DIFFERENTIATION OF ANTIDROMIC AVRT FROM VT

DR.G. ABISHEK

OUTLINE INTRODUCTION

ANTIDROMIC AVRT

PITFALLS IN DIAGNOSIS

ECG CRITERIA FOR ANTIDROMIC AVRT

ELECTROPHYSIOLOGICAL TESTING

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.

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

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.

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.

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 for 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.

ECG findings in Antidromic AVRTThe 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.

Antidromic Atrioventricular Reentrant Tachycardia (AVRT)

ECG in Wolff-Parkinson-White

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 .  

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

PITFALLS IN DIAGNOSIS

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

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

Negative concordance

Positive concordance

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.

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.

Electrophysiological Testing

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.

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.

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.

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 consistent 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.

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

ATRIAL PACING The ability to dissociate the atrium with rapid atrial pacing without influencing the

tachycardia 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 tachycardia. This results in a “V-V-A response.” On the contrary,

during antidromic AVRT or aberrantly conducted SVT, anterograde conduction occurs over a 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.

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.

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.

Thank you