What Is an External Pacemaker and When Is It Used?

An external pacemaker is a device that sends electrical impulses to the heart from outside the body, or through a temporary wire threaded inside it, to keep the heart beating at an adequate rate. Unlike a permanent pacemaker that gets surgically implanted under the skin, an external pacemaker is designed for short-term use, typically in emergencies or during hospital recovery periods when the heart’s own electrical system is temporarily unreliable. External pacing has been used clinically since the 1950s and remains one of the fastest ways to stabilize a dangerously slow heartbeat.

How It Works in Plain Terms

Your heart has its own natural pacemaker, a cluster of cells that fires regular electrical signals telling the heart muscle when to contract. When disease, injury, or medication disrupts those signals, the heart rate can drop low enough to cause dizziness, fainting, or cardiac arrest. An external pacemaker steps in by delivering small, timed electrical pulses that trigger the heart to contract, essentially taking over the job of the heart’s built-in rhythm generator until the problem resolves or a permanent solution can be arranged.

The basic setup is the same across all types: you need an electrical pulse generator (a box with controls for rate and energy output), wires or electrodes that deliver the pulse to the heart, and a way to monitor whether the heart is responding. What differs is how those electrodes make contact with the heart, and that distinction matters a lot for comfort, reliability, and how quickly the system can be set up.

The Three Main Types

External pacemakers come in three forms, each suited to different clinical situations. The choice depends on how urgent the need is, how long pacing will be required, and whether the patient is already in surgery.

Transcutaneous Pacing

This is the fastest option and the one most people picture when they hear “external pacemaker.” Two large adhesive pads are placed on the chest (front and back, or front and side), and the pulse generator delivers current through the skin and chest wall to reach the heart. Setup takes seconds, which is why transcutaneous pacing is the go-to in emergencies. Early clinical trials of the modern noninvasive temporary pacemaker found it effective in producing heart rhythm responses in the majority of patients, with stimulation tolerated well in most conscious individuals, though a small number found the sensation intolerable.¹ The current required to pace through the skin and muscle ranges widely. One early series documented thresholds between 30 and 110 milliamps, with pacing achieved in most patients without serious side effects.²

The trade-off is discomfort. Because the electrical current has to pass through skin and skeletal muscle before reaching the heart, patients feel a rhythmic thumping or stinging sensation in the chest. Some describe it as tolerable but unpleasant; others find it genuinely painful, especially at higher output settings. In that early series, roughly nine of the sedation-needing patients required additional medication to tolerate pacing. Adequate sedation and pain control are considered essential to patient comfort whenever transcutaneous pacing is used on a conscious person.³

Transvenous Pacing

When pacing needs to last more than a short time, or when transcutaneous pacing isn’t capturing reliably, a transvenous approach is typically used. A thin pacing catheter is threaded through a large vein, usually in the neck or groin, and advanced into the right ventricle. Because the electrode sits directly against the inside of the heart, far less energy is needed, and the patient feels little or nothing from the pacing itself.

The traditional way to guide the wire into position uses fluoroscopy, which is essentially a live x-ray. But fluoroscopy requires specialized equipment and exposes the patient and staff to radiation. Ultrasound guidance has emerged as a practical alternative that can be performed at the bedside, avoids radiation, and achieves results comparable to fluoroscopy-guided placement.⁴ Another technique uses the electrical signal recorded from the catheter tip itself to confirm correct positioning, making bedside placement feasible without any imaging equipment at all.⁵

Epicardial Pacing

After open-heart surgery, surgeons often sew thin pacing wires directly onto the surface of the heart before closing the chest. These epicardial wires exit through the skin and connect to an external generator at the bedside. They allow immediate pacing if the heart develops rhythm problems during the vulnerable recovery period. A review of the literature found that epicardial pacing wires are particularly valuable in high-risk patients, including older adults, those with low heart-pumping function, diabetes, elevated pressures in the lung arteries, or anyone undergoing complex valve or transplant operations.⁶ Once the patient has recovered and no longer needs pacing, the wires are gently pulled out at the bedside.

When External Pacing Is Used

The overarching reason is a heart rate too slow to sustain adequate blood flow, a condition broadly called bradycardia. But the specific clinical scenarios are varied, and understanding them helps explain why this technology remains central to emergency and hospital medicine.

Heart Block and Conduction Failure

The most classic indication is complete heart block, where the electrical connection between the upper and lower chambers of the heart fails entirely. The ventricles may still beat on their own, but often too slowly to maintain consciousness or blood pressure. A series of 200 consecutive patients receiving temporary pacing found that beyond complete heart block, the therapy was also effective for sinus bradycardia, various forms of atrioventricular conduction problems, and even certain fast rhythms like ventricular tachycardia.⁷ This range of indications underscores the flexibility of external pacing: it can rescue patients whose hearts are beating too slowly, but it can also be used in overdrive mode to break certain fast rhythms by pacing slightly faster than the abnormal rate.

Heart Attacks

A heart attack can damage the heart’s conduction system, especially when the blocked artery feeds the region where conduction tissue lives. In a study of patients needing temporary pacing, about 40% had an acute heart attack as the underlying cause, with the majority developing complete heart block from involvement of the artery supplying the conduction pathway.⁸ Whether temporary pacing actually lowers death rates in this group has been debated since the 1960s. Some researchers argued that restoring a normal heart rate should reduce the excess mortality associated with heart block during a heart attack.⁹ Others found that pacemaker use may reduce mortality in only a small subset of these patients, suggesting that the underlying heart muscle damage, not the slow rhythm alone, drives outcomes.¹⁰ In practice, temporary pacing remains standard for heart-attack patients with symptomatic bradycardia or high-grade block, even if its survival benefit is hard to prove in isolation.

Drug Overdoses and Poisoning

Several common medications can dangerously slow the heart when taken in excess, including beta-blockers, calcium channel blockers, and digoxin. External pacing can be lifesaving in these situations. A case report described successful resuscitation using transcutaneous pacing in a patient who developed cardiac arrest from a propranolol overdose.¹¹ For digoxin poisoning specifically, transvenous pacing has been found safe in accidental overdoses complicated by symptomatic bradycardia, though the same conclusion does not necessarily apply to acute intentional ingestion.¹²

That said, pacing has its limits in the overdose setting. While it can restore electrical activity and even stabilize some patients, those who develop bradycardia and low blood pressure after a drug overdose remain in a high-risk group overall. Pacing addresses the rhythm problem but cannot reverse the direct toxic effects of the drug on the heart muscle.¹³

Bridge to a Permanent Pacemaker

Many patients who need external pacing will eventually get a permanent device surgically implanted. External pacing serves as the bridge, keeping them alive and hemodynamically stable during the wait. Common reasons for the delay include active infection (you generally cannot implant hardware into a patient with bacteria in the bloodstream), the need for antibiotic treatment after removing an infected permanent device, or diagnostic uncertainty about whether the rhythm problem will resolve on its own.¹⁴

In patients with both heart block and active infection, temporary pacing using a specialized approach called VDD pacing can maintain more natural heart function while waiting for the infection to clear before permanent implantation.¹⁵ When the wait is expected to be long, some centers use an externalized permanent-type pacing lead connected to a reusable generator. This “temporary permanent pacemaker” setup offers better lead stability and allows the patient more mobility compared to a standard temporary wire.¹⁶

Preventive Standby During Procedures

External pacing pads are sometimes applied prophylactically during procedures that carry a risk of causing bradycardia. Carotid artery stenting, for example, can trigger a reflex slowing of the heart when the stent is expanded near the carotid sinus. Transcutaneous pacing set to activate only if the heart rate drops below a threshold has been shown to effectively and comfortably prevent hemodynamic problems during these procedures, with most patients paced at relatively low output.¹⁷

The Problem of False Capture

One of the trickiest aspects of transcutaneous pacing is knowing whether the electrical impulse is actually making the heart contract, not just producing a signal on the monitor. When the pacemaker fires through the chest wall, it creates a large electrical artifact that can make it look like the heart is responding even when it isn’t. This is called false electrical capture, and it’s alarmingly common in the field. A prehospital case series found that roughly 83% of patients who underwent transcutaneous pacing showed false electrical capture on the monitor, despite all of them apparently having a palpable pulse.¹⁸

Feeling for a pulse is the traditional way to check, but skeletal muscle contractions caused by the pacing current can make pulse assessment unreliable. Bedside ultrasound has emerged as a valuable tool for confirming that the heart is actually squeezing in response to pacing. In one reported case, a patient had no palpable central pulses despite electrical capture on the monitor, but ultrasound revealed ventricular contractions, confirming the pacemaker was working.¹⁹ Ultrasound can also help distinguish between successful pacing with persistent low blood pressure (which needs additional treatment like fluids or medications) and outright failure to capture (which needs higher pacing output or a different approach).²⁰

Complications and Risks

External pacing is generally safe for short-term use, but each type carries its own set of risks. With transcutaneous pacing, the main issues are skin burns or irritation under the pads, discomfort, and the possibility of not achieving reliable capture. These are inconveniences more than dangers, and they resolve once pacing is stopped.

Transvenous pacing carries more significant risks because it involves threading a catheter through a large vein and into the heart. The most feared complication is cardiac perforation, where the stiff pacing wire punctures through the thin wall of the right ventricle. This is rare, occurring in fewer than 1% of insertions, but it can be life-threatening, especially in elderly patients with fragile heart tissue or when the wire has been in place for an extended period.²¹ A systematic review comparing access sites for transvenous pacing found that catheter-related infections were significantly lower when the wire was inserted through the jugular vein compared to other sites, while bleeding, lead displacement, and perforation rates did not differ significantly between access points.²²

Epicardial wires placed during surgery carry a small risk of bleeding when removed, and rarely the wire can break and a fragment can be retained. But these complications are uncommon enough that routine use in high-risk surgical patients is still widely supported.

Why It Does Not Help in Cardiac Arrest From Asystole

A common misconception is that an external pacemaker can restart a heart that has stopped entirely. In reality, when the heart is in asystole (a flatline, with no electrical or mechanical activity), pacing almost never works. The pacemaker can deliver a signal, but if the heart muscle is too damaged or deprived of oxygen to respond, the electrical pulse accomplishes nothing.

A landmark trial randomized patients with asystolic cardiac arrest to receive early transcutaneous pacing by paramedics in the field or standard treatment. Of 278 patients who received pacing, only about 4% survived to hospital discharge, no better than the control group.²³ A systematic review reinforced this conclusion: among paced patients with bradyasystolic cardiac arrest, none of 215 in case series and only a handful in randomized trials survived to discharge, with no significant improvement over controls.²⁴

Where prehospital pacing does appear useful is in symptomatic bradycardia, when the heart is still beating but too slowly. A randomized feasibility trial comparing transcutaneous pacing to a medication (dopamine) for prehospital bradycardia found similar survival rates, around 70% in both groups, suggesting pacing is a reasonable alternative to drugs in the field for patients who still have a rhythm.²⁵ The distinction matters: external pacing is a tool for supporting a struggling heart, not for bringing back one that has quit.

External Pacing in Children

Transcutaneous pacing works in children too, though the equipment needs some adaptation. A study tested external pacing in 22 children ranging from infants to teenagers during anesthesia induction for heart surgery. Capture was achieved in 53 out of 56 pacing trials, with no complications noted. The energy needed per heartbeat was the same regardless of the child’s age or size, but larger pads required higher current output while distributing it over a wider area. The researchers concluded that children weighing less than about 15 kilograms may benefit from smaller electrode pads.²⁶ This finding is reassuring for emergency departments, where pediatric bradycardia emergencies are rare but high-stakes, and knowing that the adult-sized equipment on hand can still work in most children removes one barrier to rapid treatment.

Electronic Interference With External Pacemakers

Because external pacemakers are connected to the patient by wires and pads rather than sealed inside the body, they can be vulnerable to electromagnetic interference from nearby devices. A study testing the effects of radio-frequency identification technology on critical care equipment found that all three external pacemakers tested experienced incorrect inhibition, meaning the pacemaker stopped firing when it should not have, at distances as close as 5 centimeters and as far as 30 centimeters from the interfering signal source.²⁷ For a patient whose heart depends on continuous pacing, even a few seconds of inappropriate inhibition could trigger symptoms or worse. In practice, this means hospitals need to be thoughtful about where RFID scanners and similar technology are placed relative to patients on external pacemakers, and clinicians should be aware that unexplained pacing pauses might have an environmental cause rather than a device malfunction.