Antiarrhythmics - Class I (Fast Na+ channel blockers) Flashcards
The cardiac electrophysiology in a pacemaker cell has only 3 phases, which ultimately lead to an action potential (as seen in the image). What is occurring at stage 4?
1 - pacemaker potential phase
2 - depolarisation phase
3 - Leaky K+ phase
4 - Ca2+ leaking into cell phase
1 - pacemaker potential phase
- similar to resting membrane potential
- around -65 mV
The cardiac electrophysiology in a pacemaker cell has only 3 phases, which ultimately lead to an action potential (as seen in the image).To move between phase 4 and 0, there is a special type of channel located on the pacemaker cells that allows Na+ to flow into the pacemaker cells, raising the action potential to -50 mV. What is the channel called?
1 - Na+ channel
2 - Na+/K+ ATPase channel
3 - hyperpolarization-activated cyclic nucleotide-gated channels (HCN)
4 - Na+/Ca2+ co-transport
3 - hyperpolarization-activated cyclic nucleotide-gated channels (HCN)
- important when cells hyperpolarise following an action potential, these channels help the pacemaker cell get close to action potential and fir again
- called the funny current
The cardiac electrophysiology in a pacemaker cell has only 3 phases, which ultimately lead to an action potential (as seen in the image). The funny current (Na+ entering the pacemaker cells) then enters phase 0. What is this phase called?
1 - pacemaker potential phase
2 - depolarisation phase
3 - Leaky K+ phase
4 - Ca2+ leaking into cell phase
2 - depolarisation phase
- Na+ enters cell through HCN
- Ca2+ enters the cell through Ca2+ channels
- pacemaker cells membrane potential becomes + (around 10mV
The cardiac electrophysiology in a pacemaker cell has only 3 phases, which ultimately lead to an action potential (as seen in the image). In phase 0 Na+ and Ca2+ enter pacemaker cells causing depolarisation (aprox 10 mV). The pacemaker cell then enters phase 3. What of the following then happens here?
1 - Ca2+ channels close
2 - Na+ channels remain open
3 - K+ channels open and K+ leaves the cell
4 - all of the above
4 - all of the above
- lots of K+ channels
- overall this causes the membrane potential to drop called repolarisation
- phase 4 begins again
In a myocyte cell the cardiac electrophysiology has 5 phases (0-4), which ultimately lead to an action potential (as seen in the image). Phase 0 is the resting phase (-90mV). What then enters the myocyte through gap junctions that raises the resting membrane potential (-90mV) to the threshold potential (-70mV)?
1 - Na+
2 - K+
3 - Ca2+
4 - Mg+
3 - Ca2+
In a myocyte cell the cardiac electrophysiology has 5 phases (0-4), which ultimately lead to an action potential (as seen in the image). Phase 0 occurs when the the membrane potential reaches -70mV. Which channels then open causing depolarisation, reaching around 20mV?
1 - Na+
2 - K+
3 - Ca2+
4 - Mg+
1 - Na+
In a myocyte cell the cardiac electrophysiology has 5 phases (0-4), which ultimately lead to an action potential (as seen in the image). Following depolarisation, we reach phase 1, called initial repolarisation. Which 2 of the following occurs here?
1 - Na+ channels close
2 - K+ channels open and K+ leaves the cell
3 - Ca2+ channel opens
4 - Mg+ channel closes
1 - Na+ channels close
2 - K+ channels open and K+ leaves the cell
- causes a drop in membrane potential
In a myocyte cell the cardiac electrophysiology has 5 phases (0-4), which ultimately lead to an action potential (as seen in the image). Following initial repolarisation (phase 1), to stop the myocyte going into full repolarisation, another channel opens and the membrane potential plateaus, called the plateau phase. Which channel opens to maintain this plateau phase (phase 2)?
1 - Na+ channels
2 - K+ channels
3 - Ca2+ channels
4 - Mg+ channels
3 - Ca2+
- Ca2+ flows into the cell
- membrane charge is maintained
- responsible for heart contraction
In a myocyte cell the cardiac electrophysiology has 5 phases (0-4), which ultimately lead to an action potential (as seen in the image). Following the plateau phase (phase 2) which is when the heart contracts, which of the following occurs in phase 3, called repolarisation?
1 - Ca2+ channels close
2 - K+ channels remain open
3 - Ca2+ is pumped out of the cell
4 - all of the above
4 - all of the above
- myocyte returns to resting membrane potential of around -90mV
When looking at an ECG, what does the P wave represent in relation to an an action potential?
1 - sum of depolarisation in all atrial myocytes
2 - sum of depolarisation in all ventricle myocytes
3 - sum of repolarisation in all atrial myocytes
4 - sum of repolarisation in all ventricle myocytes
1 - sum of depolarisation in all atrial myocytes
When looking at an ECG, what does the QRS wave represent in relation to an an action potential?
1 - sum of depolarisation in all atrial myocytes
2 - sum of depolarisation in all ventricle myocytes
3 - sum of repolarisation in all atrial myocytes
4 - sum of repolarisation in all ventricle myocytes
2 - sum of depolarisation in all ventricle myocytes
- atrial myocytes also repolarise here as well, but this is masked by the QRS
When looking at an ECG, what does the ST segment represent in relation to an an action potential?
1 - sum of depolarisation in all atrial myocytes
2 - sum of depolarisation in all ventricle myocytes
3 - sum of repolarisation in all atrial myocytes
4 - plateau phase
4 - plateau phase
- this is when the ventricle contract and pump blood
When looking at an ECG, what does the T wave represent in relation to an an action potential?
1 - sum of depolarisation in all atrial myocytes
2 - sum of depolarisation in all ventricle myocytes
3 - sum of repolarisation in all ventricle myocytes
4 - plateau phase
3 - sum of repolarisation in all ventricle myocytes
When we look at an action potential, which phase would a class I (Na+ channel blocker) be able to have an affect?
1 - phase 4
2 - phase 0
3 - phase 1
4 - phase 2
5 - phase 3
2 - phase 0
- depolarisation is due to an influx of Na+
- this is only effective in myocytes and not pacemaker cells
Which of the following is a class I anti-arrhythmic core medication?
1 - Amiodarone
2 - Atenolol
3 - Verapamil
4 - Flecainide
4 - Flecainide
What is the mechanism of action of Flecainide, the class I anti-arrhythmic core medication?
1 - inhibit noradrenaline and adrenaline binding with B1 cardiac receptors
2 - inhibit fast Na+ channel blockers in cardiac myocytes
3 - Ca2+ channel blockers
4 - K+ channel blockers
2 - inhibit fast Na+ channel blockers in cardiac myocytes
- reduce Na+ influx into cells
- prolong conduction and thus slow the heart rate
Na+ channels have 3 stages, open, inactive and resting. Which stages do the class 1 anti-arrhythmias (Na+ channel blockers) have preference for?
1 - inactive and resting
2 - inactive and open
3 - resting and open
4 - all of them equally
2 - inactive and open
- more active a channel = greater inhibition, so a faster HR = a greater inhibitory effect
- keeps Na+ channel inactive for longer
- called used dependence
Flecainide, the class I anti-arrhythmic core medication are able to inhibit Na+ channel in cardiac myocytes. This drug is indicated in paroxysmal AF, supraventricular (AV reentrant (or reciprocating) tachycardia (AVRT)), Ventricular arrhythmias (both must be adminstered in hospital) and wolf parkinsons white syndrome (WPW). Why is Flecainide specifically effective in these types of arrhythmias?
1 - also inhibit Ca2+ channels
2 - low Na+ inhibits AV node and thus heart rate
3 - act on myocytes that are depolarising a lot
4 - reduce SA node firing
3 - act on myocytes that are depolarising a lot
- even more effective when an arrhythmia is severe
- more selective for abnormally over-reactive parts of the heart, so great for arrythmias
- effective at blocking accessory pathways
Flecainide, the class I anti-arrhythmic core medication are able to inhibit Na+ channel in cardiac myocytes. This drug is indicated in paroxysmal AF, supraventricular (AV reentrant (or reciprocating) tachycardia (AVRT)), Ventricular arrhythmias and wolf parkinsons white syndrome (WPW), BUT need to be administered in hospital. What affect does this drug have on an ECG tracing?
1 - prolonged PR interval
2 - shortened QRS interval
3 - long QRS interval
4 - long QT interval
3 - long QRS interval
