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AP EXAM 4 > LECTURE 23 10/28/22 (LECTURE 12 SLIDES: THE NORMAL ELECTROCARDIOGRAM) > Flashcards

LECTURE 23 10/28/22 (LECTURE 12 SLIDES: THE NORMAL ELECTROCARDIOGRAM) Flashcards

1
Q

How many action potentials occur every minute in the SA node?

A

72 times (6:30)

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2
Q

What predominately governs the SA node?

A

Parasympathetic Nervous System/ Vagal tones on the nodal tissue (07:14)

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3
Q

What is the connecting pathway that forms a direct connection between the SA node and the AV node in the right atrium of the heart called?

A

Internodal Pathway (08:57)

“The highway from SA to AV node”

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4
Q

What are the three branches of the Internodal Pathway?

What is the purpose of having three branches for the internodal pathway.

A

Anterior Internodal Pathway
Middle Internodal Pathway
Posterior Internodal Pathway
(09:44)

So the action potential can reach the AV node in an orderly manner and very quickly. (10:02)

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5
Q

What comes off the anterior internodal pathway and conduct electrical activity fairly quickly to make sure the left atria is coordinated with the right atria.

What is another name of this pathway?

A

Interatrial Conduction System (11:51)

Bachmann’s Bundle (13:00)

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6
Q

The fibers that make up the interatrial conduction system look like ________ .

A

atrial muscle cells (12:19)

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7
Q

The interatrial muscle cells have less ________ than other atrial muscle cells.

What is the benefit of this?

A

Myofibrils

Fewer myofibrils will allow the cell the conduct electricity at a faster clip. Interatrial cells are less resistant than typical atrial muscle cells. They are specialized for the purpose of fast conduction. (12:52)

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8
Q

How much time does it take to depolarize the last section of the right atria?

A

0.07 seconds

(14:29)

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9
Q

How much time does it take to depolarize the last section of the left atria?

How much longer does it take to depolarize the left atria than the right atria?

A

0.09 seconds

0.02 seconds longer to depolarize the left atria. (15:05)

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10
Q

Both right and left atria would normally be depolarized within ______ seconds.

On the EKG what would represent the depolarization of the atria?

A

0.09 seconds

P-wave (16:31)

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11
Q

What two factors did Dr. Schmidt mentioned that can affect the conduction of the Bachmann’s bundle that will slow down its speed and mess up coordination in the right and left atria?

A
  1. Stretched out atria
  2. Fibrotic Scarring from MI

(15:40)

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12
Q

What three possible orientations can the P-wave be in, if there was an issue in the conduction system for the left atria?

A
  1. Stretched out P-wave > 0.09 seconds
  2. Divided P-wave
  3. Biphasic P-wave
    (17:09)
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13
Q

What does any lengthening of the P-wave indicate?

A

Indicates that there is a problem with the left atria and the conducting tissue (Bachmann’s bundle) (18:10).

Think: “Long is Left”

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14
Q

What happens to the P-wave when the right atria hypertrophies or gets stretched out?

A

This will result in a larger P-wave (18:35)

Think: “Height is Right”

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15
Q

What is the main concern about delayed conduction to the left atria?

A

Arrhythmias

If the right atria is depolarizing before the left atria the heart can enter a circular rhythm between left and right atria that can result in a atrial flutter or atrial fibrillation. (20:00)

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16
Q

About 50% of patients with _______ have interatrial problems.

A

A-fib (20:30)

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17
Q

how do bad AV heart valves lead to dysfunction?

A

If the openings to the ventricles from the atria are too narrow or difficult to open, there will be more load placed on the atria during the filling process. (21:19)

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18
Q

If the ventricles are bad how will this make filling from the atria more difficult?

A

Bad ventricles mean a decrease ejection fraction, more blood left in the end systolic volume. The build up of blood can cause back flow can back in the lungs and/or systemic circulation. (22:20)

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19
Q

Atrial fibrillation and atrial flutter will cause turbulence in the atrial chambers leading to _______ formation.

A

Blood clot (22:30)

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20
Q

Worst case scenario:
A clot that is formed in the right atria can end up in the ________.
A clot that is formed in the left atria can end up in the _________.

A

Right atrial clot can end up in the lung (pulmonary embolism)

Left atrial clot can end up in the brain (cerebral embolism, cerebral infarcts)

(23:29)

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21
Q

What is the delay time at the AV node?

What is the delay time at the bundle of His?

A

0.09 seconds (AV nodal delay)

0.04 seconds (Bundle of His delay)

(24:51)

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22
Q

What percentage of the Bundle delay is in the distal portion of the AV bundle?

A

25%

Combine total at the Bundle of His is 0.04 seconds (24:50)
0.03 seconds is in the first part of the Bundle of His.
0.01 second is in the distal portion of the AV Bundle.

(0.01/0.04) x 100% = 25%

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23
Q

How much time does it take the action potential to reach the AV node from the SA node?

A

0.03 seconds

(25:10)

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24
Q

How long does it take for the action potential to reach the right and left bundle branches from SA node?

How long does it take for the action potential to reach the right and left bund branches from the AV node?

A

0.16 seconds (25:29)

0.13 seconds

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25
Q

On the EKG, what will represent the time the SA node is fired until the conduction reaches the right and left bundle branches?

In a healthy adult, what would this time be?

A

PR Interval.

0.16 seconds

(26:30)

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26
Q

On the EKG what will represent the depolarization of the ventricles?

A

QRS complex (26:40)

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27
Q

Why is the PR interval not called a PQ interval?

A

Sometimes there are no Q-waves. (26:47)

If there is an absence in Q-wave, we can still have a PR interval.

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28
Q

What is the first positive deflection on the EKG after atrial depolarization?

A

R-wave of the QRS complex (27:49)

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29
Q

If there is no R-wave and just downward negative deflection, what is it called instead?

What is this indicative of if you see this wave on lead II?

A

QS wave (28:16)

Dead Heart Tissue (28:30)

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30
Q

Purkinje fibers do not have many ___________. This enables them to conduct electricity at a very fast rate.

What other factors contribute to the speed of conduction in the Purkinje’s?

A

Contractile Filaments (29:36)

Purkinje fibers have fairly wide cells which will help them conduct electricity easier.

There are plenty of gap junctions between Purkinje Cells to help propagate the action potential.

31
Q

From the left bundle branch how many fascicles provide innervation to the left ventricle?

Name them.

A

Three Fascicles

Posterior Fascicle
Anterior Fascicle
Lateral Fascicle

(31:10)

32
Q

What is the total conduction time for the lower half the heart starting from the right and left bundle branches.

This time of conduction is pretty accurate for someone with a completely healthy heart. Although it is generally difficult to find someone over the age of _______ with this conduction speed.

A

0.06 seconds (32:06) – QRS complex
0.22 seconds - 0.16 seconds = 0.06 seconds

Over the age of 40 (32:30)
According to Schmidt, “Something is screwed up in a 40-year old’s heart.”

Older adults will have a longer conduction time than 0.06 seconds for the bottom half of the heart.

33
Q

How is the atrial conduction system insulated from the ventricular conduction system and muscle?

Where is the only place where the heart should have an electrical connection between the atria and ventricles?

A

There are cartilaginous rings are situated around the AV valves that act as a skeleton for the heart and insulator to keep electrical potential within the atria with the exception of an opening for the Bundle of His.

Cartilage opening for the Bundle of His (34:15)

34
Q

The Atrioventricular Node becomes the Penetrating Portion of the Bundle of His what does it penetrate or pass through?

A

The penetrating portion of the AV bundle passes through the fibrous tissues of the atrioventricular junction (AV fibrous tissue).

(34:53)

35
Q

What is the total built in delayed time between the AV node and the Bundle of His?

A

0.13 seconds (40:00)

.09 (AV node) + 0.04 (Bundle of His) = 0.13 seconds

36
Q

What is an abnormal extra or accessory conduction pathway between the atria and ventricles?

What percent of the population has this condition?

Who are more prone to have these accessory pathways?

A

Bundle of Kent (35:30)

0.2% of the population (usually asymptomatic, but may develop clinically manifestation later on)

Familial trait and genetics.

37
Q

When the Bundle of Kent is causing clinical manifestations like dyspnea, arrhythmias, or lightheadedness what is the disorder called?

What are the two types of this disorder?

A

Wolff-Parkinson-White Syndrome (38:08)

Type A- left side (Conduction from LA to LV)
Type B- right side (Conduction from RA to RV)
(37:37)

38
Q

What are we concerned about for individuals with WPW Syndrome?

What will happen to the QRS complex?

What will happen to the PR interval?

A

We are concern about the conduction bypassing the normal delay at the AP node and Bundle of His of 0.13 seconds. WPW Syndrome will cause the ventricles to depolarize too early. (40:16)

An early depolarization of the ventricles will shift the QRS to the P-wave. (40:33).
QRS complex will typically look prolonged (41:11)

Decrease in PR interval (40:40), sometimes if the conduction is so early that there will be no delay between the P-wave and QRS complex resulting in the P-wave combining with the QRS complex. (40:56)

39
Q

Why will the QRS complex be prolonged in someone with WPW?

A

WPW syndrome conduction will most likely depolarize the ventricle heart muscles first before the ventricular conduction tissues/Purkinje Fibers. Conduction through the muscle fiber isn’t as fast as conduction through the Purkinje Fibers, resulting in a prolonged QRS. (41:30)

Another explanation could be that the conduction pathway of the WPW runs into the normal conduction of the Purkinje system resulting in a prolonged QRS. (42:15)

40
Q

How will a normal conduction pathway cause an early atrial depolarization for someone with WPW syndrome?

A

When the conduction reaches the end of the Purkinje Fibers, it can go through the bundle of Kent and cause an early depolarization of the atria. In other words, the normal ventricular action could spread up into the atria. (42:57)

41
Q

What shows up clinically in someone who has WPW Syndrome?

A

Real short PR interval, if any.
Some form of tachycardia.
Prolong QRS complex.
SOB (Dyspnea)
Lightheadness

Potential select all that apply question
(38:08)
(44:39)

42
Q

What is a rogue tissue that its own action potential in the heart called?

When are they less problematic?

When are they problematic?

A

Ectopic Pacemaker, the action potential occurs anywhere in the heart other than the SA node. (44:56)

Less problematic if the action potential is isolated to only the upper or lower half of the heart (44: 58)

If there is no isolation between the lower or upper half, they tend to become more dangerous (45:16)

43
Q

If a WPW patient with bad coronary arteries experiences an ectopic pacemaker the potential for lethal ___________ is much higher than someone without accessory pathways.

A

Arrhythmias (45:50)

44
Q

What is the time interval for a healthy QRS complex?

What is time interval is classified as a prolonged QRS complex?

A

0.06 seconds

> 0.12 seconds

(49:00)

45
Q

What is the EKG measured in?

A

Millivolts (mV)
(49:38)

46
Q

In a normal lead II EKG, what waves are not positive deflection?

A

Not positive deflections = negative deflections
Q-waves and S-waves are negative deflections.

(50:00)

47
Q

In a normal lead II EKG, what waves are positive deflection?

On a perfectly healthy adult’s EKG of lead II, what percentage of total deflections are not positive?

A

P-wave
R-wave
T-wave
(50:20)

40%
What percentage of deflections are not positive (negative deflection).
Five total deflections: P, Q, R, S, and T wave.
Negative (or not positive deflections): Q and S wave
Math: (2/5) x 100% = 40%
Needs clarification*

48
Q

In a 3 lead system, our QRS complex’s magnitude is between ______ and _______ mV.

A

1.5 to 2.0 mV (53:35)
3 to 4 big boxes.

49
Q

How many mV are the large boxes?
How many mV are the small boxes?

How many seconds are the small boxes?
How many seconds are the larges boxes?

A

0.5 mV
0.1 mV

0.04 seconds
0.20 seconds

50
Q

What is the magnitude of the action potential in a ventricular myocyte?

How does this compare to the depolarization seen on the EKG?

Where did all the voltage go?

A

100 mV (52:29)

EKG’s magnitude is roughly about 2% of that (1.5 mV)

  1. The voltage is loss between the soft tissue and the heart and the leads looking at the voltage (53:00)
  2. Another contributing factor to lost of voltage is due to air in the lungs, air is bad conductor. COPD patients. (56:08)
  3. Large amount of adipose tissue can decease voltage, obese people will have smaller QRS complexes (56:35)
51
Q

What happens if we place our sensors (“eyeballs” ) closer to the heart?

A

There will be higher voltage changes. (53:50)

52
Q

What are the chest leads (V1-V6) called?

What is approximately the magnitude of the QRS complex in V4?

A

Precordial Leads (54:26)

Since V4 sit closer to the heart than the 3 leads system, QRS complex’s magnitude is about 2.5 to 3.0 mV. (55:00)

53
Q

What are the Bipolar Limb leads?

A

3 lead system (55:55)

Bipolar means that there is a negative lead and positive lead (83:26)

54
Q

What does the T-wave represent?

A

Repolarization of the ventricles (57:48)

55
Q

What does the QT interval represent?

How long is the QT interval?

A

The duration of ventricular depolarization (the time the ventricles are squeezing), which includes ventricular activation and recovery. It is measured from the beginning of the the Q wave to the end of the T wave (58:00).

An average QT interval is 0.35 seconds (70:22), it takes times for all the blood to be ejected.

56
Q

What does the ST segment represent?

How long is the ST segment?

What is the ST segment also known as?

A

ST segment represents a period of time where all of the ventricular tissue has been depolarized. There should be no changes seen in the tissue during this entire interval. (71:45)

0.16 seconds (71:15)

J-point or isoelectric point (71:56)

57
Q

How does repolarization of the ventricles give us a positive deflection?

A

The repolarization of the ventricles goes from the epicardium to the endocardium. The last cell to depolarize in the ventricles, will be the first to repolarize. The conduction is going away from the “sensor/eyeball” but in the reverse order which will register a positive deflection.(79:51)

58
Q

What is the first thing to depolarize in the lower part of the heart?

What is the correct order of depolarization between an endocardium and epicardium?

What about repolarization.

What is the significance of this?

A

Purkinje Fibers (74:53)

Endocardium will depolarize first and epicardium will depolarize second.

Reverse order for repolarization.

The extended endocardial AP gives time for the epicardial AP and contraction to occur. This overlap will ensure all of the walls inside/outside are contracting. (78:00)

59
Q

Which heart tissue is doing the most work in the ventricles?

A

Inner layer (Endocardium), it is depolarized the longest and squeezing the longest. (80:03)

60
Q

The endocardium is situated in the deepest part of the tissue where the _________ pressure is going to be exerted.

What is he coronary arteries relationship with the endocardium?

A

Highest (80:15)

The coronary arteries that are on the superficial surface of the heart have branches that reach deep into the muscle layers exposing it to the high pressure in the ventricles (80:39)

61
Q

Which part of the heart will likely be injured due to ischemia?

A

The most vulnerable tissue will be the one using the most energy (endocardium) and tissues subject to the most variation in blood flow (coronary artery). (81:31)

62
Q

In the bipolar leads, the current goes towards the ________ lead.

A

Postive (82:47)

The eyeball is the positive lead.

63
Q

Where are the electrode placements for Lead 1?

What does Lead 1 indicate?

A

Right arm: negative electrode
Left arm: positive electrode

Depolarization/Current going from the right to left side of the body (83:41)

64
Q

What are the electrode placements for Lead 2?

What does Lead 2 indicate?

A

Right arm: negative electrode
Left leg: positive electrode

Depolarization/ Current going from the right side of the body to the left foot (84:30)

65
Q

What are the electrode placements for Lead 3?

What does Lead 3 indicate?

A

Left arm: negative electrode
Left leg: positive electrode

Depolarization/ Current going from the left side of the body to the left foot (85:00)

66
Q

The bipolar leads form a triangle. What is the name for this triangle?

A

Einthoven’s Triangle (85:45)

67
Q

When current is going away from the eyeball (positive lead), the monitor will register a __________ reading.

If the current is going toward the eyeball, the monitor will registe a ________ reading.

A

Negative

Positive

(87:41)

68
Q

When will the monitor of the bipolar leads have the most positive reading?

When will the monitor of the bipolar leads have the most negative reading?

A

When the cell is half depolarized, it has the most current flowing from the depolarized side to the resting side. (95:48)

When the cell is half repolarize, you get the most current flowing from depolarized side to the repolarizing side. (101:10)

69
Q

At what point does the monitor of the bipolar leads read 0?

A

When the cell is completely at rest and when the cell is completely depolarized. (98:33)

70
Q

A one-quarter depolarized reading will the be same as a ___________ depolarized reading.

A

three-quarter (98:51)

71
Q

If a depolarization goes left to right and the repolarization goes right to left.

The repolarization will end up as a _______ deflection.

A

Positive deflection (107:48)

This is what is going on with the T-wave as repolarization goes from the epicardium to the endocardium.

72
Q

What is the mean vector through a partially depolarized heart?

What direction is the mean vector typically pointed towards?

The mean electrical vector is in the same plane as lead ____.

A

The mean vector represents the sum total of all currents moving toward the positive charge on the outside walls of the heart. (110:14)

Left foot (110:47)

II (111:01)

73
Q

What causes the negative deflection in the Q-wave?

A

There is a very brief initial period of time where the inner side of the left ventricle becomes depolarized before the septum on the right ventricular side. That produces current moving toward the right side of the heart away from lead I, resulting in a negative deflection in the QRS complex. (113:37)

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