An ischemic stroke happens when a blood vessel supplying the brain gets blocked, cutting off oxygen and nutrients to brain tissue. About 87% of all strokes are ischemic, making it by far the most common type. The blockage is caused either by a clot that forms directly in a brain artery or by a clot that forms elsewhere in the body and travels to the brain.
How the Blockage Happens
There are two main ways a brain artery gets blocked. The first is a thrombotic stroke, where a blood clot forms at the site of a fatty plaque buildup inside the artery itself. Over years, cholesterol and other deposits narrow the artery walls. Eventually, a clot forms on top of that plaque and seals off blood flow. These clots tend to develop in the larger arteries that feed the brain, including the carotid arteries in the neck.
The second type is an embolic stroke. Here, a clot forms somewhere else, usually the heart, breaks loose, and travels through the bloodstream until it lodges in a narrower brain artery. Conditions like atrial fibrillation (an irregular heartbeat) are a common source of these traveling clots, and they carry a high risk of happening again.
A third category, called lacunar strokes, accounts for 13 to 20% of all ischemic strokes. These involve tiny arteries deep inside the brain that become blocked, typically due to long-term high blood pressure damaging the vessel walls. Lacunar strokes tend to be smaller but can still cause significant disability depending on their location.
Recognizing the Symptoms
The symptoms of an ischemic stroke depend on which part of the brain loses its blood supply. Most people are familiar with the classic signs: sudden weakness or numbness on one side of the face or body, difficulty speaking, confusion, and trouble seeing out of one or both eyes. These are typical of strokes affecting the front part of the brain’s circulation.
Strokes in the back of the brain (the posterior circulation) can look different and are easier to miss. The most common symptom is dizziness, occurring in nearly half of cases. Other frequent signs include slurred speech, headache, nausea and vomiting, difficulty walking or coordinating movements, and double vision. Because these symptoms overlap with other conditions like inner ear problems or migraines, posterior circulation strokes are sometimes initially misdiagnosed.
The acronym BE-FAST can help you remember the warning signs: Balance problems, Eyes (vision changes), Face drooping, Arm weakness, Speech difficulty, and Time to call emergency services.
Major Risk Factors
High blood pressure is the single leading cause of ischemic stroke. It damages artery walls over time, accelerating plaque buildup and making clots more likely. High cholesterol contributes to the same process by depositing fatty material inside blood vessels. Diabetes raises stroke risk because elevated blood sugar impairs blood flow and is frequently accompanied by high blood pressure.
Heart disease, particularly atrial fibrillation, is a major risk factor. When the heart beats irregularly, blood can pool in the chambers and form clots that travel to the brain. Other heart conditions, including valve defects and enlarged heart chambers, carry similar risks.
Lifestyle factors play a substantial role as well:
- Smoking damages blood vessels, raises blood pressure, and reduces the oxygen your blood can carry. Secondhand smoke exposure also increases risk.
- Physical inactivity contributes to obesity, high blood pressure, high cholesterol, and diabetes, all of which compound stroke risk.
- Excessive alcohol raises blood pressure and triglyceride levels, which can harden arteries.
- A diet high in saturated fat, trans fat, and sodium is linked to the conditions that drive stroke.
Having already experienced a stroke or a transient ischemic attack (a “mini-stroke” where symptoms resolve quickly) significantly raises the likelihood of a future stroke. Sickle cell disease is another risk factor, as misshapen red blood cells can block blood flow to the brain.
How Ischemic Stroke Is Diagnosed
When someone arrives at the hospital with stroke symptoms, a CT scan of the head is almost always the first imaging study. It’s fast and widely available, and its primary job in the first minutes is to rule out bleeding in the brain, since hemorrhagic strokes require completely different treatment.
MRI is more sensitive at detecting early ischemic damage, pinpointing the exact location of the affected tissue, and distinguishing a true stroke from conditions that mimic one. It can also help estimate when a stroke began in patients who woke up with symptoms or can’t say when they started. Many hospitals now use CT angiography alongside a standard CT scan to identify exactly where the blockage is, which helps determine whether a clot-removal procedure is an option.
Emergency Treatment
Speed is everything. Brain tissue begins dying within minutes of losing blood flow, and every minute of delay means more permanent damage.
The primary emergency treatment is intravenous thrombolysis, a clot-dissolving medication given through an IV. This treatment is effective for eligible patients within 4.5 hours of symptom onset (or the last time they were known to be neurologically normal). Not everyone qualifies. Factors like recent surgery, bleeding disorders, or very high blood pressure can rule it out.
For strokes caused by a large vessel blockage, a procedure called mechanical thrombectomy can physically remove the clot. A thin catheter is threaded through an artery, typically starting from the groin, up to the blocked vessel in the brain, where the clot is pulled out. This procedure can be performed up to 24 hours after symptom onset in selected patients, a much wider window than clot-dissolving medication. It’s often used alongside the IV medication rather than as a replacement. For blockages in the back of the brain’s circulation, thrombectomy within 24 hours may also be reasonable, though the evidence is less established.
What Recovery Looks Like
Rehabilitation typically begins within 24 hours of the stroke being treated. This early start matters because the brain’s ability to reorganize and form new neural connections is at its peak in the weeks immediately following injury.
The first three months after a stroke are the most critical window for recovery. This is when patients tend to see the most improvement, and intensive therapy during this period yields the greatest gains. Rehabilitation can include physical therapy to rebuild strength and coordination, occupational therapy to relearn daily tasks, and speech therapy if language or swallowing is affected.
Recovery continues well beyond three months, but the pace typically slows. How much function a person regains depends on the size and location of the stroke, how quickly treatment was received, and how consistently they engage with rehabilitation.
Survival and Long-Term Outlook
Ischemic stroke is survivable for most people, but the numbers underscore its seriousness. In a large study of over 3,600 patients, about 7% died within the first week, roughly 13% within 30 days, and nearly 24% within a year. Outcomes vary widely based on stroke severity, the patient’s age and overall health, and how quickly treatment was delivered.
Among survivors, the range of long-term outcomes is broad. Some people recover nearly all their function, while others live with lasting disability in movement, speech, memory, or emotional regulation. Depression after stroke is common and can itself slow recovery if untreated.
Preventing a Second Stroke
Once you’ve had an ischemic stroke, the priority shifts to preventing another one. The approach depends on what caused the first stroke.
For strokes not caused by a heart rhythm problem, antiplatelet medications (which prevent blood cells from clumping into clots) are the standard. If you’re treated early after a mild stroke or high-risk mini-stroke, a short course of dual antiplatelet therapy for up to 90 days, followed by a single antiplatelet medication long-term, reduces the chance of recurrence. Beyond 90 days, using two antiplatelet drugs together increases bleeding risk without added stroke prevention benefit.
For strokes caused by atrial fibrillation, blood-thinning medications called direct oral anticoagulants are preferred. These have been shown to reduce clot-related strokes as effectively as older blood thinners while causing less bleeding.
Blood pressure management is essential regardless of stroke type. Current guidelines recommend a target below 130/80 mmHg for people who have had a stroke or mini-stroke. For cholesterol, high-intensity statin therapy is recommended, with additional medications added if cholesterol levels remain elevated despite the statin. For people with diabetes who have had a stroke, specific diabetes medications that also protect blood vessels are now recommended beyond standard blood sugar control.
Lifestyle changes, including quitting smoking, exercising regularly, eating a diet low in sodium and saturated fat, and limiting alcohol, reduce the risk of recurrence and improve the effectiveness of medications.