Fundamentals of electrophysiology

Question 1

Define ‘Automaticity’.

Answer 1

The cells ability to spontaneously depolarise or the ability to initiate an impulse.

Question 2

What is the resting membrane potential of a P-cell?

Answer 2

-50 to -60mV.

Question 3

Is progression of SND to CHB considered likely or unlikely?

Answer 3

Unlikely.

Question 4

Sarcoidosis / Giant cell myocarditis accounts for what % of unexplained AV block in <55yr old pts?

Answer 4

25%.

Question 5

Which type of 2nd degree AVB is most likely to progress to CHB?

Answer 5

2nd Degree Mobitz II.

Question 6

List 4 examples of reversible AV block.

Answer 6

1. Lyme Carditis disease
2. Drug toxicity
3. Vagotonia
4. Hypoxia

Question 7

What is the strongest predictor of whether bifascicular block will advance to CHB?

Answer 7

Symptoms are the strongest predictor of disease progression.

Question 8

Will pacing for bifascicular block improve mortality?

Answer 8

No.

It only improves symptoms.

Question 9

Define ‘Resting Membrane Potential’.

Answer 9

Intracellular charge is more negative than extracellular charge.

Due to the cell membrane being more permeable to both K and NA+.

Question 10

Define cellular ‘Depolarisation’.

Answer 10

Intracellular charge becomes less negative than extracellular charge due to the exchange of ions across the cell membrane.

Question 11

Define ‘Repolarisation’.

Answer 11

Intracellular charge to return to a more negative state than extracellular charge due to re-exchange of ions across the cell membrane.

Question 12

Phase 0 is otherwise known as?

Answer 12

Rapid Depolarisation.

Question 13

Phase 1 is otherwise known as?

Answer 13

Early Repolarisation.

Question 14

Phase 2 is otherwise known as?

Answer 14

Plateau Phase.

Question 15

Phase 3 is otherwise known as?

Answer 15

Rapid Repolarisation.

Question 16

Phase 4 is otherwise known as?

Answer 16

Resting Phase.

Question 17

During Phase 0 (Rapid Depolarisation), which ions flow into the cell and how quickly?

Answer 17

Sodium moves rapidly in.

Calcium moves slowly in.

Question 18

During Phase 1 (Early Repolarisation), which ions flow in/out of the cell?

Answer 18

Sodium channels close - Membrane is impermeable to sodium.

Calcium moves slowly in.

Activation of transient outward potassium current (Ito)

Question 19

During Phase 2 (Plateau Phase), which ions flow in/out of the cell?

Answer 19

Calcium moves slowly in.

Potassium moves slowly out.

Question 20

During Phase 3 (Rapid Repolarisation), which ions flow in/out of the cell?

Answer 20

Calcium channels close - Membrane is impermeable to calcium (& sodium still).

Potassium moves rapidly out.

Question 21

During Phase 4 (Resting Phase), which ions flow in/out of the cell?

Answer 21

Active transport pumps Potassium in.

Active transport pumps Sodium out.

Membrane still impermeable to both Calcium & Sodium.

Question 22

What phase of the cardiac cycle is responsible for myocardial contraction?

Answer 22

Phase 0.

The cellular charge changing from negative to positive triggers contraction.

Question 23

When combined, which phases equate to the Absolute Refractory Period?

Answer 23

Phases 0, 1, 2 and early phase 3.

Question 24

When combined, which phases equate to the Relative Refractory Period?

Answer 24

Late phase 3 and phase 4.

Question 25

The following statement best defines which refractory period? 'The cell cannot accept a stimulus no matter the strength'.

Answer 25

Absolute Refractory Period (AKA Effective Refractory Period). ## Footnote *The cell cannot accept a stimulus due to cellular supersaturation of ions.*

Question 26

The following statement best defines which refractory period? 'The cell can be stimulated but requires a greater than normal stimulation strength'

Answer 26

Relative Refractory Period. ## Footnote *This is due to cellular saturation of ions returning to baseline but isnt yet at true baseline.*

Question 27

Define **'Excitablity'**.

Answer 27

Threshold at which a cell will respond to a stimulus / Cells ability to respond to an impulse.

Question 28

Define **'Conductivity'**.

Answer 28

How well the cell passes on a stimulus / Cells ability to transmit an impulse.

Question 29

Under normal resting conditions, what is the automatic firing rate of the SA Node?

Answer 29

60-100bpm.

Question 30

Below what heart rate is considered Sinus Bradycardia?

Answer 30

\<60bpm.

Question 31

Above what heart rate is considered Sinus Tachycardia?

Answer 31

\>100bpm.

Question 32

How many internodal tracts are there in the Right Atrium?

Answer 32

x3 (Anterior, Middle, Posterior).

Question 33

Define the purpose of the Bachmanns Bundle.

Answer 33

To provide rapid impulse conduction to the **Left Atrium**. ## Footnote *This facilitates synchronous contraction of both the left and right Atria.*

Question 34

Define where the AV Node is located.

Answer 34

Inferior Right Atrium near osmium of Coronary Sinus. ## Footnote *Apex of Triangle of KOCH.*

Question 35

What does the AV Node do to the impulse it receives from the Atria and why?

Answer 35

Delays the signal for approximately 120 msec. This allows for ventricular filling respondent to atrial contraction.

Question 36

What is the secondary purpose of the AV Node with regards to rate control?

Answer 36

AVN has decremental conduction properties, which prevents rapid impulses originating in the atria from reaching the ventricles. ## Footnote *E.g. 250bpm Atrial-Flutter conducted 1:1 would prevent adequate ventricular filling. AVN blocks these impulses in a typically 2:1 or 3:1 fashion, which facilitates stable haemodynamics.*

Question 37

What electrical anatomical structure follows the AV Node?

Answer 37

The bundle of HIS follows the AV Node.

Question 38

What is the automatic firing rate of the bundle of HIS.

Answer 38

40-60 bpm.

Question 39

# True / False The left bundle branch divides into two arms vs. the right bundle branch's one arm.

Answer 39

True. ## Footnote *The left has both the Anterior and Posterior Fascicle.*

Question 40

# True / False Left bundle branch conduction velocity exceeds that of the right bundle branch.

Answer 40

True. ## Footnote *In order to deploarise the greater amount of tissue comprising the left ventricle, while maintaining synchronousity to the smaller right ventricle.*

Question 41

What is the final structure of the electrical conduction system.

Answer 41

Purkinje Fibres. ## Footnote *Responsible for innervating deep into the ventricular wall.*

Question 42

What is the automatic firing rate of the Purkinje Fibres?

Answer 42

15-40bpm.

Question 43

What is the most likely type of arrhythmia described below. 'Re-entry circuits within the atrium, AVN excluded, fires between 150-250bpm'.

Answer 43

Atrial Flutter.

Question 44

What structure within the Right Atrium precipitates the majority of Atrial Tachycardias?

Answer 44

Crista Terminalis.

Question 45

Describe the Crista Terminalis structure.

Answer 45

Endocardial ridge that divides smooth atrial tissue and the trabeculated appendage. ## Footnote *The meeting of different tissues with differing conduction properties forms the substrate for the majority of tachycaridas.*

Question 46

# Increase / Decrease Predominant sympathetic SA node innervation will result in which HR response?

Answer 46

Increased Heart Rate.

Question 47

# Increase / Decrease Predominant parasympathetic SA node innervation will result in which HR response?

Answer 47

Decreased Heart Rate.

Question 48

What is the most common type of SVT treated today?

Answer 48

**A**trio-**V**entricular-**N**odal-**R**e-entrant-**T**achycardia (AVNRT).

Question 49

What is the most likely type of arrhythmia described below? 'Re-entrant circuit of two anatomically & physiologically separate pathways confined to the AV node'.

Answer 49

**AVNRT**.

Question 50

Structurally, what is the major way AVNRT differs from AVRT?

Answer 50

AVNRT is a micro re-entry pathway encased within the AV Node. ## Footnote *AVRT involves accessory pathways located outside the AV node and is known as a macro circuit.*

Question 51

In the context of AVNRT, which pathway is described below? 'Has a relatively short **A**bsolute **R**efractory **P**eriod and conducts slowly'.

Answer 51

The slow pathway.

Question 52

In the context of AVNRT, which pathway is described below? 'Has a relatively long **A**bsolute **R**efractory **P**eriod and conducts quickly'

Answer 52

The fast pathway.

Question 53

For AVNRT to propagate, a person is said to have what type of nodal physiology?

Answer 53

Dual Nodal Physiology. ## Footnote *i.e. Both a Fast and Slow Pathway are present and functional.*

Question 54

What is the **typical** route for AVNRT?

Answer 54

**Antegrade** down the slow pathway. **Retrograde** up the fast pathway.

Question 55

What is the **atypical** route for AVNRT?

Answer 55

**Antegrade** down the fast pathway. **Retrograde** up the slow pathway.

Question 56

# True / False No P-wave is visible during **typical** AVNRT due to simultaneous firing of the Atria and Ventricles.

Answer 56

True. ## Footnote *P-wave is usually buried in the QRS complex and thus invisible on a surface ECG.*

Question 57

# True / False No P-wave is visible during **atypical** AVNRT due to simultaneous firing of the Atria and Ventricles.

Answer 57

False ## Footnote *P-wave is usually visible in the T-wave.*

Question 58

Delta-waves on an ECG are typically indicative of what congenital condition?

Answer 58

Wolff-Parkinson-White Syndrome (WPW).

Question 59

What structures must be present to facilitate AVRT.

Answer 59

Accessory Pathways.

Question 60

# True / False If an Accessory Pathway conducts retrograde only, a delta wave will be observable on the ECG.

Answer 60

False. ## Footnote *Any electrical activation will be buried by the QRS complex. Only Antegrade AP conduction will show delta waves.*

Question 61

If an Accessory Pathway conducts retrogradely only, it is said to be what type of pathway?

Answer 61

Concealed. ## Footnote *As there are no ECG markers visible. They are 'concealed' by the QRS complex.*

Question 62

# True / False Pre-excitation highlights early activation of the ventricular myocardium respondent to conduction through an accessory pathway ahead normal conduction through the AV Node.

Answer 62

True. ## Footnote *A slurred upstroke on the QRS shows early activation in the region of the AP. As conduction through the AV Node occurs, the QRS 'catches up' as the remainder of the ventricular myocardium depolarises.*

Question 63

What are 3 common ECG hallmarks of Wolff Parkinson White.

Answer 63

1. Short PR Interval (\<120ms) 2. Broad QRS due to delta wave (\>120ms) 3. Abnormal T-waves

Question 64

# Yes / No Can delta waves be seen during **Orthodromic** AVRT?

Answer 64

No. ## Footnote *The impulse is travelling **antegrade** through the AV Node and **retrograde** up the AP. Thus any ECG signals are concealed by the QRS.*

Question 65

# Yes / No Can delta waves be seen during **Antidromic** AVRT?

Answer 65

Yes. ## Footnote *The impulse is travelling **retrograde** up through the AV Node and **antegrade** down the AP. Thus pre-excitation of the QRS will be seen.*

Question 66

Is Orthodromic AVRT considered Typical or Atypical?

Answer 66

Typical. ## Footnote *It's the most common type.*

Question 67

Is Antidromic AVRT considered Typical or Atypical?

Answer 67

Atypical. ## Footnote *It's the less common type.*

Question 68

What arrhythmia is best described below? 'Atrial Rhythm is regular at a rate of 250-350bpm'.

Answer 68

Atrial Flutter.

Question 69

# True / False Atrial Flutter is a Micro re-entrant circuit contained predominantly within the left atrium.

Answer 69

False. ## Footnote *It is a **Macro** re-entrant circuit most commonly contained within the right atrium.*

Question 70

# True / False Typical Flutter gives rise to a sawtooth baseline pattern on an ECG.

Answer 70

True.

Question 71

# True / False Atypical Flutter is commonly negative in inferior leads II, III, and AVF.

Answer 71

False ## Footnote *Typical Flutter will commonly be negative in the inferior leads II, III, and AVF.*

Question 72

# Typical / Atypical The following statement best describes which flutter type? 'Substrate is an anatomically distinct area of delayed conduction located between the IVC, CSos and and Tricuspid Valve Annulus'.

Answer 72

Typical Flutter. ## Footnote *Atypical Flutter commonly forms around other areas of block to conduction.*

Question 73

Which ECG leads are best for observing a sawtooth baseline respondent to flutter?

Answer 73

Typically V1 or Inferior leads II, III, and AVF.

Question 74

Which is commonly faster: Typical or Atypical Flutter?

Answer 74

Atypical Flutter is generally faster than Typical.

Question 75

What arrhythmia is best described by the following statement? 'Irregular firing of the Atria and resultantly irregular contraction of the Ventricles'.

Answer 75

Atrial Fibrillation (with intrinsic conduction).

Question 76

What arrhythmia is best described by the following statement? 'Impulse originates in the Ventricles and regularly fires between 100-200bpm'.

Answer 76

Ventricular Tachycardia.

Question 77

List the 3 categories associated with structural based VT.

Answer 77

1. Automatic 2. Re-entrant 3. Triggered

Question 78

List the 2 categories associated with idiopathic non-structural VT.

Answer 78

1. RVOT (most common) 2. Fascicular VT ## Footnote 10% of all VT occurs in pts. with no apparent structural heart disease

Question 79

# True / False Automatic based VT is most commonly associated with myocardial scarring.

Answer 79

False. ## Footnote Automatic VT = Acute metabolic crisis (Dialysis) or post MI reperfusion. Re-entry VT = Myocardial Scarring.

Question 80

# True / False Re-entrant VT is most commonly associated with myocardial scarring.

Answer 80

True. ## Footnote *Scarring post MI is the most common substrate for re-entrant VT.*

Question 81

# Automatic / Triggered Which VT type is described best by the following statement? 'VT caused by leakage of IONS during the action potential and occurs spontaneously'.

Answer 81

Automatic. ## Footnote *Triggered is also caused by leakage of IONS during AP, however rarely occurs spontaneously. It almost always requires a premature impulse.*

Question 82

# Automatic / Triggered Which is described best by the following statement. 'VT caused by leakage of IONS during the action potential and occurs following a premature beat'.

Answer 82

Triggered. ## Footnote *Automatic is also caused by leakage of IONS during AP, however doesn't require a premature impulse. It almost always occurs spontaneously.*

Question 83

What arrhythmia is best described by the following statement? 'Chaotic irregular impulses that originate in the Ventricles'.

Answer 83

Ventricular fibrillation.

Question 84

The statement below best defines what quantity? 'Unit of electric current (flow of 1 coulomb per sec)'.

Answer 84

The Ampere.

Question 85

The statement below best defines what quantity? 'Unit of electric charge'.

Answer 85

The Coulomb.

Question 86

The statement below best defines what quantity? 'Unit of electric resistance'.

Answer 86

The Ohm.

Question 87

The statement below best defines what quantity? 'Unit of electric potential and electromotive force'.

Answer 87

The Volt.

Question 88

The statement below best defines what quantity? 'Unit of frequency'.

Answer 88

The Hertz.

Question 89

The statement below best defines what quantity? 'Unit of capacitance' (Ability of body to store charge).

Answer 89

The Farad.

Question 90

The statement below best defines what quantity? 'Unit of Energy'.

Answer 90

The Joule (1J per second = 1 Watt)'.

Question 91

V = I x R describes what law?

Answer 91

OHMS Law. ## Footnote *V = Power in Voltage / I = Current in Amperes / R = Impedance in Ohms.*

Question 92

E = V x I x T describes what?

Answer 92

The Energy Equation. ## Footnote *E = Energy in Joules / V = Power in Voltage / I = Current in Amperes / T = Time in seconds.*

Question 93

# True / False E = V x I x T can also be written E = V x Q.

Answer 93

True. ## Footnote *Charge (Coulomb) = Current (Ampere) x Time **Thus** I x T = Q.*

Question 94

What is the equation used to calculate battery longevity?

Answer 94

(114 x Battery capacity in Ampere hrs) / Current drain in micro Amperes (uA).

Question 95

What is the formula required in order to calculate energy usage of a device?

Answer 95

(Voltage squared / resistance) x pulse width.

Question 96

# True / False Doubling the output voltage equates to a four fold increase in energy drain.

Answer 96

True. ## Footnote *Hence setting a lower voltage and higher pulse width is almost always desirable.*

Question 97

# True / False Doubling the output pulse width equates to a four fold increase in energy drain.

Answer 97

False. ## Footnote *Doubling the pulse width **only** doubles the energy drain. Hence setting a lower voltage and higher pulse width is almost always desirable.*

Question 98

With respect to electronics, what does the following symbol pertain to? 'A'

Answer 98

The Ampere. ## Footnote *The unit of electrical current.*

Question 99

With respect to electronics, what does the following symbol pertain to? 'C'

Answer 99

The Coulomb. ## Footnote *The unit of electrical current.*

Question 100

With respect to electronics, what does the following symbol pertain to? 'Ω'

Answer 100

The Ohm. ## Footnote *The unit of electrical resistance.*

Question 101

With respect to electronics, what does the following symbol pertain to? 'V'

Answer 101

The Volt. ## Footnote *The unit of electrical potential.*

Question 102

With respect to electronics, what does the following symbol pertain to? 'Hz'

Answer 102

The Hertz. ## Footnote *The unit of Frequency.*

Question 103

With respect to electronics, what does the following symbol pertain to? 'F'

Answer 103

The Farad. ## Footnote *The unit of electrical capacitance.*

Question 104

What is the resting membrane potential of a Cardiomyocyte?

Answer 104

-90mV. ## Footnote *Remember a P-cell is -50 to 60mV.*

Question 105

Which of the 5 Phases of Action Potential is considered 'Repolarisation'?

Answer 105

Phase 3. ## Footnote *Outward flow of Ions exceed inward flow of Ions.*

Question 106

# True / False Cells capable of spontaneous automaticity exhibit gradual upward drift in transmembrane potential until threshold is reached.

Answer 106

True. ## Footnote *Examples of such cells are SA and AV Nodal Cells.*

Question 107

# True / False The resting voltage of P-Cells is more negative than that of Cardiomyocytes.

Answer 107

False. ## Footnote *P-Cell = -50 to -60mV / Cardiomyocyte = -90mV.*

Question 108

Why is the resting voltage of Cardiomyocytes is more negative than that of P-Cells?

Answer 108

P-Cells posses fewer inward rectifier K+ channels than cardiomyocytes. ## Footnote *More channels = larger voltage drop.*

Question 109

# True / False During Phase 0, Sodium (NA+) flows rapidly out of the cell.

Answer 109

False. ## Footnote *During Phase 0 Sodium Flows **inwards**.*

Question 110

# True / False During Phase 2, Calcium (Ca) flows rapidly into the cell.

Answer 110

True.

Question 111

Which of the 5 Phases of Action Potential is considered the start of 'Diastolic Depolarisation'?

Answer 111

Phase 4.

Question 112

# True / False In a circuit, electrons always leave via the Anode.

Answer 112

True. ## Footnote *Anode = Away.*

Question 113

# True / False In a circuit, electrons always enter via the Cathode.

Answer 113

True. ## Footnote *Cathode = Come towards.*

Question 114

The rapid upstroke of the purkinje fiber AP (phase 0) is related to which of the following currents? 1. ICa 2. IKr 3. IKs 4. INa

Answer 114

4 - INa ## Footnote *Rapid influx of sodium ions.*

Question 115

What is the current that flows to the myocardium for the following? 'Output is 2.5V and lead resistance is 565 Ohms'

Answer 115

V = IR thus I = V/R 2.5V / .565Kohm = 4.4mA ## Footnote *Remember ohms must be changed to Kohms to give answer in mA.*

Question 116

If one halves the output of a generator from 2V to 1V - the energy delivered is what? 1. Halved 2. Quadrupled 3. Doubled 4. Quartered

Answer 116

4 - Quartered. ## Footnote *E = (V²/R)\*T*