Perioperative Management of Implantable Cardiac Devices

Key questions:

  • What is the EMI risk of the surgery?
  • How dependent is the patient?

Implantable cardiac devices include:

ICDs generally discharge ~40J.

Risks

Include:

  • Electromechanical interference
    External electrical stimuli (e.g. due to diathermy) may interfere with pacemaker function in two ways:
    • Over-sensing
      The pacemaker interprets EMI as intrinsic activity, and does not pace despite the intrinsic rhythm being inadequate. This:
      • Will result in the underlying rhythm being the actual rhythm
        Extent of haemodynamic compromise depends on the nature of the underlying rhythm.
    • Under-sensing
      Pacemaker does not detect intrinsic activity, and paces over an intrinsic rhythm. This:
      • Leads to over-pacing
      • May cause malignant arrhythmias as if an R-on-T occurs

Clinical Manifestations

Includes both:

  • Nature of surgery
  • Device assessment

Surgery Assessment

EMI risk of the procedure:

  • Electrical
    • Diathermy
      • Particularly unipolar
        Ensure pad is placed such that current does not run through device.
      • Location
        Within 15cm is high risk.
    • Evoked potential monitors
    • External defibrillation
    • Radiofrequency ablation
    • ECT
  • Magnetic
    • MRI
  • Mechanical
    • Shivering
    • Extracorporeal shock-wave lithotripsy
    • Large tidal volumes

Device Assessment

Evaluation of pacemakers should consider:

  • Indication for pacing
  • Dependency on pacing
    What proportion of time is the patient actively paced.
    • Underlying cardiac activity on ECG
      No underlying activity, or a non-perfusing rhythm, is at higher risk.
    • Use of antiarrhythmics
  • Pacemaker function and setup
    • Presence of rate-responsive pacing modes
      Pacemaker detects a certain event (usually motion, implying exertion) and ↑ paced rate to compensate.
    • Magnet mode effect
      Usually places the devices into DOO or VOO at a set rate.
    • Last pacing check
      Within 12 months.
    • Pacing threshold
      Amplitude should be at least double the threshold.
    • Lead impedance
      High impedance suggests damage, excessively low impedance suggests insulation defect.
    • Battery life
  • Lead setup
    • Number of leads
      May be 1, 2, or 3.
    • Biventricular pacing
      Biventricular pacing is used for cardiac resynchronisation therapy, and suggests the patient has HFrEF. Indicated with LVEF <35% with LBBB and NYHA III/IV despite optimal medical therapy.
    • Unipolar or bipolar leads
      Unipolar leads are usually present in older models. In a unipolar lead, the lead is the cathode and the device is the anode; whilst a bipolar lead has both anode and cathode. Unipolar leads are associated with more myocardial scarring and ↑ impedance.

Evaluation of AICDs should consider:

  • Last pacing check
    Within 6 months.
  • Indication
  • Dependence
    • Shock history
  • Magnet mode effect
    Usually disables the ICD.

Investigations:

  • ECG
    • Pacing dependency
    • Pacing capture
  • CXR
    • Lead placement
    • Number of leads
    • Presence of ICD
      Identified by use of shock coils on lead and a capacitor in the device.

Management

Includes:

Pre-operative

General measures:

  • Measure and correct electrolytes
  • Continue prescribed anti-arrhythmics

Consider re-programming pacemaker functions if:

  • Significant pacemaker dependency and EMI present
  • Modes need to be adjusted
    • Rate-responsive modes will be triggered incorrectly:
      • Respiratory rate
      • Accelerometry
    • Sleep/rest mode
      Fall in HR and CO overnight, if late surgery is planned.
  • Augmentation of CO and DO2 helpful

Consider re-programming an AICD if:

  • EMI is expected
  • Movement from shock could be hazardous
    Patients who have defibrillation or antitachycardia functions inactivated should be on continuous monitoring with external defibrillation equipment readily available, and have their therapy reactivated prior to discharge.

Consider a magnet instead of re-programming if:

  • Magnet response present
    Exists in most devices planted after 2000.
  • Magnet response known
    Magnet function can be disabled in some Boston Scientific and St. Jude devices.
  • Magnet effect is desirable
  • Patient is supine
  • Magnet can be accessed:
    • Observed
    • Removed in case of arrhythmia

Intraoperative

Anaesthesia:

  • C
    • Avoid precipitants of arrhythmia
      • Hypoxia
      • Hypercapnoea
      • Electrolyte abnormalities
    • Have defibrillation equipment available
    • Consider induction with pads on if high risk
      Pads should be placed at least 8cm from the device.
    • Consider arterial line
    • Consider cardiac output monitor
  • D
    • Nerve stimulators can be used if:
      • Distant from the device
      • Stimulus is not parallel to pacemaker circuit
  • E
    • Avoid suxamethonium

Surgery:

  • Use bipolar diathermy if possible
  • If using unipolar diathermy:
    • Ensure the return path does not cross the ICD
    • Use in short (1-2s) bursts
    • Use cutting rather than coagulation
  • Have a magnet available

Post-operative

  • Reactivate any disabled functions
    Electrophysiologist should check the patient prior to departure from recovery.
  • Check the device if a magnet has been used
    • AICD should be examined by an electrophysiologist to confirm functions have reactivated
    • Resumption of normal pacing function can be checked at bedside with an ECG

References

  1. Bryant HC, Roberts PR, Diprose P. Perioperative management of patients with cardiac implantable electronic devices. BJA Educ. 2016;16(11):388-396. doi:10.1093/bjaed/mkw020
  2. Bersten, A. D., & Handy, J. M. (2018). Oh’s Intensive Care Manual. Elsevier Gezondheidszorg.