Supraventricular arrythmias Flashcards
Review the cardiac action potential:
What are the 4 (actually 5) phases of the cardiac action potential?
Which ion channels are open at each phase?
Rise of action potential dependent on inward Na+ current – upstroke phase (0)
(and also the overshoot at phase 1 = inward Ca2+ current)
Plateau = outward K+ current (phase 2)
Repolarization = phase 3; outward Ks current
Slow depolarization = phase 4; I-funny current (aka pacemaker current)
**T type calcium current is involved in phase 4 depolarization**
Describe the characteristics of the action potentials shown below.
Why are the SA and AV nodal APs the slowest?
Why are the QRS and T waves right after each other?
SA and AV nodal cells both have slow action potentials (in the AV nodal cells, no Na+ channels for fast depolarization)
**recall that these are the pacemakers and so their job is to literally set the pace for contraction. Key differences: no phase 1 and 2 in comparison to ventricular AP**
Atrial AP is sharp and short; His bundle and Purkinje fiber Aps are the typical cardiac Aps
Ventricular epicardial cells have shorter action potentials than endocardial cells
The epicardium repolarizes first and the endocardium depolarizes first, hence the T wave and the QRS complex are right next to each other
Explain the meaning of the following on an ECG:
P wave
QRS complex
P-R interval
T wave
U wave
QT interval
ST segment
P wave - atrial depolarization
PR interval - time from start of atrial depolarization to ventricular depolarization
QRS complex - ventricular depolarization
QT interval - ventricular depolarization >> contraction >> ventricular repolarization
T wave - ventricular repolarization
ST segment - ventricles depolarized (isoelectric)
The gradual depolarization in nodal cells in phase 4 is due to ___. The activation of which channels determines the speed of your heart rate?
The gradual depolarization in nodal cells in phase 4 is due to Ifunny current, activation of Ca2+ current and turning off of K current. The activation of the Ifunny channels and T type calcium channels in phase 4 of the cardiac AP (latter half) determine speed of heart rate
Describe the action potential of SA and AV nodal cells. What are the biggest differences between their AP and that of the ventricles?
Phase 0 - upstroke due to Ca2+ influx
No phase 1 and 2
Phase 3 - repolarization (inactivation of Ca2+ channels and activation of K+ channels - K+ efflux)
Phase 4 - slow (spontaneous diastolic) depolarization due to I funny current
Outline the order of pacemaker rates and speed of conduction
Pacemaker rates: SA nodal cells >> AV node cells >> Bundle of His >> Purkinje fibers >> ventricles
Speed of conduction: Purkinje >> atria >> ventricles >> bundle of His >> AV node
**note that Speed of Conduction and Pacemaker rates are very different so don’t confuse these**
___ current is activated by hyperpolarization to potentials more negative that -50mV, is permeable to both Na+/K+ and can be regulated by cAMP binding
I-funny current is activated by hyperpolarization to potentials more negative that -50mV, is permeable to both Na+/K+ and can be regulated by cAMP binding
In which cells of the heart are If channels located?
If current is located in nodal cells, Purkinje fibers, some atrial and ventricular cells
What does it mean for a cell to be refractory? What is the difference between an absolute refractory period and a relative refractory period?
Refractory – cell cannot be stimulated
Absolute refractory period – cells cannot be stimulated with any amount of energy
Relative refractory – cells not easy to stimulate but can be stimulated with enough energy
There are 3 mechanisms of arrhythmias, namely ___
There are 3 mechanisms of arrhythmias, namely re-entry, enhanced automaticity and triggered arrhythmias
Describe each of the mechanisms of arrhythmias (3)
Reentry – some part of the heart is being repolarized at every moment in time
Enhanced automaticity – increased heart rate
Triggered arrythmia – early after depolarization and late after depolarization; require a heart beat first to trigger them; EADs occur before full depolarization of the heart, and the DADs occur after full depolarization of the heart
What are the requirements for reentry as a mechanism of arryhthmia?
Need 2 conduction pathways, a unidirectional block in one pathway (such that electricity is conducted down one pathway and comes back up the other one)
Also need slow/delayed conduction (if fast conduction, current will hit refractory period and won’t stimulate cell) – large/macro-circuit involves 2 or more heart chambers (Wolf-Parkinson-White syndrome), or small/micro-circuit
Define supraventricular tachycardia
Supraventricular tachycardia – fast heart rate/rhythms coming from above the ventricles
Paroxysmal SVT – SVT that comes and goes
SVT can be subdivided into narrow or wide. Describe each.
Narrow complex tachycardia is when the QRS complex is <120ms - still using AV node >> His bundle >> Purkinje system
Wide complex tachycardia is when QRS complex is >120ms - regular conduction system not being used
How do you perform the initial evaluation of a pts tachycardia?
Check hemodynamics >> check if QRS complex narrow or wide (use 12 lead ECG if possible) >> Rx based on narrow (can usually treat and discharge) or wide (more dangerous)
A pt presents to the clinic with a HR of 150 bpm (high). You’ve determined from an ECG that she has a narrow complex tachycardia. What conditions will be on your differential for this issue? (3)
Sinus node tachycardia: appropriate/inappropriate
Atrial arryhthmia: atrial flutter/atrial fibrillation
AV ring tachycardia: AV nodal reentry, AVRT (bypass tract, WPW)
**
Appropriate sinus tachycardia – e.g. when you’re taking a test and you have a fast HR coz you is anxious
Inappropriate sinus tachycardia – elevated HR with only minimal activity (or for no real reason) but its still sinus rhythm
Atrial tachycardia – conduction loop within the atria
AVRT – AV re-entry tachycardia (comes as bypass tract – not seen on ECG or WPW- can be seen on ECG)
Junctional tachycardia – from automatic cell firing; only seen in kids periodically
What pathology is indicated by the ECG reading below?
Sinus tachycardia
___ is the most common arryhthmia. How would you treat this condition?
Bonus question: why wouldn’t you use a beta blocker to rx this condition?
Appropriate sinus tachycardia
Rx: treat the underlying condition
**Do NOT use no beta blockers or CCBs coz that’s gon drop your HR real low**
What is the pathology indicated by the ECG below?
Supraventricular tachycardia
Describe paroxysmal supraventricular tachycardia
PSVT is a narrow complex tachycardia that starts and stops suddenly
(doesn’t kill people but can be annoying. I’m sure. Apparently it can go away by doing a valsalva)
There are 3 mechanisms that cause PSVT. What are they?
AV nodal reentrant tachycardia (AVNRT)
AV reciprocating tachycardia (AVRT)
Atrial tachycardia (AT)
Describe the mechanism of AV nodal re-entry
Assuming that this is the AV node and that there are two pathways
One of the pathways is fast and the other is slow. Normally both of the activations would come and the fast pathway would proceed to block the slow one and conduction would continue down to the ventricle
If an early beat comes in it can travel down the slow pathway (since the fast pathway has a longer refractory period) and if its slow enough (meaning that the refractory period block goes away while the beat is still conducting), it’ll conduct back upwards
The circle will continue until something stops it
The most common type of PSVT is ___
How do you treat this condition?
The most common type of PSVT is AVNRT
Rx: beta blockers, CCBs, ablation
What is the pathology below?
ECG of WPW
Note the short PR, delta wave and relatively narrow QRS
Explain the mechanism of ventricular stimulation in Wolf-parkinson-white syndrome
The impulse coming from the SA node goes thru both the His bundle and the bypass tract, but it actually goes thru the bypass tract first THEN thru the Av node
What’s happening in the ventricle is the combination of both these mechanisms
What is the difference between orthodromic and antidromic SVT?
In orthodromic tachycardia, the early beat comes down the AV node and gets blocked in the bypass tract >> goes down into the ventricle >> comes back up the bypass tract and cycles back and forth
In Antidromic SVT, the conduction moves down the bypass pathway instead and is blocked from the Av node pathway. (same loop idea just from a different side)
There are primarily 3 ways to treat PSVT. What are they?
Vagal maneuvers - valsalva, face in cold water, carotid massage, press eyeballs
Adenosine
Cardioversion
What is the treatment for recurrent arryhthmia?
RF ablation for recurrent arryhthmia
**see below for more info**
What is the pathology indicated by the ECG below?
ECG of atrial flutter. Note there are 2 P waves for each QRS
**saw tooth pattern!!!**
Describe the mechanism thru which atrial flutter occurs
Atrial flutter: loop of electricity traveling in the right atrium, around the tricuspid valve
Loop of electricity made possible due to crista terminalis which acts as a band of electricity
What are 3 ways to treat atrial flutter? (A, BC, 4)
Anticoagulants
Blocking AV node: Beta blockers, Ca2+ channel blockers
Anti-arrhythmatic drugs (esp Type 1 and 3)**
**problem is that anti-arrhythmatics cause pro-arrhythmic effects**
What is the pathology indicated by the ECG below?
ECG of atrial fibrillation. (irregularly irregular)
Only two kinds of irregularly irregular rhythms: a-fib or v-fib
What are the overall treatment strategies for atrial fibrillation? (3)
**see below**
Anticoagulation
Control of rhythm and rate
4 ways you could control the rate in a-fib are ___ (hint: ABCD)
4 ways you could control the rate in a-fib are using CCBs, beta blockers, digoxin and ablation
Ablation
Beta blockers
Ca2+ channel blockers
Digoxin (Glycosides)
Which drugs could you give to control the rhythm (in a f-ib) if the pt has a good LV function vs if they have poor LV function?
**see below**
What is the trigger for atrial fibrillation?
What triggers atrial fibrillation is often a trigger from the pulmonary veins (so ablation and surgery - Maze procedure - aim to isolate the pulmonary veins from the rest of the heart)
