Pacemaker complication

(Redirected from Pacemaker basics)

Background

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

Nomenclature

Paced rhythm with characteristic wide LBBB and pacer spikes
PA Xray with pacemaker
Atrial Sensed Ventricular Paced ECG
Pacer type based on Xray
I II III IV V
Generic code for pacing modes[1]
Chamber(s) paced Chamber(s) sensed Response to sensing Rate modulation Multisite pacing
O = None O = None O = None O = None O = None
A = Atrium A = Atrium T = Triggered R = Rate modulation A = Atrium
V = Ventricle V = Ventricle I = Inhibited V = Ventricle
D = Dual (A+V) D = Dual (A+V) D = Dual (T+I) D = Dual (A+V)

Indications

  • Sinus Node Dysfunction-sinus bradycardia/arrest, sinoatrial block, chronotropic incompetence, a-fib.
  • Acquired AV block- 3rd degree block and 2nd degree type II
  • Chronic Bifascicular or Trifascicular block
  • After Acute MI-high mortality with persistent AV block post MI
  • Cardiac Resynchronization Therapy- Conduction delay (>150msec with mortality benefit) in chronic systolic heart failure further decreases EF, increases remodeling and increased MR.
  • Neurocardiogenic Syncope and Carotid Sinus Syndrome

Lead Location

  • Atrial
    • Right Atrial Appendage
    • Lateral RA wall
  • Right Ventricle
    • Apex
    • Septum
  • Left Ventricle (most commonly placed for cardiomyopathy or CHF)
    • Coronary veins along external LV wall via coronary sinus
    • Rarely, externally placed electrode during open surgical procedure

Additional Pacemaker Functions

  • Can record rhythm strips of AF, VT, and VF episodes for later review
  • 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 most often has 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 - with placement of a magnet over the device, the mode changes to asynchronous (i.e. DOO or VOO). Each brand has slightly different rates
    • Medtronic Inc.: 85 bpm; 65 bpm when battery is ready for replacement
    • St. Jude Medical Inc.: 98.6 bpm; 86.3 bpm when battery is ready for replacement
    • Boston Scientific Inc.: 100 bpm; 85 bpm when battery is ready for replacement
  • Manufacturer code on pulse generator is visible on Chest Xray

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

Differential Diagnosis

Pacemaker Malfunction

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

  • Pacemaker Mediated Tachycardia
    • Break with adenosine or magnet.[2]
      • Magnet placement will stop the sensing of the retrograde-conducted P waves driving PMT; this will immediately terminate the rhythm.
      • Recurrence of PMT after earlier termination means that the pacemaker settings need to be changed
    • Consider chest wall stimulation techniques[3] - transcutaneous pacing, isometric muscular exercise, precordial thump
  • Electrophysiology or cardiology consult is often needed
  • Contact a device representative for a full interrogation

Disposition

  • Resolved Pacemaker-mediated Tachycardia without recurrence - discharge
  • Infection - admission with MRSA coverage antibiotics, consult to cardiology, with likely replacement of pacemaker after 4-6 weeks of IV antibiotics
  • Pacing/sensing/capture issue - likely admit

See Also

References

  1. Bernstein AD. et al. The revised NASPE/BPEG generic code for antibradycardia, adaptive-rate, and multisite pacing. North American Society of Pacing and Electrophysiology/British Pacing and Electrophysiology Group. Pacing Clin Electrophysiol 2002 Feb; 25(2) 260-4. lmid:11916002
  2. EB Medicine- Sept 2014- Managing Pacemaker-Related Complications and Malfunctions in the Emergency Department
  3. Barold SS, Falkoff MD, Ong LS, Heinle RA. Pacemaker endless loop tachycardia: termination by simple techniques other than magnet application. Am J Med. 1988;85(6):817-22.