205 Defibrillation

Question 1

The application of an asynchronous electrical current through the heart in order to terminate a rhythm of ventricular fibrillation or pulseless ventricular tachycaradia

Answer 1

Debrillation

Question 2

A ___________ and __________ myocardium improves the chances of defibrillation success.

Answer 2

Well-oxygenated
Perfused

Question 3

_______ ________ of shockable rhythms with an electrical defibrillator carries the best chance of success

Answer 3

Early treatment

Question 4

__________ occur when cardiac myocytes depolarize in an uncoordinated fashion

Answer 4

Ventricular fibrillation

Question 5

Typically, depolarization starts at the __________ _____ and spreads in an organized fashion throughout the conducting apparatus of the heart, causing sequential contraction of the cardiac chambers.

Answer 5

Pacemaker node

Question 6

In the context of cardiopulmonary resuscitation, defibrillation is indicated to:

Answer 6

Treat patients in ventricular fibrillation or less commonly, pulseless ventricular tachycardia

Question 7

The application of an electrical current causes simultaneous depolarization of the cardiac myocytes to force them into:

Answer 7

their refractory period, which breaks the cycle of uncontrolled firing of cells, which is the cause of a fibrillating rhythm

Question 8

If enough of the myocardium enters the refractory period at the same time:

Answer 8

The malignant rhythm is terminated and the underlying pacemaker rhythm can take over

Question 9

What are the two main types of defibrillator units:

Answer 9

Monophasic
Biphasic

Question 10

In a monophasic defibrillator, the machine generates

Answer 10

A positive current only

Question 11

A biphasic device generates

Answer 11

A positive followed by a negative current

Question 12

While both types of defibrillators can be effective in terminating ventricular fibrillation or pulseless vtach, studies have demonstrated which to be better?

Answer 12

Lower energy requirements for successful arrhythmia termination using a biphasic device

Question 13

By switching out the type of defibrillator paddle attachment, many defibrillators can be used for either

Answer 13

External or internal defibrillation

Question 14

Alcohol should not be used during defibrillation due to

Answer 14

risk of fire when the electrical charge is applied

Question 15

List the three arrangements of contact paddles available

Answer 15

1. Most common: system of two handheld paddles. The animal is placed into dorsal recumbency, and the person performing defibrillation uses the paddles to stabilize the animal and prevent it from falling to either side. During the technique, operator has to take great care to avoid coming into contact with any part of the patient while discharging the defibrillator current.
2. In lateral recumbency- a long paddle (posterior paddle) that can be slide underneath the patient is placed first and a conventional paddle is then applied to the opposite side of the chest, and then defibrillation performed.
3. Preplaced adhesive patches that connect directly to the defibrillator. This requires clipping of the fur and preparation of the skin and so is typically only used in scenarios where the need for defibrillation is expected and planned for, such as interventional cardiology procedures, rather than in an emergency room setting.

Question 16

Internal defibrillator paddles are described as:

Answer 16

Sterile, wand-like with a smaller contact area

Question 17

How do you apply internal defibrillator paddles?

Answer 17

A thin layer of saline soaked gauze is placed between the metal surface of the paddle and the heart to reduce the risk of causing burn injury to the epicardium.
It is ideally performed after removal of the pericardium.

Question 18

If the arrest is of four minute duration or less, usually meaning it was a witnessed event and a shockable rhythm was/is present, when should defibrillation be utilized?

Answer 18

Immediately. The only delay should be the time it takes to prepare for defibrillation. If there is a delay, begin/continue with chest compressions. The more prompt the defib, the higher the chance of success.

Question 19

If the cardiac arrest is of a longer duration than four minutes, then it is likely that what will be present? What does that change?

Answer 19

Significant myocardial ischemia, defibrillation success will be less likely. A cycle of CPR prior to defib is recommended.

Question 20

Most published recommended defibrillation energies are for what kind of defibrillator?

Answer 20

Monophasic

biphasic may require slightly lower initial energy settings

Question 21

What is the first step for patients who are refractory to defibrillation?

Answer 21

Optimize basic life support

Question 22

A single shock approach is usually performed because?

Answer 22

Minimizing interruptions to chest compressions.
A shock is applied, then chest compressions immediately resumed for one cycle prior to another attempt at defibrillation

Question 23

Typically, after an unsuccessful defibrillation, the next shock is delivered with a:

Answer 23

~50% increased in energy

Question 24

Increasing the energy of the next shock is called an ______ _____ _____

Answer 24

Escalating energy protocol

Question 25

What two drugs are examples of what have been recommended as adjunctive treatments in patients with refractory ventricular fibrillation, along with chest compressions and electrical defibrillation.

Answer 25

Lidocaine (may increase defibrillation threshold- defib energy required with monophasic defibrillators)
Amiodarone (drug of choice)
Usually reserved for use until two to three attempts at defibrillation have been unsuccessful

Recent studies suggest ibutilide may be promising, which may have fewer negative cardiovascular effects than amiodarone. This drug has not been used clinically for this indication in veterinary medicine.

Question 26

Describe at least 3 precautions when performing defibrillation.

Answer 26

1. Performed on an insulated surface (ie rubber mat)
2. Inform about impending discharge by announcing CLEAR prior to delivering shock.
3. Visually ensure no one is touching the patient or table prior to shock delivery
4. Avoid excessive contact gel getting on their hands or arms that could conduct a shock back towards them
5. Good contact between paddles and patient reduces the risk of arcing of the current.
6. Strictly avoid the use of alcohol as a contact agent
7. Extra care when using conventional paddles in dorsal recumbency as the animal may slip or the limbs can move during current application, potentially bringing animal in contact with the operator or other staff members

Question 27

While rare, what is a potentially delayed consequence or complication to defibrillator use in the patient?

Answer 27

Burns
Monitor the skin where the pads or paddles were applied over the next several days

Question 27

What monitoring is indicated following post-ROSC care following defibrillation?

Answer 27

Extra attention paid to monitoring ECG rhythm and the potential need for antiarrhythmic therapy
Recurrence of fibrillation can occur, and the risk can be reduced by appropriate antiarrhythmic therapy and hemodynamic optimization