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Microemboli in cerebral circulation and alteration of cognitive abilities in patients with mechanical prosthetic heart valves.

Limitations of CT Angiography in Patient Selection for Thrombolytic Therapy To the Editor: We have read with great interest the article by Wildermuth et al1 on the role of CT angiography (CTA) in patient selection for thrombolytic therapy. The authors report that selection of patients with little potential for benefit from thrombolytic therapy is feasible with the use of CTA. The CTA findings, such as no vascular occlusion (ie, identification of patients with autolyzed thrombi), occlusion of internal carotid artery bifurcation, and poor leptomeningeal collaterals, indicate little potential for benefit from thrombolytic therapy. I am sure that these 3 CTA findings are useful in patient exclusion from thrombolytic therapy. However, there are 3 major problems with the use of CTA in patient selection for thrombolytic therapy. First, CTA has diagnostic limitations of precise information about lenticulostriate artery (LSA) involvement. When deciding whether to perform thrombolytic therapy, one of the most important issues is confirmation of whether the LSAs are involved in ischemia. Because LSAs are terminal vessels with poor collaterals, thrombolytic therapy for patients with middle cerebral artery (MCA) trunk occlusion involving the LSAs may be associated with a high risk of hemorrhagic complications. In our previous study 2 we found that when the LSAs are involved in ischemia and early ischemic change is present on the initial CT scan, thrombolytic therapy may result in unfavorable outcome with hemorrhagic complications. Furthermore, an arteriovenous shunt from the LSAs to the thalamostriate vein has been also reported3 to be a predictive sign for hemorrhagic complication. Therefore, in patients with MCA trunk occlusion, it may be dangerous to initiate thrombolytic therapy without precise information on LSA involvement. Second, embolic occlusion of small peripheral arteries, which is often associated with internal carotid artery (ICA) occlusive disease, may be misdiagnosed as no vascular occlusion or mere ICA occlusion by CTA alone. Even if there were ICA occlusion, clinical symptoms might be ameliorated by recanalization of peripheral embolic occlusion. It is very important to make a correct diagnosis of artery-to-artery embolic occlusion in patients with ICA occlusion. (We wonder that CTA cannot provide precise information on peripheral small arteries.) Third, because CTA requires a large amount of contrast medium, additional use of contrast medium is restricted and subsequent intra-arterial thrombolytic therapy is difficult to perform. Large emboli located in the MCA trunk may be resistant to intravenous thrombolysis, and intra-arterial thrombolytic therapy or direct percutaneous transluminal angioplasty may be required. 4