Defibrillation and Cardioversion

1
Defibrillation and Cardioversion

• EMS Professions
• Temple College

2
Defibrillation

• Mechanism
• Current depolarizes myocardium
• Induces asystole temporarily
• Allows one pacemaker to regain control

3
Defibrillation

• Factors to consider
• Duration of VF
• The longer VF lasts, the harder it is to cure
• The quicker the better
• Shock early-Shock often
• Likelihood of resuscitation decreases 7-10 with
  each passing minute

4
Defibrillation

• Factors to consider
• Myocardial environment/condition
• Hypoxia, acidosis, hypothermia, electrolyte
  imbalance, drug toxicity impede conversion
• Do NOT delay shock trying to correct problems

5
Defibrillation

• Factors to consider
• Heart size/body weight
• Pedi requirement lower than adult
• 2 J/kg initial shock
• 4 J/kg repeat shocks
• Direct size/energy relationship in adults unknown
• 200 to 360 J

6
Defibrillation

• Previous countershock
• Repeated shocks lower resistance
• Give three initial shocks in 30-45 sec
• One quickly after another with little time
  between

7
Defibrillation

• Factors to consider
• Paddle size
• Adults (large paddles)
• 10-13 cm diameter
• Pediatric (small paddles usually lt 1 yr)
• Children 8 cm
• Infants 4.5 cm

8
Defibrillation

• Use largest size that completely contacts chest
  without paddles touching
• Small paddles concentrate current, burn heart
• Large paddles reduce current density

9
Defibrillation

• Paddle placement
• One to right of sternum below clavicle Other to
  left of left nipple in anterior axillary line
• Reversing paddles marked apex--sternum does NOT
  affect defibrillation
• AP placement can be used to defib small children
  with adult paddles

10
Defibrillation

• Paddle-skin interface
• Cream, paste, saline pads, gelled pads
• Decreases resistance to current flow
• Avoid smearing or running bridges charge
• NEVER use alcohol!!!

11
Defibrillation

• Paddle contact pressure
• Firm pressure of 25 pounds
• Deflates lungs Shortens current path
• Do not lean on paddles They slip

12
Cardioversion

• Definitions
• Cardioversion
• Use of electrical shock to interrupt tachycardia
• Used in Non-Arrest patients only
• Only VF/VT (pulseless) can be defibrillated

13
Cardioversion

• Definitions
• Synchronized cardioversion
• Timing of shock to avoid peak of T-wave
• Prevents VF caused by delivering shock during
  vulnerable period

14
Cardioversion

• Indications
• Tachyarrhythmias which
• Cause or worsen hemodynamic compromise
• Cause or worsen ischemic heart disease
• Are resistant to drug therapy

15
Cardioversion

• Procedure
• Oxygen, ECG monitor, IV
• Patient must be on leads to cardiovert
• Sedate with Valium or Versed
• Do NOT make patient unresponsive

16
Cardioversion

• Procedure
• Activate synchronizer
• Observe marking of complexes
• May need to unsynchronize if
• Random synching occurs
• Double-synching occurs

17
Cardioversion

• Procedure
• Charge to desired energy setting
• Depress buttons Hold until discharge occurs
• If VF occurs, unsynchronize before defibrillating

18
Cardioversion

• If a patient is in VF, why might the
  defibrillator not discharge if the synchronizer
  is on?