Arrhythmias Flashcards
3 mechanisms of arrhythmia
reentry
autmaticity
triggered
reentry arrhythmia

Reentry termination
- stop conduction (Na channel block - IC, IA, IB)
- prolong refractoriness (K channel block - III)

Enhanced automaticity
Decreased I(K1) - which maintains RMP
increased I(f) current - enhanced diastolic depolarization (phase 4)
Looks like nodal activity (up and down)
responsive to increased sympathetic tone (CHF, post-MI)
More responsive to CCBs than Na

how to decrease automaticity
- decrease slope of phase 4 (reduced If)
- decrease deepness of phase 4
- increase threshold potential (decrease Ca channel open probability
- prolong RP

Triggered
Oscillations in membrane potential after depolarization
may trigger premature deoplarizations
if phase 2, 3 - early after depolarizations (EAD)
if phase 4 - delayed after de polarizations (DAD)

EAD mechanism and inciters
net increased inward plateau current
incited by QT prolongation drugs or mutations
long QT states triggering TdP
DAD mechanisms and inciter
intracellular Ca overload
incited by Dig, catecholamines
assoc w dig toxicitiy, ischemia, outflow tract VTs, CPVT
First degree AV Block
prolongation of normal delay between atrial and ventricle depolarization
PR interval is lengthened (still 1:1)
usually benign

Second degree AV block
-intermittent failure of AV conduction - some waves not followed by QRS
Mobitz I (Wenckeback) - degree of AV delay gradually increases with each beat until a QRS is skipped (progressive intervals) - impaired AV node conduction
Mobitz II - sudden intermittent loss of AV conduction without preceeding lengthening - QRS is often widened
Mobitz I
Mobitz I (Wenckeback) - degree of AV delay gradually increases with each beat until a QRS is skipped (progressive intervals) - impaired AV node conduction
Mobitz II
Mobitz II - sudden intermittent loss of AV conduction without preceeding lengthening - QRS is often widened
Third degree AV block
complete heart block - failure of conduction between A and V!
no relationship between P and QRS
supraventricular tach - irregular rhythms
A fib - no distinct P waves
multifocal atrial tachycardia - greater than 3 diff P wave shapes
supraventricular tach - regular rhythms
constant P-P interval
sinus tach - normal P
reentrant SVTs (AVNRT, AVRT) - hidden/retrograde P
Focal atrial tach - differs from normal P
atrial flutter - saw toothed
Sinus tachycardia mechanism
SA node discharge >100 bpm
increased sympathetic or decreased vagal tone
response to exercise or patholgoic
sinus tachycardia treatment
treat underlying disease
atrial premature beats
automaticity or reentry in an atrial focus outside SA node
often exacerbated by sympathetic stimulation
usually asyptomatic bt can cause palpitations
earlier P wave with abnormal shape
Atrial flutter mechanism
rapid regular atrial activity (180-350 bpm)
AV filter (2:1, 3:1, 4:1)
reentry over a fixed circuit (usually tricuspid valve)
often with preexisting heart disease
sawtooth ECG
atrial flutter treatment
vagal maneuvers increase AV block
electroconversion pacemaker
increase AV block (Dig, BB, CCBs)
catheter ablation
Atrial fibrilation Mechanism
chaotic rhythm with atrial rate 350-600
AV filter
Multiple wandering reentrant circuits
foci around pulmonary veins
usually AE
low CO and atrial stasis (hypotension and pulmonary congestion)
atrial fibrilation treatment
ventricular rate control (BB, CCB)
restore sinus rhythm (cardioversion)
anticoagulation
catheter ablation
AVNRT mechanism
type of PSVT
2+ potential conduction pathways in the AV node (slow with a fast RP and fast with a slow RP)
impulse usually only travels down fast pathway
unidirectional block in fast pathway - AFB travels down slow pathway and reenters backways
AVNRT ECG
regular tachycardia
normal width QRS
P may not be apparent (retrograde atrial depolarization typically occurs at same time as ventricular depolarization so P is hidden in QRS)
AVNRT Treatment
increase vagal tone (carotid massage, Valsalva)
IV adenosine to terminate
CCB, BB (acutely or chronically)
Catheter ablation
IA, IC drugs
AVRT mechanis
similar to AVNRT but includes AV bypass loop!
WPW is an example - no delay in bypass leads to ventricles excited early
or PSVT from pathway
WPW ECG
short PR (early excitation of the ventriles - earlier than normal through the accessory pathway)
QRS is slurred rather than shapr (delta wave)
QRS is windened because fusing of 2 impulses
Atrial tachycardia mechanism
focal - automaticity or reentry of an ectopic site, more common, looks like sinus tachycardia with different P wave morphology
caused by dig toxicity or elevated sym tone
multifocal - irregular rhythm with at least 3 p wave morphologyies , abnormal automaticity of several foci
ventricular premature beats
ectopic ventricular focus fires an AP
widened QRS - takes longer to get through slow cell to cell conductions
BB or nothing
ventricular tachycardia mechanism
usually in patients with structural heart disese (MI, VH, HF)
monomorphic - reentry circuit - MI or CM
polymorphic - ectopic foci or reentry
low CO, syncope, PE, CA
monomorphic VT
sustained - structural abnormality that supports a reentry circuit - scar from MI or cardiomyopathy
polymorphic VT
multiple ectopic foci or changing reentry circuit
tDP, Brugada,
VT treatment
cardioversion
amiodarone or other IV drugs
ICD
BB, CCB
catheter ablation
Amoidarone Mechanism
Class III
Blocks sodium, potassium, calcium channels
activity of class IB, II, IV
slows phase 4 depolarization
prolongs repolarization (blocks outward K in phase III)
Amiodarone Indications
SVT
AF/AFL
VT
VF
really any rhythm
Amiodarone side effects
thyroid,pulmonary inflammation
proarrhytmia (TdP rare)
drug drug (warfarin!!)
Amiodarone EKG changes
May increase PR
May increase QRS
Increase QT (NO TdP)

Adenosine Indications
SVT (AVRT, AVNRT, AT)
involve AV node involveent
Adenosine Mechanism
total block of Ca influx in AV node
5 seconds - rapid termination of SVT
block circuit
Adenosine Side Effects
Flusing
Chest discomfort
Dyspnea
Class IA Drugs Mechanism
decrease fast sodium influx (slow conduction)
slow potassium efflux (prolong QT, APD)
Class IA drug Indications
AF/AFL
SVT
VT
Class IA drug side effects
prolong QT - proarrhythmia
lupus-like
don’t really use anymore!
Class IB Mechanism
decrease in late sodium channels (shortens APD, QT)
mild decrease in fast sodium channels (mild conduction slowing)
preferentially acts on diseased/ischemic tissue
Indications of IB
no atrial arrhythmias! slowing
VT
good in MI
Side effects of IB
VT
PVC
Class IC mechanism
huge decrease in Na influx (conduction slowing)
min effect on APD
Indications for IC drugs
AF/AFL
SVT
Side effects of IC
VT
EKG changes in IC
Increase PR
Increase QRS
Increase QT (No TdP)
Use Dependency - Class I
IC>IA
IC = pill in pocket
Different indications for Class I drugs
IB - only ventricular
IC - only SVT
IA - everything
IB - preferentially diseased heart
Class II Drugs
Beta Blockers
reduces cAMP –> reduces PKA –> reduces cytosolic Ca
decrase phase 4 slope
prolongs conduction time
prolongs RP of nodal tissue
Indications for class II drugs
SVT
AF/AFL rate
VT
Long QT
ECG changes in Class II drugs
may increase PR
Side effects of class II
bradycardia
bronchospasm
Class III drugs
K blocker with beta blocking activity
(Amiodarone)
Indications for Class III drugs
SVT
AF/AFL
VT
VF
ECG changes in Class III
May increase PR, QRS
Increases QT!
Side effects of Class III
proarrhythmia
inflammation of thyroid/pulm
Class IV drugs
CCBs
block L type calcium channel
slow rise of AP
prolonged repolarization (at AV node)
decrease HR
decrease reentry
decrease AV node conduction
Indications for CLass IV
AF/AFL
AVNRT
AVRT
(SVTs - involve AV node)
Class V drugs
Digoxin
increase intracellular Ca and vagal effects
Indications for Class V
SVT
AF (rate control)
Rhythms that dep on AV node
AVNRT
AVRT
Rhythms without organized atrial activity
A fib
Regular rhythms
ST
AT
VT
AFL (block)
AVNRT/AVRT
gradual onset rhythms
ST (that’s it!)
automaticity or triggered activity
abnormal impulse initation
reentry
abnomalities in impulse conduction
conditions for reentry
- loop circuit
- unidirectional block
- zone of slow conduction
characteristics of reentrant arrhythmias
uniform morphology
stable rate
abrupt onset and termination
initated and terminated by premature beats encountering unidirectional block
most common mechanism of SVT and VT
QTc
long QT interval
prolonged depolarization
dysfunctional channels
normalize to RR interval!

normal QT length
400 msec
LQTS1
most common long QT
problem with K current, decrease K channels
AP is long and all cells in heart take a long time to reset
triggered by exercise, emotional stress

Long QT ion channel issues
can be decrease in K current or increase in NA?

Long QT Syndrome
delayed repolarization of the heart
can cause TdP
VF
reduce amt of K channels for repolarization
HERG Channel
problem with delayed rectifier K channel
leads to increased prolongation
also effect of spme meds!
Treatment for long QT
BB - don’t change QT but decrease amt of arrhythmias
ICD
Brugada syndrome
channel problems - AP collapses really early
increased risk of ventricular arrhythmias
phase 2 reentry, which generates a phase 2 reentrant extrasystole that captures the vulnerable window to precipitate ventricular tachycardia and/or ventricular fibrillation that often results in sudden cardiac death
many different mutations, but often fast Na in phase 0
SCN5A
often mutated in Brugada Syndrome
Na channel in cardiac cells responsible for upstroke
oss of the action potential dome of some epicardial areas of the right ventricle. This results in transmural and epicardial dispersion of repolarization. The transmural dispersion underlies ST-segment elevation and the development of a vulnerable window across the ventricular wall, whereas the epicardial dispersion of repolarization facilitates the development of phase 2 reentry, which generates a phase 2 reentrant extrasystole that captures the vulnerable window to precipitate ventricular tachycardia and/or ventricular fibrillation that often results in sudden cardiac death.
Action Potential in Brugada
The Notch
Since Na is dyfnctional - gradient and ready to fire again sooner than region next to it

Brugada ECG pattern

Brugada arrhytmia
phase 2 reentry
epicardial and transmural dispersion of repolarization

HOCM therapy
ICD helps!
myectomy
name the reentry arrhythmias
AVNRT
AVRT
AFL
monomorphic VT (around scar in ventricle)
A fib (due to micro reentrant circuits)
Name the automaticity arrhythmias
AT
AF (focal ectopic firing)
VT (due to automatic focus)
Name the triggered arrhythmias
long QT
Dig overdose