PACEMAKER

(see also section of  "Procedures in ER" )

Overview:

  1. 1.   Every PM has:
     
    1. pulse generator that contains battery (life span 5-15 years) and circuit
      (see below) to analyze  the rhythm 
    2. leads that sense and stimulate the myocardium. Leads can be unipolar or bipolar that on the EKG are distinguished  by size of spikes (high in unipolar).
       
  2. The circuit can pace (i.e. generate impulse) in fixed (asynchronous with heart rate) or demand mode (i.e. synchronous with heart rate and doesn't deliver stimuli if cardiac activity is present)

Indications:

  1. Classification  here is limited for ER use only and  not all the circumstances. Please see ACC and AHA for details.
     
  2. We will indicate with "PPM" if  PM is permanent and with "TPM" if PM is temporary.
     
    1. Asystole (early on). TPM.
    2. Symptomatic bradycardia or AVB. PPM or TPM
    3. MI with 2° or 3° AVB. PPM.
    4. MI with  BBB. TPM or PPM
    5. Bi- or Trifascicular block of  undetermined age during MI. TPM or PPM
    6. Bi- or Trifascicular block with symptoms (if asymptomatic PM is not needed). PPM.
    7. SSS or Tachy-Brady syndrome. PPM
    8. Torsade de Pointes. TPM.

Contraindications:

  1. Dig  toxicity
     
  2. Chronic Bi/Trifascicular block
     
  3. Technique:
    1. See chapter of  "Procedures in ER"

Vocabulary:

  1. Paces = generates impulse.
     
  2. Senses = detects chamber's activity.
     
  3. Mode of response = inhibits the PM activity if  PM senses that pt's heart  is above the predetermined rate or native QRS is present or triggers the PM if patient's activity is below the  predetermined rate and no QRS is present.
     
      1. First letter = chamber paced (V = ventricle).
      2. Second letter = chamber sensed ( V = ventricle, D = dual  i.e. both atrium and ventricle).
      3. Third letter = mode of response (I = inhibited).
      4. Fourth letter = programmability (R = rate responsive)
      5. Fifth letter = antitachycardic function ( S = shock)

Most common PM are:

      1. VVI - i.e. paces and senses the Ventricle and is inhibited by QRS produced by pt.
      2. DDD - i.e. paces and senses Dual chambers (i.e. atrium and ventricle) and can both trigger or inhibit. This PM is more physiological. Not to be used in A.fib.

EKG interpretation:

      1. This shows vertical spikes  followed by P wave (if atrium is paced) or  by QRS (if ventricle is paced).     
      2. Since R ventricle is paced EKG will show LBBB pattern making  it difficult to interpret new MI.        

PM Malfunction:

  1. Failure to Pace can be 2ry to battery or wire problem, new MI, antiarrhythmics, lyte abnormalities. Detected  by absence of spikes in bradycardic rhythm or presence of spikes without subsequent QRS complex i.e. there is no capture. Patients commonly present with  bradycardia/syncope.
     
  2. Failure to Sense (causes to consider as above). Detected on EKG by presence of spikes despite pt's own QRS complex (undersensing) or absence of  PM spikes because various activities are interpreted as cardiac activity (oversensing). The latter will present with lightheadedness, dizziness and syncope.

    The     Magnet is used to distinguish between pace and sensing problem when patient, known to have PM presents with no spikes on the EKG. When magnet is applied, this disactivates the sensing mode of the PM and enables us to distinguish whether the problem is  with oversensing and that is why no PM spikes are detectable or  if there is failure to pace (i.e. problem with the pulse generator) to explain absence of  PM spikes. When magnet is applied and patient now has spikes, we can deduct  that patient's native rate was faster  then PM rate or it was oversensing. If on the other hand no PM spikes are detected after magnet application the  pulse generator has failed. Note!! Magnet shouldn't be placed for more then 20 sec.
     
  3. PM mediated Tachycardia - occurs when PVC activates in a retrograde fashion the atrium that in  turn activates the ventricle and this starts  the tachycardic loop. This syndrome  occurs in DDD/DDDR.

Complications from PM insertion:

  1. Cardiac perforation. This can present with RBBB, hiccups (pacing the diaphragm), pericarditis or pericardial effusion/tamponade.
     
  2. Thrombosis
     
  3. Infection
     
  4. Pneumothorax
     
  5. Lead dislodgment/Fracture. PA and Lateral  chest Xray is helpful for diagnosis.

Do's and Don'ts:

  1. MRI interferes.
     
  2. Cell phones may interfere
     
  3. Electrocautery (endoscopy)
     
  4. Microwave is no longer a risk
     
  5. Difficulty to diagnose MI
     
  6. Standard BLS/ACLS protocol is applied

 

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