Ischemic Stroke

Overview

Stroke is the clinical presentation of focal or global deficits in neurological functioning caused by nontraumatic brain injury resulting from vascular disease inside the brain or in vessels leading to the brain. The onset is sudden or relatively rapid and the duration is more than 24 hours.

The neurologic deficits caused by a completed stroke persist, whereas those of a transient ischemic attack (TIA) resolve completely within 24 hours.

Classification of Stroke

Stroke is classified into two major types:

• Brain ischemia due to thrombosis, embolism, or systemic hypoperfusion
• Brain hemorrhage due to intracerebral hemorrhage or subarachnoid hemorrhage

A stroke is the acute neurologic injury that occurs as a result of one of these pathologic processes. Approximately 80 percent of strokes are due to ischemic cerebral infarction and 20 percent to brain hemorrhage.

There are three main subtypes of brain ischemia:

• Thrombosis generally refers to local in situ obstruction of an artery. The obstruction may be due to disease of the arterial wall, such as arteriosclerosis, dissection, or fibromuscular dysplasia; there may or may not be superimposed thrombosis.
• Embolism refers to particles of debris originating elsewhere that block arterial access to a particular brain region [2]. Since the process is not local (as with thrombosis), local therapy only temporarily solves the problem; further events may occur if the source of embolism is not identified and treated.
• Systemic hypoperfusion is a more general circulatory problem, manifesting itself in the brain and perhaps other organs. Blood disorders are an uncommon primary cause of stroke. However, increased blood coagulability can result in thrombus formation and subsequent cerebral embolism in the presence of an endothelial lesion located in the heart, aorta, or large arteries that supply the brain.

Embolic Stroke

Pathophysiology

Cardioembolic stroke causes approximately 20% of all ischemic strokes. Stroke caused by heart disease and cardiovascular disease is primarily due to embolism of thrombotic material forming on the atrial or ventricular wall or the left heart valves. These thrombi then detach and embolize the arterial circulation. The thrombus may fragment or lyse quickly, producing only TIA.

Alternatively, the arterial occlusion may last longer, producing, stroke. Subsequent thrombosis distal to the obstruction may occur, producing stroke in progress.

Risk Factors

Cardioembolic causes of stroke include:

• Atrial fibrillation (most common cause)
• Mural thrombus
• Myocardial infarction
• Dilated cardiomyopathy
• Valvular lesions
• Mitral stenosis
• Bacterial endocarditis
• Mechanical valve
• Paradoxical embolus
• Atrial septal defect
• Patent foramen ovale
• Atrial septal aneurysm

Clinical Presentation

The stroke is nearly always sudden and maximal (in terms of neurological deficits) at onset. As a rule, the full-blown picture evolves within seconds, exemplifying most strikingly the temporal profile of a stroke. With rare exceptions, there are no warning episodes. The embolus may strike at any time of day or night.

The neurological picture will depend on the artery involved and the site of the obstruction.

In the middle cerebral artery territory these include:

• The frontal opercular syndrome, with facial weakness and severe aphasia (difficulty understanding language) or dysarthria (motor speech disorder, poor articulation)
• The brachial or hand plegia syndrome, in which the arm or hand is paralyzed with or without cortical sensory abnormalities
• Broca’s or Wernicke’s aphasia alone
• Left visual neglect, when the nondominant parietal lobe is involved.

More often the embolus is smaller and passes into one of the branches of the middle cerebral artery, producing a strikingly focal disorder such as a motor speech disorder, a monoplegia (limb weakness), or a receptive type of aphasia with little or no motor paralysis.

Sudden hemianopia suggests a posterior cerebral artery embolus, and sudden foot and shoulder weakness suggests an anterior cerebral embolus.

Sudden sleepiness and inability to look up associated with bilateral ptosis suggest an embolus to the top of the basilar artery.

Diagnosis

A thorough cardiac evaluation should be undertaken in patients in whom the suspicion of cardioembolism is high.

Continuous EKG monitoring may reveal intermittent atrial fibrillation. The presence of atrial fibrillation alone, is sufficient to establish cause, even in the absence of a left atrial clot.

An echocardiogram may disclose mitral valve disease, an intracardiac thrombus or turmor, or a dyskinetic area of myocardium. Spontaneous echo contrast within the atrial appendage is associated with stroke and may represent a tendency for spontaneous clotting of blood within the atrium.

Transesophageal echocardiography is superior to the transthoracic technique for visualization of valves, left atrium, and aortic arch. Intravenous bubble contrast should be administered to all patients undergoing echocardiography in search of an embolic source.

On CT scanning, embolic infarction may appear as a single low-density area compatible with a pale infarction.

MRI scanning documents scanning better than CT scanning. When MRI is coupled with MR angiography, it can help identify arterial sources of emboli from either the extra- or intra-cranial vessels.

Carotid ultrasonography (ultrasound) and transcranial Doppler (TCD) techniques may reveal carotid atherosclerosis or intracranial stenosis, respectively. Arterial imaging (CT or MR angiography or TCD) performed in the early hours of embolic stroke often shows occlusion of one or more vessels. Complete lysis of emboli often occurs, and imaging performed after several days may be normal.

Complications

Any patient who has sustained a stroke is at risk for further complications because of immobility, as well as from problems relating to his or her general medical conditions.

Below is a list of complications that may be secondary to stoke:

• Deep venous thrombosis (DVT)
• Seizures
• Depression
• Dysphagia
• Incontinence
• Shoulder subluxation
• Spasticity

Prognosis People who suffer ischemic strokes have a much better chance for survival than those who experience hemorrhagic strokes.

Among the ischemic stroke categories, cardioembolic strokes have a worse prognosis and produce larger and more disabling strokes than other ischemic stroke subtypes.