Defibrillation Threshold

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Physiology

  • First Phase results in capture and synchronization
  • Second Phase called 'burping'
  • Shorter second phase improves defibrillation efficacy
  • Membrane constant is 3.5 ms +/- 1 ms
  • Standard Tilts
    • St Jude 60/60, 50/50, 42/42
    • Medtronic 50/50
    • Guidant 60/50

Management of High DFTs

  1. Change polarity. Usually the distal coil is the cathode so change the distal coil to anode.
    1. In 88% of the cases RV anodal shock is the correct choice
  2. Remove SVC coil, which is attractive in patients with impendance <40.
  3. Add CS coil
  4. Waveform. Use tables to adjust the optimal second phase duration
  5. Look for Pneumothorax
  6. Watch meds. Mexiletine, coreg, amiodarone, viagra, venlafaxine increase DFTs. Add sotalol 40 to 320 mg QD to improve DFTs
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