UNC-TV Science: Force or Finesse

UNC-TV Science: April 1, 2014
Force or Finesse? A UNC School Of Medicine Study Provides the First Evidence on How to Best Prevent Second Strokes in Certain Patients

Clots that block blood flow to the brain cause 87% of the almost 800,000 strokes that occur in the United States every year. When doctors act quickly to dissolve these clots with medicines or remove them with surgery, blood returns to the brain and the patient recovers.

Even after a patient recovers, however, the risk factors for stroke, and sometimes parts of the original clot, remain. In fact, about 185,000 of the annual strokes in the United States occur in patients who have already had at least one before.

Stroke is the fourth leading cause of death in the United States, and doctors are continually researching ways to help prevent strokes from recurring. Now a new study from the UNC School of Medicine has provided doctors with a concrete direction in which to treat a specific subset of patients.

So which subset is covered by this study? To understand that, we need a little bit of background biology. The circulatory system, which shuttles blood, oxygen and nutrients through the body, is a vast network of channels starting at the heart and travelling to every part of the body before returning to the heart. Think of it as a series of roads, and the cars are blood cells.

So imagine that Charlotte is the heart. Major arteries shuttle cars to every corner of the state, but if you want to get to the brain in Durham, your major artery will be I-85. Sometimes however, there will be a wreck somewhere along the way, and block the flow of cars to Durham. That wreck is the clot that causes a stroke.

Now the blood cells, much like the cars, will do one of two things. Many will sit behind the blockage, and wait for the road to clear. But others will detour and find another path to the brain. These detours are called collateral vessels, and while they’re not as fast as the main artery, they will still get some of the blood cells to the same region of the brain.

But just like a highway, some places along an artery are more conducive to detours than others. If there’s a wreck in Greensboro, some cars may be able to exit I-85 and get right back on a few exits down. A smaller town with fewer roads might not offer the same opportunity. A patient with a Greensboro near their stroke has what are called good collateral vessels, while a patient with a small town would have poor collateral vessels.

For years, doctors have advised patients with good collateral vessels to keep their blood pressure low, as low blood pressure helps prevent strokes in general and patients with good collateral vessels have enough detours to get enough oxygen to their brain even when blood flows more slowly.

Patients with poor collateral blood vessels, however, are trickier. Some doctors prescribe lower blood pressures, as this prevents strokes in general. Others actually recommend maintaining a slightly higher pressure, the logic being that since fewer vessels exist to supplement the main artery, a higher pressure will keep the blood flowing quickly enough to supply the brain.

Both treatments have been used clinically, but until now, their effectiveness had never been studied. Dr. William Powers, who first discovered the importance of collateral blood vessels in the 1980s, examined data from 91 stroke patients with poor collateral vessels over an eight-year period.

He found that 10 of the 51 patients with blood pressure greater than 130 over 85 suffered a second stroke. But out of the 40 with pressures less than 130 over 85, only 3 had a second stroke. That’s a 22% decrease in stroke risk just by lowering blood pressure.

Powers’ paper, published in the journal Neurology, provides the first published evidence that lowering blood pressure in stroke patients with poor collateral vessels reduces risk of further strokes.

For more information on the risk factors for stroke, click here and, as quick action is paramount for treating strokes, click here for information on the signs and symptoms of strokes.

- Daniel Lane

Daniel Lane covers science, medicine and the environment as a reporter/writer. He is currently pursuing a master's degree in medical and science journalism at UNC - Chapel Hill.