Dr. Salah Atta, MDDr. Salah Atta, MDConsultant Electrophysiolgist, SBCCConsultant Electrophysiolgist, SBCC

Professor of CardiologyProfessor of Cardiology,,Assiut UniversityAssiut University..

Part2Part2, ,

Sequence of Activation

• Determination of the sequence of antegrade and retrograde activation during spontaneous rhythms, atrial pacing, ventricular pacing, and induced rhythms is essential in diagnosis of normal vs abnormal rhythm and the type of abnormal rhythm if present.

Sequence of Activation

• The atrial activation in sinus rhythm begins in the high right atrium and spreads to the low right atrium and His bundle, with left atrial activation recorded from the coronary sinus catheter occurring signifcantly later.

• Ventricular activation normally earlier in His, then RV then LV in CS from proximal to distal.

Retrograde conduction

When ventriculoatrial conduction is present during ventricular pacing, the earliest retrograde atrial activity is recorded in the His bundle electrogram followed by the RA and coronary sinus recordings.

Abnormal or eccentric sequences of retrograde atrial activation occur in the presence of AV accessory pathways. This is discussed in more detail in subsequent sections dealing with supraventricular tachycardia and catheter ablation.

Normal sequence of Normal sequence of

retrograde activation retrograde activation

earliest at the His earliest at the His

bundle electrogram-bundle electrogram-

(1st), otherwise (1st), otherwise

accessory pathway accessory pathway

exists e.g if earliest in exists e.g if earliest in

the CS (2nd,3rd).the CS (2nd,3rd).

Basic Intervals

• After the catheters are positioned, basic conduction intervals are measured, including the basic Sinus Cycle Length (the A-to-A interval), P wave duration, AH interval, and HV interval. Measurements from the surface ECG, including the PR interval, QRS interval, and QT interval, are also recorded.

• Can measure the intervals using the system or the tracing using the ruler and knowing the recording speed:

The duration in ms = distance in mm x 1000/speed in mm e.g if speed is 100 mm/sec, then 100 mm =1000 msec and a distance of 20 mm= 20x1000/100=200 msec

Measurement of basic intervals:Measurement of basic intervals:PA interval: 20-40ms, PA interval: 20-40ms, from the onset of from the onset of

the earliest P wave on the surface ECG to the the earliest P wave on the surface ECG to the earliest rapid deflection of the atrial earliest rapid deflection of the atrial electrogram from the His Catheter, measures electrogram from the His Catheter, measures atrial conduction.atrial conduction.

AH interval: 50-140ms, AH interval: 50-140ms, represents represents conduction through the AV node to the His conduction through the AV node to the His bundle, measured in the His Catheter,bundle, measured in the His Catheter,

How to know ?!

• HV interval: 30-55 ms, HV interval: 30-55 ms, rpresents rpresents conduction from proximal His bundle conduction from proximal His bundle to the ventricular myocardium.to the ventricular myocardium.

• Cycle Length: Cycle Length: (from peak to peak)(from peak to peak)

the R-R interval or the V-V interval the R-R interval or the V-V interval

A-H interval• The AH interval represents conduction

time from the low right atrium at the interatrial septum through the AV node to the His bundle and approximates AV nodal conduction time.

• The measurement is made from the earliest reproducible rapid defection of the atrial electrogram on the His bundle recording to the onset of the His defection on that electrogram. Normal values for adults are reported to range from 50 to 140 ms.

A-H interval• The AH interval is infuenced strongly by the

patient’ s autonomic tone and may vary by 50 ms during a study in a given patient.

• The AH interval normally increases in response to increases in atrial pacing rates.

• It may also be altered by drugs that affect AV conduction, and the measurement may be infuenced artifcially by such factors as gain setting and position of the atrial catheter.

The H-V interval

• The HV interval represents conduction time from the proximal His bundle to the ventricular myocardium. The measurement is made from the earliest defection of the His spike on the His bundle recording to the earliest onset of ventricular activation recorded from any intracardiac electrogram or surface ECG. Normal values range from 30 to 55 ms. In contrast to the AH interval, the HV interval normally remains relatively constant and is not signifcantly affected by variations in autonomic tone or atrial pacing rates.

How to know ?!During pacing:During pacing:Pacing concept: Pacing concept: If an electronic If an electronic

pacemaker or a stimulator applies small pacemaker or a stimulator applies small electrical pulses „Stimuli“ to the ventricular electrical pulses „Stimuli“ to the ventricular or atrial electrode tissue interface, the or atrial electrode tissue interface, the electrical field radiates from the electrode, electrical field radiates from the electrode, triggers rapid depolarization of few cells triggers rapid depolarization of few cells which spreads by cell-to-cell conduction which spreads by cell-to-cell conduction throughout the entire muscle mass initiating throughout the entire muscle mass initiating

a cardiac impulse.a cardiac impulse.

Capture can be observed as a Capture can be observed as a depolarization observed depolarization observed immediately after the stimulus immediately after the stimulus

artifact.artifact.

Common terminologyused to describe the pacing stimuli and their subsequent

intracardiac electrograms:• S1: drive train pacing stimulus usually delivered in

groups of 5–8 beats with a pause around 2 seconds between successive trains.

• S2, S3, S4: respectively, a first, second, and third extrastimulus

• S1–S2, S2–S3, S3–S4: coupling intervals respectively between S1 and S2, S2 and S3, S3 and S4

• A1: atrial electrogram associated with S1 drive or spontaneous atrial beat

• A2, A3: atrial electrogram associated with respectively S2 and S3 or the first spontaneous atrial electrogram respectively after A1 or A2

Follow terminology

• H1, H2, H3: His bundle electrogram associated respectively with A1, A2, and A3

• V1: ventricular electrogram associated with S1 or spontaneous ventricular beat

• V2, V3: ventricular electrogram associated with respectively S2 and S3 or the first spontaneous ventricular electrogram respectively after V1 and V2.

How to know ?!Pacing methods:Pacing methods:A pulse duration of 1 or 2 milliseconds at double A pulse duration of 1 or 2 milliseconds at double

the pacing threshold is most commonly used.the pacing threshold is most commonly used.

Both atrial and ventricular Both atrial and ventricular pacing can be done in any of pacing can be done in any of the following ways:the following ways:

Fixed rate pacingFixed rate pacing (at a fixed drive cycle). (at a fixed drive cycle).

Pacing with extrastimulationPacing with extrastimulation Incremental pacingIncremental pacing: with progressive : with progressive

shortening of the pacing cycle length.shortening of the pacing cycle length.

Programmed Electrical Stimulation

The major purposes of programmed electrical stimulation are to

• 1-characterize the electrophysiologic properties of cardiac tissue (Refractory periods)

• 2- to assess sequence of activation both antegrade and retrograde

• 3- to induce and analyze the mechanism of arrhythmias and to terminate tachyarrhythmias.

Extrastimulus Techniques Extrastimulus Techniques • One or more extrastimuli (designated S2, S3, One or more extrastimuli (designated S2, S3,

SN) are introduced at specific coupling intervals SN) are introduced at specific coupling intervals based on previous drive S1s, or spontaneous based on previous drive S1s, or spontaneous beats. Thereafter the S1S2 interval is altered, beats. Thereafter the S1S2 interval is altered, usually in- 10 to 20-millisecond steps, until an usually in- 10 to 20-millisecond steps, until an end point, such as tissue refractoriness, or end point, such as tissue refractoriness, or termination or induction of a tachycardia, is termination or induction of a tachycardia, is reached. reached.

• When the physician is satisfied with the results When the physician is satisfied with the results of S1S2 testing, a second extrastimulus (S3) of S1S2 testing, a second extrastimulus (S3) may then be introduced, with the S2S3 interval may then be introduced, with the S2S3 interval altered in a fashion similar to that used for S1S2. altered in a fashion similar to that used for S1S2.

Determination of Refractory Periods

• The refractoriness of cardiac tissue is defned by the response of the tissue to the introduction of premature stimuli. For most routine EPS, the ERP is defned as the longest coupling interval between the basic drive and the premature stimulus that fails to propagate through the tissue. Normal values for AV nodal, atrial, and ventricular refractory periods have been established ). The ERP of cardiac tissue may be affected by the current strength used, the pacing rate, medications, and autonomic tone in the AV node.

How to know ?!Atrial pacing with Atrial pacing with

extrastimulation:extrastimulation:

Pacing with a train of 6-10 beats Pacing with a train of 6-10 beats at a fixed cycle length followed at a fixed cycle length followed by an extrastimulus at a shorter by an extrastimulus at a shorter cycle length which is shortened cycle length which is shortened each time.each time.

Atrial extrastimulus testing

• Atrial extrastimulus testing can determine the properties of the AV node (antegrade) and of the atrium.

• By progressively shortening the S2 extrastimulus, the AV node RRP will be reached first when A2H2 begins to be longer than A1H1

• As the S2 atrial extrastimulus cycle length decreases, the conduction over the AV node (represented by the A2H2 interval) progressively increases, known as the decremental conduction over the AV node

A-H Jump

• An increase in the A2H2 by 50 ms or more is sometimes observed with a decrease of the atrial S2 extrastimulus by 10 ms. This A2H2 increase, also called a jump, is evidence of dual AV node physiology. Briefly, this means that antegrade conduction over the AV node has shifted from the usual fast pathway to a slow pathway.

Dual AV nodal pathway if there is AH jump, Arrhythmia induction

Refractory periods

• By further decreasing the S2 interval, the ERP of the AV node will be achieved when the atrium A2 is no longer followed by the His H2 .

• Finally, the S2 spike will no longer capture the atrium (atrial ERP, also called atrial refractoriness).

Atrial pacing: Atrial pacing: Incremental Atrial pacing:Incremental Atrial pacing:

Means continuos pacing the atrium with Means continuos pacing the atrium with progressive shortening of the pacing cycle progressive shortening of the pacing cycle length, shows:length, shows:

- the wenckebach point and excludes infra - the wenckebach point and excludes infra His block, His block,

-may show pre-excitation, may induce the -may show pre-excitation, may induce the tachycardia .tachycardia .

How to know ?!

• Normal Antegrade decremental Normal Antegrade decremental conduction with gradual prolongation conduction with gradual prolongation of the AH interval, till the wenckebach of the AH interval, till the wenckebach point. point.

Atrioventricular Nodal Function Curves

• AV nodal function curves can be constructed by plotting of the coupling interval of the premature stimulus (A1A2 interval) on the horizontal axis versus the AH interval (AV nodal conduction time) of the premature stimulus (A2H2 interval) on the vertical axis. In individuals without dual AV nodal pathways, a progressive and gradual increase occurs in the AH interval before the premature stimulus blocking in the AV node, and the function curve is continuous .

A-H jump

• A sudden large increase (at least 50 ms) in the AH interval (often referred to as a jump) in response to a small decrement (10 ms) in the coupling interval of the premature beat is evidence of functional dual AV nodal pathways.

• This represents a shift from conduction over the fast AV nodal pathway to conduction over the slow AV nodal pathway (with a longer AH interval), and the AV nodal function curve is discontinuous.

Burst pacingBurst pacing• Burst pacing for tachycardia induction: Burst pacing for tachycardia induction:

Stimuli are delivered at a constant fast Stimuli are delivered at a constant fast rate for a relatively short duration but at rate for a relatively short duration but at successively faster rates with each burst successively faster rates with each burst until a predetermined maximum rate (or until a predetermined maximum rate (or minimum interval) has been reached. minimum interval) has been reached.

• Bursts for termination of tachycardia: This Bursts for termination of tachycardia: This is similar to the technique used for is similar to the technique used for induction. The initial pacing rate is faster induction. The initial pacing rate is faster than that of the tachycardia. than that of the tachycardia.

Ramps Ramps • Ramp pacing implies a smooth change in Ramp pacing implies a smooth change in

the interval between successive stimuli. the interval between successive stimuli. Ramps too can be incremental or Ramps too can be incremental or decremental as defined by either rate or decremental as defined by either rate or cycle length. Ramps have several cycle length. Ramps have several applications: for example as a test for applications: for example as a test for conduction, long ramps with small cycle conduction, long ramps with small cycle length decrements between successive length decrements between successive stimuli provide results comparable to stimuli provide results comparable to stepwise rate incremental pacing. stepwise rate incremental pacing.

Till next time InshaALLAH

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