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(J) Physiology Test 2 > Lecture 8 - Heart Rhythmicity and Normal ECG > Flashcards

Lecture 8 - Heart Rhythmicity and Normal ECG Flashcards

1
Q

What is duration of the PR interval and what is the significance of this timing?

(L8 S20)

A

-0.16 seconds; this is the delay of SA node AP conductance to the Purkinje fibers

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2
Q

What is a monophasic action potential?

A
  • depolarization and repolarization of tissue

- in the ventricle it would be the QT interval

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3
Q

What is the duration of the QT interval?

A

-0.35 secs

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4
Q

What does the P wave and QRS complex represent in the atrial and ventricular APs respectively?

(L8 S16)

A

-phase 0

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5
Q

What are the connections of lead I?
How does it look at the heart?
What is the angle of its axis?

A
  • negative on R arm
  • positive on L arm
  • look from R to L
  • 0 degrees
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6
Q

What are the connections of lead II?
How does it look at the heart?
What is the angle of its axis?

(L8 S32)

A
  • negative on R arm
  • positive on L leg
  • looks at heart from upper right to lower left
  • 60 degrees
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7
Q

What are the connections of lead III?
How does it look at the heart?
What is the angle of its axis?

A
  • negative on L arm
  • positive on L leg
  • looks at heart from upper left to lower left
  • 120 degrees
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8
Q

What is the name of the triangle around the heart formed by the limb lead placements?

A

-Einthoven’s triangle

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9
Q

A __________ charge causes a __________ deflection on an EKG.

A

Negative; positive/upward

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10
Q

The length of an vector represents __________ and the direction represents __________.

A

Magnitude of voltage; direction of current flow

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11
Q

What leads make up a standard 12 lead EKG?

L8 S39

A

Bipolar limb leads:
-I, II, and III

Augmented limb leads:
-aVR, aVF, aVL

Precordial leads (standard leads):
-V1-V6
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12
Q

What is the mean electrical axis of the heart and what is responsible for this?

A
  • 59 degrees
  • the apex of the heart remaining positive with respect to the the base of the heart during ventricular depolarization (QRS)
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13
Q

What conditions result in an abnormal QRS axis?

A
  • change in heart position
  • hypertrophy
  • bundle branch blocks
  • fluid in the pericardium
  • pulmonary emphysema
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14
Q

What conditions result in increased or decreased QRS voltages?

A

Increased:
-hypertrophy

Decreased:
-cardiomyopathies

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15
Q

What is the normal QRS duration?

A

-0.06-0.08 seconds

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16
Q

What conditions result in prolongation of the QRS complex?

A
  • destruction of cardiac tissue

- blocks in the Purkinje system

17
Q

What is the J point and conditions can alter the position of the J point?

(L8 S49-50)

A
  • the end of the QRS complex
  • represents when all ventricular tissue is depolarized
  • used to analyze current of injury

Causes of alterations:

  • mechanical injury
  • infectious processes
  • ischemia
18
Q

What is a current of injury?

L8 S49

A
  • cardiac abnormality causes a region to remain partially or fully depolarized
  • current flows away from the site of abnormality toward regular cardiac tissue
  • current flows even between heart beats
19
Q

Describe the timing of action potential conduction in the heart and what is responsible for delays.

A
  • AP generated in the SA node and arrives at the AV node 0.03 secs later.
  • Signal is delayed in the AV node for 0.09 secs
  • delay is caused by small size of cells, low magnitude of AP, and slow rate of depolarization
  • AP is delayed again in the penetrating bundles for 0.04 secs
20
Q

What is the resting membrane potential and threshold of the SA node?

A

Resting potential:
- -55 to -60mV

Threshold:
-40mV

21
Q

How does vagal nerve stimulation affect heart rate?

A
  • distributed to SA and AV nodes
  • releases acetylcholine which affect muscarinic receptors
  • increases the permeability to potassium ions, hyperpolarizing the cells to -65 to -70
  • hyperpolariziation decreases rate of SA node (negative chronotropic effect)
22
Q

How does sympathetic stimulation affect heart rate?

A
  • distributed to entire heart
  • releases norepinephrine which affects beta-1 adrenergic receptor
  • may increase the permeability to sodium and calcium ion
  • increases depolarization rate (positive chronotropic effect)
23
Q

What does the P wave represent?

A

-atrial depolarization

24
Q

What does the QRS complex represent?

A

-ventricular depolarization

25
Q

What does the T wave represent?

A

-ventricular repolarization

(J) Physiology Test 2 (10 decks)

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