I

<3 hrs from <6 hrs from >6 hrs from symptoms onset symptoms onset symptoms onset

59-85%/63-96% 83-94%/87-100% 88-91 %/94-96% 98-99%/77-97% 98%/99% 98%/98%

Figure 16.1. Blood levels and sensitivity of smooth-muscle myosin heavy-chain protein measurement in acute aortic dissection at different time intervals from symptom onset. For comparison, the sensitivity and specificity of several imaging technique are reported. Modified from reference 13.

In this setting, it is possible to demonstrate intact smooth muscle content in atherosclerotic segments of the thoracic aorta, whereas segments of the abdominal aorta show often gross fatty change with loss of smooth-muscle content. For this reason, it is likely that some patients with a dissection involving a distal aortic tract do not have elevated smooth-muscle myosin heavy-chain levels. The diagnostic performance of the assay alone is comparable if not superior to transthoracic echocardiography, conventional CT, and aortogra-phy but less effective than transesophageal echocardiography, helical CT, or MRI1314 (Figure 16.2). The main advantages of this assay are obvious: it is rapid, it can be done at a fraction of the cost of computed tomography or magnetic resonance imaging, and it can be repeated in a manner similar to that of other conventional immunoassays. One must take into account that this test would be most useful in the initial patient triage at the emergency department, especially with its negative predictive role, helping physicians to determine whether an aortic dissection is a possibility. Since biochemical diagnosis is an independent diagnostic modality compared to noninvasive imaging proce-

Figure 16.2. Temporal sensitivity curves based on the site of the entry tear for smooth muscle myosin heavy-chain protein measurement with a cutoff level of 2.5 ^g/l. Modified from reference 13.

dures, the combined use of one technique with the biochemical test should markedly increase the sensitivity and specificity in detecting aortic dissection. A multicenter international clinical study aimed at validating the clinical use of the assay is ongoing and additional analysis to define a vascular-specific smooth-muscle assay, which will also improve the usefulness of the assay, is under evaluation.

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