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Pharmacology > Antiarrhythmatics > Flashcards

Antiarrhythmatics Flashcards

1
Q

What groups do arrhythmias typically occur in?

A
  • those treated with heart failure
  • in anesthetized patients
  • in patients post MI
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2
Q

Where is the heart’s pacemaker usually located?

A
  • on the SA node- it is the impulse generator
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3
Q

What are the conduction fibres of the heart?

A
  • in the AV node, bundle of His and the parking fibres
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4
Q

Normal cardiac rhythm is known as what?

A
  • sinus rhythm
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5
Q

What is an arrhythmia?

A
  • any rhythm that is not a normal sinus rhythm with normal AV conduction
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6
Q

Describe the SA node

A
  • the main pacemaker and initiator of heart beat
  • spontaneously discharges 60-100 beats per minute
  • rate can be changed by nerves innervating the heart
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7
Q

Describe the AV node

A
  • 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
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8
Q

Describe the conduction fibres

A
  • function is to excite the ventricular mass as near simultaneously as possible
  • purkinje fibers spontaneously discharge at 20-40 beats bpm (overriden)
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9
Q

What does the P wave correspond to?

A
  • corresponds to the contraction of the atrial muscles
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10
Q

What does the QRS complex correspond to?

A
  • corresponds to the contraction of the ventricle muscle
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11
Q

What does the QT correspond to?

A
  • duration of an action potential within the ventricle muscle
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12
Q

What is the electrical conduction past the SA node?

A

SA noe pacemaker impulse

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

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13
Q

What does the T wave correspond to?

A

ventricular repolarization

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14
Q

What does the PR interval correspond to?

A
  • conduction time atria to ventricles
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15
Q

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

A
  • extension of the QT complex
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16
Q

What are class 1 anti-arrhythmic medications?

A

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

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17
Q

What are class 2 anti-arrhythmic medications?

A
  • propanolol, metoprolol, esmolol (primarily block beta adrenergic receptors)
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18
Q

What are class 3 anti-arrhythmic medications?

A
  • amiodarone, sotalol (primarily block K channels)
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19
Q

What are the class 4 anti-arrhythmic medications?

A
  • verapamil

primarily block Ca channels

20
Q

What are the class 5 anti-arrhythmic medications?

A
  • magnesium, adenosine, digoxin (other mechanisms of action)
21
Q

What is the action of calcium in the heart?

A
  • 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
22
Q

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

A

depolarization

repolarization

23
Q

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

A
  • atria, ventricles, purkinje fibers
24
Q

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

A
  • SA node, AV node
25
Q

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

A

Phase 4, 0, 1, 2 and 3

26
Q

Pacemaking cells almost express NO _____ channels

A

sodium

27
Q

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

A

low

28
Q

Describe phase 4 in non-pacemaking cells?

A
  • diastolic resting potential
  • no time-dependent currents during phase 4
  • as a result, resting potential is substantially more negative (-80V) than SA/AV nodes
29
Q

Describe phase 0 in non-pacemaking cells?

A
  • 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
30
Q

Describe phase 1 in non-pacemaking cells?

A
  • slight repolarization

- chloride channels open briefly and chloride enters the cell

31
Q

Describe phase 2 in non-pacemaking cells?

A
  • opening of voltage gated L-type Ca channels
  • Ca enters the cell- causes further release of Ca from the sarcoplasmic reticulum
  • Ca dependent contraction
32
Q

Describe phase 3 in non-pacemaking cells?

A
  • 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
33
Q

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

A
  • 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)
34
Q

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

A

Na

35
Q

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

A
  • decrease in the number of sodium channels available
  • decrease in the rate of depolarization
  • decreases the strength and speed of the impulse
36
Q

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

A
  • 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
37
Q

In pacemaking cells, the depolarization is due to ___ influx

A

Ca

38
Q

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

A
  • phase 4, 0, and 3
39
Q

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

A
  • spontaneous depolarization - pacemaker current- increased Na influx
  • increased Ca influx
  • decreased K efflux
40
Q

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

A

SA > AV > Bundle of His > parking fibres

(bundee of His and p

41
Q

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

A
  • threshold reached- voltage gated L-type Ca channels open, causing rapid repolarization
  • then L type calcium channels close
42
Q

What phases are not included in pacemaking cells?

A

phase 1 and 2 is absent

43
Q

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

A
  • voltage gated K channels open and membrane repolarizes
44
Q

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

A

fast response: -80 to -95 mV

slow response: -40 to -65 mV

45
Q

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

A

fast response: Na

slow response: Ca

46
Q

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

A

fast response: 0.5 - 5m/sec

slow response: 0.01 - 0.1m/sec

Pharmacology (23 decks)

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