of stressor required (exercise, adenosine, dobutamine) and the form of imaging to be used (ECG, echocardiography, MIBI). The symptom and the reason for which the exam is ordered should be identified (ex: for an echocardiography the reason for exam should be chest pain, evaluate for WMA or pericardial effusion).
Patient preparation:
Patients are instructed not to consume any meals or caffeinated beverages at least 3 hours prior to exam. Beta blockade medications should also be held at least 8 hours prior to exam if exam is performed in hospitalized patient.
Clinical red flags
Patients with evidence of ST elevation on ECG, with ongoing symptoms or who are clinically unstable should not undergo any form of stress test.
References
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Udelson JE, Beshansky JR, Ballin DS et al. Myocardial Perfusion Imaging for Evaluation and Triage of Patients with Suspected Acute Cardiac Ischemia. JAMA 2002; 288: 2693-2700.
Stein RA, Chaitman BR et al. Safety and Utility of Exercise Testing in Emergency Room Chest Pain Centers: An Advisory From the Committee on Exercise, Rehabilitation, and Prevention, Council on Clinical Cardiology, American Heart Association. Circulation 2000; 102: 1463-1467.
Lee TH, Goldman L. Evaluation of the Patient with Acute Chest Pain. NEJM, 2000: 342; 1187-1195
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