T. Jared Bunch, MD

Rhythm of Life

The lowdown on heartbeat disorders

Posted in: Heart Disease

Strokes, Blood Clots, Pacemakers, and Heart Holes; The Risks will Surprise You

Published Aug 20, 2013

Pacemakers and Defibrillators

Many of us will ultimately need a pacemaker or a defibrillator.  All defibrillators also work as a pacemaker, but pacemakers cannot work as a defibrillator.  Pacemakers are small implanted devices that go under the skin in our chest.  Small wires called “leads” are then threaded through the veins that go under our collar bones into the chambers of heart.  They deliver small electrical impulses that can keep the upper chambers, lower chambers, or both the upper and lower chambers from beating too slow.  They do not treat fast heart rhythms, but they treat slow ones.  Sometimes people need pacemakers who have fast heart rhythms because the medications required to treat the abnormal heart rhythm make their heart beat too slow.  Defibrillators work as a pacemaker as well and keep the heart chambers from beating too slow.  However, they also have the capability of delivering a high voltage electrical shock to stop very fast heart rhythms that cause cardiac or heart arrest.  Because they need to deliver very high voltage shocks at times, they are bigger and their battery life is often shorter.  Like pacemakers, defibrillators treat the heart through small wires or leads that are threaded into the heart through the veins.  These wires are connected to the defibrillator that is implanted under the skin in the chest, similar to a pacemaker.  Important to this topic is that both of these systems rely on wires that are in the heart and are exposed to our circulating blood.

Blood Clots on Pacemaker/Defibrillator leads

When we cut ourselves, blood that emerges from the wound is exposed to a different environment and forms a clot.  The lining of our blood vessels prevents a clot from forming.  In this way, when the lining is disrupted a clot can quickly form and by doing so the healing process begins.  A pacemaker or defibrillator lead is foreign object in the blood stream.  As such, when the blood encounters it a clot can form.  We can visualize the surface of these leads very closely with a tiny ultrasound probe that is inserted into the heart (intracardiac ultrasound).   In one study, 30% of patients had clot formation on their pacemaker leads when these were carefully examined by an intracardiac ultrasound (1).

Patent Foreman Ovale (A hole in the heart)

We all have had a small hole in our heart between the two upper chambers.  This hole is used when we are developing in the womb so the blood can cross from the right side of the heart to the left side without going through the lungs.  Since we receive oxygen from the placenta, the lungs do not need to supply oxygen to our blood until we take our first breath.  When we take our first breath, small flaps on each side of the hole between the upper heart chambers come together and close it.  In doing so, used up blood that is low on oxygen then goes from the right upper chamber to the right lower chamber and into the lungs to receive oxygen.

In 25% of us, the flaps between the upper heart chambers don’t stay together.  As a consequence at times there can be a small amount of blood that can bypass the lungs and go directly to the left side of the heart.  This often occurs when the pressure on the right side of the heart transiently goes up, such as when we cough, strain, or go quickly from a standing to a squatting position.    When these flaps don’t fully seal between the upper heart chambers, we call this a patent foreman ovale or PFO.

Our lungs not only provide oxygen to the blood returning to the heart, they also filter it.  The filtering stops any small clots that may have formed in your body from getting to the left side of the heart.  The left side of the heart pumps blood directly to the brain, heart, and other organs.  Clots that go the brain cause stroke, clots that go the heart cause heart attacks, etc.

The presence of a patent foreman ovale can be made using a common heart study called an echocardiogram.  This is an ultrasound study of the heart that gives us information on the heart structure and function.

Patent Foreman Ovales and stroke

A number of studies have shown a potential correlation between a patent foreman ovale and risk of stroke.  Also, they have shown a potential correlation between mini-strokes (transient ischemic attacks) and complex migraine headaches.  These studies are tough to interpret since 25% of us have a patent foreman ovale.  With such a common natural occurrence, it is often a challenge to determine if it was an actual cause of the stroke or something that was found incidentally because the stroke occurred.

However, when there is a potential cause, in the medical community we often develop tools to fix it.  There are a number of ways to close these holes using small tools inserted through the vein in our legs.  These tools deploy a small closure device in the middle of the heart which keeps the flaps together.  Unfortunately in many trials that have compared people who received these devices to those that did not that have a patent foreman ovale, there has not been a significant reduction in risk of a subsequent stroke.  In some studies there were no differences at all.  That being said, these technologies continue to improve, and with improvement we hope to see that stroke risks can be reduced with these tools.

Pacemakers, Patent Foreman Ovale, and Stroke

Recently, the Mayo Clinic published a study looking at 10 years of pacemaker implantations in which 6075 patients received pacemaker leads into one or both of their heart chambers (2).  The authors found that 364 had an echocardiogram that clearly demonstrated the presence of a patent foreman ovale that at times would allow blood to move from the right side of the heart to the left.  Over time, 8.2% of the patients that received a pacemaker that had a patent foreman ovale had a stroke or a mini-stroke (TIA).  Compared to patients without a patent foreman ovale, patients with a small hole in their heart were over 3 times more likely to have a stroke.  The higher risk for stroke could not be accounted for by other risk factors such as diabetes, high blood pressure, heart failure, or prior stroke.

What are the next steps?

These findings are very intriguing and may provide a unique understanding of stroke risk in people with a pacemaker or a defibrillator.  However, additional studies from other centers are needed to confirm that this risk is real.  In addition, we need more information regarding if screening all pacemaker patients for a patent foreman ovale will be helpful and guide therapy.  We need to know if all patent foreman ovales create risk, or if it is just those that are more likely to open and shunt blood from the right side of the heart to the left.  Also, additional studies are needed to guide us as to what are the best treatment options.  These options may include using blood thinners, closing the patent foreman ovale, or using pacemaker systems that do not use leads that are in the blood stream.   There is currently a defibrillator that does not have leads that are put in the blood stream.  Right now there is not a pacemaker counterpart, but systems that do not need to be put into the blood stream remain an area of active research and innovation.


1.  Supple GE, Ren J-F, Zado ES, Marchlinski FE.  Mobile thrombus on device leads in patients undergoing ablation.  Circulation. 2011; 124:772-778.

2.  DeSimone CV, Friedman PA, Noheria A, Patel NA, DeSimone DC, Bdeir S, Aakre CA, Vaidya VR, Slusser JP, Hodge DO, Ackerman AJ, Rabinstein AA, Asirvtham SJ.  Stroke or Transient Sichemic Attack in Patients with Transvenous Pacemaker of Defibrillator  and Echocardiographically Detected Patent Foreman Ovale.  Circulation (published online August 14, 2013)

Posted in: Heart Disease

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