CCM 205: Defibrillation Flashcards
What is the mechanism of action of Defibrillation?
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
Explain the difference between monophasic and biphasic defibrillators
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
How do you perform internal defibrillation
- 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
What is the current recommendation for timing of defibrillation during CPR in small animals?
- 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
If a defibrillation attempt was unsuccessful, what do you increase the J/kg to?
Increase by 50%
What are the contraindications for Lidocaine in a dog with Vfib?
If only monophasic defibrillation is available –> has been shown to increased the defibrillaiton threshold (i.e., how much energy is needed)