1) Antidromic atrioventricular reentrant tachycardia (AVRT) occurs in less than 10% of patients with Wolff-Parkinson-White syndrome and can be difficult to distinguish from ventricular tachycardia on ECG. 2) Electrophysiological testing is often required to make the distinction, looking at features such as the His-ventricular interval, the effect of atrial and ventricular pacing on the tachycardia, and the response to pharmacological interventions. 3) Diagnostic maneuvers like atrial extrastimulation that advances ventricular activation or termination of the tachycardia with ventricular pacing support the diagnosis of antidromic AVRT rather than ventricular tachycard

1. DIFFERENTIATION OF
ANTIDROMIC AVRT FROM VT
DR.G. ABISHEK

2. OUTLINE
 INTRODUCTION
 ANTIDROMIC AVRT
 PITFALLS IN DIAGNOSIS
 ECG CRITERIA FOR ANTIDROMIC AVRT
 ELECTROPHYSIOLOGICAL TESTING

5.  Antidromic AVRT clinically documented in ,5% of patients with WPW syndrome, and may be induced
in ,10% in the electrophysiology laboratory.
 In adults, this usually happens in patients with multiple pathways or with free wall pathways located at
least .4 cm from the AV node, but in children it may be also seen with septal pathways.
 Although patients with inducible antidromic tachycardia had accessory pathways with shorter ERPs
and there is an increased incidence of induced AF.
 the occurrence of adverse events such as death or fast pre-excited AF within a mean follow-up of 6
years did not differ from patients without inducible antidromic tachycardia.

6. Prognostic Significance Of Inducible Antidromic AVRT
 In children, it may represent an adverse prognostic sign.
 This difference between children and adults might be related :-
 Incidence of AVRT increases with age, but the tachycardia cycle length and antegrade refractory
period of the pathway also decreases , and one-third of patients may lose the WPW pattern at ages 30
– 70 years.
 Induction of pre-excited tachycardia appears to be a surrogate marker of a more ‘aggressive’
accessory pathway.
 Inducibility or clinical detection of antidromic AVRT may suggest an increased risk only in children.
 In the adult population, the prognostic significance of pre-excited tachycardia is not established

7. ANTIDROMIC AVRT
 Antidromic AVRT is the least common arrhythmia associated with Wolff-Parkinson-White
syndrome, occurring in less than 10 percent of patients.
 As with orthodromic AVRT, antidromic AVRT can be initiated by atrial or ventricular premature
beats (APBs or VPB).
 APBs initiating antidromic AVRT are blocked in the AV node/His-Purkinje system but conduct
antegrade to the ventricles over the accessory pathway.
 After conduction through the ventricles, the impulse then travels back to the atria in a retrograde
fashion via the AV node/His-Purkinje system to complete the first reentrant loop.
 VPBs initiating antidromic AVRT are blocked in the accessory pathway but conduct retrograde to
the atria over the AV node/His-Purkinje system. After conduction through the atria, the impulse
then travels back to the ventricles in an antegrade fashion via the accessory pathway to complete
the reentrant circuit.

8. ANTIDROMIC ATRIOVENTRICULAR REENTRANT TACHYCARDIA.
The initiation of classic antidromic AVRT by an AES requires the following:-
1) intact anterograde conduction over the BT
2) anterograde block in the AVN or HPS
3) intact retrograde conduction over the HPS-AVN once the AVN resumes
excitability following partial anterograde penetration .
 retrograde conduction over the HPS-AVN is usually the limiting factor for the
initiation of antidromic AVRT.
 A delay of more than 150 milliseconds between atrial insertion of the BT and
HB is probably required for the initiation of antidromic AVRT.

10.  ATRIAL ACTIVATION SEQUENCE. The initial site of atrial activation in classic antidromic AVRT is
consistent with retrograde conduction over the AVN. If the antidromic AVRT is using a second BT
retrograde conduction, then the atrial activation sequence will depend on the location of that BT.
 ventricular activation precedes HB activation during classic antidromic AVRT. Therefore, during
preexcited SVT, a positive HV interval favors preexcited AVNRT over antidromic AVRT.
 ATRIAL-VENTRICULAR RELATIONSHIP. Conduction time over classic (fast) BTs is approximately 30 to
120 milliseconds. Therefore, the PR is short and fixed, regardless of oscillations in the tachycardia CL
from whatever cause.
 Similar to all types of AVRT, the A/V ratio is always equal to 1. If the SVT persists in the presence of
AV block, antidromic AVRT is excluded.

11. ECG findings in Antidromic AVRT
The ECG during antidromic AVRT typically shows the following:-
 Ventricular rate ranging from 150 to 250 (or greater) beats per minute and usually regular.
 Wide QRS complexes which are fully preexcited.
 Inverted P waves with an RP interval that is usually more than one-half the tachycardia RR interval
and a short PR interval.
 Constant RP interval regardless of the tachycardia cycle length.
 Susceptibility to antidromic AVRT also appears to be dependent upon a transverse distance of at
least 4 cm between the bypass tract and the normal AV conduction system. Consequently, most
antidromic AVRTs use a left-sided accessory pathway as the antegrade route for conduction.

12. Antidromic Atrioventricular Reentrant Tachycardia (AVRT)

13. ECG in Wolff-Parkinson-White

14.  In some patients with antidromic AVRT and a left-sided accessory pathway, preexcitation may not be
apparent in sinus rhythm because the time for the atrial impulse to reach the atrial insertion of the
accessory pathway is longer than the time to reach the AV node.
 A rare variant of antidromic AVRT can occur in patients with multiple accessory pathways when
anterograde conduction occurs over one accessory pathways and retrograde conduction returns to
the atrium via a second accessory pathway.
 In such cases, the AV node is not necessary for maintenance of reentry.
 The ECG during pathway-pathway tachycardia is indistinguishable from conventional antidromic
AVRT, and confirmation of the precise circuit usually requires mapping at electrophysiology study.
Approximately 10 percent of patients undergoing catheter ablation can be found to have multiple
accessory pathways .

15. Preexcited QRS Tachycardia
1. A Fib with AP
2. A Flu with AP: 250~300/min
3. Tachycardia with Mahaim fiber
4. Antidromic AVRT
5. Tachycardia using 2 Aps
6. AVNRT with bystander AP

17. PITFALLS IN DIAGNOSIS

18. Brugada algorithm for distinguishing ventricular tachycardia (VT) from supraventricular
tachycardia (SVT)

19.  Negative concordance is strongly suggestive of VT
 exception:SVT with LBBB aberrancy may demonstrate negative concordance
 Positive concordance -also indicates VT
 exception: antidromic AVRT with a left posterior accessory pathway

20. Negative concordance

21. Positive concordance

22.  Differentiation between VT and preexcited SVT is particularly difficult, because ventricular activation
begins outside the normal intraventricular conduction system in both tachycardias.
 As a result, algorithms for WCT, like QRS morphology criteria, tend to misclassify SVTs with preexcitation as
VT.
 However, preexcitation is an uncommon cause of WCT, particularly if other factors, such as age and past
medical history,suggest another diagnosis.

24. Brugada algorithm for distinguishing ventricular tachycardia ( VT ) from preexcited
supraventricular tachycardia (SVT )
The final
sensitivity and
specificity of
these three
consecutive
steps to
diagnose
ventricular
tachycardia
were 0.75 and
1.OO,
respectively.

25. Electrophysiological Testing

26. Baseline Observations during Normal
Sinus Rhythm
 The presence of preexcitation during NSR or atrial pacing suggests SVT, and the absence of
preexcitation during NSR and atrial pacing excludes preexcited SVT.
Induction of Tachycardia
 The mode of induction cannot distinguish between SVT and VT. Both atrial and ventricular
stimulation may induce SVT or VT.
 VTs that can be induced with atrial pacing include verapamil-sensitive VT, adenosine-sensitive VT,
and BBRVT.

27. Tachycardia Features
QRS MORPHOLOGY
 when the QRS configuration of the WCT is not compatible with any known form of aberration,
the rhythm is likely to be VT or preexcited SVT.
 QRS morphology during WCT that is identical to that during NSR may occur in SVT with BBB ,
preexcited SVT (when NSR is also fully preexcited), BBR VT, and interfascicular VT.

28. HIS BUNDLE–VENTRICULAR INTERVAL
 When the His bundle–ventricular (HV) interval is positive (i.e.,the His potential precedes the QRS
onset), an HV interval during the WCT shorter than that during NSR (HVWCT < HVNSR) indicates
VT or preexcited SVT. In contrast, an HVWCT equal to or longer than HVNSR indicates SVT with
aberrancy, BBR VT.
 When the HV interval is negative (i.e., the His potential follows the QRS onset), BBR VT and SVT
with aberrancy are excluded. However, myocardial VTs and preexcited SVT generally have negative
HV intervals.
 Prolongation of the VA (and VH) interval and tachycardia cycle length (CL) with transient RBBB
(caused by catheter- induced trauma or introduction of a ventricular extrastimulus [VES]) is
diagnostic of antidromic AVRT using a right-sided.

29. OSCILLATION IN THE TACHYCARDIA CYCLE LENGTH
 Variations in the tachycardia CL (the V-V intervals) that are dictated and preceded by similar
variations in the A-A or H-H intervals are suggestive of SVT with aberrancy or BBR VT.
 variations in the V-V intervals that predict the subsequent H-H interval changes are
with myocardial VT or preexcited SVT.
HIS BUNDLE–RIGHT BUNDLE BRANCH POTENTIAL SEQUENCE
 When both the HB and right bundle branch (RB) potentials are recorded,an HB-RB-V
activation sequence occurs in SVT with aberrancy and BBR VT with an LBBB pattern.
 an RB-HB-V activation sequence occurs in antidromic AVRT using an atriofascicular or
right-sided BT, the uncommon type of BBR VT with RBBB pattern, or myocardial VT
originating in the RV.
 RB-V-HB activation sequence occurs in antidromic AVRT using atriofascicular BT.
 V-RB-HB or a V-HB-RB activation sequence can occur in VT.

30. Diagnostic Maneuvers During Tachycardia
ATRIAL EXTRASTIMULATION
 Atrial extrastimulus (AES), regardless of its timing, that advances the next ventricular activation
with similar QRS morphology to that of the WCT excludes VT.
 AES that delays the next ventricular activation excludes VT.
 If the AES advances the next ventricular activation with similar QRS morphology as that of the
WCT, it proves that the BT is mediating ventricular activation during the WCT and that the WCT
is A preexcited SVT, and VT is excluded.
 If the AES advances the timing of both the next ventricular activation and the subsequent atrial
activation, it proves that the SVT is an antidromic AVRT using an atrioventricular or
atriofascicular BT anterogradely, and excludes preexcited AVNRT and VT .
 If the AES delays the next ventricular activation, it proves that the svt is an antidromic avrt using
an atrioventricular or atriofascicular BT anterogradely, and excludes preexcited AVNRT and VT

31. ATRIAL PACING
 The ability to dissociate the atrium with rapid atrial pacing without influencing the
CL (V-V interval) or QRS morphology suggests VT and excludes preexcited SVTs, AT with
aberran cy,and orthodromic AVRT with aberrancy.
 During VT, atrial overdrive pacing at a CL 20 to 60 milliseconds shorter than the tachycardia
CL with 1:1 AV conduction results in anterograde capture with changing or narrowing of the
tachycardia QRS morphology.
 During VT when the tachycardia resumes after cessation of pacing, the earliest occurs in the
ventricle because the atrium is being passively driven by the ventricle during the
This results in a “V-V-A response.” On the contrary,
 during antidromic AVRT or aberrantly conducted SVT, anterograde conduction occurs over
BT or AVN; and on cessation of atrial pacing, the last reset ventricular activation conducts to
the atrium over the retrograde limb of the circuit, resulting in a “V-A response” and
continuation of the tachycardia.

32. VENTRICULAR PACING
 Antidromic AVRT usually can be terminated by ventricular pacing.
 Termination occurs by retrograde invasion and concealment in the BT,resulting in anterograde
block over the BT following conduction to the atrium through the AVN.

33. TERMINATION AND RESPONSE TO PHYSIOLOGICAL AND PHARMACOLOGICAL
MANEUVERS
 Carotid sinus massage and adenosine terminate classic antidromic AVRT after ventricular
activation, secondary to retrograde block up the AVN.
 Preexcited typical AVNRT terminates after atrial activation, secondary to anterograde block
down the slow AVN pathway.
 Termination or prolongation of the VA (and V-H) interval and tachycardia CL with transient
RBBB,caused by mechanical trauma or introduction of VES, is diagnostic of antidromic AVRT
using a right-sided or septal BT and excludes preexcited AVNRT.
 Continuation of an SVT at the same tachycardia CL, despite anterograde block in the BT (by
drugs, mechanical trauma caused by catheter manipulation, or ablation), excludes antidromic
AVRT.

34. Thank you