For most people, strokes are one of the most feared medical events imaginable. While people don’t necessarily die of a stroke, they are often left severely limited, either in their speech, physical functioning or thought processes. Many of my patients have told me that they would rather die than have a stroke.
Strokes are “brain attacks” where a part of the brain is damaged due to loss of a blood supply to that area (“ischemic” strokes) or due to a ruptured vessel that leads to bleeding (“hemorrhagic” strokes). There are many causes of a stroke, including hypertension (high blood pressure), excessive alcohol use, brain aneurysms, and atherosclerosis (clogging of arteries) in the carotid arteries, vertebral arteries, or the arteries inside the brain. Two cardiac causes of stroke are ones that we cardiologists will often screen patients for: patent foramen ovale (PFO) and atrial fibrillation.
A PFO is a connection between the right and left atria. Blood normally returns to the right atrium via the body’s veins, passing on to the right ventricle, out the pulmonary artery into the lungs, and then out the pulmonary veins into the left atrium. So a PFO is a shortcut in the circulation. The foramen ovale (Latin for “oval opening”) is a normal part of the circulation when the fetus is developing in the uterus. For most people, this opening closes shortly after birth, but in 25% of people the foramen remains at least partially patent. The size of this opening varies from person to person.
What is potentially a problem with a PFO is that a small clot may break off from a vein and travel across the PFO into the arterial circulation, and lodge in a brain artery, causing a stroke. Small clots like this sometimes form and generally will pass into the pulmonary circulation, stopping when they reach a small artery they can’t pass beyond. A small clot does no harm to the pulmonary circulation because it is a large vascular bed and a tiny branch that gets clotted off has no appreciable effect. But even small brain arteries are sometimes very important, potentially supplying a critical structure.
Because PFO’s are common and the vast majority of people have no consequences from their presence, we don’t generally treat them. But in people with a PFO who have had a TIA (transient ischemic attack—a “mini-stroke”) or stroke, it is imperative to modify a person’s future risk of a stroke. Medications that thin the blood, like aspirin, will lower the risk of a subsequent stroke. In people who have a particularly large PFO, we consider closing it. In the past, closure meant having a surgical procedure, but nowadays most PFO’s can be closed percutaneously (Latin for “through the skin”) using a device delivered on a catheter.
The second cardiac culprit of stroke is an abnormal heart rhythm called atrial fibrillation. Atrial fibrillation is an irregular heart rhythm caused when the atria (the upper chambers) develop completely disorganized electrical activity and the impulses come so rapidly that the mechanical function can’t keep up, so the atria just quiver—or fibrillate.
While most people have symptoms from atrial fibrillation—most commonly palpitations or shortness of breath—a sizable number will not know they have it. And people can have strokes from atrial fibrillation whether they are aware of the atrial fibrillation or not. In fact, when looking at people older than 55 who have had a stroke with no known cause, subsequent monitoring reveals atrial fibrillation in 10-20% of them, making it important to screen these people for atrial fibrillation.
Why does atrial fibrillation cause strokes? When the atria are fibrillating, they aren’t pumping, and blood can sit in nooks and crannies within these chambers and form clots due to stasis (lack of movement). One large cavity that accounts for 90% of the clots that we find in atrial fibrillation is called the left atrial appendage. If a clot dislodges from within the heart, it travels into the arterial circulation and can potentially go to one of the brain vessels and block it off. Then that part of the brain loses its blood supply and dies—this is what we call a stroke.
We learned years ago that aspirin—while beneficial for preventing some types of strokes—has minimal impact on lowering stroke risk from atrial fibrillation. At the same time, we discovered that warfarin (often used as the brand Coumadin) lowered the risk by 70%! However, warfarin is difficult to use, as we have to monitor a blood test called the INR anywhere from weekly to monthly, and the drug interacts with multiple medications, as well as foods, making for instability in its dosing.
Luckily, we have four drugs that have been available during the last decade—apixaban, dabigatran, rivaroxaban, and edoxaban—that don’t require blood tests, as their blood levels are quite stable. They are generally safer and more effective than warfarin, so we preferentially use them instead. Their downside is that they are more expensive, all them still being on patent—their brand names are Eliquis, Pradaxa, Xarelto and Savaysa. And the downside to all anticoagulants (the category of medications that all these drugs are part of) is that they increase the risk of bleeding.
For people who cannot tolerate an anticoagulant, there are new devices that are equally effective. These devices (including Watchman, Lariat, Amulet) take advantage of the fact that most of the stroke risk from atrial fibrillation comes from clot in the left atrial appendage. In various ways, these devices seal off the connection between the left atrial appendage from the rest of the left atrium, preventing clot there from entering the general circulation.
Since we have the ability to drastically reduce the risk of strokes from atrial fibrillation, it’s imperative that we find out who is having it! We do so by monitoring people who have had TIAs or strokes or have palpitations that suggest atrial fibrillation. There are monitors that are worn for 24-48 hours, as well as those than can be worn for 1-4 weeks. We also have small implantable monitors that are placed just under the skin overlying the heart and can monitor a person for 3 years or more.
So, if you or a loved one have had a stroke or feel your heart beating irregularly at times, see a cardiologist. He or she can obtain an echocardiogram to look for a PFO and arrange monitoring to screen for atrial fibrillation. It’s a worthwhile investment of your time.
Greg Koshkarian, MD, FACC