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Block 6 - Physiology > Intro And Electrical Activity Of Heart > Flashcards

Intro And Electrical Activity Of Heart Flashcards

1
Q

Describe arrangement and general functions of Cardiovascular System.
(7)

A
  • The heart has a Right (pulmonary) and Left (systemic) side
  • 4 Chambers (2 Atria, 2 Ventricles)
  • 4 Valves (2 Atrioventricular - Bicuspid/Mitral on left and Tricuspid on right; 2 Semilunar - Aortic on left and Pulmonary on right)
  • Systole: contraction, force generation, blood expulsion
  • Diastole: relaxation, filling with blood, readying for next systole
  • Heart ejects blood into circulation, carried to capillary beds in organs via arteries, returned to heart via veins
  • Blood volume is always constant
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2
Q

Describe the path blood flows through the body.

A
  • Blood enters heart via superior and inferior vena cava and coronary sinus into Right Atrium
  • Through Tricuspid Valve to Right Ventricle
  • Through Pulmonary Semilunar Valve into pulmonary trunk –> Pulmonary arteries –> lungs –> capillaries exchange CO2 for O2
  • Blood flows into heart from Pulmonary Veins to the Left Atrium
  • Through Bicuspid Valve to Left Ventricle
  • Through Aortic Semilunar Valve into Ascending Aorta
  • Goes throughout body to exchange cargo
  • Beings CO2 back via veins
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3
Q

Beginning in the SA node, describe the depolarization and repolarization wave as it travels through the heart (4)

A
  • SA Node fires
  • Atria depolarize (right first, base to apex direction)
  • Septum and inner layer of ventricular muscle depolarizes
  • Ventricles depolarize (nearly all at once)
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4
Q

Predict consequences of conduction failure (depolarization block) at every level

A

Conduction block on right bundle branch will cause right side to take longer to depolarize and then it will be out of sync with the left side.
Could also lead to the interventricular septum to not be as stiff as it should, also leading to right depolarization to slow and not be able to generate as much force and eject enough blood

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5
Q

Explain what causes AV Nodal Delay?

Why is this important?

A

AV node depolarizes more slowly due to fewer gap junctions.

It allows the atria to completely contract before the ventricles do - ensuring all of the blood is moved out of atrium

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6
Q

Define pacemaker.

What is the pacemaker of the heart?

A
  • Sets how fast the heart beats

- SA Node because it is first and fastest to depolarize - it fires while others are still slowly depolarizing

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7
Q

Define auto-rhythmicity

A
  • Set rate that the heart will depolarize and repolarize at (due to funny channels and calcium channels)
  • Heart is auto-rhythmic, but it is controlled by ANS (Muscarinic’s and Beta 1’s)
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8
Q

Define overdrive suppression

A

SA Node is pacemaker…fastest to depolarize and fires while other parts are still slowly depolarizing

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9
Q

Define ectopic pacemaker.

When does this come into play?

A
  • Ectopic pacemaker is a pacemaker that is not where it should be (not the SA Node). It will overtake SA Node if…
  • SA Node slows
  • Ectopic (alternative) is faster
  • Pathology introduces a conduction block
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10
Q

Describe modulation of heart rate (general terms)

A
  • Altering the SA node firing rate

- Altering conduction through the AV node

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11
Q

Explain the relationship of the P-wave to the electrical/mechanical events of the heart

Predict info that can be drawn from the P-wave

A
  • SA Node starts here

- Atrial depolarization (repolarization is hidden by QRS

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12
Q

Explain the relationship of the QRS Complex to the electrical/mechanical events of the heart

Predict info that can be drawn from the QRS Complex

A
  • AV Node starts here

- Ventricular depolarization

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13
Q

Explain the relationship of the T-wave to the electrical/mechanical events of the heart

Predict info that can be drawn from the T-wave

A
  • Ventricular repolarization
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14
Q

Explain the relationship of the P-R Interval to the electrical/mechanical events of the heart

Predict info that can be drawn from the P-R Interval

A
  • Time from initiation of atrial depolarization to initiation of ventricular depolarization
  • Under 0.2 seconds
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15
Q

Explain the relationship of the P-R Segment to the electrical/mechanical events of the heart

Predict info that can be drawn from the P-R Segment

A
  • Time from end of atrial depolarization to initiation of ventricular depolarization
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16
Q

Explain the relationship of the QRS Interval to the electrical/mechanical events of the heart

Predict info that can be drawn from the QRS Interval

A
  • Total time to depolarize ventricles
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17
Q

Explain the relationship of the Q-T Interval to the electrical/mechanical events of the heart

Predict info that can be drawn from the Q-T Interval

A
  • Time from first ventricular depolarization to last ventricular repolarization
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18
Q

Explain the relationship of the S-T Segment to the electrical/mechanical events of the heart

Predict info that can be drawn from the S-T Segment

A
  • Time from last ventricular depolarization to initiation of ventricular repolarization
  • Elevated during myocardial infarction (MI)
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19
Q

Identify the standard conventions used in annotating an ECG strip

A
  • ECG measures electrical activity of heart over time (seconds vs mV)
  • Waves: measures changes in voltage
  • Intervals: time periods that include the wave
  • Segments: time periods that do not include the wave
20
Q

Define chronotrope.
Which node has to to with this?
Describe positive vs negative and give examples

A
  • Something that affects heart rate
  • SA Node
  • Positive: Increases HR (B1 receptors, increase funny current, increase Ca current)
  • Negative: Decreases HR (M2 receptors, decrease funny current, decrease Ca current, increase K current)
21
Q

Define dromotrope.
Which node has to do with this?
Describe positive vs negative and give examples

A
  • Something that affects conduction velocity.
  • AV Node
  • Positive: increases conduction velocity (B1 receptors, Increase Ca current during upstroke, Shortens ERP)
  • Negative: reduces conduction velocity (M2 receptors, Decrease Ca current during upstroke, Increase K current to hyperpolarize, Lengthens ERP)
22
Q

Which chambers play a less significant role in heart function?

Most significant?

A
  • Atria: healthy human only needs atria to get blood to ventricle; thin walled
  • Ventricle (esp. left): eject blood out to circulation; bigger than atria; thicker walls; produces more force
23
Q

What is an important role of valves?

A

Prevent backflow of blood

24
Q

List the 4 heart valves

A

Bicuspid/Mitral
Tricuspid
Aortic
Pulmonary

25
Q

How would retaining water or hemorrhage affect blood volume?

A
  • In a healthy patient, blood volume is always constant.

- Hemorrhage or retaining water would alter the blood volume

26
Q

If you are being chased and need more blood to go to skeletal muscle, can this be achieved? How?

A
  • If skeletal muscle is being used and needs more O2 and glucose (more blood to deliver nutrients), blood needs to be shifted away from somewhere else (blood volume is constant)
  • Sympathetic nerve stimulation will shift blood away from GI Tract and toward skeletal muscle
27
Q

Left atrial fibrillation (improper excitation and contraction) would most greatly affect filling of which chamber?
Which chamber would be second?
Explain both.

A
  1. Left Ventricle - if atria is not properly contracting, it will not be able to completely fill left ventricle
  2. Right Ventricle - Behind the left atria is the pulmonary tree and behind that is the right ventricle. Everything is in series so things in front of and behind the dysfunction will be affected.
28
Q

If the left ventricle cannot adequately pump blood, explain what would happen to the blood

A

Blood will back up into the left atria which will back up into lungs which will back up into right ventricle.

29
Q

How are specialized nodal cells connected to the rest of the myocytes (muscle cells)?

A

Gap junctions - this makes it easy for depolarization to get out to the muscles

30
Q

What does the SA Node cause contraction of?

A

Atria

31
Q

Are the atria and ventricles electrically separated?

Explain the type of tissue between them.

A

Yes - There are no gap junctions between atria and ventricles. There is a fibrous tissue between them that electrical signal cannot pass across.

32
Q

What is the only way depolarization can get from atria to ventricle?

A

AV Node

33
Q

What would happen if part of the heart started contracting before another part was complete?

A

Less force would be generated

34
Q

What affect do perkinje fibers have on the speed of conduction to ventricular myocytes?
Describe in terms of diameter of the cells.

A

Speed it up - they are very large, thick cells - if you increase diameter of something carrying action potential it will increase speed

35
Q

Why are perkinje fibers important?

A

They speed up the conduction to myocytes and they help make sure the entire ventricle contracts in a coordinated/simultaneous fashion

36
Q

What factor of depolarization allows for maximal blood ejection?

A

Coordination (in the ventricles)

37
Q

Can you rely on AV Node to be the pacemaker of cell?
Bundle of His?
Purkinje Fibers?

A

AV Node - yes, because it is only slightly slower than SA Node
Anything slower - no, pace of bundle of his and purkinje fibers are too slow to be sufficient for life

38
Q

What type of autonomic control speeds up heart rate?

Slows down?

A

Speed up: Sympathetic

Slow down: Parasympathetic

39
Q

Under normal conditions, which autonomic system primarily controls heart rate?

A

Parasympathetic

40
Q

How do the SA and AV Node’s affect heart rate modulation

A

SA Node: how fast it fires/depolarizes (heart rate)

AV Node: how long it takes impulse to move from atria to ventrcile (conduction rate)

41
Q

When do you see a U Wave on an ECG? What could this indicate?

A
  • Perkinje repolarization
  • Ionic imbalance such as hypokalemia or hypercalcemia
  • Usually not seen
42
Q

What affect will autonomic innervation have on the PR Interval?

A

Parasympathetic: Longer PR Interval (slows down AV Nodal Conduction)
Sympathetic: Shorter PR Interval

43
Q

What effect would a sodium channel (Na-v) blocker have on the ECG?

A
  • Increase the QT Interval
44
Q

What wave/complex/interval/segment do Na channels affect most on an ECG?

A

Ventricular Depolarization - QRS Complex

45
Q

Identify the steps in conduction (6)

A
  1. SA Node fires and causes atria contraction
  2. AV Node carries AP from atria to ventricles. Allowing atria to fully contract before ventricles do.
  3. Bundle of His (AV Bundle)
  4. Bundle Branches (Right and Left; feed each ventricle)
  5. Perkinje system
  6. Ventricular Myocytes

Block 6 - Physiology (3 decks)

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