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Management of Type B Aortic Dissection
Abstract & Commentary
By Michael H. Crawford, MD
Source: Chang CP, et al. The role of false lumen size in prediction of in-hospital complications after acute type B aortic dissection. J Am Coll Cardiol. 2008;52:1170-1176.
Uncomplicated type B aortic dissection (origin distal to left subclavian artery) is usually treated medically. However, early mortality is 10%-12%, and is due to complications. The ability to predict who will develop complications could help reduce mortality by permitting earlier interventions. Thus, Chang et al from Taiwan assessed CT scans in 55 consecutive type B dissections to see if there were anatomical clues to subsequent complications. Complications were defined as death due to dissection; progression of dissection; rupture of the aorta; and end-organ hypoperfusion. Of the 55 patients, 31 had a stable in-hospital course and 24 had complications. CT measurements included maximum aortic diameter, maximal false lumen area (MFLA), minimal true lumen, number of branch vessels involved (BVI), and total longitudinal length of the dissection. MFLA was significantly larger in the complications group (1,899 vs 558 mm2, p < .001), and BVI was higher (3.3 vs 1.0, p < .001). Only MFLA and BVI were independent predictors of complications on multivariable analysis. An initial MFLA > 922 mm2 or a BVI of two or more were associated with a higher incidence of in-hospital complications. Chang et al concluded that a large initial MFLA and higher BVI by CT are predictors of a complicated hospital course in type B aortic dissection.
The management of type B aortic dissection is problematic. Most patients do well with medical therapy, but some have complications which are often fatal. In this consecutive series, 44% had complications, of which 17% died in the hospital. If these patients could be intervened upon earlier, especially with stent-grafts, prognosis may be improved. In this series and others, clinical features did not predict outcomes, but aortic characteristics on CT scans do. Prior studies have shown some relation between aortic size and outcomes, but this study focused on the two lumens in a dissection and came up with more powerful predictors. All the CT aortic measures made were univariate predictors of complications, but two, MFLA and BVI, were independent predictors of any complication. MFLA was a robust predictor of all complications, but BVI predicted organ hypoperfusion and progressive dissection better than rupture. This makes sense because if the thin-walled false lumen continues to expand, it would be reasonable to predict rupture, progressive dissection, and eventual organ under perfusion. So the false lumen size seems to be the key variable. Chang et al suggest that if the MFLA is greater than around 900 mm2, one should consider an intervention to prevent complications. This is a small trial, and this hypothesis will need to be tested prospectively, but until that is accomplished, this seems to represent good advice for the management of acute type B aortic dissection.