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