Pacemaker Malfunction 

Updated: Sep 19, 2016
Author: Chakri Yarlagadda, MD, FACC, FSCAI, FASNC, CCDS; Chief Editor: Jeffrey N Rottman, MD 



The number of pacemaker implants is growing because of newer indications. There are a few million pacemaker patients worldwide with hundreds of thousands of new implants yearly. Knowledge of different modes, timing cycles, and event markers, as well as newer algorithms, is necessary for accurate diagnosis of pacing system malfunction.


Although true pulse generator failure is very rare, pacing system malfunction occurs occasionally. Pacing system malfunction can be due to malfunction of lead, electrode-tissue interface, or pulse generator. Most of these malfunctions can be corrected by simple reprogramming of the device. The majority of malfunctions in fact are due to normal programmed pacemaker function. Thorough understanding of the cause of malfunction is extremely important for accurate diagnosis and management.



United States

Maisel reported pacemaker generator failure rate of 0.46% based on US FDA reports and 1.3 malfunctions per 1000 person-years based on device registries.[1, 2] Actual incidence of pacemaker malfunction, however, would be higher since these numbers are exclusive of lead failure. Hauser et al reported a 2% device electronic failure rate at their center.[3]


Actual incidence of pacemaker malfunction is unknown.


Overall morbidity and mortality depend on the underlying cause of malfunction as well as the patient's dependency on the pacemaker. Most pacing system malfunctions are benign, although conditions such as cross-talk inhibition or runaway pacemaker can be life threatening. Maisel reported a 1 in 75,000 death rate among pacer implants.[2]




Clinical symptoms of pacemaker malfunction are variable and include syncope, dizziness, palpitations, and slow or fast heart rate. Extracardiac stimulation or hiccough may be present. Obtain as much information as possible regarding the pulse generator, leads, and programmed values. Information on indication for pacemaker implant, special programming features particular to that model or patient, and knowledge of any manufacturer recalls or alerts on pacing systems may provide clues to underlying malfunction.


Look for the following signs in patients with pacing system malfunction:

  • Pocket stimulation

  • Erosion of packet

  • Diaphragmatic stimulation

  • Cannon A waves during atrioventricular (AV) dyssynchrony

  • Bradycardia

  • Tachycardia

  • Hypotension


Causes of pacing system malfunction can be classified into the several groups.


Causes of undersensing include the following:

  • Improper lead position: Lead has to be positioned at an ideal location for optimal function, otherwise it can cause undersensing.

  • Improper programming: Programming the lead sensitivity too high may cause undersensing.

  • Lead maturation or dislodgement (as shown below): Lead maturation or dislodgement cause sensing and capture malfunction due to poor signal strength.

    Atrial lead dislodgement. Chest radiograph film de Atrial lead dislodgement. Chest radiograph film detail showing dislodged atrial lead with tip in the right ventricular cavity.
  • Lead insulation break: Insulation failure causes undersensing.

  • Loose connection at connector block (see image below): Due to inadequate contact of the pin and connector there is intermittent undersensing and loss of capture.

    This is an artifact due to monitor malfunction or This is an artifact due to monitor malfunction or loose limb lead connection. An abrupt loss of a portion of the QRS complex followed by a flat line can be observed. If R-R intervals are matched, 2 QRS complexes are missing during the pause. If it is due to a dislodged lead, a pacing artifact with no capture should be observed.
  • Incompatible connector: Incompatible connector causes sensing and pacing malfunction.

  • Battery depletion: This can cause undersensing, loss of capture, or loss of output.

  • Magnet application: Magnet inhibits sensing of cardiac or noncardiac electrical events by the pacemaker and it reverts to fixed-rate pacing function. Pacemaker reverts back to the programmed routine upon removal of the magnet.

  • Electromagnetic interference (EMI): EMI has several effects on pacemakers. DC shock cause reversion to back-up mode, transient increases in capture threshold and loss of capture, and damage to the pulse generator and circuitry. Electrocautery can inhibit the pacing stimuli or trigger ventricular pacing due to atrial oversensing. Radiotherapy can cause sensing malfunction, failure of telemetry function, and runaway pacemaker. Cellular phones may cause asynchronous pacing.

  • Reed switch malfunction: This causes pacemakers to revert to an asynchronous pacing mode with loss of sensing.

  • Dry (air) pocket in unipolar pacers: In unipolar pacers, lead has a single stimulating electrode, the cathode, with the anode connected to an indifferent electrode, usually the outer surface of the pulse generator that has to be in constant contact with the subcutaneous tissue of the person. In dry pocket situations there is inadequate contact between pulse generator and tissue causing inappropriate sensing and pacing.

  • Circuit failure and partial open circuit: Although rare, this can cause inappropriate sensing and pacing.

  • Change in signal morphology or amplitude of intrinsic event: This can cause either undersensing or oversensing due to signal deterioration.

  • Post defibrillation or cardioversion: DC shock causes pacemaker reversion to back-up mode, transient increases in capture threshold and loss of capture, and damage to the pulse generator and circuitry.

  • Electrolyte abnormality such as hyperkalemia: Hyperkalemia causes both sensing and pacing malfunction due to a reduction of the electronegativity of the resting myocardial potential. There are also reports of endless loop tachycardia due to atrial channel far-field sensing of ventricular activation.

  • The images below illustrate undersensing.

    Atrial undersensing. Rhythm strip showing an atria Atrial undersensing. Rhythm strip showing an atrial pacing artifact after the intrinsic P wave.
    Ventricular undersensing. Rhythm strip showing ven Ventricular undersensing. Rhythm strip showing ventricular pacing artifacts despite normal underlying ventricular activity.


Causes of oversensing include the following:

  • Pacemaker crosstalk: Pacemaker generated electrical event in 1 chamber is sensed by the lead in another chamber, which results in inappropriate inhibition of pacing artifact in the second chamber. Crosstalk is only seen in dual chamber or biventricular pacemakers. Also called crosstalk inhibition, far-field sensing, or self-inhibition. Note the following

    • Crosstalk is more common in unipolar systems due to larger pacing spike.

    • Crosstalk can occur in the pulse generator circuit itself.

    • Crosstalk is seen rarely with the current dual chamber pacemakers due to ventricular blanking period, which coincides with the atrial stimulus to prevent ventricular channel oversensing of atrial output, bipolar leads with smaller pacing spike, and steroid eluting leads with lower pacing threshold.

    • Causes of crosstalk include atrial lead dislodgement into the ventricle, ventricular lead dislodgement into the atrium, high atrial output current, high ventricular sensitivity, and short ventricular blanking period.

    • Treatment includes decreasing atrial pacing output, decreasing atrial pulse width, decreasing ventricular sensitivity, increasing the ventricular blanking period, activating ventricular safety pacing, and new atrial lead implant if insulation failure mandates unipolar programming.

  • Electromagnetic interference (EMI): (See above under undersensing.)

  • Improper programming: Programming the lead sensitivity too low may cause oversensing.

  • Myopotential inhibition: Oversensing of the skeletal muscle electrical activity causes temporary inhibition of the pacemaker with no pacing current.

  • Noise from pacemaker lead fracture: Due to oversensing of the lead noise there is inappropriate inhibition of the pacemaker.

  • The image below illustrates oversensing.

    This is a typical example of ventricular oversensi This is a typical example of ventricular oversensing with inhibition of ventricular pacing. In ventricular noncapture, a ventricular pacing artifact should be present after the third P wave.

Loss of capture (noncapture)

Causes of loss of capture include the following:

  • Dry (air) pocket in unipolar pacer

  • Circuit failure

  • Impending battery depletion

  • Inadequate programmed output with higher threshold

  • Insulation break

  • Partial conductor coil fracture

  • Lead maturation, dislodgement, or perforation

  • Poor or incompatible connection at connector block

  • Conditions that increase the capture threshold, such as metabolic and electrolyte abnormalities, medications, and myocardial infarction

  • The images below illustrate loss of capture.

    Ventricular noncapture. Rhythm strip showing atria Ventricular noncapture. Rhythm strip showing atrial (P wave) sensing followed by ventricular spike, which failed to capture the ventricle.
    Loss of atrial capture. Rhythm strip showing inter Loss of atrial capture. Rhythm strip showing intermittent loss of atrial capture.

Loss of output (no pacer artifact and no QRS)

Causes of loss of output include the following:

  • Dry (air) pocket in unipolar pacer

  • Circuit failure

  • Impending battery depletion

  • Inadequate programmed output with higher threshold

  • Insulation break

  • Partial conductor coil fracture

  • Lead maturation, dislodgement, or perforation

  • Poor or incompatible connection at connector block

  • Conditions that increase the capture threshold, such as metabolic and electrolyte abnormalities, medications, and myocardial infarction

Failure to output

Causes of failure to output include the following:

  • Cross-talk inhibition due to oversensing

  • Total battery depletion

  • Conductor coil fracture

  • Lead fracture

  • Loose set-screw

  • Incompatible lead or header

  • Open circuit

  • Internal insulation break in bipolar lead

  • Myopotential inhibition or far-field sensing

Inappropriate rate

Causes of inappropriate rate include the following:

  • Battery depletion

  • Oversensing

  • Runaway pacemaker

  • Undersensing

  • Pacer reset

Inappropriate lead position

Causes of inappropriate position include the following:

  • Left ventricle (LV) position of transvenous lead through atrial septal defect (ASD), patent foramen ovale (PFO), or interventricular septal perforation or inadvertent position through arterial system

  • Coronary sinus or gastric vein position instead of right ventricle (RV)

  • Left atrial position of atrial lead through ASD or PFO

Inappropriate mode

Causes of inappropriate mode include the following:

  • Magnet application

  • Battery depletion

  • Power on reset

  • Noise reversion

  • Programmed mode switch such as VVIR or DDIR during supraventricular tachycardia

Extracardiac stimulation

Causes of extracardiac stimulation include the following:

  • Phrenic nerve stimulation from atrial lead or dislodged ventricular lead

  • Diaphragmatic stimulation from RV lead perforation or high output

  • Pocket stimulation from insulation break or upside down pacer in pocket

True pulse generator failure

Causes of true pulse generator failure include the following:

  • Battery depletion

  • Direct trauma

  • Circuit or component failure

  • EMI because of cardioversion, defibrillation, electrocautery, lithotripsy, radiofrequency ablation, MRI, electroconvulsive therapy, therapeutic radiation, or lightening

Pacemaker-mediated tachycardia (PMT)

PMT (see image below) is observed in dual-chamber pacemakers with DDD, VDD, and DDDR modes. Causes of PMT include endless-loop tachycardia, maximum tracking rate during atrial arrhythmias, sensor-driven tachycardia, myopotential tracking, and runaway pacemaker.

Pacemaker-mediated tachycardia. Rhythm strip showi Pacemaker-mediated tachycardia. Rhythm strip showing ventricular pacing at 110 beats per minute (programmed maximal track rate).

Note the following:

  • The classic form of PMT is endless-loop tachycardia (ELT). Usually, ELT is initiated by a premature ventricular beat. The atrial channel senses the retrograde atrial activation from the premature ventricular contraction (PVC), and the ventricular channel paces the ventricle after the programmed AV delay, which again is sensed by the atrial channel after retrograde ventriculoatrial (VA) conduction and results in ELT.

  • Conditions that initiate ELT include any condition that can result in AV dissociation such as atrial noncapture, atrial oversensing, atrial undersensing, long AV interval, and magnet application and removal.

  • Measures to prevent PMT include long postventricular atrial refractory period (PVARP), short AV delay, post-PVC PVARP extension, and high maximum tracking rate.

  • Termination of PMT (see image below): Magnet application results in loss of sensing and termination of the tachycardia. PVARP extension and withholding ventricular channel output also terminate PMT.

    Termination of pacemaker-mediated tachycardia. Aut Termination of pacemaker-mediated tachycardia. Automatic postventricular atrial refractory period (PVARP) extension terminated the PMT.

Pacemaker syndrome (PS)

PS is usually observed with ventricular pacing (eg, usually VOO, VVI, VVIR modes and sometimes VDD mode) because of atrial contraction against the closed AV valves during ventricular pacing. Note the following:

  • PS can occur in any other pacing modes where AV dyssynchrony occurs.

  • The reported incidence of PS varies from 5-20%, depending on the severity of symptoms.

  • Most common symptoms include pulsation and fullness in neck, dizziness, palpitations, and near syncope.

  • Treatment involves upgrading the pacemaker to a dual-chamber pacing system.

Twiddler syndrome

Patient manipulation of the pulse generator within the pocket results in coiling of the lead, lead dislodgement, or rotation and/or reversal of the anterior and posterior surfaces of the pulse generator. Note the following:

  • Treatment includes uncoiling the lead, new lead implant, and repositioning of the pulse generator.

  • Educate patients not to manipulate the pacing system.



Diagnostic Considerations


In pseudomalfunction of the pacemaker, although an apparent pacing system malfunction is suggested clinically, the apparent malfunction is a normal programmed pacer function. This is partly due to new algorithms to preserve intrinsic conduction and more physiologic pacing.

Examples of pseudomalfunction include the following:

  • Functional undersense with magnet application, safety pacing, triggered mode, fusion and pseudofusion beats, and blanking period

  • Functional oversense with short ventricular blanking period

  • Inappropriate rate with rate hysteresis, rate-drop response, rate smoothing, rate-responsive mode, programmed rest/sleep rate, and mode switch

  • Inappropriate mode with magnet application and mode switch

Manufacturers' advisories: Manufacturer recall or advisories due to unanticipated device malfunction after its release may require replacement of pulse generator, lead, or both. A decision analysis model by Amin et al warrant device replacement in pacemaker-dependent patients if a manufacturer advisory device failure rate is >0.3%.[4]

Differential Diagnoses



Laboratory Studies

The following laboratory studies may be useful in cases of pacemaker malfunction:

  • Creatine kinase (CK) and isoenzymes - Elevated in myocardial injury and cardiac trauma

  • Coagulation panel - Required to prevent bleeding complications during invasive procedures

  • Electrolytes - To exclude electrolyte abnormalities that may affect pacing thresholds

  • Drug levels - For drugs, such as digoxin and antiarrhythmics (particularly flecainide), that may alter pacing thresholds

Imaging Studies

The following imaging studies may be considered in cases of pacemaker malfunction:

  • Chest radiography: Overpenetrated film helps to evaluate lead position, fracture, and the set-screws. Specific markers on pulse generator are useful for identification.

  • Fluoroscopy: To evaluate common sites of lead fracture such as an area of acute angulation or compression by real-time imaging while applying gentle traction on the lead.

  • Echocardiogram: It has limited use in the diagnosis of pacing system malfunction. Inappropriate lead position (ie, left ventricle, left atrium, or pericardial space), pericardial effusion/tamponade, or lead fracture may be observed on 2-dimensional echocardiogram.

  • Computed tomography: CT scanning of the chest helps to evaluate lead position, especially in patients with suboptimal radiograph and echocardiogram results. Preprocedural ECG-gated multidetector CT scanning may aid clinicians in identifying patients at high risk for mechanical complications and significant perforation during lead extraction for lead malfunction, class I lead advisories, and infection.[5]

Other Tests

Several other studies may be indicated in cases of pacemaker malfunction. Consider the following:

  • Pacemaker interrogation: Evaluation of thresholds, lead impedance, and battery voltage, as well as review of histograms, mode switch episodes, and stored electrograms.

  • Magnet application: After magnet application, pacemaker goes to asynchronous pacing mode at a programmed rate that is unique to that model. This is helpful in the diagnosis of loss of capture and battery depletion.

  • 12-lead electrocardiogram: This simple bedside test is useful to diagnose undersensing, oversensing, and capture loss.

  • Telemetry monitoring: This is useful in early recognition of loss of sensing and capture from lead dislodgement in the immediate postimplant period.

  • Holter monitoring: This 24-48-hour simple test is helpful in the diagnosis of atrial and ventricular arrhythmias and abnormal sensing or capture. Sometimes an event monitoring may be required to diagnose intermittent pacemaker dysfunction.

  • Transtelephonic monitoring: Periodic transtelephonic monitoring is very useful in early recognition of battery depletion based on the magnet rate, which is unique to each pacemaker model.

  • Fluoroscopy is useful to evaluate lead fracture, especially during provocative maneuvers.



Medical Care

Medical therapy has a limited role in pacemaker malfunction. Note the following:

  • Correction of electrolyte and metabolic abnormalities

  • Apply transcutaneous pacing pads if external pacing is necessary.

  • Intravenous fluids and inotropic support if symptomatic hypotension

  • Adjust the dose or withhold the medication.

  • Pulse generator reprogramming based on underlying pacing malfunction.

Surgical Care

Surgical care depends on underlying cause for pacing malfunction. Note the following:

  • Exploration of pacemaker pocket, lead, connectors, and set-screws

  • Repair, reposition, extraction, or replacement of lead

  • Removal of air from dry-pocket

  • Upgrading single chamber to dual chamber generator in pacemaker syndrome

  • Tightening of loose set-screws

  • Replacement of pulse generator

  • Uncoiling the lead, new lead implant, or repositioning of the pulse generator in twiddler syndrome

In 2013, the American College of Cardiology Foundation/American Heart Association and the Heart Rhythm Society jointly issued guidelines for device-based therapy of cardiac rhythm abnormalities.[6]

In the multicenter European Heart Rhythm Association survey which used a questionnaire to evaluate management strategies for malfunctioning and recalled pacemaker and defibrillator leads across Europe, investigators found 85% of responding centers performed lead extraction.[7] Primary factors in decision making were the patient's age, the presence of damaged leads, and the lead dwelling time.

In a study that retrospectively reviewed the outcomes of the transvenous extraction of superfluous leads of cardiovascular implantable electronic devices, Huang et al found that this procedure is highly successful. They reviewed transvenous lead extraction procedures performed at the Mayo Clinic, including 123 procedures to remove 167 superfluous functional or nonfunctional leads. The procedural complete-success rate for the removal of superfluous leads was 97%.[8]


Consider consultations with the following:

  • Cardiologist - To reprogram the pacemaker to prevent, eliminate, or minimize the pacing system malfunction; for pulse generator change or lead insertion or extraction

  • Cardiovascular surgeon - If thoracotomy is needed


To minimize risk of lead dislodgement, advise patient not to raise ipsilateral arm over and above the shoulder for approximately 2 weeks after lead implant.



Medication Summary

Medical therapy has a limited role in pacemaker malfunction. In case of abnormal thresholds, correct electrolyte abnormalities (eg, hypokalemia, hyperkalemia, or hypomagnesemia) and adjust medication dose as needed.



Further Outpatient Care

Most cases require only follow-up device interrogation and chest radiograph.

Further Inpatient Care

Additional inpatient care may include the following:

  • Device interrogation

  • Chest radiograph for lead position and any complications such as pneumothorax

  • Wound care after pulse generator change or lead implant


Complications during pulse generator change and lead insertion or extraction include the following:

  • Vascular injury

  • Venous thrombosis

  • Cardiac tamponade

  • Hemothorax

  • Pneumothorax

  • Perforation of heart

  • Avulsion of RV

  • Bleeding

  • Infection: The rate of infection has been widely debated. Johansen et al studied the incidence of pacemaker infection and its associated risk factors and found the overall risk of infection after pacemaker implantation was low. However, the rate of infection is higher as more operations are performed, and this should be taken into consideration.[9]


Prognosis depends on the underlying cause of pacemaker failure. Most of the pacing system malfunctions are benign and can be corrected with appropriate reprogramming.

Patient Education

Patient education needed for optimal pacemaker function and early diagnosis of malfunction includes the following:

  • Advise patients not to manipulate the pulse generator to prevent twiddler syndrome.

  • Advise patients not to operate digital cellular phones close to the pulse generator to avoid inappropriate inhibition from oversensing.

  • Advise patients to seek medical attention for any unusual symptoms, such as dizziness, palpitations, and syncope, and for any pain, swelling, or drainage from pacemaker area.