Future Strategies of Defib led

Question 1

Define defibrillation

Answer 1

Non-synchronised random administration of high-energy shock during a cardiac cycle

Question 2

Define cardioversion

Answer 2

Synchronised administration of low-energy shock during the R waves or QRS complex of a cardiac cycle

Question 3

When is cardioversion indicated?

Answer 3

• Haemodynamically unstable Supraventricular Tachycardias (including Atrial Fibrillation and Atrial Flutter).
• Atrial Fibrillation or Flutter that is resistant to pharmacological therapies.
• Pulsed Ventricular Tachycardia

Question 4

Define: charge

Answer 4

Proportion of electrons to protons in a unit of matter (coulombs)

Question 5

Define: voltage

Answer 5

Difference in charge between two points (volts)

Question 6

Define: current

Answer 6

Rate at which charge is flowing (amps)

DC/AC

Question 7

Define: resistance

Answer 7

Material’s tendency to resist the current (ohms)

Question 8

Define: impedance

Answer 8

Combination of resistance and reactance.

Question 9

Define:
AED
ICD

Answer 9

Automated External Defibrillator.

Internal Cardioverter Defibrillator

Question 10

Monophasic and biphasic?

Answer 10

Shock delivered in one or two vectors

Question 11

Define: polarity

Answer 11

Degree of positivity or negativity in relation to voltage

Question 12

Anode/cathode

Answer 12

Anode = positive electorde -> flows to cathode (negative)

Question 13

Basic principle of defibrillation

Answer 13

Shock: stuns cardiac tissue - unexcitable, preventing uncoordinated, and allowing coordinated electrical activity to resume control.

Question 14

Theory of total extinction? Year?

Answer 14

1933: shock needs to stimulate all myocardium during any state (i.e. refractory, resting, repolarising etc)

Question 15

Critical mass hypothesis? Year?

Answer 15

1940: not all myocardium needs to be stimulated - based on the idea that a min mass of tissue required to maintain fibrillation.

Question 16

Vulnerable window and defibrillation thresholds - year/what?

Answer 16

1980s -
Shocks can induce arrthymias if shocked in vulnerable window (refractory period -> could cause depolarisation).
DFT = defibrillation threshold correlates with the ULV (upper limit of vulnerability)

Question 17

What does the DFT correlate with?

Answer 17

ULV

Question 18

ULV and LLV

Answer 18

Upper and lower limits of vulnerability

Question 19

Progressive depolarisation - year? and what?

Answer 19

1991
Optical mapping to look at causes of defib failure.

Theory: Progressively stronger shocks depolarise, progressively more refractory myocardium, to progressively prevent post-shock wavefronts, and prolong and synchronise post-shock repolarisation, in a progressively larger volume of the ventricle, to progressively decrease the probability of fibrillation after the shock

Question 20

What is the most complete explanation of the defib theories?

Answer 20

The virtual electrode hypothesis.
Shocks hyperpolarised cardiac tissues, in addition to depolarising tissues. Key message: different types of stimulation result in different virtual electrode patterns and heterogeneity of action potential duration.

Question 21

Why is this theory important?

Answer 21

Virtual Electrode Theory: identifies v es as secondary focusses to induce fibrillation

Question 22

Why are biphasic waveforms more superior?

Answer 22

Require less energy (therefore less damage for same effect).
Reverse polarity and distribution of virtual electordes, decreasing heterogeneity of post-shock tissue.

Question 23

Two forms of biphasic waveforms?

Answer 23

Biphasic Truncated Exponential Waveforms. (BTE)

Rectilinear Biphasic Waveforms. (RBW)

Question 24

What is the determinant of defibrillation success?

Answer 24

Current, not energy

Question 25

Why are varying currents produced in different people with fixed energy?

Answer 25

Transthoracic Impedance (TTI):

• Energy level
• Electrode size
• Interelectrode size
• Skin-electrode interface
• Phase of ventilation
• Tissue conductive properties

Question 26

How does each minute of delay to defib affect survival?

Answer 26

Reduces survival to discharge by 10-12%

Question 27

Energy of first shock? and after?

Answer 27

150 J, then increasing

Question 28

Where are the knowledge gaps in defib?

Answer 28

• The minimal acceptable first-shock energy level
• The characteristics of the optimal biphasic waveform
• The optimal energy levels for specific waveforms
• The best shock strategy (fixed versus escalating)