6. Preexcitation and SVT Flashcards
what are the two possible electrical pathways to the ventricles?
- normal AV node pathway
- abnormal accessory pathways (in the AV node or myocardium)
most common electrical pathway to ventricles
normal AV node pathway
alpha pathway
beta pathway
abnormal conduction pathways
av node or myocardium
other names for beta pathways
accessory pathways
bypass tracts
preexcitation pathway
aberrant pathway
do pts just have alpha or beta pathways?
they have both but beta pathways are normally dormant
when the beta pathways are activated what is the pt at risk for?
developing arrhythmias
triggers to activate beta pathways
stress, catecholamine surge
caffeine, tobacco, street drugs
electrolyte abnormalities
acid base imbalance
electrical properties of alpha pathway
- slow conduction
- short refractory period (fast reset)
electrical properties of beta pathway
- rapid conduction
- long refractory period (slow reset)
when a current travels the beta pathway would we expect that the ventricles would depolarize earlier or later than normal
earlier because of the rapid conduction
when a beta pathway is activated, does the current continue to flow to the alpha pathway?
yes - the current goes to both alpha and beta
preexcitation
anytime the ventricles depolarize earlier than they were supposed to
preexcitation + tachycardia =?
form reentrant loops that lead to SVT (supraventricular tachycardia)
What will the PR interval look like if a beta pathway in the AV node is activated? (normal, short, or prolonged?)
short
due to rapid conduction in beta pathway
What will the QRS complex look like if a beta pathway in the AV node is activated? (normal or wide?)
normal
signal travels through normal conduction pathways in ventricles
What will the PR interval look like if an accessory pathway in the myocardium is activated? (normal, short, or prolonged?)
short
rapid conduction through beta pathway
What will the QRS complex look like if an accessory pathway in the myocardium is activated? (normal or wide?)
wide (delta wave)
upper vent depolarized by myocardium and rest of vent by purkinje (Fast)
2 types of preexcitation
wolff parkinson white
lgl syndrome
what is the accessory pathway for WPW called?
kent bundle
direct connection between atria and ventricle
what are the two things that will be on an ECG for WPW
short pr interval delta wave (upward slurring of Q wave)
why does the delta wave occur?
upper ventricle is depolarized by myocardium and the rest of ventricle is depolarized by purkinje system
symptoms of WPW without tachycardia
preexcitation
asymtomatic
why is WPW with tachycardia a problem?
turns symptomatic
need to avoid ketamine, pain, hypovolemia, anxiety
What can WPW tachycardia be confused with on ECG?
ventricular tachycardia bc QRS are wide
look for delta wave
what are the 3 treatments for stable SVT/AVRT
transvenous catheter ablation
beta blockers
antiarrhythmic drugs
what is the treatment for unstable SVT/AVRT
synchronized cardiaoversion
what is the most effective and permanent solution for WPW?
transvenous catheter ablation
what antiarrhythmic drugs should be avoided in SVT/AVRT?
drugs that block conduction through AV node
adenosine, calcium channel blockers, digoxin
what antiarrhythmic drugs can be given to pts with SVT/AVRT?
beta blockers
amiodarone
why do we not want to fully block the AV node?
then the entire conduction is going through the beta pathway and that can lead to serious arrhythmias
Lown Ganong Levine (LGL) syndrome accessory pathway
james bundle
direct connection between atria and bundle of His (bypass AV node)
activation of LGL pathway on ECG
- short PR interval
- NO delta wave
LGL syndrome symptoms
usually asymptomatic and no treatment required
technically what does SVT refer to?
tachycardia originating above ventricles (sinus tach, afib, aflutter)
clincally what does SVT refer to?
tachycardia greater than 150bpm caused by reentry loops/beta pathways
ECG of SVT
HR >150
QRS normal
difficult to differentiate between sinus and junctional tachycardia (p wave may not be present)
symptoms of SVT
ventricular filling decreased
CO decreased
paroxysmal SVT
SVT when it begins and ends abruptly “occuring in spasms”
irregularly irregular with p waves
what can paroxymal SVT look like on ECG?
afib
Suppose a patient has an active accessory pathway in the myocardium. When the SA node depolarizes, which pathway will the current travel to get to the ventricles?
travels antegrade down both alpha and beta pathways
preexcitation occurs
Suppose that in this same patient with an active accessory pathway in the myocardium, a premature atrial contraction (PAC) occurs. From this PAC, which path will the current travel through to get to the ventricles?
4
1- impulse goes through slow alpha pathway (bc beta pathway from previous beat is still in refractory)
2- beta pathway repolarizes when impulse is traveling down av node
3- travels retrograde through accessory pathway
4- travels antegrade through the alpha pathway again
REENTRANT LOOP
what does the reentrant loop in the myocardium look like on ECG?
delta wave
wide QRS
what does the reentrant loop in the av node look like on ECG?
normal QRS complex
the majority of SVT originates in
SVT in AV node
AV Nodal Reentrant Tachycardia (AVNRT)
incidence of AVNRT vs AVRT
AVNRT is 2x AVRT
ECG for AVNRT
narrow QRS
may or may not have p wave
treatments for SVT in AV node (AVNRT) that slow conduction of AV node
vagal maneuvers
adenosine
calcium channel blockers
sotalol
digoxin
amiodarone
vagal maneuver
- valsalva- ask pt to blow through a straw
- carotid massage
- cold stimulus
when should you avoid a carotid massage? why?
could dislodge plaque
avoid in geriatric, high cholesterol, previous stroke
pharmacology of adenosine
5-10 sec acting
uncomfortable for pt (can stop heart)
dose of adenosine
inital 6mg bolus
up to 2 more doses of 12mg
what does sotalol do?
beta blocker
antiarrythmic
slow conduction in AV node
suppress ventricular ectopy
dose for sotalol to treat SVT?
100mg or 1.5mg/kg
when should sotalol be avoided?
pts with prolonged QT syndrome
full list of treatment for SVT within the AV node
slow conduction through AV node antiarrhythmics beta blocker synchronized cardioversion transvenous catheter ablation
what is SVT in the myocardium referred to as?
atrioventricular reentrant tachycardia (AVRT)
ECG for AVRT
p waves
possible delta waves
Is AVRT the same thing as Wolff Parkinson White?
WPW can become AVRT if has tachycardia
treatment for SVT within myocardium
antiarrhythmics
beta blockers
synchonized cardioversion
transvenous catheter ablation
should you avoid av node blockers in AVRT?
yes
what is the treatment option for people who have arrhythmias (usually afib) that are unrespinsive to medications
doctors map area that is causing the disturbance and ablate the abnormal conduction pathways
cardiac ablation goes into the heart via _______ access
femoral vein
if you need to ablate the Left side of heart, what does the surgeon do?
creates a hole in the interartrial septum
monitoring for cardiac ablation cases?
central line
arterial line
what side of the heart is more risky for cardiac ablation?
left side
what additional items do we place during cardiac ablation cases?
OG tube w/special stylet
LET esophageal temp probe
what does the LET probe measure
esophageal temperature during posterior left atrium ablation
what drug do you avoid in cardiac ablation?
lidocaine
(suppresses ectopy)
when should you avoid paralytics in cardiac ablation?
if surgeon is using cryoablation, to avoid phrenic nerve injury
when will the cardiologist ask for apnea during cardiac ablation?
when ablating near the carina
what MAP should you keep during cardiac ablation?
> 60mmHg
when should you alert surgeon of temperature changes during cardiac ablation?
> 0.5C changes in temp during posterior wall ablation
what infusion is started at end of cardiac ablation?
isoproterenol infusion
SE of isoproterenol infusion?
dramatic BP decrease
treat w/phenylephrine
kent bundle pathway
RA to RV
james bundle pathway
RA to BoH
