eMedicine Specialties > Cardiology > Electrophysiology Procedures

Pacemaker Malfunction

Author: Chakri Yarlagadda, MD, FACC, FASNC, Consulting Cardiologist, St Elizabeth Hospital, Youngstown, OH
Contributor Information and Disclosures

Updated: Feb 18, 2009

Introduction

Background

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.

Pathophysiology

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.

Frequency

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

International

Actual incidence of pacemaker malfunction is unknown.

Mortality/Morbidity

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

History

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.

Physical

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

Causes of pacing system malfunction can be classified into the following groups:

• Undersensing (see Media file 1, Media file 2): 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 (see Media file 3): Lead maturation or dislodgement cause sensing and capture malfunction due to poor signal strength.
  • Lead insulation break: Insulation failure causes undersensing. 
  • Loose connection at connector block: Due to inadequate contact of the pin and connector there is intermittent undersensing and loss of capture.  
  • 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.
• Oversensing: 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.
    • 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.
• Loss of capture (noncapture [see Media file 4, Media file 5]): 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
• 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 Media file 6) 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.   
  • 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 Media file 7): Magnet application results in loss of sensing and termination of the tachycardia. PVARP extension and withholding ventricular channel output also terminate 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.
  • 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.
  • Treatment includes uncoiling the lead, new lead implant, and repositioning of the pulse generator.
  • Educate patients not to manipulate the pacing system.

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