in this lecture I'' m mosting likely to speak about
antiarrhythmic medicines so allow'' s solve into it as you might currently recognize the pumping action of the heart is regulated by the heart'' s electric system the heart includes specialized cells that are able to produce their own electrical impulses as well as send them to the cardiac muscle creating it to contract now the heart transmission system is composed of five elements leading the
sinoatrial node SA node for short number two the atrioventricular node AV node for brief number three the bundle of His number four the bundle branches and number 5 the Purkinje fibers so the regular heart rhythm starts when electrical signals are sent out from the SA node the signal from the SA node causes the room to contract pushing blood with the open shutoffs right into the ventricles on the typical electrocardiogram this is represented by the P wave next electrical signal comes to the AV node and also is briefly postponed so that the contracting atria have sufficient time to pump all the blood right into the ventricles this is represented by the line between the P and also the Q wave at this point the signal takes a trip to the package of His into the package branches this is represented by the Q wave and also lastly this signal travels via the Purkinje fibers which causes the ventricles to contract as well as thus pump blood from the ideal ventricle right into the lungs as well as from the left ventricle right into the remainder of the body this is represented by the R and S swing the last T wave stands for the recuperation of the ventricles now heart cells can be divided right into 2 types initially contractile cells which make up a lot of the walls of the atria and also ventricles and when stimulated they generate force for contraction of the heart and also the 2nd type conducting cells which initiate the electrical impulse that regulates those contractions currently while contractile fibers can'' t produce an activity possibility on their own the carrying out fibers are capable of spontaneously launching an action potential by themselves they show so-called automaticity the doing cells are mainly concentrated in the cells of the SA node AV node package of His as well as Purkinje fibers currently usually SA node gets to threshold possibility the fastest which is why it works as the all-natural pacemaker of the heart when the SA node drives the heart price the cells of AV node bundle of His as well as Purkinje fibers do not reveal automaticity or to put it simply their spontaneous depolarization is suppressed nevertheless under certain conditions when activity of the SA node comes to be reduced or the shooting price of these various other performing cells ends up being quicker among them can end up being the new pacemaker of the heart this is why the AV node package of His and Purkinje fibers are called unexposed pacemakers now prior to we proceed let'' s take a closer consider the action capacity of the pacemaker cells versus the heart muscle mass cells as there are some essential distinctions between them so in the heart each cardiac cell has and is bordered by electrolyte liquids the primary ions in charge of the electrical activity within the heart are salt calcium and also potassium when cardiac cells are boosted by an electrical impulse their membrane'' s leaks in the structure adjustment and ions cross the membrane layer therefore producing an activity potential so currently the membrane layer possibility in the pacemaker cells begins at concerning negative 60 millivolt when spontaneous flow of salt generally with sluggish sodium channels and also opening of the voltage-gated T-type calcium networks continue sluggish depolarization this is described as stage 4 as soon as threshold possibility of about adverse 40 millivolt is gotten to the voltage-gated L-type calcium channels open calcium enters and quickly depolarizes cell to about favorable 10 millivolts this is referred to as stage 0 finally the L-type calcium channels close as well as the voltage-gated potassium channels open which enables potassium ions to run away hence repolarizing the cell back to adverse 60 millivolts this is referred to as phase 3 after this the cycle simply repeats itself additionally keep in mind that there is no phase 1 or stage 2 in the activity possibility of the pacemaker cells okay so now allow'' s take a.
consider the activity capacity of the heart muscle cells unlike pacemaker.
cells the cardiac muscular tissue cells have resting membrane capacity of about.
unfavorable 90 millivolts as a result of the continuous outside leak of.
potassium through the inward-rectifier channels this relaxing phase is referred.
to as stage 4 now when an action capacity is triggered in a bordering.
cell the voltage-gated salt networks open and salt rushes in triggering a.
fast depolarization to concerning positive 40 millivolts this is referred to as.
stage 0 at this moment the sodium networks end up being inactivated and also other.
voltage-gated channels begin to open up generally potassium networks which allow.
potassium to get away hence causing a little dip in membrane potential this.
is described as phase 1 currently something that I didn'' t mention is that. throughout depolarization at phase 0 voltage-gated L-type calcium channels.
started to open up slowly enabling calcium participate in the cell so currently with the.
positive potassium ions leaving as well as the favorable calcium ions progressively can be found in.
we have this electrically balanced ion exchange which maintains the membrane.
potential on a plateau this is referred to as phase 2.
last but not least the plateau phase is followed by a rapid repolarization referred to as phase 3 which is triggered by a progressive inactivation of the calcium channels and also.
continuous outflow of potassium this brings the membrane potential back.
to the resting stage 4 so currently let'' s switch over gears as well as let'' s discuss. arrhythmias so what is arrhythmia well arrhythmia is just a deviation of.
heart from a normal rhythm so typical heart rhythm will have a heart rate of.
between 60 to 100 beats per min with each beat created from the SA node.
each cardiac impulse will also proliferate with regular conduction pathway with.
normal speed currently arrhythmias are generally identified based on heart.
price as bradyarrhythmias when the rate is listed below 60 beats per min or.
tachyarrhythmias when the rate is over 100 beats per min nevertheless in order to.
recognize pharmacology of antiarrhythmic drugs we require to concentrate on mechanisms of.
tachyarrhythmias so there are 3 basic devices in charge of the.
initiation of tachyarrhythmias initially irregular automaticity also described as.
boosted automaticity this takes place when the cell membrane layer comes to be unusually.
permeable to sodium throughout phase 4 which leads to.
boost in the incline of stage 4 depolarization this can trigger other.
cells to accelerate their automaticity and hence create impulses faster than the SA.
node the second system is called triggered activity triggered activity.
involves the abnormal leakage of favorable ions right into the cardiac cell.
causing this bump on the activity prospective called afterdepolarization.
these afterdepolarizations can take place throughout stage 2 3 or 4 as well as if.
they have enough size they can cause early action capacities.
now the third system of tachyarrhythmias is called reentry.
instance of this is wolff-parkinson-white disorder in which an additional or supposed.
device pathway exists in between the upper and reduced chambers of the heart so.
generally the electric signal takes a trip from the SA node to AV node to bundle.
branches and when it reaches the Purkinje fibers it quits as well as waits on.
one more signal from the SA node currently when the device path shows up.
the signal travels with this pathway from ventricles back to room causing.
them to agreement before SA node fires once again this creates this abnormal loop of.
electrical activation circulating through an area of heart tissue triggering.
tachyarrhythmia an additional instance of reentry is atrioventricular nodal.
reentry tachycardia AVNRT for short so normally there are 2 structural.
pathways for bring signal via the AV node very first pathway is called the quick.
pathway because it permits rapid transmission nonetheless it has a lengthy refractory duration meaning it recoups slowly on the other side this 2nd.
path is called the slow pathway because it just permits slow-moving transmission.
and also since of that it has short refractory period meaning it recuperates.
quickly so currently the signal comes down from the SA node and afterwards it splits as well as.
journeys quick through the quick path and also slow with the slow-moving pathway so the.
quickly path signal reaches the usual path on the other end well prior to the.
slow-moving path signal gets there from there the fast path signal infects.
the ventricles in addition to up the slow path where it strikes the slow-moving signal.
causing it to end now if a premature beat takes place at the.
time when the rapid path signal is still in the refractory duration the.
signal will certainly travel down the slow-moving path as the sluggish signal comes close to the typical.
pathway rapid path appears of refractory period so now the sluggish signal.
spreads to the ventricles and it also travels up the rapid pathway however let'' s. not neglect that the slow pathway has a short refractory period so by the time.
the signal arrives the slow-moving pathway prepares to perform an additional.
signal so what inevitably occurs right here is that this signal remains to circle.
around sending out rapid impulses which result in tachycardia now let'' s carry on. to reviewing the actual antiarrhythmic medications so most commonly utilized.
classification of antiarrhythmics is the Vaughan Williams classification which.
teams most antiarrhythmics right into 4 classes based upon their dominant.
device of activity currently let'' s go over each of these classes so initially we have.
course 1 medicines which work mostly by obstructing salt channels in the open or.
suspended state restraint of sodium networks decreases the rate of surge of.
phase 0 depolarization and reduces transmission velocity course 1 medications are.
subdivided into 3 subclasses according to their result on the heart.
action possibility initially we have class 1A medicines which moderately depress the phase 0 depolarization by obstructing rapid salt channels they likewise extend repolarization by blocking some potassium channels so what we'' ll. see with course 1A agents is prolonged action possibility and prolonged efficient.
refractory period the agents in this course include Procainamide Quinidine and.
Disopyramide these agents are utilized in the treatment of a variety of.
arrhythmias such as ventricular tachycardias and.
frequent atrial fibrillation adverse results consist of obscured vision migraine.
and ringing in the ears which may occur with huge doses of Quinidine and some.
anticholinergic effects which might accompany making use of Disopyramide second of all.
we have course 1B medications which have reasonably weak result on the phase 0.
depolarization due to marginal blockade of quick sodium channels however these.
agents shorten repolarization by blocking salt networks that turn on.
during late stage 2 of the activity prospective so what we'' ll see with class. 1B agents is reduce period of action possibility and also shorten efficient.
refractory period the agents in this class include Lidocaine and also Mexiletine.
which are mostly used in the therapy of ventricular arrhythmias when it comes.
to adverse effects Lidocaine can cause CNS toxicity consisting of seizures while.
Mexiletine can cause nausea and also vomiting currently the third as well as the last.
subtype that we have is class 1C medications which are powerful rapid salt channel.
blockers which dispirit the phase 0 depolarization considerably they also.
hinder the His-Purkinje conduction system with a restricted result on.
repolarization and also refractory duration the representatives in this class consist of Flecainide.
as well as Propafenone which are primarily made use of in the treatment of refractory ventricular.
arrhythmias when it comes to damaging effects one of the most typical ones consist of dizziness.
blurred vision as well as nausea additionally something that I place'' t mentioned yet is that one.
of the risk related to the class 1 agents in fact every one of them is that.
they have possible to actually trigger arrhythmias themselves so evaluating the danger versus advantage is very vital prior to initiating treatment with these agents currently.
allow'' s proceed to course 2 antiarrhythmic drugs so representatives in
this. course act upon the beta-1 receptors avoiding the activity of.
catecholamines on the heart so class 2 agents are merely beta blockers beta blockers.
dispirit sinus node automaticity as well as slow-moving conduction via the AV node which.
results in reduced heart price and decreased contractility examples of beta.
blockers commonly made use of for arrhythmia are Propranolol Metoprolol Atenolol as well as.
Esmolol currently Esmolol unlike the various other beta blockers is rather unique in.
that it'' s provided intravenously in an emergency acute arrhythmias and the.
reason for that is that it has fast onset of action as well as extremely brief half-life.
which permits it to be titrated rapidly when essential so the lower line is.
that beta blockers are good choice for therapy of arrhythmias prompted by.
increased understanding task as well as if you want to find out more about them check.
out my various other video clips regarding adrenergic receptors and beta blockers now let'' s. relocation on to course 3 antiarrhythmic medications so class 3 agents function mostly.
by blocking the potassium channels that are accountable for the Stage 3.
repolarization this results in increase in period of activity possibility and.
increase in reliable refractory duration the representatives in this class include.
Amiodarone Dronedarone Sotalol Dofetilide and also Ibutilide there are.
generally utilized in therapy of supraventricular and also ventricular tachyarrhythmias as well as atrial fibrillation and also flutter the most commonly utilized.
drug in this course is Amiodarone which is extremely reliable for the treatment of.
these previously mentioned arrhythmias Amiodarone has numerous activities as well as.
besides obstructing potassium networks Amiodarone additionally blocks salt channels.
calcium networks and also some alpha and beta receptors regrettably Amiodarone is additionally related to lots of unfavorable effects such as lung fibrosis blue-grey skin staining neuropathy hepatotoxicity corneal microdeposits and also because it has iodine Amiodarone likewise can cause thyroid dysfunction causing hypo or.
hyperthyroidism lastly due to its lengthy half-life Amiodarone can stick around in numerous.
cells for months after discontinuation of therapy now on the various other hand we have.
Dronedarone which is derivative of Amiodarone it'' s less lipophilic and also has.
much shorter half-life it also doesn'' t contain iodine so in basic it has.
much better side impact profile sadly in a lot of cases Dronedarone doesn'' t appear. to be as effective as Amiodarone currently Sotalol is a special drug in this course.
because it not just has potassium network stopping task yet likewise beta.
receptor stopping task finally Dofetilide as well as Ibutilide are.
one of the most selective potassium network blockers in this course however they'' re. also most likely to cause arrhythmias themselves as well as therefore are usually.
launched in the inpatient setup only currently let'' s go on to class 4 antiarrhythmic medicines so course 4 agents job by blocking voltage-sensitive calcium.
networks during depolarization specifically in the SA as well as AV nodes.
which leads to slower transmission in these tissues and reduced contractility.
of the heart the representatives in this course consist of Verapamil and also Diltiazem which.
are the nondihydropyridine calcium network blockers unlike dihydropyridines which act primarily in the perimeter creating vasodilation nondihydropyridines are a lot more selective for the myocardium and therefore they.
program antiarrhythmic activities Verapamil and Diltiazem are most commonly made use of in.
treatment of supraventricular tachycardia and also atrial fibrillation and.
currently before we end this lecture I wanted to briefly review some various other.
antiarrhythmic agents that do not fairly suit any of the courses that we.
covered so far and these are Digoxin Adenosine and Magnesium Sulfate.
so allow'' s discuss Digoxin first and also in.
order to comprehend exactly how it functions let'' s imagine a cardiac cell under relaxing.
conditions sodium gradually leaks right into the cell and potassium leaks out however.
during an action potential added sodium goes into in together with calcium and also.
added potassium leaves the cell so eventually we have this discrepancy.
that has actually to be restored and also this repair is completed by pumps.
such as sodium-potassium ATPase which carries salt ions to the beyond.
the cell and also potassium to the inside of the cell and we likewise have sodium-calcium.
exchanger which gets rid of calcium from the cell for salt and also as a.
side note right here bear in mind that sodium-calcium exchanger can carry sodium and also calcium in both instructions so now what happens when Digoxin comes about is.
that it prevents sodium-potassium pump by binding to the potassium binding site.
this results in the increase in intracellular sodium which then in turn.
causes the sodium-calcium exchanger to pump salt out as well as bring even more calcium.
in now this boost in intracellular calcium leads to enhanced myocardial.
contractility Digoxin also boosts parasympathetic system which.
increases activity of the vagus nerve this results in the slowing down of sinus.
node discharge rate and decreased conduction through the AV node these.
actions make Digoxin especially beneficial for people with both cardiac arrest and.
atrial fibrillation currently let'' s discuss the second representative which is Adenosine. unlike all the other representatives Adenosine is a normally happening nucleoside it.
works by promoting A1 kind adenosine receptors on the atrium as.
well as on the SA node as well as AV node which causes lowered automaticity.
decreased conduction velocity as well as prolonged refractory period.
as a result of its really short duration of activity adenosine needs to be supervised by IV.
its primary indicator is a severe supraventricular tachycardia among the.
greatest benefits of Adenosine is that it'' s fairly safe with one of the most.
typical side results being breast discomfort flushing and also hypotension now lastly.
allow'' s discuss our third representative which is Magnesium Sulfate Magnesium Sulfate.
plays an important role in transportation of sodium potassium as well as calcium throughout the.
cell membranes regrettably its accurate mechanism of activity for treating.
arrhythmias is largely unidentified however what we understand is that Magnesium Sulfate.
provided intravenously is extremely efficient for therapy of torsades de pointes and Digoxin induced arrhythmias as well as with that said I wished to.
thanks for enjoying I hope you appreciated this lecture and also as always remain.
tuned for more.
