Defibrillation

Question 1

What is ventricular fibrillation?

Answer 1

Cardiac myocytes deploarize in an uncoordinated fashion –> does not result in an organized cardiac contraction

Question 2

What is defibrillation?

Answer 2

Application of an asynchronized electrical shock through the heart to terminate severe cardiac arrhythmias (VFib, pulseless VT).

–> causes simultaneous depolarization of the cardiac myocytes –> forces them into refractory period –> breaks cycle of uncontrolled firing –> if enough of the myocardium enters refractory period at the same time, the malignant rhythm is terminated –> underlying pacemaker rhythm can take over

Question 3

What are the types of defibrillators? What is the difference between them? Which one is recommended?

Answer 3

Monophasic vs. Biphasic

Monophasic –> positive current only
Biphasic –> positive current followed by negative current

biphasic –> requires less energy to successfully terminate arrhythmia

biphasic > monophasic

Other classification: external vs. internal defibrillator panels

Question 4

What are 3 defibrillation set-ups that can be used?

Answer 4

1. dorsal recumbency with paddles applied through operater on both sides of the thorax
2. lateral recumbency with long paddle (posterior paddle) slid unterneath the patients thorax (safer, less movement neccessary)
3. preplaced adhesive patches

Question 5

What needs to be remembered when an internal defibrillator is used?

Answer 5

• place saline soaked gazue between metal surface of defibrillator + heart to reduce risk of burn injury to the epicardium
• ideally performed after removal of pericardium

Question 6

When should defibrillation be attempted during CPB when a shockable rhythm is present?

Answer 6

if CPA duration ≤ 4min –> immediately
if CPA duration > 4min –> 1 2min cycle of CPR first before defibrillation attempt

Question 7

Why should a full cycle of CPR be done prior a defibrillation attempt if the CPA duration is > 4min?

Answer 7

If CPA > 4min then likely myocardial ischemia is present –> reduces likelihood of successful defibrillation

Question 8

What is a “single-shock approach”?

Answer 8

Chest compressions are immediately resumend after defibrillation for one full 2min cycle

Question 9

What is an “escalating energy protocol”?

Answer 9

Increase in energy by 50% if unsuccessful defibrillation attempt

Question 10

What should be otimized in refractory shockable rhythms?

Answer 10

Basic life support to decrease myocardial ischemia –> minimize interruptions of chest compressions

Question 11

What drugs can be considered in refractory shockable rhythms?

Answer 11

1. Lidocaine
2. Amiodarone
3. Ibutilide (not yet present in vetmed)

Question 12

What is the downside of using lidocaine in refractory shockable rhythms?

Answer 12

Lidocain can increase the defibrillation threshold (energy required for successful defibrillation) in monophasic defibrillators

Question 13

What is the benefit of using Ibutilide over amiodarone in refractory shockable rhythms?

Answer 13

fewer negative cardiovascular effects

Question 14

What energies are used for defibrillation in monophasic and biphasic defibrillators?

Answer 14

Question 15

What precautions should be made to make defibrillation as safe as possible?

Answer 15

• performed on insulated surface (rubber mat)
• inform people verbally of discharge attempt (CLEAR)
• visually ensure that no one is touching the patient
• avoid exessive gel application that may come in contact with the person defibrillating
• avoid alcohol (inflammable)

Question 16

What drug may be used in people to decrease the rate of recurrence of VFib?

Answer 16

Flunarizine