Paradoxical Embolism: What You Need to Know

Medically Reviewed by Melinda Ratini, MS, DO on May 04, 2022
4 min read

Your heart is normally a well-oiled machine. Blood that carries oxygen all over your body enters the right side through veins and flows through your lungs to pick up more oxygen. Then blood moves to the left side where it's pumped through arteries to make the round-trip all over again.

A paradoxical embolism happens when an embolus – typically a blood clot – travels from the right side of the heart to the left without going through the lungs, explains Omar Lattouf, MD, a cardiovascular surgeon at Mount Sinai Morningside Hospital in New York. Normally, the lungs filter and catch this possibly dangerous blockage before it’s pumped to the rest of the body. A paradoxical embolism (PDE) can do major damage, including a stroke, Lattouf says.

The embolus forms somewhere in your body, breaks free, and enters the heart through the veins. It’s able to bypass the lungs when there’s a hole in the heart between the right and left side. The opening can be:

A patent foramen ovale (PFO). When you’re in your mother’s womb, your lungs don’t work yet. You get your oxygen through the sack called the placenta. A foramen ovale is a hole in a fetus’ heart that lets blood flow from the right to the left without going through the lungs. In most people, it closes shortly after birth. But in others, it doesn’t shut completely. “Patent” means it's not fully closed.

It’s estimated a quarter of people have a PFO. Most don’t know it. It normally doesn’t cause a problem if it’s very tiny. If the PFO is big enough, an embolus can skip the lungs and go directly from right to left.

Atrial septal defect (ASD). This is a birth defect in the wall (septum) that separates the two tops chambers of your heart called the atria. In this case, the hole is typically bigger because the wall was never fully developed, Lattouf says.

Some people can have a hole in the wall between the two lower chambers called the ventricles. It’s less common, but it also can allow some blood to flow paradoxically, meaning not going the normal route through the lungs.

The embolus could be a clot or something seemingly innocent like an air bubble. If it’s a blood clot, it usually forms deep in the veins of the legs or pelvis, Lattouf says. That’s called a deep vein thrombosis (DVT). A number of things may cause the blood to clot:

  • Your legs aren’t moving enough, like during a long flight or other trip
  • You spend a long time in bed because of sickness or injury
  • You’ve just had a baby or take birth control pills
  • You have cancer or any condition that makes your blood clot very easily

Lifestyle factors can play a role too. These include:

Lattouf gave two examples of how an air bubble can cause a paradoxical embolism:

A PFO that is closed most of the time may be forced open if you strain while lifting weights or even while having a bowel movement. That pressure could force air from your lungs to travel through an artery and cause a stroke.

You have an undiagnosed hole in your heart and get an intravenous line. An air bubble could enter your heart, cross over directly to the left side, and travel to your brain or somewhere else.

An embolus can be a piece of fat or even a tumor, too.

The paradoxical embolism can block blood flow to organs or other parts of your body. If this happens, oxygen can’t reach these areas and tissue can die. It can cause problems including:

  • A stroke in the brain (most common complication of a PDE)
  • A heart attack
  • Blindness if it blocks a vessel to the eye
  • Kidney damage or failure
  • A blockage in the arms or legs

Symptoms from a PDE are usually painful and sudden, Lattouf says.

A paradoxical embolism is rare. Doctors usually look for more common things first. You may have many tests including:

  • An EKG to look for heart rhythm problems like atrial fibrillation
  • A special echocardiogram that looks for abnormal blood flow through the heart, blood clots, and other things
  • Blood tests
  • Imaging tests to look for a DVT, a pulmonary embolism, or blocked blood flow to the kidneys, limbs, or other areas

Your treatment will depend on where the embolism is and any other health conditions you have.

You may get drugs to break up a clot or thin your blood. Or, you may get a procedure to suck out the blockage. Doctors also will plug the hole in your heart with a device. This is usually done through a catheter that’s inserted into the groin and moved to the heart to patch it.

The only way to prevent one is to find and close the hole in the heart beforehand. You may find out you have one when you’re getting tested for another health problem.

So are there any clues that you may have a possibly dangerous hole in your heart? If you have vision or speech problems that come and go or feel dizzy, you may have had a transient ischemic attack (ministroke). That could mean the heart defect caused a temporary blockage, Lattouf says.

PFOs have been linked to migraine headaches. But the jury is still out on whether it’s a cause or just a coincidence.