Septal Abnormalities for Paradoxical Embolism

Atrial septal defects

Patent foramen ovale

Atrial septal aneurysms

Pulmonary arteriovenous fistulas

Modified from Caplan LR: Stroke. A Clinical Approach, 2nd ed. Boston, Butterworth-Heinemann, 1993.

or months. The region of ischemia is also smaller than it is in patients with embolism, and the signs tend to accumulate over a longer period of time, producing frequent fluctuations and stepwise changes in neurological signs.

Angiography performed in the first 12 hours shows emboli in a high percentage of cases, but after 48 hours most emboli are no longer detectable. The most common recipient arteries are the MCAs and ACAs in the anterior circulation and the VAs, distal basilar artery (BA), and PCAs in the posterior circulation. The clinical signs and imaging findings are the same as those described in the discussion of these vessels in the section on thrombotic stroke. In patients in whom brain embolism is suspected, the possible embolic sources should be evaluated to prevent further strokes. Evaluation of cardiac and aortic sources usually involves transesophageal echocardiography (TEE) and sometimes cardiac rhythm monitoring.^ Noninvasive vascular tests (ultrasound, MRA, CTA) can be used to evaluate arterial sources. TCD monitoring for embolic signals can help identify the presence of embolism and may suggest the source.

Management. Treatment of cerebral embolism consists of two major strategies: acute thrombolytic therapy to lyse the embolus and long-term prophylactic therapy to prevent recurrence of embolic stroke.

Thrombolytic therapy has usually been tried in patients with acute embolic stroke to recanalize the occluded artery, restore cerebral blood flow, reduce ischemia, and limit neurological disability. Recanalization may assist the recovery of reversibly ischemic tissue. Several thrombolytic agents have been tested in uncontrolled trials (urokinase, recombinant tissue plasminogen activator [rt-PA], streptokinase) using either intra-arterial y or intravenous administration. y , y So far the efficacy and safety of thrombolytic therapy have not been confirmed, but timely recanalization may benefit patients with acute thromboembolic stroke if it is started early enough. Two recent placebo-controlled studies using intravenous rt-PA have shown that thrombolytic therapy may be effective and relatively safe when it is started within 3 to 6 hours.y , y The most feared complication of this therapy is severe intracranial hemorrhage.

After an acute stroke the goal of treatment is to prevent the next embolus, using anticoagulation or removal of embolic sources. Cardiac sources may be corrected surgically. Usually intravenous heparin is used, followed by oral warfarin. Because it has been generally accepted that hemorrhagic complications are common in patients with large infarctions, early anticoagulation should be carefully monitored in such patients. y

If a tightly stenotic carotid artery is present, either surgery (if feasible) or longer-term warfarin is indicated. When stenosis is not as severe, antiplatelet agents such as aspirin or ticlopidine may be used. Warfarin is effective in preventing embolism in patients with nonrheumatic atrial fibrillation. y Warfarin also decreases the incidence of embolism in patients with rheumatic mitral stenosis and in those with mechanical heart valves. y When warfarin anticoagulation is used, it is advisable to keep the international normalized ratios at around 3. y , y In older patients, long-term anticoagulation poses important risks and problems. Aspirin may be useful for prophylaxis in some patients with cardiac

lesions of low embolic potential and in patients with absolute or relative contraindications to warfarin use.

Carotid artery stenosis is a very common source of intra-arterial embolism. Carotid endarterectomy has been used as a method of stroke prophylaxis, but there has been controversy about its safety and efficacy.y Recent studies suggest that symptomatic carotid stenosis of 70 percent or morey and asymptomatic carotid stenosis of 60 percent or more may be indications for carotid endarterectomy. y

Prognosis and Future Perspectives. Prognosis depends on the nature of the potential embolic sources and the effectiveness of prophylaxis. The advent of monitoring for emboli with TCD technology has opened new diagnostic possibilities. Further advances in this technology with the use of multiple concurrent channels (such as EEG) will allow better recognition of the source and of the nature and frequency of release of embolic material.

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