Basic EP Intervals

8/10/2019 Basic EP Intervals

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Dr Mohammed Haroon RashidFellow, Electrophysiology.

Basic EP Intervals


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Basic Principles Determination of atrioventricular conduction

properties to stimuli helps to evaluate the AVconduction system.

Decremental Conduction: The development of AV

Block at fast atrial rates is a normal response & iscalled as Decremental conduction.

The cycle length at which the relationshipbetween atrial stimulus & ventricular response is

no longer 1:1 is called the atrioventricular blockcycle length (AVBCL)

Gradual prolongation of AV node conduction untila dropped beat, that is only atrial electrogram &no His electrogram is know as WenckebachBlock.


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Basic Principles Traditionally a train of 8 beats at a cycle length

faster than the spontaneous sinus rate is calledDrive Cycle Length (S1).

The addition of a premature stimuli within the

DCL is known as Premature Stimuli (S2). The interval in which no action potential can be

produced is called the Absolute Refractory Period& the period in which abnormal activation occurs

is called as Relative Refractory period. It is the relative differences in refractoriness that

are responsible for the development of reentry,which is the most common mechanism fortachyarrhythmias.


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Recognition of delayed conduction to

atrial extrastimuli

Tissue Response

Atrial tissue Prolongation of the interval between the stimuli & atrial

electrogram

AV Node Prolongation between the interval of atrial electrogram

to His electrogram

His-Purkinje

system

Prolongation between the interval of His electrogram to

initial deflection in the QRS complex

Ventricular

activation

Widening of QRS interval

cardiacep.wordpress.com 2011


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Important Refractory PeriodsRefractory Period Signal Observed

Atrioventricular Node Effective

refractory Period (AVN-ERP)

Premature atrial stimulus, atrial

depolarization, but no His Signal & no

ventricular depolarization

Atrial Effective Refractory Period (A-

ERP)

Premature atrial stimulus without atrial

depolarization

Ventriculoatrial Refractory Period (VA-

ERP)

Premature ventricular stimulus, ventricular

depolarization but no atrial activity

Ventricular effective refractory period

(V-ERP)

Premature ventricular stimulus with no

ventricular response.

cardiacep.wordpress.com 2011


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Normal

Haroon6

Capture

Atrial

Capture

Normal Conductioncardiacep.wordpress.com


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r a ec ve e rac ory er o -ERP)

Haroon7Haroon

280ms

No Atrial Signal

cardiacep.wordpress.c


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AVN-ERP

Haroon

No QRS Complex

No His Signal subsequently

Haroon8


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V-ERP

Haroon9

RetrogradeAtrialActivation

NoretrogradeAtrialActivation


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Source PA interval AH Interval HV Interval

Mark Josephson

(ms)

60-125 35-55 10-25

Francis Murgatroyd

(ms)

25-55 55-125 35-55


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Entrainment of Reentrant

Tachycardia

Defined as an increase in the rate of a tachycardia toa faster pacing rate, with resumption of the intrinsic

rate of the tachycardia upon either abrupt cessation of

pacing or slowing of pacing beyond the intrinsic rate

of the tachycardia Entrainment is the continuous resetting of a reentrant

circuit by train of capturing stimuli.

Entrainment is said to be present when two

consecutive extrastimuli conduct orthodromicallythrough the circuit with the same conduction time,

while colliding antidromically with the preceding paced

wave front.

Entrainment is the continuous resetting of atachycardia circuit.


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Entrainment of Reentrant

Tachycardia

Surface ECG criteria for establishing thepresence of entrainment

Fixed fusion of the paced complexes at a constant

pacing rate

Progressive fusion or different degrees of fusion atdifferent pacing rate

Resumption of the same tachycardia morphology

following cessation of pacing, with the first post

pacing complex displaying no fusion but occurringat a return cycle equal to the pacing cycle length.

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Basic EP Intervals