circuits in avrt,avnrt i.tammi raju

GRAPHICSCircuits in AVNRT,AVRT

Dr.I.Tammi Raju

• Circuits in AVNRT,AVRT• VPC’S in AVRT,AVNRT• BBB IN AVRT

AV NODE

• ANATOMY• The normal AV junctional area can be divided into distinct regions:

– The transitional cell zone, also called nodal approaches; – The compact portion, or the AV node itself; and – The penetrating part of the AV bundle (His bundle), which continues as a

nonbranching portion

• TRANSITIONAL CELL ZONE. • The transitional cells or nodal approaches are located in posterior, superficial,

and deep groups of cells. • They differ histologically from atrial myocardium and connect the latter with the

compact portion of the AV node. • Some fibers may pass from the posterior internodal tract to the distal portion of

the AV node or His bundle and provide the anatomical substrate for conduction to bypass AV nodal slowing.

• The compact portion of the AV node

• Is a superficial structure lying just

beneath the RA endocardium, anterior to the ostium of the coronary sinus, and directly above the insertion of the septal leaflet of the TV.

• It is at the apex of a triangle formed by the tricuspid annulus and the tendon of Todaro, which originates in the central fibrous body.

• The term triangle of Koch, however, has to be used with caution because in normal adult hearts the tendon of Todaro, is absent in about two thirds

of hearts

• Bundle of His (Penetrating Portion of the Atrioventricular Bundle)

• Connects with the distal part of the compact AV node, perforates the central fibrous body, and continues through the annulus fibrosis, where it is called the nonbranching portion).

• Proximal cells of the penetrating portion are heterogeneous and resemble those of the compact AV node; distal cells are similar to cells in the proximal bundle branches.

• Branches from the anterior and posterior descending coronary arteries supply the upper muscular interventricular septum with blood, which makes the conduction system at this site more impervious to ischemic damage unless the ischemia is extensive

• ARTERIAL SUPPLY

• In 85 to 90 percent of human hearts, the arterial supply to the AV

node is a branch from the RCA

• A branch of the LCX provides the AV nodal artery in the remaining

hearts.

• Fibers in the lower part of the AV node may exhibit automatic impulse

formation.

• The main function of the AV node is modulation of atrial impulse

transmission to the ventricles, there by coordinating atrial and

ventricular contractions

AVNRT

AVNRT INTRODUCTION

Most common of the PSVTs, accounting for nearly two-thirds of cases.

synonyms  AV junctional reentrant tachycardia. Reciprocal or reciprocating AV nodal reentrant tachycardia.

Junctional reciprocating tachycardia.

• Commonest cause of palpitations in patients with structurally normal hearts.

• AVNRT is typically paroxysmal and may occur spontaneously or provocation).

• It is more common in women than men (~ 75% of cases occurring in women)

• complain of the sudden onset of rapid, regular palpitations, presyncope. angina.

• The patient may complain of shortness of breath, anxiety and occasionally

polyuria.

• The tachycardia typically ranges between 140-280 bpm and is regular in nature. 

It may cease spontaneously (and abruptly) or continue indefinitely until medical

treatment is sought.

• The condition is generally well tolerated and is rarely life threatening in patients

with pre-existing heart disease.

AVNRT

ELECTROPHYSIOLOGIC FEATURES

  Dual AV nodal physiology

may be distinct anatomic structures, or may be functionally separate 

fast or beta pathway : conducts rapidly and has a relatively long refractory period.

slow or alpha pathway : conducts relatively slowly and has a shorter refractory period.

The origins of the fast and slow pathways are probably in perinodal atrial tissue. These pathways join and enter a final common pathway in the AV node. While atrial tissue above the AV node appears to be part of the reentrant circuit, the

bundle of His below the node is probably not a necessary part of the circuit.

• VA conduction time• Traditionally, a VA interval measured from the onset of ventricular activation

on surface ECG to the earliest deflection of the atrial activation in the His bundle electrogram

• VA< 60 ms, or a VA interval measured at the high right atrium < 95 ms, has been considered as diagnostic for the slow–fast form of AVNRT.

TYPES• Typical AVNRT• Slow–fast• In the slow–fast form of AVNRT, the onset of atrial activation appears early, at the

onset or just after the QRS complex• Maintaining an atrial-His/His-atrial ratio AH/HA.> 1.• AH/HA ratio > 3, and a VA interval measured from the onset of ventricular

activation on surface ECG to the earliest deflection of the atrial activation in the His bundle electrogram <60 ms, or

• VA interval measured at the high right atrium< 95 ms are diagnostic of the slow–fast AVNRT type.

• Slow-Fast AVNRT (common type)

P waves are buried in the QRS complexes –simultaneous activation of atria and ventricles – most common presentation of AVNRT –66%.If not synchronous –pseudo s wave in inferior leads ,pseudo r’ wave in lead V1---30% cases .

REGULAR SVTNARROW QRS TACHYCARDIA

REGULAR SVT

Slow-Fast (Typical) AVNRT:•Narrow complex tachycardia at ~ 150 bpm.•No visible P waves.•There are pseudo R’ waves in V1-2.

NARROW QRS TACHYCARDIA

• Atypical AVNRT• Fast–slow.• In the fast–slow form of AVNRT (5–10% of all AVNRT cases),

retrograde atrial electrograms begin well after ventricular activation with an AH/HA ratio <1, indicating that retrograde conduction is slower than antegrade conduction

• The VA interval is > 60 ms, and in the high right atrium > 100 ms.• In the majority of fast–slow cases, the site of the earliest atrial

activation is posterior to the AV node near the orifice of the coronary sinus

• Accounts for 10% of AVNRT• Associated with Fast AV nodal pathway for anterograde conduction

and Slow AV nodal pathway for retrograde conduction.• Due to the relatively long ventriculo-atrial interval, the retrograde P

wave is more likely to be visible after the corresponding QRS.

Fast-Slow AVNRT (Uncommon AVNRT)

REGULAR SVT

NARROW QRS TACHYCARDIA

NARROW QRS TACHYCARDIA

• Slow–slow• 1-5% AVNRT• Associated with Slow AV nodal pathway for anterograde conduction and Slow

left atrial fibres as the pathway for retrograde conduction.• In the slow–slow form, the AH/HA ratio is >1 but the VA interval is >60 ms,

suggesting that two slow pathways are utilized for both anterograde and retrograde activations.

• Usually, but not always, the earliest atrial activation is at the posterior septum (coronary sinus ostium).

• Slow-Slow AVNRT (Atypical AVNRT)• ECG features:• Tachycardia with a P-wave seen in mid-diastole… effectively appearing “before”

the QRS complex.• Confusing as a P wave appearing before the QRS complex in the face of a

tachycardia might be read as a sinus tachycardia.

Summary of AVNRT subtypes

What are “Pre-excitation syndromes” ?

• Term coined by Ohnell

• First described in 1930 by Louis Wolff, John Parkinson and Paul Dudley White.

• A group of ECG and Electrophysiological abnormalities in which

– The atrial impulses are conducted partly or completely, PREMATURELY, to the

ventricles via a mechanism other than the normal AV-node

– Associated with a wide array of tachycardias with both normal QRS and

prolonged QRS durations

Origin of the Accessory pathways ?

• In early stages of cardiac development, there is direct physical and electrical contact between the atrial and ventricular myocardium

• ….disrupted by subsequent in-growth of the AV sulcus tissue and formation of the annulus fibrosus

• Defects in this annulus results in accessory pathhways

Most of these connections are of ventricular myocardial origin, rather than of atrial tissue origin

May be found anywhere across the tricuspid or mitral valve annulus – whether endocardial or epicardial

Most common pathways in are Left Free Wall followed by Posteroseptal and Right Free Wall ; Midseptal and Anteroseptal are least common *

*Calkin et al, Circulation 1999

Atrioventricular Reentry Tachycardias .AVRT

• AVRT is a form of paroxysmal supraventricular tachycardia.

• A reentry circuit is formed by the normal conduction system and the accessory pathway resulting in circus movement.

• During tachyarrythmias the features of pre-excitation are lost as the accessory pathway forms part of the reentry circuit.

• AVRT often triggered by premature atrial or premature ventricular beats.

• Bundle of KentThe classic accessory pathway is the AV bypass tract or in WPW that directly connects atrial and ventricular myocardium, bypassing the AVnode/His-Purkinje system

• James fibers, atrionodal tracts, connect atrium to distal or compact AV node ( "Lown-Ganong-Levine syndrome and enhanced atrioventricular nodal conduction")

• Brechenmacher fibers (atrio-Hisian tracts) connect the atrium to His bundle

• Mahaim fibers-Hisian-fascicular tracts, connect the atrium (atriofascicular pathways), AV node (nodofascicular pathways) or His bundle (fasciculoventricular) to distal Purkinje fibers or ventricular myocardium.

• Transverse plane — In the transverse plane, bypass tracts can cross the AV groove anywhere except between the left and right fibrous trigones where the atrial myocardium is not in direct juxtaposition with ventricular myocardium.

• The remainder of the transverse plane can then be divided into quadrants consisting of the left free wall, posteroseptal, right free wall, and anteroseptal spaces .

• The distribution of accessory pathways within these regions is not homogeneous .– 46 to 60 percent of accessory pathways are

found within the left free wall space– 25 percent are within the posteroseptal

space– 13 to 21 percent of pathways are within the

right free wall space– 2 percent are within the anteroseptal space

Propagation Direction

Antegrade Retrograde Unidirectional

Bidirectional

Propagation Velocity

Non-Decrement

al

Decremental

10%

• Understanding the variations in “Pathway – electrophysiology – • Direction of Propagation & Propagation velocities

• “Manifest Pathways”– Per se, WPW refers to patients with pre-excitation in ECG + symptomatic

episodes of tachycardia –

• “VPE pattern”-Asymptomatic patients with pre-excitation pattern are simply.

• “Concealed Pathways”- Patients with Accessory Pathways, but no pre-excitation .– Pathways may become manifest during episodes of tachycardia

• PR interval <120ms• Delta wave – slurring slow

rise of initial portion of the QRS

• QRS prolongation >110ms• ST Segment and T wave

discordant changes – i.e. in the opposite direction to the major component of the QRS complex

• Pseudo-infarction pattern can be seen in up to 70% of patients – due to negatively deflected delta waves in the inferior / anterior leads (“pseudo-Q waves”), or as a prominent R wave in V1-3 (mimicking posterior infarction).

WPW in sinus rhythm

• AVRT With Orthodromic Conduction• In orthodromic AVRT antegrade conduction occurs via the AV node

with retrograde conduction occurring via the accessory pathway. This can occur in patients with a concealed pathway.

WPW - ORT

Initiation of Tachycardia Critically timed Atrial premature stimulus that blocks anterograde in the Accessory connection, and encounters an appropriate delay in AV Node conduction so that AP and Atria are excitable when the re-entrant wave-front reaches them

That is, at an interval < ERP of the AP

Isoproterenol

Other intiating events : High catecholamine states, exercise, sinus acceleration, junctional beats (conducting antegrade only in AVN) , VPBs ( conducting retrograde, only in the AP)

Termination of tachycardia

Spontaneous OR drug-induced block in either the AVN OR AP

OR placement of a critically timed APC that encounters AVN or AP when they are

refractory

Spontaneous termination occurs more frequently with AVN due to increases in the

vagal tone

When the last beat of the tachycardia is manifest as an atrial stimulus without the

following ventricular stimulus = Termination in the AVN

When the last beat of the tachycardia is manifest as a ventricular stimulus without

the following atrial stimulus = Termination in the AP

Electrophysiological features for differentiating ORT from AVNRT

Atrial recording ( INTRACARDIAC or ESOPHAGEAL )

ORT : VA interval > 95 milliseconds (intracardiac recording) or > 70

milliseconds ( esophageal recording) in ORT

Typical AVNRT : VA interval < 70 milliseconds by either method

{ Positive predictive value 94% ; Negative predictive value 100% ;

Sensitivity 100% ; Specificity 92% }

• AVRT With Antidromic Conduction• In antidromic AVRT antegrade conduction occurs via the accessory pathway

with retrograde conduction via the AV node. • Much less common than orthodromic AVRT occuring in ~5% of patients with

WPW.• ECG features of AVRT with antidromic conduction are:

– Rate usually 200 – 300 bpm.– Wide QRS complexes due to abnormal ventricular depolarisation via accessory

pathway.

Antidromic WPW

• Requirements for occurrence of ART– AVN anterograde conduction be blocked, while it continues in the AP , i.e.

Anterograde ERP of AP < ERP of AVN

• Requirements for maintenance of ART– Retrograde RP of AVN < tachycardia cycle length

• Infrequency of both of these occurring makes it an infrequent tachyarrhythmia

ANTIDROMIC AVRT-REGULAR BROAD COMPLEX TACHYCARDIA

Other Pre-Excitation Syndromes / Accessory Pathways

Lown-Ganong-Levine (LGL) Syndrome•Proposed pre-excitation syndrome

•Accessory pathway composed of James fibres

•ECG features:

•PR interval <120ms

•Normal QRS morphology

•The term should not be used in the absence of paroxysmal tachycardia

•Existence is disputed and may not exist

Lown-Ganong-Levine Syndrome

Mahaim-Type Pre-excitation•Right sided accessory pathways connecting either AV node to ventricles, fascicles

to ventricles,

or atria to fascicles

•proximal AV nodal-like electrophysiologic properties and distal bundle branch-like

properties

•Accessory pathway with features similar to normal atrioventricular nodal tissue

•Would account for the decremental properties seen in Mahaim fibers

•ECG features:

•Sinus rhythm ECG may be normal

•May result in variation in ventricular morphology

•Reentry tachycardia typically has LBBB morphology

Mahaim

Tachycardia with a left bundle branch block patternQRS axis between 0 and -75º

• QRS duration of 0.15 seconds or less• R-wave in lead 1• rS complex in lead V1• Precordial transition in lead V4 or

later• Cycle length between 220 and 450

milliseconds (heart rates of 130 to 270

• 1 – 6% of SVTs in childhood• Rarely presents past early adolescence• 80% present in childhood ; 50% within the first year of life• In the past, thought to be ‘fast-slow’ form of AVNRT.• Actually an ORT via an AP with decremental conduction• Usually, the QRS morphology is normal, both in sinus rhythm AND during

tachycardia• Rarely, MAY be associated with antegrade conduction and Pre-excitation in sinus

rhythm

PJRT

PJRT

PJRT• Multiple APs are common

• Unlike what was previously thought, APs may be located anywhere along the AV groove

• Results in an incessant tachycardia with relatively slow rates (150 – 250 BPM)

• During the first several years, the rate tends to slow down as a function of delay in

conduction not only in the AV node AND in the concealed pathway.

• 50% of patients present with fatigue or even CCF

• Palpitations and syncope are unusual and occur in older patients

• May lead on to LV dysfunction

• AV node – like response to autonomic stimuli• Long VA interval ( > 150 ms )• Tachycardia cycle length depends upon conduction times in the AVN and the AP• Major contribution (nearly 64%) to the increase in cycle lengths with age is due

to the decremental retrograde conduction across the AP• Can be initiated / terminated with critically timed APB / VPB

• Concealed accessory pathways — • Although AV accessory pathways usually conduct antegradely and retrogradely,

some AV bypass tracts are capable of propagating impulses in only one direction .

• Bypass tracts that conduct only in the retrograde direction occur more frequently with an incidence reported as high as 16 percent .

• Bypass tracts that conduct only in an antegrade direction are uncommon. They often cross the right AV groove, and frequently possess decremental conduction properties.

• Because they do not preexcite the ventricles, the surface ECG during sinus rhythm appears normal and therefore these pathways are called "concealed.

• Preexcitation can sometimes be seen in patients with this type of a concealed accessory pathway after a long sinus pause, such as immediately after termination of AV reciprocating tachycardia.

• Most concealed AV bypass tracts exhibit nondecremental conduction and, because they serve as conduit for retrograde ventriculoatrial (VA) conduction, they are associated with reentrant arrhythmias.

• Concealed accessory pathways that have decremental properties are usually located in the posteroseptal region. However, these pathways also occur in nonseptal locations with an incidence as high as 25 percent in one series

BBB IN AVRT

• Development of bundle branch block• It is not unusual to observe aberration during SVT. • The rapidity of the conduction can lead to functional block in one of the bundles. • Development of left bundle branch block (BBB) favors the diagnosis of AVRT with

a positive predictive value of 92%. • An increase in the VA interval of more than 20 ms during development of BBB

has a positive predictive value of nearly 100% for AVRT and also helps with the localization of the accessory pathway. 

• Coumel’s Law• In the setting of AVRT, sudden aberration with prolongation in the VA time

localizes the involved accessory pathway to the side on which the functional block is occurring

EFFECT OF VPC’S

• His-synchronous premature ventricular contractions• Extrasystole, whether spontaneous or induced, can often help identify the

mechanism of arrhythmia.• A commonly used maneuver is to the deliver a His-synchronous premature

ventricular contraction (PVC), delivered on time or within 40 ms of the His potential.

• During SVT, when the HB is refractory, a VPD cannot retrogradely conduct over the HB to reach the atrium

• Once this PVC is delivered, careful measurements should be made to assess whether the subsequent atrial signal has been advanced.

• If the subsequent atrial signal arrives earlier than expected, an accessory pathway is present.

• As in more typical forms of AVRT, the ability to preexcite the atria with single VPC during tachycardia at a time when the His is refractory proves that an accessory connection is present.

• If the tachycardia terminates during this maneuver without conducting to the atrium, an accessory pathway is present and is a necessary part of the arrhythmia circuit and not just a possible bystander accessory pathway .

• Relatively late VPC introduced during tachycardia at a time when the His Bundle is known to be refractory will block retrogradely in the AP & reproducibly terminate the tachycardia, without reaching the atrium

• this preclude atrial tachycardia as a mechanism,

• the anterograde His-Bundle refractory,the VPC could not have reached AV node.The possibility of AVNRT is ruled out .

• Pre-excitation index• A PVC delivered during the tachycardia (but not in a His-synchronous fashion)

can potentially affect the tachycardia either by pre-exciting, post-exciting, or terminating it and can be used to calculate a measurement known as the pre-excitation index (PI).

• A single PVC delivered much earlier can potentially penetrate the circuit of not just AVRT but also AVNRT.

• The degree of prematurity of the PVC that can advance the subsequent atrial signal can be used to identify AVNRT or localize the accessory pathway in AVRT. 

•  Miles et al. has previously reported on two methods of calculating the PI. • PI1 is the difference between tachycardia cycle length (TCL) and the longest

coupling interval of the delivered PVC that is capable of advancing the next atrial electrogram

• PI1 = TCL–longest coupling interval that pre-excites the atrium (V1V2)• PI2 is the difference in the coupling interval that advances the next atrial

electrogram divided by the TCL:• PI2 = (V1−V2)/TCL

• In using this maneuver, it is important that the atrial activation sequence remains unchanged.

• Because of the proximity of the RV catheter to the tachycardia circuit in orthodromic reciprocating tachycardia (ORT) it is much easier to pre-excite the atrium than AVNRT, where the circuit is away from the RV catheter.

• A PI1 of >100 is consistent with the diagnosis of AVNRT. • In case of ORT using a

– septal pathway, PI is usually <45 ms, and – a left free wall pathway PI is usually >75 ms.

• The mean PI2 were 0.75 for left free wall pathway, 0.88 for posteroseptal pathway, 0.95 for anteroseptal pathway, and 0.75 for AVNRT.

• Thus the PI1 measurement appears to better differentiate location and mechanism of the tachycardia and should be preferentially used over PI2 

AVNRT AVRT

Incidence Most common Less than AVNRT

sex female males

Pathway Slow-fast,Ventricles not required for activation

AccesoryVentricles required for activation

Activation Simultaneous activation Sequential activation

Rate <200 >200

P-wave Burried in QRS Will be seen after QRS

Pseudo-r,pseudo-s,pseudo-q present absent

RP-interval <70msec >70msec

ST-T changes Less common more

ST elevation in aVR lesss more

Notch in aVL more less

QRS alternans Rare common

Abberancy Rare common

BBB Doesnot alter rate Alters rate(coumel’s law)

AV block Possible Not possible in its presence