An ischemic stroke happens when a blood clot blocks an artery supplying the brain, cutting off oxygen and killing brain tissue. It accounts for about 87% of all strokes, making it by far the most common type. The other 13% are hemorrhagic strokes, which involve bleeding into or around the brain rather than a blockage.
How a Blockage Forms
There are two main ways an ischemic stroke occurs: a clot forms inside a brain artery (thrombotic stroke) or a clot forms somewhere else in the body and travels to the brain (embolic stroke). The distinction matters because the underlying cause, and therefore the prevention strategy, differs for each.
In a thrombotic stroke, the blockage builds up right where it causes damage. The most common culprit is atherosclerosis, a gradual narrowing of arteries caused by fatty plaque deposits on the vessel walls. Over years, the plaque grows until it either blocks blood flow on its own or ruptures, triggering a clot that seals off the artery. Less common causes include tears in the artery wall (arterial dissection) and inflammatory conditions affecting blood vessels.
In an embolic stroke, a clot forms elsewhere and then drifts through the bloodstream until it gets stuck in a narrower brain artery. The most common source is the heart. In people with atrial fibrillation, an irregular heart rhythm, blood pools in the heart’s upper chambers and can form clots that break loose. Clots can also originate from plaque in the carotid arteries in the neck. In rarer cases, a clot from a vein passes through a small hole between the heart’s chambers (a patent foramen ovale) and enters the brain’s arterial system.
Recognizing the Symptoms
Stroke symptoms come on suddenly and depend on which part of the brain loses blood flow. The BE FAST acronym covers the major warning signs:
- Balance: sudden loss of balance or coordination
- Eyes: sudden blurred or double vision, or vision loss in one or both eyes
- Face: one side of the face droops, especially when trying to smile
- Arms: one arm drifts downward when both are raised
- Speech: slurred or garbled speech, or difficulty understanding others
- Time: call emergency services immediately
The “Balance” and “Eyes” components were added to the older FAST acronym specifically to catch strokes in the back of the brain, which affect coordination and vision rather than the face and arms. Research in Frontiers in Neurology found that patients identified through BE FAST screening were more than twice as likely to show significant neurological improvement at discharge compared to those identified without it. Arriving at the hospital within three hours of symptom onset was also independently linked to better outcomes.
Who Is Most at Risk
High blood pressure is the single biggest risk factor for ischemic stroke. It damages artery walls over time, accelerating plaque buildup and making clots more likely. Atrial fibrillation is another major driver, particularly for embolic strokes. Other significant risk factors include type 2 diabetes, high cholesterol, coronary heart disease, smoking, and older age. Women with atrial fibrillation face a particularly elevated risk compared to men with the same condition.
Many of these risk factors overlap and compound each other. Someone with high blood pressure, diabetes, and high cholesterol has a substantially higher stroke risk than someone with just one of those conditions. Smoking further accelerates the process by damaging blood vessels and promoting clot formation.
How It Is Diagnosed
The first step when someone arrives at the hospital with stroke symptoms is a brain scan, typically a non-contrast CT scan. This scan takes only minutes and serves one critical purpose: ruling out bleeding in the brain. If there’s no hemorrhage, the diagnosis shifts to ischemic stroke. The CT can sometimes show early signs of ischemia, such as subtle loss of contrast between gray and white matter or a bright spot where a clot sits in a major artery.
MRI is more sensitive and specific than CT for detecting ischemic damage, particularly in the early hours when CT findings may be subtle. MRI is also better at ruling out stroke mimics, conditions like seizures or migraines that can look like a stroke. However, MRI takes longer and is more complicated to perform, so CT remains the standard first-line scan when speed is critical. CT or MR angiography can also be used to visualize the blood vessels directly and locate the blockage.
Emergency Treatment
The phrase “time is brain” exists for a reason. Every minute a stroke goes untreated, roughly 1.9 million neurons die. Two main treatments can restore blood flow, and both are highly time-sensitive.
The first is a clot-dissolving medication given through an IV, which works by breaking down the clot chemically. This treatment is generally limited to within 4.5 hours of symptom onset. A trial published in the New England Journal of Medicine showed it can be effective up to 9 hours in select patients when advanced brain imaging confirms there is still salvageable tissue, but the standard window remains 4.5 hours for most people.
The second is a mechanical procedure called thrombectomy, in which a doctor threads a thin catheter through an artery (usually starting at the groin) up to the brain and physically removes the clot. This procedure is the standard of care for strokes caused by large vessel blockages and is most effective within the first 6 hours. Landmark trials called DAWN and DEFUSE-3 showed that thrombectomy can still produce good outcomes up to 24 hours after symptom onset, but only in carefully selected patients who have a small area of irreversible damage and a large area of brain tissue still at risk. Younger patients (under 80) tend to have better outcomes from the procedure.
Recovery and Rehabilitation
Rehabilitation typically starts within 24 hours of treatment, often while the patient is still in the hospital. During a hospital stay that averages five to seven days, therapy sessions may happen up to six times per day. These sessions help the medical team assess the extent of damage while also kickstarting the recovery process. The focus is on activities of daily living: eating, dressing, bathing, walking, and communicating.
The first three months are the most critical window for recovery. This is when the brain is most actively reorganizing itself, forming new neural pathways to compensate for damaged ones. During this period, many patients experience what’s called spontaneous recovery, where an ability that seemed lost suddenly returns as the brain finds alternative routes to perform the task. Most patients will go through either an inpatient rehabilitation program or outpatient therapy during these months.
After six months, most stroke survivors reach a relatively steady state. For some, that means a full recovery. Others live with ongoing impairments in movement, speech, or cognition. Improvement beyond six months is still possible but happens much more slowly. Recovery milestones look different for everyone. Something as simple as needing less help to get dressed or being able to hold a fork again represents meaningful progress.
Preventing a Second Stroke
About 1 in 4 strokes is a recurrent stroke, so prevention after a first event is essential. For people whose stroke was not caused by a heart-related clot, daily antiplatelet medication is the standard approach. For those whose stroke was caused by atrial fibrillation, blood thinners (anticoagulants) are used instead to prevent clots from forming in the heart.
Beyond medication, the same risk factors that caused the first stroke remain targets. Managing blood pressure, controlling blood sugar, lowering cholesterol, quitting smoking, and staying physically active all reduce the chance of recurrence.
Transient Ischemic Attacks as a Warning
A transient ischemic attack, often called a mini-stroke, produces the same symptoms as a full ischemic stroke but resolves on its own, usually within minutes to an hour. The blockage clears before permanent damage occurs. It can be tempting to dismiss a TIA once symptoms pass, but the numbers tell a different story. Within 2 days of a TIA, 1.5% of people will have a full stroke. Within 90 days, that number climbs to 3.7%, and within a year, 5.1% will have had a stroke. A TIA is the clearest warning sign the brain gives, and it creates a narrow window to identify and treat the underlying cause before a larger stroke occurs.