EKG preexcitation pt 1

Question 1

What is the opposite of a conduction delay (SA node block, AV block, BBB)?

Answer 1

Preexcitation syndrome

Question 2

The normal conduction delay at AV node is what?

Answer 2

~ 0.1 sec delay (PR segment)

Question 3

Accessory pathways:
1) How common are they? What sex are they more common in?
2) Is it pathologic? Explain

Answer 3

1) < 1% of population; Male > Female
2) Isolated finding in normal hearts
May occur associated with MVP, HoCM, & various congenital abnl.

Question 4

_______________________________ is the most important and easily ID’d accessory pathway on EKG

Answer 4

Wolff-Parkinson-White (WPW)

Question 5

Describe WPW

Answer 5

1) Accessory pathway (short circuit) connects atria to ventricles
2) Left or right sided
3) Premature ventricular depolarization results in:
-Shortened PR interval
-Delta wave - widens QRS duration

Question 6

Describe the QRS complex in WPW

Answer 6

QRS complex in WPW is combination beat:
1) Most of ventricle depolarized via normal conduction system
2) Part of ventricle depolarized early via accessory pathway resulting in delta wave (initial slurred upstroke of QRS complex), may only be seen in a few of the leads

Question 7

Short PR interval without delta wave:
1) Is it common?
2) What is the pathway?
3) Is it pathologic?

Answer 7

1) More common than WPW
2) No single pathway consistently found
3) May be normal variation of AV node delay
Or
Some may have bypass pathway close to AV node

Question 8

Why do we care about Preexcitation?

Answer 8

1) In some patients no clinical problems, BUT
2) May predispose to various supraventricular tachyarrhythmias; 50-75% of patients with WPW experience at least one SV arrhythmia
-Sx: dyspnea, palpitations, syncope
-Usually, symptoms only occur during the tachyarrhythmia – AVRT or A. Fib

Question 9

WPW accessory pathway is perfect set up for re-entry; more precisely called _______________________________ or __________

Answer 9

AV reciprocating tachycardia or AVRT

Question 10

slide 10

Answer 10

WPW – normal beat QRS is a combination
Delta wave via accessory path/bundle…… accessary path/bundle has longer refractory period
Normal conduction via AV node & HIS …. normal refractory period
Set up: Normal sinus beat followed by PAC
PAC conducted normal pathway, but blocked at accessory path - still not repolarized
Wave of depolarization via normal path then encounters accessory pathway and transmitted to atria…passes back thru AV node and re-entry circuit self sustains….SVT with narrow QRS as the depolarization is thru normal conduction
PAC may be conducted thru accessory pathway and up thru AV node….self sustaining….SVT with wide and bizarre QRS – often indistinguishable from VT on ECG

Question 11

Describe SVT (AVRT) in WPW

Answer 11

1) Antegrade thru AV nodeorthodromic (correct or orthodox) reentry circuitQRS < 0.12 (narrow)
2) Looks like AVNRT – regular fast SV rhythm

Question 12

WPW:
________% of patients have multiple accessory pathways; forming multiple reentry loops between atria and ventricles

Answer 12

10-15