Читать книгу Practical Cardiovascular Medicine - Elias B. Hanna - Страница 27

The absence of wall motion abnormalities during active chest pain argues against ischemia. For optimal sensitivity, the patient must have active ischemia while the test is performed. Wall motion abnormalities may persist after pain resolution in case of stunning or in case of subendocardial necrosis involving > 20% of the inner myocardial thickness (< 20% subendocardial necrosis or mild troponin rise may not lead to any discernible contractile abnormality).⁴⁶ Conversely, wall motion abnormalities, when present, are not very specific for acute ischemia and may reflect an old infarct. However, the patient is already in at least an intermediate risk category.

Figure 1.2 Kinetics of troponin release. Troponin rises above MI cutoff at 2-3 hours, then peaks and plateaus at ~24 hours. Note the slow decline that mimics a plateau pattern. Reperfused MI has a much narrower curve; the troponin area under the curve, rather than the peak, corresponds to the infarct size. An elevated troponin may be repeated every 8 hours until it trends down, to assess the area under the curve/infarct size.

Strain echocardiography (global or regional) improves the sensitivity and negative predictive value of echo for ACS diagnosis in patients with normal initial troponin and non-diagnostic ECG (91%), even several hours after the chest pain episode, but is non-specific and has a poor positive predictive value (13% in one study).⁴⁶

Acute resting nuclear scan, with the nuclear injection performed during active chest pain or within ~3 hours of the last chest pain episode, has an even higher sensitivity than echo in detecting ischemia. An abnormal resting scan, however, is not specific, as the defect may be an old infarct or an artifact.