90-95%). The negative predictive value is high (approximately 95%), but the positive predictive value is much lower and more variable.14 This may partly relate to interpretation difficulties in the presence of prior infarction, and aggressive interpretation of minor abnormalities by physicians anxious to avoid false negatives. From these studies, echocardiography appears more sensitive than standard criteria for the diagnosis of infarction; it is also sensitive for the diagnosis of myocardial ischaemia, but only if performed during pain. Echocardio-graphy provides incremental prognostic information in the identification of patients at risk of cardiac events. However, if echocardiography is used alone, a small number of patients with subendocardial infarction will be discharged.
The study by Trippi and colleagues15 is an example of how echocardiography might be aggressively used in the emergency room. These authors enrolled 163 patients with no evidence of MI on initial cardiac markers or ECG, who were recommended for admission. If rest echocardiographic images were normal, dobutamine stress echocardiography was performed, initially supervised by a cardiologist and, in later stages, by a trained nurse. Echocardiographic images were transmitted by tele-echocardiography and interpreted off-site. In the first three stages, all patients were admitted. In the final stage, patients were discharged if the stress echocardiogram was negative. Average length of stay was only 5.4 hours. In the third and fourth stages recruitment was less selective, so that in the final phase mild residual chest pain, a non-diagnostic rather than normal ECG, and mild elevation of initial creatine kinase (CK) with normal CK-MB were permitted. The negative predictive value of dobutamine stress echocardio-graphy was 98.5% based on final diagnosis, which was largely based on clinical follow up. There were two false negative results—one in a patient who was admitted in the third stage but discharged without a clinical diagnosis, and one in a patient who was discharged following a normal stress echocardiogram. The study is interesting because of the aggressive approach to achieving discharges, the use of tele-echocardiography and nursing supervision to avoid having a cardiologist on-site, and the choice of pharmacological stress to avoid the noise of a treadmill and the requirement for patient cooperation with exercise. However, most authors would argue that MI should be fully excluded by serial markers and ECGs, and that there be complete resolution of chest pain before stress testing.
In summary, echocardiography in the emergency room may facilitate early diagnosis and management in those patients with a high clinical suspicion of MI but a non-diagnostic ECG. It may also diagnose unstable angina if performed during pain. Aggressive use of rest and stress echocardiography can reduce admissions, but some false negatives will occur and
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