Antiarrhythmatics

Question 1

What groups do arrhythmias typically occur in?

Answer 1

• those treated with heart failure
• in anesthetized patients
• in patients post MI

Question 2

Where is the heart’s pacemaker usually located?

Answer 2

• on the SA node- it is the impulse generator

Question 3

What are the conduction fibres of the heart?

Answer 3

• in the AV node, bundle of His and the parking fibres

Question 4

Normal cardiac rhythm is known as what?

Answer 4

• sinus rhythm

Question 5

What is an arrhythmia?

Answer 5

• any rhythm that is not a normal sinus rhythm with normal AV conduction

Question 6

Describe the SA node

Answer 6

• the main pacemaker and initiator of heart beat
• spontaneously discharges 60-100 beats per minute
• rate can be changed by nerves innervating the heart

Question 7

Describe the AV node

Answer 7

• only normal electrical connection between the atria and the ventricles
• delays conduction of action potential by 0.1 second. Important to allow atria to contract and ventricles to fill before
• spontaneously discharges at 40-60 bpm (normally overridden)
• rate can be changed by nerves innervating the heart

Question 8

Describe the conduction fibres

Answer 8

• function is to excite the ventricular mass as near simultaneously as possible
• purkinje fibers spontaneously discharge at 20-40 beats bpm (overriden)

Question 9

What does the P wave correspond to?

Answer 9

• corresponds to the contraction of the atrial muscles

Question 10

What does the QRS complex correspond to?

Answer 10

• corresponds to the contraction of the ventricle muscle

Question 11

What does the QT correspond to?

Answer 11

• duration of an action potential within the ventricle muscle

Question 12

What is the electrical conduction past the SA node?

Answer 12

SA noe pacemaker impulse

-> conduction to atria -> AV node -> bundle of His- Purkinje fibers -> ventricular myocardium -> contraction

Question 13

What does the T wave correspond to?

Answer 13

ventricular repolarization

Question 14

What does the PR interval correspond to?

Answer 14

• conduction time atria to ventricles

Question 15

What will be noticeable on the action potential that can show a dangerous arrhythmia that can occur with different drugs?

Answer 15

• extension of the QT complex

Question 16

What are class 1 anti-arrhythmic medications?

Answer 16

-procainamide, lidocaine, flecanide (primarily block Na channel)

Question 17

What are class 2 anti-arrhythmic medications?

Answer 17

• propanolol, metoprolol, esmolol (primarily block beta adrenergic receptors)

Question 18

What are class 3 anti-arrhythmic medications?

Answer 18

• amiodarone, sotalol (primarily block K channels)

Question 19

What are the class 4 anti-arrhythmic medications?

Answer 19

• verapamil

primarily block Ca channels

Question 20

What are the class 5 anti-arrhythmic medications?

Answer 20

• magnesium, adenosine, digoxin (other mechanisms of action)

Question 21

What is the action of calcium in the heart?

Answer 21

• calcium is for excitation and contraction - entry of calcium has an important consequence for the mechanical operation of the heart
• calcium and sodium are pumped into the cell - this is the basis for the action potential

Question 22

The inward flow of ions are always going to cause ______, while the outward flow of ions is always going to cause ______

Answer 22

depolarization

repolarization

Question 23

What are the non-pacemaking parts of the heart (fast)?

Answer 23

• atria, ventricles, purkinje fibers

Question 24

What are the pacemaking parts of the heart (slow)?

Answer 24

• SA node, AV node

Question 25

What are the phases that affect non-pacemaking cells in the heart?

Answer 25

Phase 4, 0, 1, 2 and 3

Question 26

Pacemaking cells almost express NO _____ channels

Answer 26

sodium

Question 27

Non-pacemaking cells have a ____ threshold, and when the action potential is reached it is very rapid

Answer 27

low

Question 28

Describe phase 4 in non-pacemaking cells?

Answer 28

- diastolic resting potential - no time-dependent currents during phase 4 - as a result, resting potential is substantially more negative (-80V) than SA/AV nodes

Question 29

Describe phase 0 in non-pacemaking cells?

Answer 29

- depolarization phase - lots of voltage gated Na channels -- has a low threshold potential that is easily opened - threshold reached- active collage gated Na channels open - rapid depolarization - Na channels quickly become inactive - ends depolarization - if resting membrane potential depolarized - decreased available Na channels

Question 30

Describe phase 1 in non-pacemaking cells?

Answer 30

- slight repolarization | - chloride channels open briefly and chloride enters the cell

Question 31

Describe phase 2 in non-pacemaking cells?

Answer 31

- opening of voltage gated L-type Ca channels - Ca enters the cell- causes further release of Ca from the sarcoplasmic reticulum - Ca dependent contraction

Question 32

Describe phase 3 in non-pacemaking cells?

Answer 32

- repolarization - K channels activate (open) - movement of K out of the cell repolarizes the membrane -- returns to resting membrane potential - Ca is removed from the cytoplasm and tissue relaxes

Question 33

How quickly can this non-pacemaking tissue be re-stimulated?

Answer 33

- there is an absolute refractory period - phase 3: Na channels recover from "inactive" to "resting" state - repolarization switches sodium channels from inactive to resting - if the Na channels are in the inactive state, then myocytes can not depolarize - there is an absolute refractory period - if only a portion of the Na channels are in the "inactive" state, then the myocyte may depolarize, but it leads to a much less rapid depolarization (fever Na channels to be opened- this is called the relative refractory period)

Question 34

Opening of the ___ channels is responsible for the rapid depolarization of the non-pacemaking cells

Answer 34

Na

Question 35

What is the effect of depolarization of the resting membrane potential in these cells?

Answer 35

- decrease in the number of sodium channels available - decrease in the rate of depolarization - decreases the strength and speed of the impulse

Question 36

What is slow depolarization of the resting membrane potential caused by?

Answer 36

- caused by hyperkalemia, ischemia, drugs blocking sodium channels - will decrease the upstroke or eliminate it all together - -- THEREFORE, need to completely repolarize the membrane and resting sodium channels

Question 37

In pacemaking cells, the depolarization is due to ___ influx

Answer 37

Ca

Question 38

What are the different phases that take pace in pacemaking cells?

Answer 38

- phase 4, 0, and 3

Question 39

Describe how phase 4 occurs in SA nodes/AV nodes?

Answer 39

- spontaneous depolarization - pacemaker current- increased Na influx - increased Ca influx - decreased K efflux

Question 40

What is the comparable intrinsic firing rate in the different areas where pacemaking cells are?

Answer 40

SA > AV > Bundle of His > parking fibres | (bundee of His and p

Question 41

Describe how phase 0 occurs in SA nodes/AV nodes?

Answer 41

- threshold reached- voltage gated L-type Ca channels open, causing rapid repolarization - then L type calcium channels close

Question 42

What phases are not included in pacemaking cells?

Answer 42

phase 1 and 2 is absent

Question 43

Describe how phase 3 occurs in SA nodes/AV nodes?

Answer 43

- voltage gated K channels open and membrane repolarizes

Question 44

What is the resting membrane potential in fast response times vs slow response time?

Answer 44

fast response: -80 to -95 mV | slow response: -40 to -65 mV

Question 45

What is the phase 0 current in fast response times vs slow response times?

Answer 45

fast response: Na | slow response: Ca

Question 46

How fast the conduction velocity in fast response times vs slow response times?

Answer 46

fast response: 0.5 - 5m/sec | slow response: 0.01 - 0.1m/sec