Antiarrhythmatics part 2 Flashcards
1
Q
What is the resting membrane potential of pacemaking cells?
A
-40 to -65
2
Q
What is the resting membrane potential of non-pacemaking cells?
A
-80 to -95
3
Q
What is an arrhythmia?
A
any rhythm that is not a normal sinus rhythm with normal atrioventricular (AV) conduction
4
Q
What are the different arrhythmia patterns?
A
- irregular
- tachycardia
- bradycardia
- problems related to abnormal conduction and/or muscle depolarization
5
Q
What is considered bradycardia?
A
HR < 50-60 bpm
- sinus sick syndrome
- atrio-ventricular conduction block
6
Q
What is considered a tachycardia?
A
HR > 100 bpm
7
Q
What is considered a paroxysmal tachycardia?
A
HR of 150-250 bpm
8
Q
What is considered an atrial flutter?
A
atria beat at 250-350 bp, regular heart rhythm
9
Q
What is considered atrial fibrillation?
A
atria beat up to 500 bpm, irregular rhythm, uncoordinated contraction
10
Q
What is considered a ventricular tachycardia?
A
over 120 bpm, regular heart rhythm
11
Q
What is considered a ventricular fibrillation?
A
irregular rhythm with uncoordinated contraction, immediate cause of death
12
Q
What is a tornado de points?
A
Long QT syndrome
13
Q
What is an arrhythmia caused by?
A
- alteration in the movement of ions responsible for the action potentials int he pacemaker calls, conduction system and/or muscle
14
Q
What are the 2 important ions in the action potential?
A
- pacemaking (slow) cells (SA node, AV node)
- Ca and K are most important
- this is in the atria - Conduction and muscle (fast) cells (atria, parking fibres, ventricles)
- Na, Ca and K are the most important
15
Q
What are some common causes of cardiac arrhythmias?
A
- insufficient oxygen to myocardial cells
- acidosis or accumulation of waste products
- electrolyte disturbances
- structural damage of the conduction pathway (can be patients with heart failure and patients with the previous MI)
- drugs (antipsychotic and anti-arrythmias. Drugs can also participate an MI)
16
Q
What are the 2 mechanisms of cardiac arrhythmias?
A
- Abnormal impulse formation
(abnormal automaticity and triggered activity) - Abnormal conduction
(impaired AV node leads to bradyarrhythmias, re-entry conduction leads to tachyarrhythmias)
17
Q
What is triggered activity?
A
slow and poorly conducted action potential in the atria or the ventricles
18
Q
Describe abnormal automaticity
A
- altered SA node firing rate through changes in autonomic activity
- enhanced activity of spontaneous pacemakers (ie. AV node, purkinje fibres) - ectopic pacemakers
- — decrease in phase 4 K conductance (hypokalemia) - increases spontaneous depolarization
- —- inactivation of Na channels in depolarized cells (schema)- converts fast cells into ectopic pacemakers
- — localized supersensitivity to catecholamines following ischemia
19
Q
What happens when you increase the rate of depolarization? When you decrease the rate of depolarization?
A
Increase: increased HR
Decrease: decreased HR
20
Q
What happens when you make the RMP more depolarized? More hyper polarized?
A
depolarized: increased HR
more hyperpolarized: decreased HR
21
Q
What happens when there is a more negative threshold? What happens with a more positive threshold?
A
negative: inreased HR
more positive threshold: decreased HR
22
Q
What is the action of the NT acetylcholine?
A
- released from parasympathetic nerve
- acts on the muscarininc receptors
- phase 4- slows depolarization rate
- decreases automaticity (SA node), slowed conduction (AV node)
23
Q
What is the action NT norepinephrine and epinephrine?
A
- released from the sympathetic nerves
- acts on B-adrenergic receptors
- phase 4 - increases depolarization rate and reduces AP firing threshold
- increases automaticity (SA node), increased conduction (AV node)
24
Q
What is the triggered activity?
A
- cells depolarize before complete depolarization has occurred
- non-automatic myocardial cells (atria, ventricles)
- – repolarization is required to change Na channels from inactive to resting
- – Ca channel availability is based on time
- – may be caused by prolonged duration of the action potential- prolonged QT interval? (i.e.. blockade of K channels by class 1 and 3 anti arrhythmic drugs)
- – with increased action potential duration (QT interval) calcium channels may be ready before the sodium channels
25
What happens when EAD is sub threshold?
prolonged action potential leads to early after depolarization
26
What happens when EAD reaches threshold?
prolonged action potential leads to a run of spontaneous activity
27
What can EADs trigger?
Torsade de pointes
28
Conditions/drugs which prolong the QT interval may precipitate _____
Torsades de Pointes
29
What is a torsades de pointes?
- it is characterized by twisting of isoelectric points on ECG and prolonged QT interval
- inherited and/or drug induced (increased QT interval)
- can lead to ventricular fibrillation and sudden death
- responds to magnesium
30
What drugs can increase the QT interval?
- antiarrhythmics
- antihistamines
- anti-psychotics
- antibiotics (e.g. erythromycin)
- can cause sudden death - hERG assays now routine during drug development
31
What is the mechanism of cardiac arrythmias that lead to abnormal conduction reentry?
- local differences in conduction velocity and membrane characteristics lead to development of electrical circuits (circus conduction)
- re-reouting of the normal electrical circuitry results in multiple beats before the next sinus beat is generated, resulting in tachycardia
32
What does normal conduction reentry involve?
- reentry requires an available circuit (closed conduction loop)
- unidirectional block
- different conduction speed in limbs of circuit: conduction time (CT) > effective refractory period (ERP)
33
What does unidirectional block re-entry involve?
- available circuit (closed conduction loop)
- unidirectional block
- different conduction speed in limbs of circuit: conduction time (CT) > effective refractory period (ERP)
34
What are the main causes of re-entry?
- ischemia
- congenital
- hyperkalemia
35
What parts of the heart can re-entry occur in?
- AV node
- between the SA node and the atria
- between atria and ventricles
- accounts for most tachyarrhythmias in cardiac patients
36
How can re-entry be stopped?
```
can be stopped by converting the unidirectional block tissue to bi-directional block
- in non-pacemaker (fast) cells, this can be done with drugs that block Na channels directly (class 1 drugs )
```
37
What is paroxysmal supra ventricular tachycardia?
- its a special case of reentry in the AV node
| - the cause is not clear and is often short lasting
38
What can a paroxysmal supra ventricular tachycardia?
- controlled by drugs that depress AV conduction, causing bidirectional block
- calcium channel blockers (Class 4)
- B-adrenergic receptor blockers (class 2)
- adenosine (class 5)
39
What is it called when there is an an abnormal electrical pathway in the paroxysmal supra ventricular tachycardia?
Wolff-Parkinson-White syndrome (conducts from the ventricles to atria - bundle of Kent)
40
What is the treatment options of Wolff-Parkinson-White syndrome?
- treated by catheter ablation of abnormal electrical pathway
- amiodarone first choice agent used to stabilize heart rate
41
Should void AV node blockers if _________ or _______. What drugs do these include?
atrial fibrillation
flutter
B-adrenergic receptor blocker, calcium antagonist, adenosine or digoxin
42
What are the three mechanisms of action of anti-arrhythmic drugs?
1. reducing automaticity
2. blocking re-entry mechanisms
3. normalize ventricular rate (supra-ventriular tachycardia)
43
Blocking inactivated Na+ or Ca++ channels depolarizing tissues (preventing conversion to "resting" state) lead stop reduced ________
triggered activity
44
Hyperpolarizing resting membrane potential (more negative RMP) leads to reduced _______ activity
pacemaker
45
When you have an increasing membrane threshold potential for activation of Na+ (fast cells) or Ca++ channels (slow cells) leads to what?
reduced pacemaker activity
46
What is 1 way that you can block re-rentry mechanisms via anti-arrythmic drugs?
reduce phase 0 depolarization -> slows conduction in ischemia area -> converts region of unidirectional block of bidirectional block
47
What is another mechanism of blocking re-entry mechanisms?
prolong the action potential depolarization -> increases the effective refractory period (ERP) -> conduction time < ERP = re-entry blocked
48
How to antiarrhythmic drugs work to normalize ventricular rates in supra-ventricular tachycardia?
slowing AV nodal conduction (beta blockers, calcium channel blockers and digoxin) -> reduces ventricular rate -> increasing time for ventricular filling from atrium -> improves stroke volume -> increase cardiac output (CO =HRx increases SV) -> improved hemodynamics
49
What are examples of class 1 antiarrhythmic drugs and what is their action in the cell?
- procainamide, lidocaine, flecainide
| - primarily block Na channels
50
What are the examples of class 2 antiarrythmic drugs and what is their action inside the cell?
- propanolol, metoprolol, esmolol
| - primarily blocks B-adrenergic receptors
51
What are the examples of class 3 antiarrythmic drugs and what is their action inside of the cell?
- amiodarone, sotalol
| - primarily blocks K channels
52
What are the example of class 4 antiarrythmic drugs and what is their action inside of the cell?
- verapamil
| - primarily blocks Ca channels
53
What are the examples of class 5 antiarrythmic drugs and what is their action inside of the cell?
- magnesium, adenosine and digoxin
| - block calcium gated channels - K blockers target on pacemaking cells
54
Describe IA sodium channel blockers. What is an example of this?
- moderate phase 0 depression and slow conduction; usually prolong repolarization
- procainamide
55
Describe IB sodium channel blockers. What is an example of this?
- minimal phase 0 depression and slow conduction; usually shorten repolarization (lidocaine)
56
Describe IC sodium channel blockers. What is an example of this?
- shows marked depression and slow conduction; little effect on repolarization
(flecainide)
57
Class 1A Na channel blockers primarily block _______, especially in depolarized cells
Na channels
58
What are the two things that cane seen on an ECG after giving a class 1A drug that corresponds to the bloc?
slowing of the phase 0 depolarization
| - slowing conduction velocity (widening of the QRD complex of the ECG)
