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Emrg 1230 > Week 1- Electrophysiology of the Heart > Flashcards

Week 1- Electrophysiology of the Heart Flashcards

1
Q

What is the main function of the electrical conduction system?

A
  • to create an electrical impulse and transmit to the rest of the myocardium
  • this is an electrochemical process that creates electrical energy, picked up by the electrodes in an ECG
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2
Q

What are some things to keep in mind about the conduction system?

A
  • Actually inside the heart walls
  • Atrial myocytes are innervated by direct contact from one cell to another
  • Internodal pathways transmit the impulse from the SA node to the AV node
  • Purkinje system is the final component- innervates myocardial cells
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3
Q

What is the pacemaker function?

A
  • Dictates the rate at which the heart will cycle through its pumping action to circulate the blood
  • Creates an organized beating of all cardiac cells in a specialized sequence
  • Sets the pace of all other cells that will follow
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4
Q

What is the SA Node?

A
  • The main area that acts as the heart’s pacemaker
  • Controls the beat based on information it receives from the nervous, circulatory, and endocrine system
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5
Q

What is the pacemaker setting for the SA Node?

A
  • 60-100 BPM
  • 60-80 BPM
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6
Q

What is the pacemaker setting for the atrial cells?

A
  • 55-60 BPM
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7
Q

What is the pacemaker setting for the AV Node?

A
  • 45-50 BPM
  • 40-6 BPM
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8
Q

What is the pacemaker setting for the Bundle of His?

A
  • 40-45 BPM
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9
Q

What is the pacemaker setting for the Bundle branch?

A
  • 40-45 BPM
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10
Q

What is the pacemaker setting for the Purkinje Cells?

A
  • 20-40 BPM
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11
Q

What is the pacemaker setting for Purkinje system?

A
  • 20-40 BPM
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12
Q

What is the pacemaker setting for Myocardial Cells?

A
  • 30-35 BPM
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13
Q

Where is the SA Node located?

A
  • Found in the upper part of the wall of the right atrium at its junction with the superior vena cava
  • Electrical impulses are generated here
  • The farther away the impulse is generated from the SA node the slower it becomes
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14
Q

What is the main purpose of the Internodal Pathways?

A
  • Main purpose is to transmit the pacing impulse from the SA node to the AV node
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15
Q

Where are the Internodal pathways found?

A
  • they are found in the walls of the right atrium and interatrial septum
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16
Q

What are the three pathways of the internodal?

A
  • Anterior
  • Middle
  • Posterior
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17
Q

What is the Bachmann bundle?

A
  • small tract of specialized cells that transmits impulses through the interatrial septum, preferred path for electrical activity for left atrium
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18
Q

What does the AV node do?

A
  • Controls HR (electrical relay station)
  • Slows down conduction from atria to ventricles long enough for atrial contraction- then allows the signal to pass into the ventricles
  • Helps maintain output of heart at the maximum level
  • Always supplied by right coronary artery
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19
Q

Where is the AV node located?

A
  • In the wall of the right atrium next to the opening of the coronary sinus, near the coronary sinus and the septal leaflet of the tricuspid valve
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20
Q

What is the Bundle of His?

A
  • Collection of heart muscle cells specialized for electrical conduction
  • Transmits impulses from the AV node to purkinje fibers then to the ventricles
  • The ONLY route of communication between the atria and ventricles
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21
Q

Where is the Bundle of His located?

A
  • Starts at the AV node
  • Found partially in right atrium, and interventricular septum
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22
Q

What is the Left Bundle Branch? (LBB)

A
  • First area to depolarize
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23
Q

Where is the LBB located?

A
  • Begins at the end of bundle of His
  • Travels through interventricular system
  • Ends at beginning of left anterior and left posterior fascicles
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24
Q

What is the Right Bundle Branch?

A
  • Gives rise to fibers that innervate RV and right face of interventricular septum
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25
Q

Where is the RBB located?

A
  • Begins at the bundle of His
  • Terminates in Purkinje fibers
26
Q

What is the Purkinje System?

A
  • Carry contraction impulses from the left and right bundle branches to the ventricles
  • Initiates ventricular depolarization cycle (contraction, pumping blood outside of your body)
27
Q

Electrophysiology

A
  • Electrical stimulus= muscle tissue contraction
  • Cardiac muscle is unique as it can produce it’s own impulse- pacemaker cells
  • Common characteristics of pacemaker cells
28
Q

What is automaticity?

A
  • Generate their own electrical impulses
29
Q

What is excitability?

A
  • Irritability
  • Ability to respond to a change
30
Q

What is conductivity?

A
  • Pass a charge on to the next cell
31
Q

What is contractility?

A
  • Ability to shorten
  • Contraction
32
Q

What are the phases of normal electrical activity of the heart?

A
  • Cardiac conduction is essentially split into 2 phases: systole (contraction) and diastole (relaxation)
  • Polarization (relaxed)
  • Depolarization (contract)
  • Repolarization (getting ready to have another contraction)
33
Q

What is polarization?

A
  • State of readiness
  • Muscle is relaxed and ready to receive electrical impulses
  • Potassium inside, Sodium outside, Calcium outside
34
Q

What is depolarization?

A
  • Contraction
  • Electrical impulse transmitted
  • 1- opening of sodium channels to allow Sodium to move inside the cell
  • 2- Potassium moves to the outside
  • Ca++ moves inside and stays longer

REFRACTORY PERIOD

35
Q

What is Repolarization?

A
  • Recovery phase
  • Cells returning to a ready state
  • After a delay (absolute refractory) termination of action potential occurs as potassium channels open allowing K+ to leave the cell
36
Q

What is the action potential- electrical activity of a single cell?

A
  • Phase 4- polarized- resting membrane potential
  • Phase 0- depolarization (Na inside)
  • Phase 1- early repolarization (K out)
  • Phase 2- Plateau phase (Ca moves in) (2nd depolarization)
  • Phase 3- Rapid Repolarization
  • For contraction sodium in, potassium out
  • For resting potential you need equal sides (Ca+ in)
37
Q

What is action potential?

A
  • Stimulation of the cardiac nerve to transmit an impulse to the cardiac cells
  • Start of a heart beat
38
Q

What are the steps to follow for action potential?

A
  1. when an adequate stimulus is applied, the stimuli gated Na+ channels open and Na+ rapidly diffuses into the cell. This causes depolarization.
  2. As the threshold potential is reached, voltage gated Na+ channels open
  3. As more Na+ enters the cell through the voltage gated Na+ channels, the membrane depolarizes even further
  4. The magnitude of the action potential peaks when the voltage gated Na+ channels close (+30mv)
  5. Repolarization begins when voltage gated K+ channels open allowing outward diffusion of K+ calcium goes into the cell
  6. After a brief period of hyperpolarization, the resting potential is restored by the sodium/ potassium pump and the ion channels return to their resting state
39
Q

What is refractory period?

A
  • Brief period during which the cells will resist stimulation
  • Last approx. 0.5 ms after the membrane reaches the threshold potential
40
Q

What is the absolute refractory?

A
  • Will not respond to any stimulus, no matter how strong
41
Q

What is relative refractory?

A
  • Few ms after the absolute- the membrane is repolarizing and restoring the membrane potential
  • During this time, the membrane will only respond to very strong stimuli
42
Q

What is the conduction pathways?

A
  • Sinoatrial node
  • Internodal and interatrial pathways
  • Atrioventricular node
  • Bundle of his
  • Right and left bundle branches
  • Perkinje’s fibers
  • Ventricular muscle
43
Q

What is the first step?

A
  • SA node activity and atrial activation begin
  • Time= 0 msec
44
Q

What is the second step?

A
  • Stimulus reaches the AV node
45
Q

What is the third step?

A
  • 100 msec delay at the AV node
  • Atrial Contraction begins
46
Q

What is the fourth step?

A
  • Impulse travels along the septum wall within the AV bundle and branches to the Purkinje fibers
47
Q

What is the fifth step?

A
  • Impulse is distrubted and relayed through the ventricular myocardium
  • Atrial contraction complete
  • Ventricular contraction starts
48
Q

What does atrial depolarization on the ECG look like?

A
  • The P wave on the ECG represents atrial depolarization (Atrial Contraction)
  • First wave on the ECG
49
Q

What does ventricular depolarization look like on the ECG?

A
  • QRS complex on the ECG (ventricular contraction)
  • The action potential here is moving from the AV node through the bundle of His and into the Purkinje Fibers
50
Q

What ventricular repolarization look like on the ECG?

A
  • The T wave on the ECG represents ventricular repolarization
  • Ventricles relax during this phase
51
Q

What does repolarization of Purkinje Fibers look like on ECG?

A
  • U wave on the ECG
  • This is not always visble on the ECG
  • Very small wave
  • Depends on the rate of re-stimulation of the cardiac cells
52
Q

What is the basic principles of electrode placement?

A
  • May be necessary to shave body hair
  • Rub the electrode site briskly with an alcohol swab before application
  • Gently scrape the site with the plastic backing of the electrode
  • Attach the electrodes to the ECG cables before placement
53
Q

Lead Placement

A
  • Remember these leads are considered Limb Leads- they should preferably be placed on the limbs
  • If not possible, use chest/ torso
54
Q

What is in lead II?

A
  • White electrode= RA
  • Red electrode= LL
  • Black electrode= LA
  • Green electrode= RL
55
Q

What happens when the electrodes are positioned correctly?

A
  • When positioned correctly on the chest, these leads form a triangle around the heart called the Einthoven Triangle
56
Q

What are the 4 limb leads?

A
  • The 4 limb leads are bipolar
  • They will switch between - and + depending on which view you are looking at
57
Q

What are the 6 chest leads?

A
  • The 6 chest leads are unipolar
  • They can only look in one direction
58
Q

What are leads I, II, and II?

A
  • They are bipolar leads and contain a positive and negative pole
59
Q

Where is lead I formed?

A
  • formed between the right and left arm electrodes.
  • The left arm electrode is the positive terminal
60
Q

Where is lead II formed?

A
  • formed between the right arm and left leg
  • The left leg electrode is positive terminal

Emrg 1230 (24 decks)

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