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:

• Pacemaker Basics
• Electrical Concepts 
• Pacemaker Complications
• Dysfunctional Pacemakers
• Indications, complications and malfunctions of 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

AAI

• 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

VVI

• 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

VOO

• 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

DDD

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

DOO

• 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