Preexcitation & SVT Flashcards
2 possible pathways to the ventricles
- Normal AV node pathway
2. “abnormal” accessory pathway
What is the alpha pathway?
The normal AV node pathway
What is the beta pathway?
The abnormal conduction pathways in the AV node or myocardium
Other names for beta pathways
- Accessory pathways
- Bypass tracts
- Preexcitation pathways
- Aberrant pathways
What happens if a beta pathway is activated?
The pt is at risk for developing arrhythmias
Possible triggers that can activate beta pathways
- Stress, catecholamine surges
- Caffeine, tobacco, street drugs
- Electrolyte abnormalities
- Acid-base imbalance
In normal conduction, if a beta pathway is activated, where does the current go?
In both the alpha and beta pathways
What kind of conduction and refractory period does the alpha pathway have?
- Slow conduction
2. Short refractory period (fast reset)
What kind of conduction and refractory period does the beta pathway have?
- Rapid conduction
2. Long refractory period (slow reset)
What will the PR interval look like if the accessory pathway in the AV node is activated?
Short
What will the QRS complex look like if an accessory pathway in the AV node is activated?
Normal
What will the PR interval look like if an accessory pathway in the myocardium is activated?
Short
What will the QRS complex look like if an accessory pathway in the myocardium is activated?
Wide
What occurs anytime current travels down a beta pathway?
Preexcitation
What is the clinical significance of preexcitation?
Not a big deal unless associated with tachycardia
-can lead to arrhythmias such as SVT
From a PAC with an activated beta pathway, which path will the current travel through to get to the ventricles?
Alpha pathway only bc the beta pathway is still in refractory
After the PAC impulse gets to the ventricles, what pathway does it travel?
The rapid beta pathway
If the reentrant tachycardic loop occurs in the myocardium, what would you expect to see on the EKG?
A delta wave and wide QRS complex
What accessory path is activated in Wolff Parkinson White syndrome?
The Kent bundle in the myocardium that forms a direct connection between the atria and ventricle
What does the EKG of WPW have?
- Short PR interval
2. Delta wave
When is WPW symptomatic?
With tachycardia
Anesthetic management of symptomatic WPW w/tachycardia
Avoid/limit sympathetic stimulation (ketamine, pain, hypovolemia, anxiety)
What can WPW with tachycardia be confused with on the EKG?
Vtach due to the wide QRS
Treatment for symptomatic WPW
- Transvenous catheter ablation
- Antiarrhythmic drugs (beta blockers, amiodarone)
- Synchronized cardioversion (if tachycardic and unstable)
Most effective and permanent solution to treat WPW
Transvenous catheter ablation
What antiarrhytmics should be avoided in WPW patients?
Drugs that block conduction through the AV node (adenosine, CCBs, digoxin)
What accessory pathway is activated in Lown Ganong Levine syndrome (LGL)?
James bundle in the myocardium, forms a direct connection between the atria and Bundle of His (bypasses the AV node)
EKG of LGL
- Short PR interval
2. No delta wave
Treatment of LGL syndrome
Usually asymptomatic and requires no treatment
What is the activated accessory path of Mahaim preexcitation?
Mahaim fibers that connect the AV node and R ventricle by bypassing the Bundle of His
EKG of Mahaim preexcitation
- Normal PR interval
2. Widened QRS complex with or without a delta wave
Clinical definition of SVT
- Tachycardia greater than 150 bpm caused by reentry.
- QRS is normal width.
- P waves may or may not be present
Reentry tachycardia/SVT resembles what rhythm?
Junctional tachycardia
What does paroxysmal SVT resemble on the EKG?
Afib, but you can see the P waves, especially when the heart slows down
Most common type of reentry
AV nodal reentrant tachycardia (AVNRT)
EKG for AVNRT
- Narrow QRS
2. May or may not have P wave
AVNRT treatment to slow conduction through AV node
- Vagal maneuvers
- Adenosine
- CCBs
- Sotalol
- Digoxin
Duration of action of adenosine
5-10 seconds
Dose of adenosine for SVT
initial 6mg bolus, NS flush
Up to 2 additional doses of 12 mg
Mechanism of action of Sotalol
Beta blocker, decreases conduction/increases refractoriness in AV node
ACLS dose of Sotalol
100mg or 1.5mg/kg
When should Sotalol be avoided?
In patients with prolonged QT syndrome
Treatment for SVT AVNRT
- Slow AV node conduction
- Antiarrhythmics
- Beta blockers
- Synchronized cardioversion
- Transvenous catheter ablation
EKG for SVT within myocardium
Delta wave or wide QRS complex
AVRT treatment
- Antiarrhythmics
- Beta blocker
- Synchronized cardioversion
- Transvenous catheter ablation
Why do you want to avoid treatments that block AV node conduction in SVT AVRT?
Blocking antegrade conduction through the AV node may promote very rapid, even life-threatening vtach or vfib response
What patients are at highest risk for a life-threatening response with AV node conduction blocking in AVRT?
Pts who develop afib or flutter with a bypass tract
Purpose of Maze procedure
To treat afib
How does the Maze procedure treat afib?
Inflicting scar tissue through incisions, cold temperatures/cryomaze, ablation lines to disrupt abnormal conduction pathways
When are Maze procedures commonly done?
With another heart operation while the chest is open via sternotomy or thoracotomy
What is the purpose of closing the L atrial appendage?
To prevent clot release from the L atrium in pts with a history of afib
What are options for L atrial appendage closure?
- Ligation of the L atrial appendage (open heart)
2. Insertion of the “watchman” device (endovascular)
