Electrophysiology: EP 1 EP study- diagnostics

Question 1

Explain electrodes in EP study

Answer 1

-Quadrupolar electrode in high right atrium (aligns with p wave)
-Quadrupolar electrode in the His/AV node position
-Right ventricular electrode - usually quadrupolar in the apex
-Coronary sinus electrode with multiple poles (8-10) aids diagnosis of SVTs

Question 2

How are electrodes placed in heart in EP study?

Answer 2

-Guided by fluoroscopy
-Advanced up femoral vein

Question 3

How do quadrupolar electrodes work?

Answer 3

-Record off 2 poles (bipolar)
-Pace off 2 poles

Question 4

Why do we take baseline measurements

Answer 4

-Assess any abnormalities
-Help make decisions about which testing manoeuvres should be used
-Compare after an ablation (improvements/accidental damage)

Question 5

What do measurements indicate?

Answer 5

AA - cycle length
AH - conduction delay between atrium and His bundle
HV - conduction delay between His bundle and ventricle
Delay in top or bottom part of AV node?

Question 6

What are the normal ranges of AH and HV?

Answer 6

AH: 50-130ms
HV: 35-55ms

Question 7

What is the EP protocol

Answer 7

1) Measure baseline conduction intervals

2) Atrial pacing
-assessment of SA node automaticity and conductivity
-assessment of AV node/His-Purkinje conductivity and refractoriness
-Induction of atrial arrhythmias

3) Ventricular pacing
-assessment of retrograde conduction
-Induction of ventricular arrhythmias

Question 8

2 ways signal can go from ventricle to atrium (retrograde)?

Answer 8

-Through accessory pathway
-Through AV node retrograde

Question 9

What are AH and HV examples of?

Answer 9

Conduction velocities
-Speed of electrical impulse across heart
-Relates to rate of depolarisation

Question 10

What happens when you increase pacing rate?

Answer 10

-You pace and it goes through AV node
-Pace faster, still refractory, doesn’t go through
-Pace again, it’s recovered, it goes through

Question 11

How are refractory periods measured in EP sudy?

Answer 11

-Heart tissue response to premature paced beats is used to test and measure refractory periods
-In EP study, measure effective, relative and functional refractory periods

Question 12

What is the effective refractory period (ERP)?

Answer 12

-You pace faster and faster
-Then you get a block due to ERP
ERP - longest coupling interval that a premature impulse fails to propagate through cardiac tissue (absolute refractory period)

Question 13

How do you evaluate sinus node dysfunction?

Answer 13

SNRT - Sinus Node Recovery Time
-Right atrial pacing at Basic Cycle Length suppresses the sinus node from firing
-In sinus node dysfunction, SA node has a longer recovery time
SNRT-BCL = CSNRT
CNSRT > 525ms = abnormal

Question 14

What is Sinus node dysfunction associated with?

Answer 14

Atrial fibrillation (AF)

Question 15

How do you evaluate Sinoatrial Conduction time?

Answer 15

-SACT measures conduction from sinus impulse to surrounding atrial tissue
-Prolonged SACT suggests sinus exit block
-Single premature paced beat introduced and return cycle measured

Question 16

What is the only part of the heart that has decremental properties?

Answer 16

AV node

Question 17

What is the Wenckebach point?

Answer 17

-Heart rate at which AV node slows the ventricular rate by extension of conduction time (decrement) and dropped beats

Question 18

What is the normal Wenckebach point?

Answer 18

-Seen at paced atrial cycle length of 500-350ms (120-170bpm)
-Low Wenckebach point indicates AV node disease

Question 19

Why should you check Wenckebach point in patients with sick sinus syndrome?

Answer 19

-If Wenckebach point at low rates (e.g. 80-90bpm)
-Give dual chamber instead of AAI
-AV node isn’t healthy and they’d go into 2:1 block with AAI

Question 20

Example of decremental conduction

Answer 20

-Decremental conduction also seen in coronary sinus channels

Question 21

Example of block (Wenckebach point)

Answer 21

Question 22

3 properties of AV node:

Answer 22

-Antegrade/retrograde conduction
-Decremental conduction (Wenckebach point)
-Refractory period

Question 23

Can you use coronary sinus channel to see if you’ve got V to A conduction?

Answer 23

Yes
-Coronary sinus records left atrium
-Signal goes from right ventricle, through AV node, to left atrium

Question 24

Things to look for when pacing from the ventricle

Answer 24

-Does AV node allow depolarisation up to atria (retrograde)?
-If there is retrograde, at what cycle length does conduction block?
-What is refractory period of ventricle?
-Is the AV node the only tract that conducts up to atria? Is there an accessory pathway?

Question 25

How would you know if there was an accessory pathway?

Answer 25

-Retrograde conduction with no decrement
-Because not AV tissue
-Conduct, conduct, conduct, block

Question 26

What does this picture show?

Answer 26

V to A conduction
-Pacing V
-Farfield V
-High rate atrial signal