Implantable Cardioverter-Defibrillator complication

Background

Nomenclature

• All ICDs are also pacemakers (i.e. have pacing functionality) but pacemakers are not ICDs (i.e. do not have shocking functionality)

Parts

• Pulse Generator
  • Typically implanted in L upper chest wall
  • Contains device hardware and battery
  • Acts as a shocking electrode in defibrillation
• Leads
  • Insulated and antimicrobial-coated
  • Atrial lead
    • Pacing and sensing functionality
    • Typical bipolar (pacing and sensing are performed by two electrodes, located several millimeters apart at the tip of the lead)
  • Right ventricular lead
    • Pacing, sensing, and defibrillation functionality
    • Has one or two coils to facilitate defibrillation
      • Easily identified on Chest X-Ray and can hep differentiate an ICD from a pacemaker
    • Typical bipolar (pacing and sensing are performed by two electrodes, located several millimeters apart at the tip of the lead)
  • Left Ventricular Lead
    • Pacing and sensing functionality
    • Bipolar or unipolar (pacing and sensing are performed by one electrode at the tip of the LV lead and a second remote electrode, typically either one of the RV electrodes or the pulse generator)

Indications for ICD implantation

• Secondary Prevention
  • Previous episode of unstable VT or VF
    • Not indicated if VT/VF occurs <48 hours after myocardial infarction
  • Sustained VT in setting of cardiomyopathy or channelopathy
• Primary Prevention
  • Myocardial infarction >40 days ago with LVEF <30%
  • Cardiomyopathy + NYHA Functional Class II or III, and LVEF <35%
    • Controversy exists over applying the above criteria to non-ischemic cardiomyopathy
  • Patients with underlying disorders placing them at high risk for unstable VT or VF
    • Congenital long QT syndrome
    • High-risk HOCM
    • Brugada syndrome
    • ARVD
    • Other channelopathies
• Biventricular ICD (i.e. Cardiac Resynchronization Therapy)
  • Any of the above with intraventricular conduction delay of >120ms

Functions

• Can perform all functions of pacemakers
• Anti-tachycardia pacing
  • In response to a ventricular rate within a pre-set range (typically ~150-220 bpm), the device will compare the ongoing QRS morphology to a saved image of a QRS complex that is known to be a sinus beat; if the ICD algorithm determines that the ongoing morphology is significantly different (i.e. is unlikely to be a sinus tachycardia), it will deliver a series of paced beats at a rate slightly faster than the ongoing rate in an attempt to break the re-entrant cycle
  • A device will typically be programmed to attempt anti-tachycardia pacing several times; if unsuccessful, it will move on to defibrillation
• Defibrillation
  • Delivery of a large electrical shock (up to 42 joules) from one electrode to the other in response to VT or VF
• Magnet Mode
  • Placement of a magnet over the generator will deactivate anti-tachycardia pacing and defibrillation modes as long as the magnet is in place.
• Diagnostics
  • Records rhythm strips of AF, VT, and VF episodes for later review
    • If anti-tachycardia pacing or defibrillation has occurred, there will be a large alert on the device's interrogation home screen
  • Keeps track of % of paced vs intrinsic beats
  • Keeps a rate histogram, as well as % of time spent in AF

Methods to Identify Manufacturer

• Patient should carry a pocket card indicating manufacturer
• Manufacturer Hotline has patient database
  • Medtronic Inc. (1-800-328-2518)
  • St. Jude Medical Inc. (recently acquired by Abbott, Inc.) (1-800-722-3774)
  • Boston Scientific Inc. (1-800-227-3422)
• Magnet mode
  • Does not help differentiate ICDs (different than pacemakers)

Electromagnetic Interference

• Nonmedical
  • Cell phones: do not interact with device
  • Airport security: may trigger alarm, no alteration of activity
• Medical Sources
  • MRI: mostly safe, consult cards on device specific recs
  • Cardioversion: Use AP pads >8cm from device to minimize adverse effects
  • Unipolar Cautery - can cause sensing and pacing malfunction as well as reprogramming

Complications

Defibrillator Shocks

• Approximately 1/3 - 1/2 of ICD patients receive a shock within one year of placement
  • Generally described by patients as a powerful "kick to the chest"
  • Can be very distressing and a source of anxiety for patients

• Inappropriate Shocks
  • Causes
    • Misclassification by device of SVT or AF as VT or VF
    • Electrical Noise
    • Fractured Lead
  • Can be diagnosed by interrogation of device after a reported shock

• Phantom Shocks
  • The perception of a shock without a delivered shock
  • Generally described by patients as a mild electrical pain or pain around the defibrillator site
  • More common in patients who have never had an actual shock
  • Occurs in 9% of patients each year

Pacemaker Malfunctions

Problems with pocket

• Infection
  • Most commonly S. aureus or S. epidermidis
  • 2% local wound infection; 1% sepsis/bacteremia
• Hematoma
  • Typically occurs shortly after placement

Problems with leads

• Dislodgment
• Perforation (most commonly at RV apex)
• Infection can cause severe sepsis
• Tricuspid regurgitation
• Coiling (ie: Twiddler's Syndrome)
  

  Twiddler Syndrome after large pocket and defibrillator wires coiled around the generator

Failure to Capture

• Delivery of pacing stimulus without depolarization
  • Functional - refractory myocardium, desensitized local tissue around the lead
  • Medical - drugs, myocardial disease, electrolytes
  • Technical - insufficient device output, lead dislodgment, fracture, insulation defect, ventricular wall perforation
• Battery of End of Life (EOL)

Failure to Pace

• Failure to deliver a stimulus to the heart
  • Oversensing - most common cause: retrograde P’s, T’s, skeletal muscle myopotentials,
  • Crosstalk - type of oversensing where the ventricular lead senses atrial pacing stimulus, and ventilator output inhibited

Failure to Sense

• Normal function: a sensed myocardial depolarization greater than the programmed threshold causes inhibition of pacing
• Failure to sense results in a paced beat on top of an intrinsic beat (as the device is "unaware" of the intrinsic beat")
  • Voltages of patient's intrinsic QRS complex is too low to be detected
  • New intrinsic arrhythmia (AF has a smaller depolarization than sinus beat), AMI, electrolyte abnormalities, lead separation, battery depletion

Runaway Pacing

• Physiologic electrical activity (T waves, muscle potentials)
• External electromagnetic interference
• Signals generated by interaction of different portions of the pacing system
• Potentially life-threatening as it can cause V-Fib or (paradoxically) bradycardia due to failure to capture

Pacemaker Mediated Tachycardia

• Also known as Endless Loop Tachycardia
• Formation of a re-entrant circuit causing inappropriate tachycardia
  • Most commonly: paced ventricular beat -> retrograde AV node conduction -> intrinsic P wave -> device reacts to intrinsic P wave by looking for intrinsic QRS, but since AV node is now refractory it delivers a paced beat at the programmed P-R interval (typically ~200-250ms), starting the process anew
• Tachycardia does not exceed programmed upper limit rate on pacemaker

Evaluation

Work-Up

• BMP and Mg
• CXR
• ECG
• Troponin
• Interrogation
  • Each company has on-call representatives who will come interrogate a device 24/7 (phone numbers above)
  • Most cath labs will have machines capable of interrogating each brand

Expected ECG Patterns

• Absence of pacer artifact indicates intrinsic depolarization
  • With newer pacemakers, pacer spikes may not appear on some or all paced beats, depending on EKG machine
• Pacing artifacts preceding depolarizations indicate successful pacing and capture
• Leads in RV apex produce LBBB pattern with appropriate discordance
• New RBBB pattern may indicate lead in LV
• Bi-ventricular devices can produce paced QRS complexes that are either narrow or wide and bizarre, depending on device programming
• Simultaneous depolarization of ventricles produces dominant R wave in V1

Plain Film Findings

• Obtain PA/Lateral Films to confirm pulse generator, manufacturer, lead placement/number/integrity
• R atrial lead J shaped(tip medially on AP) entering right atrial appendage
• RV leads point downward with tip between left spine and cardiac apex--lateral XR shows inferior and anterior
• Coronary sinus lead- courses posteriorly on lateral XR
• Extra leads may be appropriately abandoned and capped
• ICD component appears as thickened shock coil

Management

• Reported Shock
  • If unable to prove a phantom shock, electrophysiology or cardiology consult is often needed
  • Interrogation is mandatory, either by an experienced clinician or by device representative
    • Some devices can be remotely interrogated; contact the respective company representative at the above phone numbers to discuss this possibility

• Repeated Shocks
  • Before placement of a magnet or changing the device parameters, you must determine if the shocks are appropriate (i.e. the patient is in VT storm or having recurrent episodes of VF) or inappropriate
    • If it is determined that the shocks are inappropriate, a magnet will deactivate the shocking function while placed over the device
  • Electrophysiology consult

• Pacemaker Mediated Tachycardia
  • Break with adenosine - magnet will not fix PMT in a patient with a defibrillator

Disposition

• Consider discharge if:
  • Proven Phantom Shock
  • Resolved Pacemaker Mediated Tachycardia
  • Single shock only AND Currently asymptomatic AND No concerning associated symptoms (e.g. chest pain, dyspnea, syncope)
    • Ensure patient has Electrophysiology/Cardiology follow-up
    • Consider Electrophysiology/Cardiology consult
• Admit all others

See Also

• Pacemaker complication
• Medical device complications

External Links

• ECG Pointers: ICDs and when they malfunction