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Cardio Exam 1 > 2 - Cardiac Electrical Physiology > Flashcards

2 - Cardiac Electrical Physiology Flashcards

1
Q

Five phases of an action potential

A
  • Phase 0 = rapid upstroke, depolarization
  • Phase 1 = early repolarization
  • Phase 2 = plateau phase
  • Phase 3 = rapid repolarization
  • Phase 4 = resting membrane potential
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2
Q

Phase 0

A
  • Rapid influx of sodium
  • Fast phase due to opening of sodium channels
  • Sodium ions and positive charges really want to get inside the cell, so the depolarization occurs rapidly
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3
Q

Phase 1

A

Early repolarization

  • Sodium channels close, but some potassium channels open
  • Repolarization is incomplete
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4
Q

Phase 2

A

Plateau

  • Membrane potential is approximately ZERO (which is very important for ECGs!!)
  • The plateau occurs due to slow calcium channels (which must be matched by an equal and opposite force by potassium channels - offsets the calcium flow)
  • Requires concurrent movement opposite to calcium
  • Allows blood to be ejected from the heart
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5
Q

Phase 3

A

Rapid repolarization

  • More calcium channels are closing
  • More potassium channels are opening
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6
Q

Phase 4

A

Resting membrane potential

  • Only potassium chanels are open
  • Resting potential is maintained until the next stimulus
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7
Q

Resting membrane potential of a cardiac muscle cell

A

Approx. -90 mV

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8
Q

Resting cell - Potassium

A

Potassium (K+) is very high inside the cell and low outside the cell

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9
Q

Resting cell - Sodium

A

Sodium (Na+) is high outside the cell and low inside the cell.

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10
Q

Resting cell - Calcium

A

Calcium (Ca++) is low outside the cell and REALLY low inside the cell.

This is advantageous for muscle contraction, which requires calcium for cross bridge cycling at the level of the actin and myosin filaments, and allows for exquisite sensitivity of the muscle to small changes in intracellular calcium concentration

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11
Q

What four membrane proteins are present on a generic cardiac cell?

A
  • Na+ transporter
  • Ca++ transporter
  • K+ transporter
  • Cation transporter
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12
Q

What is the role of the Na+ transporter?

A

Rapid, depolarizing (non-nodal)

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13
Q

What is the role of the Ca++ transporter?

A

Slow, depolarizing

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14
Q

What is the role of the K+ transporter?

A

Re-polarization

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15
Q

What is the role of the cation transporter?

A

Allows for the “funny” current to flow

This cation transporter is a hyperpolarization-activated cyclic nucleotide-gated channel (esp. cAMP)- (nodal)

“Pacemaker channels” allow positive charge to enter cell during repolarization or hyperpolarization and are closed during depolarization

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16
Q

Where in the heart do we find different types of action potentials?

A

Nodal tissue

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17
Q

How many phases are there of cardiac action potentials in nodal tissue?

A

Three

  • Phase 0
  • Phase 3
  • Phase 4
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18
Q

Describe phase 0

A
  • Once threshold potential is met, calcium channels open
  • “No” fast sodium channels
  • Slow response
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19
Q

Describe phase 3

A

After depolarization, potassium channels open

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20
Q

Describe phase 4

A

“Funny current” slowly depolarizes the cell

  • Progressive reduction in potassium efflux
  • Progressive increase in calcium influx
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21
Q

What is the sequence of depolarization within the heart?

A 
1 - SA node
2 - Atria
3 - AV node
4 - Bundle of His
5 - Bundle branches
6 - Purkinje fibers
7 - Ventricles (septum, apex, ventricular free walls)
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22
Q

What does the conduction velocity of a certain part of the heart tell you?

A

It is related to how fast an action potential can spread from one part of the heart to another

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23
Q

What is an ECG or EKG?

A

AKA electrocardiogram

- An instantaneous recording of all the CHANGES in membrane potential in the heart cells

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24
Q

Why can only membrane potential changes of a relatively LARGE number of cells be detected by and ECG?

A

Because it is recorded on the surface of the body

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25
Q

What accounts for the characteristic wave forms in the ECG?

A

The characteristic sequence of depolarization

26
Q

Describe the depolarization of purkinje fibers

A

PURKINJE FIBERS = little “lighters” to start the “fire” of electrical impulse in several places at once- so the heart can “burn” in a uniform fashion

27
Q

Describe the placement of leads in the FRONTAL plane

A

Standard bipolar limb leads

  • i
  • II
  • III

Augmented unipolar limb leads

  • aVR
  • aVL
  • aVF

See slide 21 for placement diagram

28
Q

Describe the placement of leads in the HORIZONTAL (transverse) plane

A

Chest leads (precordial leads)

  • V1
  • V2
  • V3
  • V4
  • V5
  • V6
29
Q

Chest leads are placed in order to emphasize the ______ ventricle

A

Left

30
Q

Placement of V1

A

4th intercostal space

Right sternal border

31
Q

Placement of V2

A

4th intercostal space

Left sternal border

32
Q

Placement of V4

A

5th left intercostal space

Midclavicular line

33
Q

Placement of V3

A

Between V2 and V4

34
Q

Placement of V5

A

In line with V4, in anterior axillary line

35
Q

Placement of V6

A

In line with V4 and V5 in midaxillary line (“down from mid-armpit”)

36
Q

When determining heart rate from ECG paper, what do we measure?

A

Number of large boxes in an R-R interval

37
Q

If there is one large box in the R to R interval…

A

The heart rate is 300 bpm

38
Q

What about for 2, 3, 4, 5, 6 and 7 large boxes in an R-R interval?

A 
1 - 300
2 - 150
3 - 100
4 - 75
5 - 60
6 - 50
7 - 43
39
Q

Segments and intervals of an ECG wave form

A

Look at slide 25

  • P wave
  • PR interval
  • QRS complex
  • ST segment
  • T wave
  • QT interval
40
Q

Define a P wave

A

Deflection from and return to isoelectric line

41
Q

What is the physiological correlate of a P wave?

A

atrial myocyte depolarization (phase 0)

42
Q

What is the normal duration of a P wave?

A

0.06-0.11 sec

1-2 small boxes

43
Q

Define a QRS complex (interval)

A

deflection from and return to isoelectric line

44
Q

What is the physiological correlate of a QRS complex?

A

ventricular myocyte depolarization (phase 0)

45
Q

What is the normal duration of a QRS complex?

A

0.03-0.12 sec

(

46
Q

Define a PR interval

A

beginning of P wave deflection to beginning of QRS complex

47
Q

What is the physiological correlate of a PR interval?

A

all electrical events (depolarization- phase 0’s) upstream of ventricular myocytes (atrial myocyte, AV node, bundle, bundle branches, Purkinje fibers)

48
Q

What is the normal duration of a PR interval?

A

0.12-0.2 sec

3-5 small boxes

49
Q

Define a T wave

A

deflection from and return to isoelectric line

50
Q

What is the physiological correlate of a T wave?

A

ventricular myocyte repolarization (phase 3)

51
Q

What is the normal duration of a T wave?

A

variable

52
Q

Define a QT interval

A

beginning of QRS complex to the end of the T wave

53
Q

What is the physiological correlate of a QT interval?

A

the entire action potential for the ventricular myocytes (depolarization- plateau- repolarization)

54
Q

What is the normal duration of a QT interval?

A

variable
(roughly half
R-R interval)

55
Q

Define an ST segment

A

end of the QRS complex to the beginning of the T wave deflection

56
Q

What is the physiological correlate of an ST segment?

A

ventricular myocyte plateau phase (phase 2)

57
Q

What is the normal duration of an ST segment?

A

variable

with HR

58
Q

What does it mean if there are no P waves?

A

No atrial depolarization

59
Q

What does it mean if there is a P wave following every QRS complex?

A

There is ventricular polarization following every atrial polarization

60
Q

What is pacing the heart?

A

SA node and AV node

61
Q

Interpreting an ECG

A

Need to review this from physiology material

Cardio Exam 1 (15 decks)

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