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Patho 1 > 2- EKG and Excitation > Flashcards

2- EKG and Excitation Flashcards

1
Q

What is the resting membrane potential of SA node cells?

Why?

A

-55

cell membranes of the sinus fibers are naturally leaky to sodium and calcium

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2
Q

What causes self-excitation in SA node cells?

A

Leakiness to sodium and calcium lowers resting and threshold potentials

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3
Q

If SA cells leak Na and Ca, why are they not constantly depolarized?

A
  1. Ca channel inactivation
  2. increased number of potassium channels means a large number of K ions leave the membrane and it becomes hyperpolarized for a period of time, protecting it from repolarizing
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4
Q

What is the threshold potential of an SA cell?

A

-40

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5
Q

How does an impulse from the SA node travel to the AV node?

A

Three atrial fibers:

Anterior (bachman’s - L atria)

Lateral

Posterior

Join together at the AV node

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6
Q

Where is the AV node located?

A

Posterior RA wall

Behind the tricuspid

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7
Q

Stokes-Adams Syndrome

A

When the AV node becomes suddenly blocked, it can take 5-20 seconds for the purkinje fibers to initiate their own intrinsic rate, because at baseline they are oversaturated. This is why people generally faint.

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8
Q

Vagal stimulation in the heart results in release of what neurotransmiter?

A

Acetylcholine

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9
Q

What effect does acetylcholine have on cardiac muscle cell membrane?

A

Opens potassium channels, creating hyperpolarization and decreasing excitability

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10
Q

Sympathetic stimulation in the heart results in release of what neurotransmitter?

A

Norepinephrine

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11
Q

Does sympathetic stimulation alter the conduction of the SA node or the AV node?

A

both

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12
Q

What are adrenergic receptors?

A

nerve receptors that are stimulated by either norepinephrine or acetylcholine

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13
Q

What is an adrenergic agonist?

A

A drug that stimulates a response from an adrenergic receptor

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14
Q

When norepinephrine stimulates Beta 1 receptors, what happens?

Why?

A

Sympathetic activation

Increased heart rate, conduction, contractility

increases permeability to sodium and potassium channels (hypopolarizes)

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15
Q

On an ECG print out, the darker squares represent ____ seconds.

The smaller subsquares represent _____ seconds

A
  1. 2
  2. 04
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16
Q

What is the instantaneous mean vector?

Which direction does it point?

A

The summated vector of all the potentials in the heart from moment to moment

Considerably more current flows downward from base to apex, so the arrow points down along the ventricular septum

17
Q

What vector represents zero, and what degree vector is the standard mean QRS vector?

A

Exactly horizontal and directed toward the left side

+59 degrees (down and to the left)

18
Q

What is the axis of a lead?

A

The direction from negative electrode to positive electrode

19
Q

What repolarizes first: the inner or outer muscle layers of the ventricle?

A

The outer. Because during contraction coronary blood flow to the ventricle is substantially decreased, so it takes longer to relax contraction

20
Q

What is the mean electrical axis of the ventricle?

A

The instantaneous mean vector of the ventricle

+5

21
Q

When and why does the mean electrical axis of the heart shift to the left in a healthy heart?

A
  1. At the end of deep expiration
  2. When a person lies down
  3. In obese people

Caused if the heart is angulated to the left

22
Q

When and why does the mean electrical axis of the heart shift to the right?

A
  1. At the end of deep inspiration
  2. When a person stands up
  3. In tall lanky people whose hearts hang downward
23
Q

If the left ventricle is hypertrophied, which way will the mean electrical axis shift?

A

To the Left

The normal ventricle is depolarized much faster than the hypertrophied one

24
Q

What are some causes of depressed QRS voltage?

A

Old myocardial infarctions (signals take longer to get through the tissue)

Pericardial effusion (fluid short circuits signals)

Pulmonary Emphysema (increased air in the lungs decreases voltage picked up by electrodes)

25
Q

What is the electrical cause of ST elevation?

A

The injured muscle remains depolarized when the rest of the cell is completely polarized, so it always causes an altered baseline (J point). The ventricular baseline (J point) becomes different from the atrial baseline (zero).

26
Q

An injured area of the myocardium is permanently depolarized or polarized?

A

Depolarized

27
Q

When observing the injury vector during the J point, how is the location of the injury determined?

A

when you lay the vecor analysis over a picture of the ventricles, the negative end of the vector will point to the site of injury

28
Q

What does it mean if the PR interval is less than 0.12 seconds?

A

The AV node is not conducting that signal, so a secondary pathological pathway must be present

Patho 1 (17 decks)

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