New insights about the risks from a "hole" in the heart
In certain people, this common heart variant — called a patent foramen ovale — can raise the risk of stroke and possibly dementia.
- Reviewed by Christopher P. Cannon, MD, Editor in Chief, Harvard Heart Letter; Editorial Advisory Board Member, Harvard Health Publishing
About one in four people has a flaplike opening between the two upper chambers of the heart (see illustration). Known as a patent foramen ovale (PFO), this common anatomical variation only rarely causes any symptoms. Most people with a PFO never know they have it, and the condition is usually harmless.
However, PFOs can raise the risk of stroke, especially in people who are prone to blood clots or who experience pressure changes inside their hearts for various reasons. The larger the PFO, the higher the risk of stroke. And growing evidence suggests that people with large PFOs also face a higher risk of vascular dementia, says neurologist Dr. MingMing Ning, director of the Cardio-Neurology Division at Harvard-affiliated Massachusetts General Hospital. "We're excited to now explore possible new interventions to lower this risk," she says.
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In the womb, all fetuses have a small opening called a foramen ovale in the wall between the left and right upper chambers of the heart (the atria). This opening allows blood to take a shortcut within the heart rather than following a longer path through the lungs, which cannot work until they are exposed to air. With a newborn's first breath, the foramen ovale starts to close. It usually seals completely within a few months. But in about one in four people, that doesn't happen, which results in a variation called a patent foramen ovale (patent means open). |
The PFO-stroke connection
Having a PFO, especially a larger one, is linked to a higher risk of ischemic strokes (those caused by a clot blocking a blood vessel). What's the connection? Normally, the network of blood vessels in the lungs traps and destroys small clots and other harmful substances moving through the bloodstream. But in people with a PFO, venous blood can leak across the heart from the right atrium to the left atrium. If that blood contains a clot, it can travel directly to the arteries that send blood throughout the body. A stroke can occur if that clot lodges in an artery supplying the brain.
In addition, by allowing unfiltered harmful substances into the circulation, a PFO may make clots more likely to form, which also contributes to the higher risk of stroke, says Dr. Ning. Other factors that increase clots can further compound a person's risk. These include obesity, sleep apnea, and pregnancy, as well as uncommon genetic conditions such as protein C/S deficiency and factor V Leiden. Being immobile for long stretches of time, including during long-distance travel, can also raise the risk of clots.
Under pressure
Situations that cause pressure shifts in the chest can speed up blood flow through a PFO, causing a clot to shoot through the opening, says Dr. Ning. Bearing down while holding your breath — for example, when you're pushing through a bowel movement, lifting a very heavy weight, or giving birth — can augment this phenomenon.
PFO-related strokes increased during the COVID pandemic, probably related to two reasons: First, COVID triggers an inflammatory response that activates the body's clotting system. Second, people with serious lung damage from the infection often had a tube inserted into their windpipe to help them breathe. "The pressure changes during intubation can 'pop open' the PFO, potentially pushing a clot into the circulation," says Dr. Ning.
The dementia dimension
The blood circulating in someone with a large PFO contains higher levels of potentially harmful substances. Over time, an accumulation of these substances may contribute to vascular dementia. Dr. Ning and colleagues are exploring the mechanisms behind this phenomenon, with an eye toward possible ways to prevent it.
Finding and treating PFOs
When doctors suspect someone has a PFO — usually following an unexplained stroke — they may recommend a specialized heart ultrasound and a bubble study, which involves injecting a solution with air bubbles into a vein. If the bubbles travel to the left side of the heart, that suggests the person has a PFO. While most people don't need treatment, those with a history or high risk of strokes or blood clots may need clot-preventing drugs, such as aspirin or blood thinners, or a special procedure to close the opening.
Image: © rabbitteam/Getty Images
About the Author
Julie Corliss, Executive Editor, Harvard Heart Letter
About the Reviewer
Christopher P. Cannon, MD, Editor in Chief, Harvard Heart Letter; Editorial Advisory Board Member, Harvard Health Publishing
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