1. GRAPHICS
Circuits in AVNRT,AVRT
Dr.I.Tammi Raju

2. • Circuits in AVNRT,AVRT
• VPC‘S in AVRT,AVNRT
• BBB IN AVRT

3. 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

4. • 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.

5. • 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

7. • 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

8. • 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

9. AVNRT

10. 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.

11. • 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

12. 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.

17. • 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.

18. 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.

19. • 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 .

20. REGULAR SVT
NARROW QRS TACHYCARDIA

21. REGULAR SVT

22. 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

23. • 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

24. • 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

25. NARROW QRS TACHYCARDIA

26. NARROW QRS TACHYCARDIA

27. • 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).

28. • 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.

30. Summary of AVNRT subtypes

31. 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

32. 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

33.  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

34. 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.

35. • 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.

36. • 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

37. Propagation
Direction
Antegrade Retrograde Unidirectional Bidirectional
Propagation
Velocity
Non-
Decremental
Decremental
10%
• Understanding the variations in ―Pathway – electrophysiology –
• Direction of Propagation & Propagation velocities

38. • ―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

39. • 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

40. • 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.

41. WPW - ORT

43. 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)

44. 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

45. 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% }

46. • 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.

47. Antidromic WPW

48. • 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

49. ANTIDROMIC AVRT-REGULAR BROAD COMPLEX TACHYCARDIA

50. 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

51. Lown-Ganong-Levine Syndrome

52. 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

53. Mahaim

54. 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

56. • 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

57. PJRT

58. 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

59. • 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

60. • 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.

61. • 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

62. 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

65. 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.

66. • 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 .

71. • 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.

72. • 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

73. • 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

75. AVNRT AVRT
Incidence Most common Less than AVNRT
sex female males
Pathway Slow-fast,
Ventricles not required for activation
Accesory
Ventricles 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