In the setting of acute coronary ischemia, insufficient blood flow to the myocardium results in abnormalities of wall motion and abnormalities of normal systolic wall thickening. Echocardiographic imaging can detect these abnormalities but cannot distinguish ischemia from acute infarction. However, in patients with chest pain without clear ischemia on ECG and atypical or low risk clinical features, echocardiographic imaging may help clarify the diagnosis. In general, the greatest value has been shown in young male patients without prior cardiac history. Small studies in highly selected populations of patients without known CAD or prior infarction have shown sensitivities from 86-92% and specificities from 53-90% depending on the timing of the ECG with chest pain symptoms and whether acute MI or acute coronary ischemia was the endpoint (39). In a larger study of unselected chest pain patients, Sabia and colleagues reported that 94% of studies were technically adequate with a sensitivity of 93% and a specificity of 57% for acute MI (40).
When considering the use of echocardiographic imaging for diagnosis of MI in ED chest pain patients, keep in mind that obtaining good images of all segments of the myocardium is critical for the accuracy of this means of evaluation. In addition, assessing wall motion abnormalities due to ischemia in patients with prior infarction or left bundle-branch block or after bypass surgery is challenging due to baseline abnormalities of wall motion. Specialized equipment and highly trained individuals capable of performing and interpreting the studies are necessary on-site 24 h a day. The use of telemedicine interpretation of ED ECGs as described by Trippi and colleagues (41) could obviate the need to have a cardiologist available on-site for interpretation.
Although early work offers promise, it is not clear that echocardiography adds to the diagnostic accuracy of simpler and more routine ECG and cardiac marker evaluation. At least one small study in the ED setting has shown no advantage from the addition of echocardiographic imaging in the evaluation of chest pain patients (42). Further studies in this group will be needed to assess echocardiography's effect on clinical outcomes, as well as its cost-effectiveness.
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