Can a Pacemaker Cause a Stroke and What Are the Risks?

A pacemaker does not directly cause strokes in the way a blocked artery or a burst blood vessel does, but having one introduces several pathways that can raise stroke risk. The most important of these involve blood clots forming on the device’s leads, silent atrial fibrillation that the pacemaker itself detects, and in rare cases, infections spreading from the leads into the bloodstream. For most patients the overall stroke risk remains low, but certain anatomical and rhythm-related factors can push it considerably higher.

Blood Clots on Pacemaker Leads

Traditional pacemakers use thin wires called leads that thread through a vein into the heart’s right chambers. Those leads sit in constant contact with flowing blood, and over time, small clots can form along their surface. In most people, these tiny clots either dissolve on their own or stay on the right side of the heart, where they pose little immediate danger. The situation changes in people who have a patent foramen ovale, a small opening between the heart’s upper chambers that persists from fetal development. Roughly one in four adults has one without knowing it.

When a PFO is present, a clot that breaks free from a lead in the right atrium can slip through the opening into the left side of the heart and travel to the brain. A study of over 6,000 patients with pacemakers or defibrillators found that stroke or transient ischemic attack occurred in about 8% of those who also had a PFO, compared with about 2% of those without one. After adjusting for age, sex, prior strokes, atrial fibrillation, and use of blood thinners, the PFO group still faced roughly three times the risk.¹ A smaller case series has documented instances where patients with leads and a PFO suffered cardioembolic strokes severe enough to require closing the PFO surgically or with a catheter-based device.²

This does not mean every pacemaker patient needs screening for a PFO, but doctors increasingly consider it when a patient with an implanted device has an unexplained stroke. The connection highlights why the leads themselves, not just the electrical therapy they deliver, matter for stroke risk.

Silent Atrial Fibrillation Detected by the Pacemaker

One of the more useful things a modern pacemaker does is continuously monitor the heart’s rhythm. When the atrial lead senses the heart beating abnormally fast for a stretch, the device logs what clinicians call an atrial high-rate episode. Many of these episodes are short, cause no symptoms, and would never be caught on a standard electrocardiogram. Yet they often represent brief runs of atrial fibrillation, the irregular heart rhythm most strongly linked to stroke.

The landmark MOST trial found that pacemaker patients who had any atrial high-rate episodes were nearly three times as likely to suffer death or nonfatal stroke as those who did not.³ Broader data show an annual stroke rate of roughly 2% in patients whose devices record these episodes, compared with about 1% in those whose devices stay quiet.⁴ Those numbers are meaningful, but they are still lower than the stroke rates typically seen in patients with clinically diagnosed atrial fibrillation. That gap matters because it raises an uncomfortable question: should these device-detected episodes be treated as aggressively as confirmed AF?

Adding to the complexity, only a fraction of patients who have atrial high-rate episodes will ever develop sustained AF, and some episodes turn out to be electrical noise or other arrhythmias rather than true AF.⁵ So the pacemaker is raising a flag, but interpreting that flag requires judgment.

How Long an Episode Needs to Last

Not all atrial high-rate episodes carry the same weight. A systematic review pooling data from several large studies found that episodes lasting at least 30 seconds were associated with more than four times the risk of stroke or systemic embolism. That risk remained elevated at every duration threshold tested, including five minutes, six hours, and 24 hours.⁶ When the cumulative burden crossed 24 hours, meaning the total time spent in rapid atrial rhythm added up to at least a full day over the monitoring period, the risk climbed further.

A Japanese study of patients with dual-chamber pacemakers found that even episodes as short as one minute had independent predictive value for cardiovascular and cerebrovascular events, though the sensitivity was modest.⁷ In practice, most clinical guidelines focus on episodes longer than five or six minutes as the threshold where action should be considered, but the research makes clear that no sharp boundary exists. The risk is graded, not binary.

The Puzzling Timing Between AF Episodes and Strokes

If atrial fibrillation causes blood clots that travel to the brain, you might expect a stroke to happen during or right after an episode. The data tell a different story. A subanalysis of the ASSERT trial looked at 51 patients who had both device-detected subclinical AF and a subsequent stroke or systemic embolism. Only four of them, about 8%, had an AF episode recorded within 30 days before their stroke. In the 14 patients whose most recent episode came more than 30 days earlier, the median gap was nearly a year. And in eight patients, the device had not detected any AF at all until after the stroke happened, despite continuous monitoring for months beforehand.⁸

This finding has reshaped how researchers think about the connection between AF and stroke. Rather than a simple cause-and-effect chain where an episode forms a clot that dislodges days later, device-detected AF may be a marker for a heart that is vulnerable to clot formation in general, perhaps because of structural changes in the atrium, sluggish blood flow, or inflammation. That reframing matters for treatment decisions: it suggests that the presence of any episodes, not just recent ones, signals an underlying risk that deserves attention.

How Pacing Choices Affect Atrial Fibrillation Risk

The way a pacemaker delivers its electrical impulses can itself influence whether a patient develops atrial fibrillation. Traditional right ventricular pacing, where the lead stimulates the bottom of the right ventricle, forces the heart to contract in an abnormal pattern. Over time, this can remodel the heart’s structure and promote AF. A study of patients with paroxysmal AF found that more right ventricular pacing led to a greater burden of AF and accelerated the progression from occasional to persistent episodes.⁹

Minimizing how often the ventricle is paced makes a measurable difference. A randomized trial of over 1,000 patients with sick sinus syndrome found that a pacing algorithm designed to avoid unnecessary ventricular stimulation reduced the development of persistent AF by about 40% compared with conventional dual-chamber pacing.¹⁰ A Cochrane review pooling data from multiple trials confirmed that physiologic pacing modes, primarily dual-chamber designs, significantly reduced AF compared with single-chamber ventricular pacing, though the direct benefit for stroke prevention did not reach statistical significance.¹¹

A newer approach called conduction system pacing goes a step further. Instead of pacing the muscle wall of the ventricle, the lead is placed on the heart’s natural electrical highway, the His bundle or the left bundle branch, so the ventricle contracts in its normal sequence. Meta-analyses have found that conduction system pacing roughly halves the rate of new-onset AF compared with conventional right ventricular pacing, with one pooled analysis reporting AF rates of about 12% versus 26%.¹² Another meta-analysis found a similar pattern, with a roughly 60% lower risk of new-onset AF in the conduction system pacing group.¹³ Because AF is the single largest contributor to pacemaker-related stroke risk, these pacing choices have real downstream implications even if no trial has yet shown a direct stroke reduction from one pacing mode over another.

Blood Thinners for Pacemaker-Detected Atrial Fibrillation

The discovery that pacemakers detect silent AF in many patients created an urgent clinical question: should those patients take blood thinners the way patients with diagnosed AF do? Two large randomized trials, NOAH-AFNET 6 and ARTESiA, tested this directly. A meta-analysis combining both found that oral anticoagulants reduced ischemic stroke by about a third compared with either aspirin or placebo. The results were consistent across both trials.¹⁴

The ARTESiA trial specifically compared apixaban with aspirin in patients whose devices had detected subclinical AF. Over an average follow-up of three and a half years, stroke or systemic embolism occurred at a rate of about 0.78% per year with apixaban versus 1.24% per year with aspirin. But the trade-off was real: major bleeding was almost twice as frequent in the apixaban group.¹⁵ There was also no reduction in overall death, which means the benefit is specifically about preventing strokes, not extending life span.

So the answer is not as simple as “take a blood thinner.” Patients with longer episodes, higher stroke risk scores, and fewer bleeding risk factors are more likely to benefit. Those with very short episodes or high bleeding risk may be better served by aspirin alone or by watchful waiting with close device monitoring. This is one of the areas where conversation between patient and doctor matters most.

Stroke Risk When a Device Gets Infected

Device infections are uncommon but serious. Bacteria can colonize the leads, forming clumps of infected material called vegetations. When leads are extracted to treat the infection, fragments of those vegetations can break loose and enter the bloodstream. In a study of 774 patients who underwent lead removal for device infection, the overall stroke rate was about 2%, split roughly equally between strokes that happened before the procedure and strokes that occurred after it.¹⁶

Once again, a PFO dramatically raised the odds. Nearly half of the patients who had a stroke during or around lead extraction also had a PFO, compared with about 13% of those who did not have a stroke. Patients with infected material on the right side of the heart and a PFO that allowed blood to cross from right to left faced roughly six times the odds of stroke.¹⁶ In rare cases, these are septic emboli, meaning the clots carry bacteria to the brain, which is harder to treat than a standard stroke.

Predicting Stroke Risk in Pacemaker Patients

Cardiologists have long used a scoring system called CHA₂DS₂-VASc to estimate stroke risk in people with atrial fibrillation. It tallies points for heart failure, high blood pressure, age, diabetes, prior stroke, vascular disease, and sex. The interesting finding from pacemaker research is that this score predicts strokes and death in pacemaker patients whether or not they have documented AF.

A study following over 1,600 pacemaker patients without AF for nearly five years found that those with high scores (6 to 9) had a thromboembolic event rate of about 27%, compared with 3% in the lowest-risk group (scores 0 to 2). The hazard ratio was roughly ten times higher in the highest-risk group.¹⁷ Separate work confirmed that the predictive value of these scores held regardless of whether patients had a history of AF.¹⁸

This matters because it reinforces the idea that pacemaker patients carry stroke risk from their underlying cardiovascular conditions, not just from the device itself. The pacemaker treats a heart rhythm problem, but it does not erase the vascular risk factors that come along with it. A high risk score should prompt a conversation about prevention even if the device has never logged an atrial high-rate episode.

Managing Blood Thinners Around Pacemaker Surgery

Patients who already take blood thinners face a practical dilemma when they need a pacemaker implanted or a generator replaced: stop the blood thinner and risk a clot, or continue it and risk surgical bleeding. The BRUISE CONTROL trial randomized patients on warfarin to either continue warfarin through surgery or stop it and bridge with heparin injections. Both strategies were safe in terms of stroke risk, with only isolated events in each group, but continuing warfarin actually caused fewer bleeding complications at the surgical pocket.¹⁹ A study of 200 patients undergoing pacemaker implantation with bridging anticoagulation using enoxaparin similarly reported zero thromboembolic complications.²⁰

The takeaway for patients is reassuring: the perioperative stroke risk from pacemaker implantation itself is very low. The bigger risk around surgery turns out to be pocket hematomas and bleeding, not clots. Current practice increasingly favors continuing oral anticoagulation uninterrupted when possible.

Leadless Pacemakers and the Lead Question

Because several of the stroke-related risks described above involve the leads, a natural question is whether leadless pacemakers change the picture. Leadless devices are small capsules implanted directly into the heart through a catheter in the leg, with no wires running through the veins. A systematic review and meta-analysis of the Micra leadless pacemaker found that the overall complication rate at one year was under 2%, and compared with transvenous pacemakers, Micra was associated with about half the odds of complications.²¹

Without a lead threading through a vein and sitting in the right atrium, the risk of lead-related thrombus is eliminated, and the PFO-related paradoxical embolism pathway effectively disappears. Leadless pacemakers do not, however, address the atrial fibrillation pathway. Current leadless devices are single-chamber, pacing only the ventricle, which means they cannot detect atrial high-rate episodes and cannot deliver the atrial pacing strategies that help prevent AF. For patients who need atrial sensing or dual-chamber pacing, transvenous leads remain necessary for now, though dual-chamber leadless systems are in development.

Left Atrial Appendage Closure

For pacemaker patients who develop AF but cannot safely take long-term blood thinners, left atrial appendage closure offers an alternative way to reduce stroke risk. The left atrial appendage is a small pouch in the heart where most AF-related clots form. A plug-like device can be placed inside it through a catheter to seal it off. The EWOLUTION registry, which tracked the WATCHMAN closure device in over a thousand real-world patients, reported an ischemic stroke rate of about 1% at one year, even though nearly three-quarters of patients were not taking oral anticoagulation.²² This option does not interact directly with the pacemaker, but it fills a gap for a population that frequently overlaps with device patients: older adults with AF, bleeding risk, and limited anticoagulation options.