An electrocardiogram taken at a routine follow-up in a Chinese hospital showed something that should not have been possible. Two distinct QRS morphologies, meaning two different electrical signatures of a heartbeat, were appearing in the same tracing. The patient's heart was being paced by two devices at once.
Only one of them was supposed to be switched on. The other was an older single-chamber pacemaker, deliberately disabled during a 2018 upgrade and left inside the chest. It had turned itself back on.
The case is reported in the Journal of Electrocardiology by Xiaomao Wu and colleagues at Hangzhou Red Cross Hospital.
Two Sets of Pacing Spikes on a Single Tracing
When the patient's system was upgraded, the old generator had not yet reached its elective replacement indicator, the point at which a pacemaker's battery is nearing exhaustion. Rather than remove a device with life left in it, the team reprogrammed it to OVO mode, a setting that preserves the device's ability to sense the heart's own activity while switching off its pacing output. On paper, it was a bystander.
For two years, it behaved like one, and the newly implanted dual-chamber device managed the patient's rhythm without incident. Nothing in that stretch suggested the older generator was anything other than inert hardware. Then Holter monitoring, imaging and a review of the original procedure records confirmed that the retained unit had resumed delivering pacing pulses, producing competitive ventricular pacing: two independent devices firing at the ventricle on separate schedules.
That is not a cosmetic problem. Competitive pacing means stimuli can land during the heart's vulnerable repolarization window, and clinicians have understood since the 1960s that pacing spikes falling on the T wave can, in the wrong circumstances, provoke dangerous ventricular rhythms. The Hangzhou team traced the cause of the inadvertent reactivation and adjusted the system, resolving the dual-device conflict.
Why Old Generators Get Left Behind in the First Place
Retaining hardware is routine, not negligent. Extracting a pacemaker generator and its leads from an older patient carries real procedural risk, and leads that have been in place for years become embedded in scar tissue.
A Mayo Clinic review of 433 patients with retained, non-functional leads, published in the Journal of Interventional Cardiac Electrophysiology, found pacemaker-related complications in 24 of them, or 5.5 percent, and concluded that the adverse outcome of abandoning a lead is small. The complications clustered in patients with three or more abandoned leads, four or more total lead implantations, or three or more separate lead procedures, and in those who were younger at their first implant.
The calculation has shifted as device implantation has climbed and patients accumulate more hardware over longer lifespans. Pacemakers and implantable defibrillators are being placed in far greater numbers than a generation ago, which means more replacements, more upgrades, and more abandoned generators sitting alongside working ones. The Hangzhou authors treat that trend as the reason their case is worth publishing at all: a scenario that was once a curiosity becomes foreseeable as the number of patients carrying two devices grows.
A German Case Showed the Same Failure at Battery End of Life
The Hangzhou report is not the only recent documentation of a dormant device waking up. A German team described a 79-year-old man with sudden presyncope who had a working leadless pacemaker and an abandoned abdominal pacemaker with epicardial leads. As that old device reached its end-of-life mode, it automatically reactivated and began interfering with the functioning system, inhibiting it while failing to reliably capture the heart itself. The fix was to replace the old generator.
Their stated learning point is unambiguous: deactivated devices left switched off can reactivate themselves and resume pacing, and explantation should be considered even in older patients.
A separate report in Heart Rhythm Case Reports described a 62-year-old woman whose abandoned epicardial pacemaker, with its battery nearly depleted, was inadvertently switched into end-of-service mode during radiofrequency ablation for atrial fibrillation. The result was uncontrolled pacing, requiring device removal, which revealed a fractured lead and severe insulation damage.
Guidance Still Stops Short of Telling Doctors What to Do
The Hangzhou authors point out that the 2021 European Society of Cardiology pacing guidelines set out management principles for devices no longer in use but do not provide specific operational instructions for the scenario their patient encountered.
None of the three reports describes a patient who came to lasting harm. In each, the problem was identified and fixed, in two of them by removing the retired device outright. What links them is that the trouble started with hardware everyone had written off.
For patients, the takeaway is narrower than it may sound. This is not a reason for anyone with a pacemaker to be alarmed. It is a reason for people who have had a device replaced or upgraded to know whether old hardware remains in their chest, to mention it at every cardiology visit, and to report new palpitations, dizziness, fainting, or breathlessness promptly rather than assuming that a working device rules out a device problem.
Key Questions Answered
What is an abandoned pacemaker?
A generator or lead left in the body after a replacement or upgrade, typically switched off, because removing it would carry more risk than leaving it in place.
How can a disabled device turn itself back on?
Reported mechanisms include automatic mode changes as a battery reaches the end of its life and inadvertent activation during other medical procedures. The Hangzhou report attributes its case to the unexpected reactivation of the retained unit.
Why is competitive pacing a concern?
Two devices pacing independently can deliver a stimulus during the heart's electrically vulnerable phase, which carries a risk of triggering serious ventricular rhythm disturbances.
How was it detected?
The electrocardiogram showed two different QRS shapes. Holter monitoring, imaging and a review of the original procedure records confirmed the source.
Should old pacemakers be removed?
There is no blanket answer. The German team argues explantation deserves consideration even in older patients, while the Mayo data show that carefully managed abandonment is usually uneventful. It is a decision for a patient and their cardiologist.
What should patients do?
Know your device history, keep an up-to-date device card, and report new symptoms rather than assuming a recently implanted pacemaker rules out a hardware issue.
