I read around pacemakers SO often throughout my residency, but it was a topic that I found was often a struggle to absorb. So, here we’re going to tackle what the ED Physician should know about managing patients with pacemaker and ICDs:


Part 1 – Pacemakers 101

1. Indications for Pacemaker Implantation:

  • Guidelines for pacemaker insertion have been established by a task force formed by the American College of Cardiology (ACC), American Heart Association (AHA), and the Heart Rhythm Society (HRS).
  • They divide the indications for pacemaker implantation into 3 specific classes:
    • Class 1: Conditions where implantation is necessary and beneficial
    • Class 2: Conditions where they are indicated by there is conflicting evidence
    • Class 3: Conditions where implantation is not recommended and may be harmful
  • Below is a brief list of class 1 and 2 indications specifically sinus node dysfunction (SND) and AV blockade – which represent the vast majority of implanted pacemakers


2. Types of Pacemakers

There are 3 main types of pacemakers:

  • Single chamber system
    • Single lead in either
      • Right atrium – detect P waves
      • Right ventricle (most common) – detects R waves
    • This is rare to see
    • Vast majority of patients will have a dual chamber system
  • Dual chamber system
    • Two leads
      • One in the right atrium and one in the right ventricle
    • Provides AV synchrony and pacing support in both atrium and ventricle
    • Used in sinus node disease
  • Triple chamber system
    • Aka bi-ventricular pacemaker or Cardiac Resynchronization Therapy (CRT-P)
    • Three leads
      • Right atrium
      • Right ventricle
      • Left ventricle (via the coronary sinus vein)
    • Paces both ventricles together to resynchronize the beat
    • Used exclusively in certain types of heart failure with reduced ejection fraction

3. Pacemaker Code


  • Pacemaker code is broken down into 5 letters
  • These 5 letters tells us what the different pacemaker settings are and what the pacemaker can do
  • First 3 letters are most relevant to us – we are only going to focus on those
    • First letter: Chamber paced
    • Second letter: Chamber sensed
    • Third letter: Sensing response – that is, what the pacemaker does in response to a sense beat
      • Triggered – occurs when there is no sense beat so the pacemaker will trigger an impulse (not used in current PPMs)
      • Inhibited – occurs when an intrinsic depolarization is sensed which results in inhibition of the pacemaker
      • Dual – dual inhibition of both atria and ventricular pacing in response to intrinsic ventricular depolarization
      • None – does not trigger or inhibit regardless of native activity



  • Single lead system where the atria is both paced and sensed
  • Response is to inhibit the pacemaker from firing
  • If there is no intrinsic depolorization detected, this pacemaker will send an electrical discharge and cause atrial contraction
  • These pacemakers are primarily used for sinus node disease and sinus bradycardia



  • Single lead system where the ventricle is both paced and sensed
  • When ventricular depolorization is sensed, the pacemaker is inhibited from discharging
  • If there is no sensed depolorization, the pacemaker sends an impulse down the lead to the RV causing ventricular contraction



  • Here the ventricle is paced with no sensing and thus no response to sensing
  • Also called asynchronous pacing where the pacemaker will continuously depolarize at a set pre-programed rate regardless of intrinsic activity
  • This is the default setting for all single chamber pacemakers




  • Here both atria and ventricles are paced and sensed
  • There can be a combination of atrial sensing or pacing or ventricular sensing or pacing




  • This is the default setting for dual chamber pacemakers and the setting when a magnet is applied
  • Equivalent to VOO for single system pacemakers


Components of a Pacemaker

  • Implantable pulse generator (IPG)
    • Delivers an electrical charge down the lead to the heart which triggers a heartbeat
    • To do this there needs to be a battery, sensing circuit, and microprocessor
      • These components are housed within the IPG
    • Sensing circuit
      • This detects any naturally occurring electrical activity and brings this information to the microprocessor
    • Microprocessor
      • Brain of the pacemaker that controls what the pacemaker does in response to sensing
    • Connectors
  • Leads
    • These connect the pacemaker to the heart muscle itself
    • Function of leads
      • Delivers electrical impulses from the pulse generator to the heart
      • Senses cardiac depolarization
    • Leads are fixed into the myocardium
    • Electrodes are implanted on fixation ends
    • Unipolar vs bipolar leads
      • Most leads have two electrodes
        • Can alter whether one is used (unipolar) or both are (bipolar)
      • Unipolar pacing system
        • One electrode (cathode) at the tip
        • IPG functions as the anode
        • With pacing
          • Impulse flows through the electrode tip
          • Stimulates the heart
          • Returns through cardiac or body tissue to the IPG
      • Bipolar pacing system
          • Lead has both an anode and cathode
          • With pacing
            • Impulse flows through the electrode tip (cathode)
            • Stimulates the heart at the electrode tip
            • Travels to the ring electrode (anode) which is a few inches from the lead tip
            • Returns to the IPG via the lead wire
    • Important to know what type of lead is implanted because it can be helpful for diagnosing a problem and determining solutions


Part 2: Electrical Concepts

  • Physics 101
    • Ohm’s law
    • V=IR
      • Voltage – potential difference between two electrodes
      • Provided by PPM battery
      • Can also be referred to as amplitude
    • Current – the flow of electrons through a completed circuit
      • Calculated by the voltage that is programed and the impedance of the pacing system
    • Impedance – resistance to current flow
      • For our sake this is the same thing as resistance
        • High impedance occurs with lead fractures or displacements
        • Low impedance occurs with breaks in insulation
      • Capture and Threshold
        • Capture: The minimum electrical stimulus needed to consistently capture to trigger a heartbeat
          • Dependent on both voltage and pulse width
        • Threshold: the minimum electrical stimulus needed to trigger a heartbeat, regardless of consistency

  • Here we see paced beats at 1.75 volts
  • As we slowly decrease the voltage to 0.5 volts we no longer see ventricular contractions
  • 75 volts was the amount of voltage needed to get a ventricular contraction – this is the threshold


  • Sensing
    • Is the ability of the pacemaker to detect whether or not the heart is beating
    • If the pacemaker receives an intrinsic electrical signal, it will be satisfied that the heart just contracted
    • If it did not receive a signal, it will assume that the heart has failed to beat when it should have and would initiate an impulse

  • On the above graph, we have programed out pacemaker to have a maximum sensitivity of 2.5 mV
    • If we increased our sensitivity above 2.5 mV, the pacemaker would not see intrinsic activity and would initiate impulses
    • If we decrease our sensitivity below 2.5 mV, the pacemaker would see more incoming signals and would not initiate impulses
    • Adequate sensitivity is important
      • Filters out extraneous signals
        • T waves
        • Skeletal muscle myopotentials
      • Sensing accuracy affected by
        • Pacemaker lead integrity
          • Insulation break
          • Wire fracture
        • Electrode placement within the heart
        • Electrophysiologic properties of the myocardium
        • Electromagnetic interference
  • Role of Magnets in Pacemakers
    • Magnets can be placed over pacemakers to facilitate interrogation or troubleshooting
    • For us, as emergency physicians, we place magnets over pacemakers when the pacemaker is malfunctioning
      • This changes the pacemaker to asynchronous mode
      • VOO or DOO
      • Pacemaker here will pace at a rate of 85 beats per minute regardless of intrinsic cardiac activity

When the magnet is removed, the pacemaker returns back to its programmed operation within 2 seconds.


Part 3: Pacemaker Complications

  • Complications can arise at any time following device implantation
    • This can be directed from the procedure itself or a complication of the pacemaker

  • Bleeding occurs in 3% of patients
  • Most hematomas can be treated with a local compressive dressing
  • A pocket hematoma (above), should not be drained in the ED as there is an increased risk for infection
    • This warrant a cardiology consultation
  • Pocket infections or systemic infections occur in 1-3% of patients
    • These warrant a cardiology consultation as these patients often require IV antibiotics and device removal
  • Lead displacement or perforation
    • This is fairly common occurring in 5% of patients
    • Leads may perforate through the myocardium
    • An ECG may show evidence of failure to capture
    • A chest XR may be helpful in visualizing the fracture or displacement


Part 4: Dysfunctional Pacemakers

1. Failure to Capture 

Electrical stimulus does not result in depolarization of the myocardium

  • ECG: shows pacemaker spikes throughout the strip
    • Some are followed by QRS complexes and others are not
  • Causes:

2. Failure to Pace

  • No paced stimulus is generated from the device resulting in either decreased or absent pacemaker function


  • ECG: shows decreased or no pacer spikes or pacer-induced QRS complexes but rather the native rhythm
  • Causes:



3. Undersensing

  • This occurs when the pacemaker does not see the intrinsic beat and thus delivers a scheduled pace
  • Undersensing = overpacing


  • ECG: shows pacer spikes within the QRS complexes
  • Causes:


4. Oversensing 

  • Here the sensitivity threshold is set too low, so electrical signals are inappropriately recognized as native cardiac activity and pacing is inhibited
  • Oversensing = under-pacing


5. Pacemaker Mediated Tachycardia (PMT)

  • Ventricular depolorization conducts backwards into the atria leading the atrial lead to detect activity as an incoming p wave resulting in ventricular depolorization
  • Paced ventricular complex then results in further retrograde conduction with retrograde p wave generation thus forming a continuous cycle
  • For sequence to be maintained
    • AV node and atrium need to be able to conduct retrograde
    • Pacemaker must be able to sense this retrograde depolarization
  • Similar to a re-entrant tachycardia with the pacemaker forming part of the re-entrant circuit


  • Treatment
    • Magnet application
      • If this was truly PMT, the tachycardia would be instantly abated
    • AV blocker – Adenosine, BB, CCB

6. Runaway Pacemaker

  • Seen in older generation pacemakers
  • Results from low battery voltage
  • Pacemaker delivers runs of spikes in excess of 200 bpm which can provoke VF of cause FTC causing bradycardia as the pacing spike are low in amplitude
  • Today pacemakers have security designed to prevent runaway
    • Maximum rate, hermetic sealing and a decrease in pulse amplitude at high rate with concomitant loss of capture


  • ECG shows intermittent ventricular capture at a rate slower than normal with numerous spikes at a very high rate with different voltages and often without capture beats, simulating an ECG artifact
  • Treatment
    • Apply magnet
    • Replace pacemaker

7. Pacemaker Induced Extra-Cardiac Stimulation 

  • Diaphragmatic stimulation
    • Lead close to phrenic nerve
    • Lead incorrectly positioned
      • Cardiac vein, myocardial perforation, migration
    • Pectoralis muscle
    • Intercostal muscle

8. Twiddler’s Syndrome

  • Occurs when the patient self-manipulates the pulse generator that is implanted in the skin
  • Causes the pulse generator to rotate on itself which subsequently pulls on the leads and displaces them
  • Can result in extra-cardiac pacing
  • These need to be replaced



Part 5: Approach to the Dysfunctional Pacemaker in the ED

There are a variety of tools that we can use at our disposal to diagnose and manage dysfunctional pacemakers in the ED

  • Patient history and physical exam
  • PoCUS
  • Pacemaker device card
    • Provides details on who implanted the device, indication, manufacturer, type, model and date of implantation
  • Cardiac Device Check (this is specifically under the Media tab in Epic)
  • 12-lead ECG +/- a rhythm strip
  • CXR
    • Leads – number, kinks, fractures, displacement
    • Assess the pulse generator location
    • Assess for the presence of a pneumothorax and/or hemothorax
    • Compare to previous CXR
  • Blood work – electrolytes, VBG and lactate, TSH, Digoxin level (if appropriate)
  • Below is an approach to interpreting an ECG



  • If the patient is unstable, proceed down standard ACLS
  • Consider magnet application
  • Cardiology consultation for device interrogation and troubleshooting


  • Darren Wong

    Dr. Darren Wong is a FRCPC Emergency Medicine Physician who has an interest in the care of critically ill patients and trauma care.

    View all posts