FRCA Notes

Cardiac Implantable Electronic Devices

This topic was an SAQ in 2018 (45% pass rate); the examiners lamented poor 'basic medical knowledge'.

The curriculum asks for 'Cardiac pacemakers: principles and classification' and 'Defibrillators: implantable devices'.

Resources

  • Cardiac implantable electronic devices can be generally classified as either:
    • Pacemakers
    • Implantable cardioverter defibrillators (ICDs)
    • Biventricular pacemakers i.e. cardiac resynchronisation therapy
    • Implantable loop recorders
  • Pacemakers generate electrical impulses to re-establish regular cardiac myocyte contraction
  • They can be sub-classified as:
    • Temporary
      • Transcutaneous pacing
      • Temporary pacing wires, dealing with the three key parameters of pacing rate (bpm), output (mA) and sensitivity
      • Epicardial leads placed during cardiac surgery, which are removed post-operatively

    • Permanent (PPMs)
      • Leads placed via central vein (typically left subclavian or axillary) into the endocardium of the RA/RV

Indications

  • 58% are implanted for symptomatic 2nd or 3rd degree AV block, i.e. associated with:
    • Symptomatic bradycardia
    • Arrhythmia requiring drug therapy intervention
    • Documented asystole
    • Neuromuscular disorders
    • Cardiomegaly or LV dysfunction
    • Exercise-induced dysrhythmia

  • 24% are for sick sinus syndrome

  • Remaining indications include:
    • Symptomatic bradycardia in the transplanted heart
    • Hypersensitive carotid sinus syndrome
    • Drug-refractory dysrhythmias
    • Asystole not associated with AVN block

The Generic Pacemaker Code

Chamber(s) paced Chamber(s) sensed Response(s) to sensing Programmability Multi-site function
O = none O = none O = none O = none O = none
A = atrium A = atrium I = inhibited R = rate modulation A = atrium
V = ventricles V = ventricles T = triggered V = ventricles
D = dual (A & V) D = dual (A & V) D = dual (T & I) D = dual (A & V)

Choice of pacing mode

Code Indication Notes
DDD Most rhythms except atrial tachyarrhythmia Preserves AV synchrony
Protects against ventricular bradycardia
Enables a normal chronotropic response to activity
AAI Relative bradycardia +
endogenous atrial rhythm sufficient to compete with pacemaker rate		 Only in patients with intact/reliable AV conducting system
Contra-indicated in AF/flutter/atrial tachycardia/AVN block
VVI Chronic AF, atrial flutter, SSS or ventricular pauses Senses intrinsic R wave
Does not maintain AV synchrony
No atrial contribution to ventricular preload
AOO Bradycardia + intact AVN conduction
Where synchronous modes are contra-indicated i.e. diathermy		 Contra-indicated in AF/flutter/atrial tachycardia/AVN block
VOO Bradycardia w/o intact AVN conduction
Where synchronous modes are contra-indicated i.e. diathermy		 Competition with intrinsic rhythm
Possibility of R-on-T
No atrial contribution to ventricular preload
DOO As for VOO, but where atrial contribution to preload is desired Risk of R-on-T
Not as efficient as AOO
DVI Acute AF


  • Sense and analyse myocardial electrical activity
  • Deliver shock therapy ± pacing function when required

Indications

  • Secondary prevention in patients with:
    • Survived cardiac arrest from shockable rhythm
    • Haemodynamic compromise from tachyarrhythmias
    • At risk of scar-related VT post-MI
  • Congenital heart disease e.g.

  • Some patients with indications for biventricular PPM's and ICD's can have a CRT-D inserted

ICD Nomenclature

Chamber(s) shocked Anti-tachycardia pacing chamber Tachycardia detection Anti-bradycardia pacing chamber
O = none O = none E = electrogram i.e. ECG O = none
A = atrium A = atrium H = haemodynamic A = atrium
V = ventricles V = ventricles V = ventricles
D = dual (A & V) D = dual (A & V) D = dual (A & V)

ICD mechanism

  • Larger generator than PPMs that houses batteries, electronic circuitry and a capacitor
  • Continuously senses native electrical activity (R-R interval) to detect VT/VF
  • May incorporate anti-tachycardia pacing (ATP) activity

  • If VT is detected a burst of overdrive pacing is used to attempt to terminate the VT

  • If ATP fails or the rhythm is VF:
    • 750V battery charges the capacitance plate
    • Deliver electrical energy of 45J directly to the myocardium

  • Typically also have anti-bradycardia pacing activity in the event of 'post-shock bradyarrhythmia'

CRT devices

  • Optimise timing of RV and LV contraction
  • Indications:
    • NYHA III or IV heart failure
    • Moderate-severe HF with LVEF <35% and QRS >150ms
    • Mechanical dyssynchrony on TTE
  • Leadless cardiac monitoring devices solely for diagnostic use
  • For patients with unexplained syncope and/or palpitations
  • Sometimes used to monitor AF

Sensitivity

  • The sensitivity of a PPM is the minimal intrinsic atrial/ventricular electrical activity (mV) that is sensed by the device
  • Pacemaker sensitivity is set during insertion; the pacing threshold is the sensitivty at which the sense indicator is first triggered by each endogenous depolarisation
  • The pacing generator is typically set at half the pacing threshold to account for variability, or set at 2mV in those without an endogenous rhythm

  • If this is incorrectly set, the device may either:
    1. Under-sense i.e. fails to detect intrinsic myocardial activity
      • Thus over-pacing can occur, which may cause malignant arrhythmias if occurring on top of normal activity

    2. Over-sense i.e. detects activity when there is none
      • This may lead to a failure to pace in the face of no/inappropriate intrinsic electrical activity

Implications of electromagnetic interference (EMI)

  • EMI with PPMs typically causes over-sensing, which may be particularly pertinent if the patient is pacemaker-dependent
  • EMI with ICDs is typically falsely sensed as shockable electrical activity, leading to inappropriate (intra-operative) shock delivery

  • Sources of EMI include:
    • Diathermy
    • Radiofrequency ablation
    • Medical equipment incorporating wireless technology
    • ESWL
    • Mobile phones
    • ECT
    • TENS

Insertion

  • Typically inserted subcutaneously below left clavicle, often under LA ± sedation
  • Trans-venous access via cephalic, subclavian or axillary veins
    • The atrial lead is typically placed in the right atrial appendage
    • The ventricular lead is typically placed in the RV apex
    • Biventricular pacemakers have another lead passing into the LV

  • Complications include:
Early Late
Pneumothorax (3.7%) Lead displacement (4.8%)
Vascular injury Infection (1.5%)
Failure

Removal

Indications for CIED removal
Infection (53%)
Device recall/malfunction
Venous access issues
Severe TR
Chronic pain
Facilitate MRI or radiotherapy
  • Can risk-stratify patients having CIED removed using the ELECTRa Registry Outcome Score (EROS)
  • Stratifies patients into low (EROS 1), intermediate (EROS 2) or high (EROS 3) risk groups
  • Risk of serious complications 1% for EROS 1 and 2 patients
  • EROS 3 patients have 4x risk of major complications than EROS 1 or 2 patients

  • Risk factors include: female gender, advanced age, anticoagulation, BMI <25kg/m2 and dual-coil leads
  • Complications of removal include:
Major complications Minor complications
Death/cardiac arrest Haematoma
Cardiac avulsion Migrated lead fragment w/o sequelae
Vascular laceration e.g. SVC Need for vascular repair at entry site
Stroke AV fistula
Need for pericardiocentesis/drain Small pericardial effusion
Haemothorax Pneumothorax
Major haemorrhage Minor haemorrhage
Massive PE or other embolism Small thrombosis
Flail TV leaflet Worsening TV function (12%)


Perioperative management of the patient with a CIED


Focussed history and examination

  • Current symptoms (if any):
    • (Pre-)syncope
    • Dizziness
    • Those of deteriorating cardiac function e.g. dyspnoea, oedema, PND, orthopnoea, chest pain

  • Device-related
    • Indication for device insertion
    • Manufacturers device card
    • Electrical generator location

  • Co-existing cardiovascular pathologies
  • Anti-arrhythmic drugs

Diagnostic evaluation

  • Electrolyte levels, especially potassium - hyperkalaemia risks failure to capture
  • Recent ECG; may indicate pacing-dependent if pacing spikes before all complexes
  • Check CXR to ensure appropriate lead positions and no features of e.g. worsening pulmonary oedema

  • Recent device check
    • PPM within 12 months, ICD within 6 months
    • Percentage of time paced i.e. degree of pacemaker dependency
    • Underlying rate & rhythm

MDT discussion

  • MDT input from surgical and cardiology/EP colleagues on:
    • Surgery type and timing
    • Sources of EMI

    • Need for re-programming perioperatively or back-up pacing
    • Response to magnet

  • Consider need for CCU/HDU bed post-operatively

Device management

  • In an elective setting may need device re-programming if there's significant EMI anticipated or surgical site within 15cm of the generator
    • Any patient with significant PPM dependency + a risk of EMI may need temporary re-programming to an asynchronous (AOO/VOO/DOO) mode with a rate set higher than the intrinsic rare
    • Any PPM with rate-responsive functions may need to be re-programmed to avoid mechanical ventilation stimulating excessive pacing rates
    • Any defibrillator function risks EMI triggering inappropriate defibrillation, so will need to be turned off for surgery

  • In an emergency setting placing a magnet over the device should:
    • PPM → asynchronous mode
    • ICD → inhibits shock and anti-tachycardia functions (but no effect on anti-bradycardia pacing function)

  • Tailored to an individual's need based on existing co-morbidities and surgery

Monitoring and access

  • AAGBI monitoring but avoid placing wires/cables directly over subcutaneous CIED site
  • Arterial line may be necessary
  • ± Central line ± CO monitoring if significant cardiac disease or fluid shifts expected

Anaesthetic technique

  • Avoid features that increase risk of arrhythmia e.g. hypoxia, hypercapnia, electrolyte or acid-base disturbance
  • Avoid suxamethonium as may cause fasciculations that are mistaken for tachyarrhythmia
  • Avoid excessive negative or positive inotropy, especially drugs that may cause tachyarrhythmia
  • Cautious fluid therapy as fixed heart rate may preclude ability to respond to hyper/hypovolaemia

ICD

  • Switch off e.g. by EP or with magnet taped to chest wall
  • Have defibrillator pads already applied in an A-P fashion (or 10 - 15cm from the device)
    • Placing pads near the CIED can lead to excess current flow via the wires and damage to the myocardium
  • Manage arrhythmias as per ALS algorithms
  • At the end of the case either remove the magnet or have EP turn the device back on

Diathermy

  • Avoid diathermy where possible
  • Use bipolar diathermy preferentially
  • If unipolar diathermy is to be used then:
    • Diathermy plate far from CIED so that current won't flow through it
    • Short <5s bursts
    • 10s pauses between bursts
    • It should be used in cutting mode not coagulation mode

Risks with CIEDs

  • Electromagnetic interference
  • Lead dislodgement e.g. CVC insertion
  • Theoretical microshock via PPM lead
  • PPM failure and dysrhythmia

  • Continue to avoid features that increase risk of arrhythmia e.g. hypoxia, hypercapnia, electrolyte or acid-base disturbance
  • Appropriate temperature management; excessive shivering may trigger ICDs
  • Continuous monitoring until device re-instated to its pre-operative settings
  • Cardiac physiology review to:
    • Check any ICD which was de-activated by a magnet
    • Re-instate any functions that were intentionally halted
    • Alter pacing rate to better meet post-operative metabolic demands
  • Consider need for CCU or HDU