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EP STUDYREENTRYAVNRT

WEVE TALKED ABOUTEQUIPMENTRELEVANT ANATOMYCATHETERS and PLACEMENTBASIC INTERVALSTESTS OF SN FUNCTION

EXTRASTIMULUS TESTINGREFRACTORY PERIODSINCREMENTAL PACINGMINIMUM PROTOCOL FOR DIAGNOSTIC EPS

AND NOWTACHYARRHYTHMIA MECHREENTRY MECHSVTAVNRT

Tachyarrhythmias

Basic mechanisms of tachyarrhythmiasEnhanced impulse formationAbnormal conduction

Enhanced impulse formationAbnormal automaticity (Phase 4)Least affected by Extrastimulus testingOverdrive pacing either overdrive suppression orNo effect

Enhanced impulse formationTriggered activity (Phase 3)Least common mech of SVT eg. Digitalis induced Initiated by overdrive pacing without conduction delay or blockOverdrive pacing Acceleration

Abnormal conduction impulse propagationReentryPathway - Anatomic, Functional, Both

reentry

3 conditions for reentryAtleast 2 functional (or anatomic) distinct pathways Joining proximally and distallyForming a closed circuit of conduction

3 conditions for reentryUnidirectional block in 1 of the pathways

3 conditions for reentrySlow conduction down the unblocked pathway allowing the previously blocked pathway time to recover excitability

3 characteristics of reentryInitiated by timed extrastimulus more effectively than rapid pacingProgrammed stimulation can also terminate Tachy

3 characteristics of reentryNo direct relation of pacing cycle length to the tachy cycle length

3 characteristics of reentryExtrastimulus can reset or entrain the Tachy in presence of fusion

Reentry is the MC mech of SVTs

EP evaluation of svt

6 tenets

1Mode of initiationRelation ofBasic drive cycle lengthES coupling intervalOnset of tachyTachy cycle length

Differentiates triggered activity from reentry

2Atrial activation sequenceP-QRS relation

3Effect of BBB during TachySpontaneous or induced BBBOn cycle lengthV-A conduction time

4Requirement of atria, HB, Ventricle in initation and maintenance of tachyEffect of AV dissociation on tachy

5Effect of atrial or ventricular stimulation during tachy

Differentiates AT, AVNRT, CBTEXCITABLE GAP

6Effect of drugs or physiological maneuvers during Tachy

AVNRT

MC SVT >50% SVTs

Concept by Mines in 1913Moe demonstrated on rabbit AVN! Dual AVN pathways

Typical or Common AVNRT

Typical or Common AVNRT

AlphaBeta

Atypical or uncommon AVNRT

Evidence of dual AVN pathways2 PR or AH intervals during NSR or at similar paced cycle lengthDouble response to an APC or VPCAbility to preempt Atrial echo by VPC during Slow pathway conduction during SVT

Definition of Dual AVN pathway

Definition of JUMP

Definition of JUMP> 50 ms increment in A-H interval with a small (~10 ms) decrease in coupling interval of Atrial extrastimulus

Definition of JUMP> 50 ms increment in A-H interval with a small (~10 ms) decrease in coupling interval of Atrial extrastimulus

Usually 70-100 ms jumpMaybe upto 500ms or more!

Apart from the typical JUMP by AESOther markers of dual AVN pathways Jump during NSR/Drive pacingBeat to beat change of > 50 ms in AH during pacingPacing induced increase in AH > PCL!

Apart from the typical JUMP by AESOther markers of dual AVN pathways Jump during NSR/Drive pacingBeat to beat change of > 50 ms in AH during pacingPacing induced increase in AH > PCL!

Double response to an APC or VPC

Apart from the typical JUMP by AESOther markers of dual AVN pathways Jump during NSR/Drive pacingBeat to beat change of > 50 ms in AH during pacingPacing induced increase in AH > PCL!Double response to an APC or VPC

May even lead to 1:2 Nonreentrant Tachy!

AV nodal conduction delay (A-H) is of prime importance in AVNRT Not coupling interval of AES

CRITICAL AV DELAY or CRITICAL AH INTERVAL

AES from CS vs HRASite of stimulation can affect ability to induce Dual pathway conduction and AVNRT

Critical AV nodal delay (A-H)required to initiate reentry is shorter in CS stimulation vs HRA

AES from CS vs HRADual pathway conduction and AVNRT EASIER to induce from HRA

AES from CS vs HRADual pathway conduction and AVNRT EASIER to induce from HRA

ImplicationPace from CS if no induction from HRAPost RFA check induction from both HRA and CS

InductionIf single AES doesnt increase AH sufficientlyDouble APCAtrial pacingShorter drive cycle lengthIsoproterenol, AtropineCS stimulation

Induction85% Typical AVNRTDual pathway seen in response to single HRA AES

Induction85% Typical AVNRTDual pathway seen in response to single HRA AES

Using all above methods Dual Pathway seen in 95% patients

Induction5-10% show MULTIPLE pathwaysMultiple jumps of >50 ms with shorter coupling intervals

AVNRT of different rates

InductionUpto 25% Non-AVNRT population also Dual pathway seen by these protocols

But

Only JUMP seen

InductionUpto 25% Non-AVNRT population also Dual pathway seen by these protocols

But

Only JUMP seenNo EchoNo Reentry over fast pathwayNo AVNRT

InductionUpto 25% Non-AVNRT population also Dual pathway seen by these protocols

But

Only JUMP seenNo EchoNo Reentry over fast pathwayNo AVNRTTherefore,LIMITATION IS RETROGRADE CONDUCTION OVER FAST PATHWAY

Induction by VESVentricular stimulation inducing AVNRT10-40% Typical AVNRT patientsVentr PACING more effective than VESOnly 10% induction by single VESDue to H-P refractoriness

Induction by VESTypical AVNRT patients retrograde conduction over FP very good

Ventr PACING more effective than VESOnly 10% induction by single VESDue to H-P refractoriness

Induction by V Pacing MechanismRetrograde over fast, concealed over slowDual pathway not seen No critical VA delay BEFORE AVNRT VA increases only when AVNRT induced

Induction by V Pacing MechanismFP retrograde refractory period > Slow pathwayDual AV pathway seenAtypical AVNRT induced

DETERMINANTS OF INDUCTION OF AVNRT

DETERMINANTS OF INDUCTION OF AVNRTRapid retograde conduction in FPTypical AVNRT patients 1:1 VA conduction at