Flashcards in Antiarrhythmatics Deck (46):
What groups do arrhythmias typically occur in?
- those treated with heart failure
- in anesthetized patients
- in patients post MI
Where is the heart's pacemaker usually located?
- on the SA node- it is the impulse generator
What are the conduction fibres of the heart?
- in the AV node, bundle of His and the parking fibres
Normal cardiac rhythm is known as what?
- sinus rhythm
What is an arrhythmia?
- any rhythm that is not a normal sinus rhythm with normal AV conduction
Describe the SA node
- the main pacemaker and initiator of heart beat
- spontaneously discharges 60-100 beats per minute
- rate can be changed by nerves innervating the heart
Describe the AV node
- 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
Describe the conduction fibres
- function is to excite the ventricular mass as near simultaneously as possible
- purkinje fibers spontaneously discharge at 20-40 beats bpm (overriden)
What does the P wave correspond to?
- corresponds to the contraction of the atrial muscles
What does the QRS complex correspond to?
- corresponds to the contraction of the ventricle muscle
What does the QT correspond to?
- duration of an action potential within the ventricle muscle
What is the electrical conduction past the SA node?
SA noe pacemaker impulse
-> conduction to atria -> AV node -> bundle of His- Purkinje fibers -> ventricular myocardium -> contraction
What does the T wave correspond to?
What does the PR interval correspond to?
- conduction time atria to ventricles
What will be noticeable on the action potential that can show a dangerous arrhythmia that can occur with different drugs?
- extension of the QT complex
What are class 1 anti-arrhythmic medications?
-procainamide, lidocaine, flecanide (primarily block Na channel)
What are class 2 anti-arrhythmic medications?
- propanolol, metoprolol, esmolol (primarily block beta adrenergic receptors)
What are class 3 anti-arrhythmic medications?
- amiodarone, sotalol (primarily block K channels)
What are the class 4 anti-arrhythmic medications?
(primarily block Ca channels)
What are the class 5 anti-arrhythmic medications?
- magnesium, adenosine, digoxin (other mechanisms of action)
What is the action of calcium in the heart?
- 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
The inward flow of ions are always going to cause ______, while the outward flow of ions is always going to cause ______
What are the non-pacemaking parts of the heart (fast)?
- atria, ventricles, purkinje fibers
What are the pacemaking parts of the heart (slow)?
- SA node, AV node
What are the phases that affect non-pacemaking cells in the heart?
Phase 4, 0, 1, 2 and 3
Pacemaking cells almost express NO _____ channels
Non-pacemaking cells have a ____ threshold, and when the action potential is reached it is very rapid
Describe phase 4 in non-pacemaking cells?
- diastolic resting potential
- no time-dependent currents during phase 4
- as a result, resting potential is substantially more negative (-80V) than SA/AV nodes
Describe phase 0 in non-pacemaking cells?
- 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
Describe phase 1 in non-pacemaking cells?
- slight repolarization
- chloride channels open briefly and chloride enters the cell
Describe phase 2 in non-pacemaking cells?
- opening of voltage gated L-type Ca channels
- Ca enters the cell- causes further release of Ca from the sarcoplasmic reticulum
- Ca dependent contraction
Describe phase 3 in non-pacemaking cells?
- 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
How quickly can this non-pacemaking tissue be re-stimulated?
- 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)
Opening of the ___ channels is responsible for the rapid depolarization of the non-pacemaking cells
What is the effect of depolarization of the resting membrane potential in these cells?
- decrease in the number of sodium channels available
- decrease in the rate of depolarization
- decreases the strength and speed of the impulse
What is slow depolarization of the resting membrane potential caused by?
- 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
In pacemaking cells, the depolarization is due to ___ influx
What are the different phases that take pace in pacemaking cells?
- phase 4, 0, and 3
Describe how phase 4 occurs in SA nodes/AV nodes?
- spontaneous depolarization - pacemaker current- increased Na influx
- increased Ca influx
- decreased K efflux
What is the comparable intrinsic firing rate in the different areas where pacemaking cells are?
SA > AV > Bundle of His > parking fibres
(bundee of His and p
Describe how phase 0 occurs in SA nodes/AV nodes?
- threshold reached- voltage gated L-type Ca channels open, causing rapid repolarization
- then L type calcium channels close
What phases are not included in pacemaking cells?
phase 1 and 2 is absent
Describe how phase 3 occurs in SA nodes/AV nodes?
- voltage gated K channels open and membrane repolarizes
What is the resting membrane potential in fast response times vs slow response time?
fast response: -80 to -95 mV
slow response: -40 to -65 mV
What is the phase 0 current in fast response times vs slow response times?
fast response: Na
slow response: Ca