Stroke

A stroke, also known as cerebrovascular accident (CVA), is an acute neurologic injury whereby the blood supply to a part of the brain is interrupted. Stroke can also be said to be a syndrome of sudden loss of neuronal function due to disturbance in cerebral perfusion. This disturbance in perfusion is commonly on the arterial side of the circulation, but can be on the venous side.

The part of the brain with disturbed perfusion can no longer receive adequate oxygen carried by the blood; brain cells are therefore damaged or die, impairing function from that part of the brain. Stroke is a medical emergency and can cause permanent neurologic damage or even death if not promptly diagnosed and treated. It is the third leading cause of death and adult disability in the US and industrialized European nations. On average, a stroke occurs every 45 seconds and someone dies every 3 minutes. Of every 5 deaths from stroke, 2 occur in men and 3 in women.

Risk factors include advanced age, hypertension (high blood pressure), diabetes mellitus, high cholesterol, and cigarette smoking. Cigarette smoking is the most important modifiable risk factor of stroke.

The term “brain attack” is starting to come into use in the United States for stroke, just as the term “heart attack” is used for myocardial infarction, where a cutoff of blood causes necrosis to the tissue of the heart. Many hospitals have “brain attack” teams within their neurology departments specifically for swift treatment of stroke.

Types of stroke:

Strokes can be classified into two major categories: ischemic and hemorrhagic. Ischemia can be due to thrombosis, embolism, or systemic hypoperfusion. Hemorrhage can be due to intracerebral hemorrhage or subarachnoid hemorrhage. ~80% of strokes are due to ischemia.

Ischemic stroke:

In ischemic stroke, which occurs in approximately 85-90% of strokes, a blood vessel becomes occluded and the blood supply to part of the brain is totally or partially blocked. Ischemic stroke is commonly divided into thrombotic stroke, embolic stroke, systemic hypoperfusion (Watershed or Border Zone stroke), or venous thrombosis

Thrombotic stroke:

In thrombotic stroke, a thrombus forming process develops in the affected artery and gradually the thrombus—built up clot—narrows the lumen of the artery and impedes blood flow to distal tissue. These clots usually form around atherosclerotic plaques. Since occlusion of the artery is gradual, onset of symptomatic thrombotic strokes is slower. A thrombus itself (even if non-occluding) can lead to an embolic stroke (see below) if the thrombus breaks off—at which point it is then called an “embolus.” Thrombotic stroke can be divided into two types depending on the type of vessel the thrombus is formed on:

* Large vessel disease involves the common and internal carotids, vertebral, and the Circle of Willis. Diseases that may form thrombus in the large vessels include (in descending incidence):
o Atherosclerosis
o Vasoconstriction
o Dissection
o Takayasu arteritis
o Giant cell arteritis
o Arteritis/vasculitis
o Noninflammatory vasculopathy
o Moyamoya syndrome
o Fibromuscular dysplasia
* Small vessel disease involves the intracerebral arteries, branches of the Circle of Willis, middle cerebral artery stem, and arteries arising from the distal vertebral and basilar artery. Diseases that may form thrombus in the small vessels include (in descending incidence):
o Lipohyalinosis (lipid hyaline build-up secondary to hypertension and aging) and fibrinoid degeneration. Stroke involving these vessels are known as lacunar infarcts
o Microatheromas from larger arteries that extend into the smaller arteries (atheromatous branch disease)

Embolic stroke:

Embolic stroke refers to the blockage of arterial access to a part of the brain by an embolus — a travelling particle or debris in the arterial bloodstream originating from elsewhere. An embolus is most frequently a blood clot, but it can also be a plaque broken off from an atherosclerotic blood vessel or a number of other substances including fat, air, and even cancerous cells. Because an embolus arises from elsewhere, local therapy only solves the problem temporarily; source of the embolus must be identified. Because the embolic blockage is sudden in onset, symptoms usually are maximal at start. Also, symptoms may be transient as the embolus lyses and moves to a different location or dissipates altogether. Embolic stroke can be divided into four categories:

* those with known cardiac source
* those with potential cardiac or aortic source (from transthoracic or transesophageal echocardiogram)
* those with an arterial source
* those with unknown source

High risk cardiac causes include:

* Atrial fibrillation and paroxysmal atrial fibrillation
* Rheumatic mitral or aortic valve disease
* Bioprosthetic and mechanical heart valves
* Atrial or ventricular thrombus
* Sick sinus syndrome
* Sustained atrial flutter
* Recent myocardial infarction (within one month)
* Chronic myocardial infarction together with ejection fraction <28 percent
* Symptomatic congestive heart failure with ejection fraction <30 percent
* Dilated cardiomyopathy
* Libman-Sacks endocarditis
* Antiphospholipid syndrome
* Marantic endocarditis from cancer
* Infective endocarditis
* Papillary fibroelastoma
* Left atrial myxoma
* Coronary artery bypass graft (CABG) surgery

Potential cardiac causes include:

* Mitral annular calcification
* Patent foramen ovale
* Atrial septal aneurysm
* Atrial septal aneurysm with patent foramen ovale
* Left ventricular aneurysm without thrombus
* Isolated left atrial smoke on echocardiography (no mitral stenosis or atrial fibrillation)
* Complex atheroma in the ascending aorta or proximal arch

Systemic hypoperfusion (Watershed stroke):

Systemic hypoperfusion is the reduction of blood flow to all parts of the body. It is most commonly due to cardiac pump failure from cardiac arrest or arrhythmias, or from reduced cardiac output as a result of myocardial infarction, pulmonary embolism, pericardial effusion, or bleeding. Hypoxemia (low blood oxygen content) may precipitate the hypoperfusion. Because the reduction in blood flow is global, all parts of the brain may be affected, especially “watershed” areas — border zone regions supplied by the major cerebral arteries. Blood flow to these areas does not necessarily stop, but instead it may lessen to the point where brain damage can occur.

Venous thrombosis:

Veins in the brain function to drain the blood back to the body. When veins are occluded due to thrombosis, the draining of blood is blocked and the blood backs up, causing cerebral edema. This can result in both ischemic and hemorrhagic strokes. This commonly occurs in the rare disease sinus vein thrombosis.

Hemorrhagic stroke:

A hemorrhagic stroke, or cerebral hemorrhage, is a form of stroke that occurs when a blood vessel in the brain ruptures or bleeds. Like ischemic strokes, hemorrhagic strokes interrupt the brain’s blood supply because the bleeding vessel can no longer carry the blood to its target tissue. In addition, blood irritates brain tissue, disrupting the delicate chemical balance, and, if the bleeding continues, it can cause increased intracranial pressure which physically impinges on brain tissue and restricts blood flow into the brain. In this respect, hemorrhagic strokes are more dangerous than their more common counterpart, ischemic strokes. There are two types of hemorrhagic stroke: intracerebral hemorrhage, and subarachnoid hemorrhage.

Intracerebral hemorrhage:

Intracerebral hemorrhage (ICH) is bleeding directly into the brain tissue, forming a gradually enlarging hematoma (pooling of blood). It generally occurs in small arteries or arterioles and is commonly due to hypertension, trauma, bleeding disorders, amyloid angiopathy, illicit drug use (amphetamines and cocaine), and vascular malformations. The hematoma enlarges until pressure from surrounding tissue limits its growth, or until it decompresses by emptying into the ventricular system, CSF or the pial surface. A third of intracerebral bleed is into the brain’s ventricles. ICH has a mortality rate of 44 percent after 30 days, higher than ischemic stroke or even the very deadly subarachnoid hemorrhage.

Subarachnoid hemorrhage:

Subarachnoid hemorrhage (SAH) is bleeding into the cerebrospinal fluid (CSF) of the subarachnoid space surrounding the brain. The two most common causes of SAH are rupture of aneurysms from the base of the brain and bleeding from vascular malformations near the pial surface. Bleeding into the CSF from a ruptured aneurysm occurs very quickly, causing rapidly increased intracranial pressure. The bleeding usually only lasts a few seconds but rebleeding is common. Death or deep coma ensues if the bleeding continues. Hemorrhage from other sources is less abrupt and may continue for a longer period of time. SAH has a 40% mortality over 30 day period.

Signs and symptoms:

The symptoms of stroke depend on the type of stroke and the area of the brain affected. Ischemic strokes usually only affect regional areas of the brain perfused by the blocked artery. Hemorrhagic strokes can affect local areas, but often can also cause more global symptoms due to bleeding and increased intracranial pressure.

If the area of the brain affected contains one of the three prominent Central nervous system pathways — the spinothalamic tract, corticospinal tract, and dorsal column (medial lemniscus), symptoms may include:

* muscle weakness or numbness (hemiplegia)
* reduction of pain or temperature sensation
* reduction in sensory or vibratory sensation

In most cases, the symptoms affect one side of the body, from the neck downwards, excluding the face. The defect in the brain is usually on the opposite side of the body (depending on which part of the brain is affected). However, the presence of any one of these symptoms does not necessarily suggest a stroke, since these pathways also travel in the spinal cord and any lesion there can also produce these symptoms.

In addition to the above CNS pathways, the brainstem also consists of the 12 cranial nerves. A stroke affecting the brainstem therefore can produce symptoms relating to deficits in these cranial nerves:

* altered smell, taste, hearing, or vision (total or partial)
* drooping of eyelid (ptosis) and weakness of ocular muscles
* decreased reflexes: gag, swallow, pupil reactivity to light
* decreased sensation and muscle weakness of the face
* balance problems and nystagmus
* altered breathing and heart rate
* weakness in sternocleidomastoid muscle (SCM) with inability to turn head to one side
* weakness in tongue (inability to protrude and/or move from side to side)

If the cerebral cortex is involved, the CNS pathways can again be affected, but also can produce the following symptoms:

* aphasia (inability to speak or understand language from involvement of Broca’s or Wernicke’s area)
* apraxia (altered voluntary movements)
* disorganized thinking, confusion, hypersexual gestures (with involvement of frontal lobe)
* altered vision (involvement of occipital lobe)
* memory deficits (involvement of temporal lobe)
* hemineglect (involvement of parietal lobe)

If the cerebellum is involved, the patient may have the following:

* trouble walking
* altered movement coordination
* dizziness

Loss of consciousness, headache, and vomiting usually occurs more often in hemorrhagic stroke than in thrombosis because of the increased intracranial pressure from the leaking blood compressing on the brain.

If symptoms are maximal at onset, the cause is more likely to be a subarachnoid hemorrhage or an embolic stroke.

Subarachnoid hemorrhage:

The symptoms of SAH occur abruptly due to the sudden onset of increased intracranial pressure. Often, patients complain of a sudden, extremely severe and widespread headache. The pain may or may not radiate down into neck and legs. Vomiting soon occurs after the onset of headache. Usually the neurologic exam is nonfocal — meaning no deficits can be identified that attributes to certain areas of the brain — unless the bleeding also occurs into the brain. The combination of headache and vomiting is uncommon in ischemic stroke.

Transient ischemic attack (TIA):

If the symptoms resolve within an hour, or maximum 24 hours, the diagnosis is transient ischemic attack (TIA), and not a stroke. This syndrome may be a warning sign, and a large proportion of patients develop strokes in the future. Recent data indicate that there is about a ten to fifteen percent chance of suffering a stroke in the year following a TIA, with half of that risk manifest in the first month, and, further, with much of that risk manifest in the first 48 hours. The chances of suffering an ischemic stroke can be reduced by using aspirin or related compounds such as clopidogrel, which inhibit platelets from aggregating and forming obstructive clots; but, for the same reason, such treatments (slightly) increase the likelihood and effects of hemorrhagic stroke since they impair clotting.

Diagnosis:

Stroke is diagnosed through several techniques: a neurological examination, blood tests, CT scans (without contrast enhancements) or MRI scans, Doppler ultrasound, and arteriography.

If a stroke is confirmed on imaging, various other studies may be performed to determine whether there is a peripheral source of emboli:

* an ultrasound/doppler study of the carotid arteries (to detect carotid stenosis)
* an electrocardiogram (ECG) and echocardiogram (to identify arrhythmias and resultant clots in the heart which may spread to the brain vessels through the bloodstream)
* a Holter monitor study to identify intermittent arrhythmias
* an angiogram of the cerebral vasculature (if a bleed is thought to have originated from an aneurysm or arteriovenous malformation)

Treatment:

Early assessment:

It is important to identify a stroke as early as possible because patients who are treated earlier are more likely to survive and have better recoveries.

If a patient is suspected of having a stroke, emergency services should be contacted immediately. The patient should be transported to the nearest hospital that can provide a rapid evaluation and treatment with the latest available therapies targeted to the type of stroke. The faster these therapies are started for hemorrhagic and ischemic stroke, the chances for recovery from each type improves greatly. Quick decisions about medication and the need for surgery have been shown to improve outcome.

Only detailed physical examination and medical imaging provide information on the presence, type, and extent of stroke.

Studies show that patients treated in hospitals with a dedicated Stroke Team or Stroke Unit and a specialized care program for stroke patients have improved odds of recovery.

Ischemic stroke:

As ischemic stroke is due to a thrombus (blood clot) occluding a cerebral artery, a patient is given antiplatelet medication (aspirin, clopidogrel, dipyridamole), or anticoagulant medication (warfarin), dependent on the cause, when this type of stroke has been found. Hemorrhagic stroke must be ruled out with medical imaging, since this therapy would be harmful to patients with that type of stroke.

In increasing numbers of primary stroke centers, pharmacologic thrombolysis (”clot busting”) is used to dissolve the clot and unblock the artery. However, there is a time constraint: the more time that goes by, the more brain that has irreversibly died. There is also a small risk of making the patient worse by causing bleeding. When used within the first 3 hours, thrombolysis improves the outcome in 1 of every 3.1 patients and worsens the outcome in 1 in every 32 patients. The routine use of thrombolysis is not approved beyond 3 hours. As an easily administered therapy that can be given at any hospital with a CAT scanner, thrombolysis is available at most hospitals in the US, but not where no institutional commitment to stroke care has occurred.

Another intervention for acute ischemic stroke is removal of the offending thrombus directly. This is accomplished by inserting a catheter into the femoral artery, directing it up into the cerebral circulation, and deploying a corkscrew-like device to ensnare the clot, which is then withdrawn from the body. In August 2004, the FDA cleared one such device, called the Merci Retriever.

Whether thrombolysis is performed or not, the following investigations are required:

* Stroke symptoms are documented, often using scoring systems such as the National Institutes of Health Stroke Scale, the Cincinnati Stroke Scale, and the Los Angeles Prehospital Stroke Screen. The latter is used by emergency medical technicians (EMTs) to determine whether a patient needs transport to a stroke center.
* A CT scan is performed to rule out hemorrhagic stroke
* Blood tests, such as a full blood count, coagulation studies (PT/INR and APTT), and tests of electrolytes, renal function, liver function tests and glucose levels are carried out.

Other immediate strategies to protect the brain during stroke include ensuring that blood sugar is as normal as possible (such as commencement of an insulin sliding scale in known diabetics), and that the stroke patient is receiving adequate oxygen and intravenous fluids. The patient may be positioned so that his or her head is flat on the stretcher, rather than sitting up, since studies have shown that this increases blood flow to the brain. Additional therapies for ischemic stroke include aspirin (50 to 325 mg daily), clopidogrel (75 mg daily), and combined aspirin and dipyridamole extended release (25/200 mg twice daily).

It is common for the blood pressure to be elevated immediately following a stroke. Studies indicated that while high blood pressure causes stroke, it is actually beneficial in the emergency period to allow better blood flow to the brain.

If studies show carotid stenosis, and the patient has residual function in the affected side, carotid endarterectomy (surgical removal of the stenosis) may decrease the risk of recurrence.

If the stroke has been the result of cardiac arrhythmia (such as atrial fibrillation) with cardiogenic emboli, treatment of the arrhythmia and anticoagulation with warfarin or high-dose aspirin may decrease the risk of recurrence.

Hemorrhagic stroke:

Patients with bleeding into (intracerebral hemorrhage) or around the brain (subarachnoid hemorrhage), require neurosurgical evaluation to detect and treat the cause of the bleeding. Anticoagulants and antithrombotics, key in treating ischemic stroke, can make bleeding worse and cannot be used in intracerebral hemorrhage. Patients are monitored and their blood pressure, blood sugar, and oxygenation are kept at optimum levels.

Care and rehabilitation:

Stroke rehabilitation is the process by which patients with disabling strokes undergo treatment to help them return to normal life as much as possible by regaining and relearning the skills of everyday living. It also aims to help the survivor understand and adapt to difficulties, prevent secondary complications and educate family members to play a supporting role.

A rehabilitation team is usually multidisciplinary as it involves staff with different skills working together to help the patient. These include nursing staff, physiotherapy, occupational therapy, speech and language therapy, and usually a physician trained in rehabilitation medicine. Some teams may also include psychologists, social workers, and pharmacists since at least one third of the patients manifest post stroke depression.

Good nursing care is fundamental in maintaining skin care, feeding, hydration, positioning, and monitoring vital signs such as temperature, pulse, and blood pressure. Stroke rehabilitation begins almost immediately.

For most stroke patients, physical therapy is the cornerstone of the rehabilitation process. Often, assistive technology such as a wheelchair and standing frame may be beneficial. Another type of therapy involving relearning daily activities is occupational therapy (OT). OT involves exercise and training to help the stroke patient relearn everyday activities sometimes called the Activities of daily living (ADLs) such as eating, drinking and swallowing, dressing, bathing, cooking, reading and writing, and toileting. Speech and language therapy is appropriate for patients with problems understanding speech or written words, or problems forming speech.

Patients may have particular problems, such as complete or partial inability to swallow, which can cause swallowed material to pass into the lungs and cause aspiration pneumonia. The condition may improve with time, but in the interim, a nasogastric tube may be inserted, enabling liquid food to be given directly into the stomach. If swallowing is still unsafe after a week, then a percutaneous endoscopic gastrostomy (PEG) tube is passed and this can remain indefinitely.

Stroke rehabilitation can last anywhere from a few days to several months. Most return of function is seen in the first few days and weeks, and then improvement falls off. However, patients may continue to improve for years, regaining and strengthening abilities like writing, walking, running, and talking. Complete recovery is unusual but not impossible. Most patients will improve to some extent.