CCM 205: Defibrillation

Question 1

What is the mechanism of action of Defibrillation?

Answer 1

Electrical current causes simultaneous depolarization of the cardiac myocytes - forcing them into the refractory period

If enough myocytes enter the refractory period –> malignant rhythm stops propagating and underlying pacemaker rhythm can take over

Question 2

Explain the difference between monophasic and biphasic defibrillators

Answer 2

Monophasic - single pulse of positive current (i.e., from one paddle to the other), unidirectional

Biphasic - first positive current, followed by negative current - the oppositve direction
* requires lower total energy - i.e., lower risk of myocardial damage
* case reports where monophasic currents were not successful but biphasic was - potential more effective as well

Question 3

How do you perform internal defibrillation

Answer 3

• requires access to chest - i.e., open chest
• internal paddles - sterilized - wand-like with smaller surface area
• placed on either side of the heart with saline soaked gauze inbetween heart and paddle - to prevent burn injury
• ideally remove pericardium first

Question 4

What is the current recommendation for timing of defibrillation during CPR in small animals?

Answer 4

• if cardiac arrest witnessed and shockable rhythm present - defibrillate immediately
• chest compressions while defibrillator is prepared
• if malignant rhythm was present for >4 min - one cycle of CPR should be performed first

Question 5

If a defibrillation attempt was unsuccessful, what do you increase the J/kg to?

Answer 5

Increase by 50%

Question 6

What are the contraindications for Lidocaine in a dog with Vfib?

Answer 6

If only monophasic defibrillation is available –> has been shown to increased the defibrillaiton threshold (i.e., how much energy is needed)