Wolff-Parkinson-White syndrome and atrioventricular reentrant tachycardias





Definitions


The anatomic basis of atrioventricular reentrant tachycardia (AVRT) is an abnormal connection ( accessory pathway [AP] ) between the atrial and ventricular myocardium. One limb of the reentrant circuit is the atrioventricular (AV) node and the other is the AP. On rare occasions the circuit includes two or more APs.


The term preexcitation refers to earlier activation of the ventricle by a wave front arising in the atrium than would be expected if conduction occurred via the normal atrioventricular conduction pathway.


Wolff-Parkinson-White (WPW) syndrome refers to the combination of preexcitation on an electrocardiogram and episodic tachycardias using the AP ( Fig. 15.1 ).




Fig. 15.1.


Wolff-Parkinson-White syndrome caused by a left lateral accessory pathway.

Application of radiofrequency energy during catheter ablation (arrow) results in loss of preexcitation and restoration of normal conduction.


The AP is located along the mitral or tricuspid annulus, and during sinus rhythm a typical pattern with the following characteristics is present on the electrocardiogram (ECG): (1) short PR interval (≤120 ms), (2) slurred upstroke or downstroke of the QRS complex (“delta wave”), and (3) a widened QRS complex during sinus rhythm. However, WPW patients with a fasciculoventricular pathway have a QRS width 120 ms or less. , Occasionally, preexcitation may not be fully apparent because of fusion of wave fronts progressing through the AP and the normal conduction system ( Figs. 15.2 and 15.3 ). In most cases accessory pathways giving rise to the WPW pattern are seen in structurally normal hearts.




Fig. 15.2.


A 12-lead electrocardiogram (ECG) of a patient with frequent episodes of narrow-QRS tachycardia.

The ECG superficially looks normal, but there is a short PR interval and a hint of delta waves.



Fig. 15.3.


Same patient as in Fig. 15.2 .

Upper panel: A relatively slowly antegrade conducting left-sided pathway that allows fusion of conduction with that through the His bundle. Note the close A and V electrograms at the CS catheter electrodes. Mapping identified its location in the posterior aspect of the mitral annulus, close to the septum. Lower panel: After successful ablation, A and V electrograms are clearly separated in the CS catheter electrodes. I, III, V1, V5, Electrocardiogram leads; CS, coronary sinus; His, His bundle.


Electrophysiology and classification of accessory pathways


APs are single or multiple strands of myocardial cells that bypass the physiologic conduction system and directly connect atrial and ventricular myocardium. These AV connections are due to incomplete embryologic development of the AV annuli, without complete separation between the atria and ventricles. There are different types of APs. The most common ones connect the atrium and the ventricle along the mitral or tricuspid annulus. Approximately 60% are located along the mitral valve and are referred to as left free wall APs; 25% insert along the septal aspect of the mitral or tricuspid annulus; and approximately 15% insert along the right free wall. Because ventricular muscle is lacking in the proximity of the anterior leaflet of the mitral valve, left-sided APs are usually limited to the region of the mitral annulus at the attachment of the mural (posterior) leaflet. APs can be located in the superoparaseptal area in close proximity to the His bundle and AV node. Accessory pathways exhibit rapid conduction.


Concealed accessory pathways


Approximately 50% of APs conduct in both antegrade and retrograde directions, and the majority of the others conducted only in the retrograde direction are labeled as “concealed” because there is no evidence of preexcitation on the ECG. A small percentage conduct only in the anterograde direction. Concealed APs give rise only to orthodromic AVRT and occasionally have decremental properties. They are not associated with an increased risk of sudden cardiac death. No gender predilection is found, and these pathways tend to become clinically apparent at an earlier age than atrioventricular nodal reentrant tachycardia (AVNRT); however, significant overlap exists. Concealed APs are predominantly localized along the left free wall (65%) and less often at septal (30%) and right free wall locations. ,


Multiple accessory pathways


Multiple APs occur in up to 12% of patients with preexcitation and in up to 50% in patients with Ebstein anomaly. Characteristics suggestive of two or more APs are as follows:



  • 1.

    Delta wave pattern not typical of any single location.


  • 2.

    Changes in delta wave during atrial fibrillation or during right atrial versus coronary sinus (CS) pacing.


  • 3.

    Retrograde fusion during orthodromic AVRT.


  • 4.

    Changes in retrograde atrial activation sequence during orthodromic AVRT, either spontaneous or during radiofrequency (RF) ablation



Atypical accessory pathways


Atypical APs (previously called Mahaim fibers) are connections between the right atrium or the AV node (AVN) and the right ventricle into or close to the right bundle branch. Pathways with atypical characteristics can be atriofascicular, nodofascicular, or nodoventricular, depending on their proximal and distal insertions. , Left-sided atypical pathways have also been described but are extremely rare. They usually contain accessory nodal tissue, which results in decremental properties, and connect the atrium to the fascicles by crossing the lateral aspect of the tricuspid annulus, but posteroseptal locations can also be found in rare cases. Conduction is usually anterograde only, but concealed nodoventricular and nodofascicular fibers have also been described and may give rise to incessant tachycardias. , The baseline QRS of patients with atypical APs is normal or displays different degrees of manifest preexcitation with left bundle branch block morphology. Programmed or incremental atrial pacing results in manifest preexcitation when there has been sufficient delay in the AH interval. An increase in AV interval plus shortening of the HV interval and QRS widening is observed at shorter pacing cycle lengths. Atypical pathways can participate in antidromic AVRT ( Fig. 15.4 ).




Fig. 15.4.


Atypical AP physiology.

Change in QRS morphology from short to long V-A AVRT. (A) During short V-A AVRT (tachycardia cycle length 300 ms), there is also antegrade activation over the left anterior fascicle to produce a fused QRS complex with a normal axis. (B) With retrograde right bundle branch block, antegrade conduction over the left anterior fascicle is no longer possible and conduction to the left ventricle proceeds only via the right free wall. Therefore the long V-A AVRT (tachycardia cycle length 350 ms) has a leftward axis. During the change from short V-A AVRT to long V-A AVRT, the QRS width also increases from 120 to 150 ms. A, Atrial electrogram; AF, anterior fascicle; AVN, atrioventricular node; AVRT, atrioventricular reentrant tachycardia; LBB, left bundle branch catheter; M, Mahaim potential; PF, posterior fascicle; RB, right bundle potential; RBB, right bundle-branch catheter.

(Gandhavadi M, Sternick EB, Jackman WM, et al. Characterization of the distal insertion of atriofascicular accessory pathways and mechanisms of QRS patterns in atriofascicular antidromic tachycardia. Heart Rhythm. 2013;10:1385-1392.)


Diagnosis


Patients present with symptoms of paroxysmal tachycardia or with preexcited AF. AVRT is the most common tachycardia associated with the WPW syndrome. WPW predisposes to development of AF, which may or may not be eliminated after ablation of the pathway. , It is more common in patients with WPW syndrome than in the general population and may be the presenting arrhythmia in affected patients.


Antegrade-conducting APs may produce a typical WPW pattern on the ECG or may be latent. Latent pathways, when conducting antegrade, may be revealed by infusion of adenosine, which not only that blocks the AV node but also facilitates AP conduction. A small percentage of APs are dependent on sympathetic activation and become manifest only during infusion of isoprenaline. In the presence of a WPW pattern, localization of the AP may be accomplished from the 12-lead ECG ( Figs. 15.5 and 15.6 ).




Fig. 15.5.


The St. George algorithm for localization of accessory pathways.

+, Positive QRS complex; –, negative QRS complex; ±, equiphasic QRS complex; LAL, left anterolateral; LP, left posterior; LPL, left posterolateral; LPS, left posteroseptal; MS, midseptal; RAS, right anteroseptal; RP, right posterior; RPS, right posteroseptal; RL , right lateral; RW, R wave width in V1; RWH, the highest R wave recorded in precordial leads; YES, QRS complex negative in both lead III and lead V1.

(Xie B, Heald SC, Bashir Y, et al. Localization of accessory pathways from the 12-lead electrocardiogram using a new algorithm. Am J Cardiol. 1994;74:161-165.)



Fig. 15.6.


Localization of accessory pathway in the presence of maximum preexcitation.

Accessory pathway (AP) locations are green when right sided and red when left sided. LPL APs can have 0, 1, or 2 inferior leads with positive polarity, whereas NH APs can have 1, 2, or 3 inferior leads with positive polarity. Right-sided APs are framed orange or yellow when the V3 lead is negative or positive, respectively. Left posterior APs are framed blue when V1/I ratio is less than 1 or purple when V1/I ratio is 1 or more. DCS, Deep coronary sinus; LPL, left posterolateral; LL, left lateral; LPS, left paraseptal; NH, nodo-Hisian; RA, right anterior, RL, right lateral; RP, right posterior; RPS, right paraseptal.

(Pambrun T, El Bouazzaoui R, Combes N, et al. Maximal pre-excitation based algorithm for localization of manifest accessory pathways in adults. JACC Clin Electrophysiol. 2018;4: 1052-1061.)


Orthodromic AVRT


Orthodromic AVRT refers to a reentrant tachycardia that uses the AV node–His bundle axis as the antegrade limb and the AP as the retrograde limp ( Figs. 15.7 and 15.8 ).




Fig. 15.7.


Orthodromic AVRT caused by a left posterolateral pathway.

Atrial pacing results in a preexcited electrocardiogram (ECG) with close A and V electrograms in the CS. After the last atrial extrastimulus, the AH interval gets prolonged because of refractoriness of the accessory pathway, as indicated by the absence of a V component in the CS electrograms and decremental conduction through the AVN. This allows retrograde conduction through the pathway and induction of an orthodromic tachycardia with antegrade conduction through the AVN-His axis. I, III, V1, V5, ECG leads; AVN, atrioventricular node; CS, coronary sinus His, his bundle; HRA, high right atrium; RVA, right ventricular apex.



Fig. 15.8.


Orthodromic AVRT with earliest atrial activation at the distal CS, consistent with a left-lateral AP.

The sharp component recorded by the distal CS electrodes (arrows) may represent an early atrial electrogram or a pathway potential. I, III, V1, V5, Electrocardiogram leads; AP, accessory pathway; AVRT, atrioventricular reentrant tachycardia; CS, coronary sinus; His, His bundle.


Orthodromic AVRT accounts for more than 90% of AVRTs and 20% to 30% of all sustained SVTs. , The rate usually is 170 to 220 beats per minute. During tachycardia, the QRS is narrow unless there is a functional or underlying bundle branch block. ST segment depression often is present and has been shown to usually not be due to myocardial ischemia. Ipsilateral bundle branch block during AVRT results in an increase in VA time, which can also increase the cycle length of the tachycardia, although no change in rate may also be seen because of a compensatory reduction in AH interval. A contralateral bundle branch block has no effect on the tachycardia, as it is not a part of the tachycardia circuit.


The differential diagnosis of narrow-QRS complex tachycardias is discussed in Chapter 10 . In certain cases of tachycardias with atypical characteristics, multiple pacing techniques are required to reach a diagnosis. Figs. 15.9 to 15.11 present a case of a narrow-QRS tachycardia with prolonged RP intervals that was easily induced by both atrial and ventricular pacing.




Fig. 15.9.


Electrograms during narrow-QRS tachycardia with prolonged RP intervals.

I, aVR, aVF, V1, V5, Electrocardiogram leads; AH, atrial-to-His interval; CS, coronary sinus; HA, His-to-atrium interval ; His, His bundle; HRA, high right atrium; TCL, tachycardia cycle length; VA, ventriculoatrial interval measured at the His bundle electrode.



Fig. 15.10.


Entrainment of the tachycardia from the RV apex.

The PPI-TCL is 447 – 322 = 125 ms and the StimA-VA is 592 – 134 = 458 ms. After correcting the PPI-TCL by taking into account the pacing induced AV incremental conduction, the cPPI-TCL ms is 125 – (224 – 172) = 73 ms. This value is consistent with AVRT using a slowly conducting posteroseptal AP. A StimA-VA > 85 ms and a PPI-CL > 115 ms indicate atypical AVNRT rather than AVRT (see Chapter 10 ). However, correcting the PPI-TCL by taking into account the pacing induced incremental AV nodal conduction results in a cPPI-TCL = 125 – (224 – 172) ms = 73 ms. This suggests AVRT rather than AVNRT because the cutoff value is 110 ms. AVNRT, atrioventricular nodal reentrant tachycardia; AVRT, atrioventricular reentrant tachycardia; Pp AH, postpacing AH interval; PPI, postpacing interval; RV, right ventricle; Stim-AQ, stimulus-atrial interval measured on the HRA electrograms; TCL, tachycardia cycle length; VA, ventriculoatrial interval measured on the HRA electrograms; other abbreviations as in Fig. 15.9 .

(Katritsis DG. A tachycardia with narrow-QRS morphology and prolonged RP intervals. Europace. 2013;15:969.)



Fig. 15.11.


Entrainment of the tachycardia from the RV base.

The PPI-TCL is 407 – 322 = 85 ms, the StimA-VA is 524 – 134 = 390 ms, and the cPPI-TCL = 85 – (222 – 172) = 35 ms. The RV apex is closer to the AVNRT circuit in the vicinity of the AV node than the RV base because the impulse is conducted retrogradely through the His-Purkinje network. Thus basal entrainment produces longer cPPI-TCL and StimA-VA intervals in atypical AVNRT. Pp AH, postpacing AH interval; PPI, postpacing interval; RV, right ventricle; Stim-AQ, stimulus-atrial interval measured on the HRA electrograms; TCL, tachycardia cycle length; VA, ventriculoatrial interval measured on the HRA electrograms; other abbreviations as in Fig. 15.9 .

(Katritsis DG. A tachycardia with narrow-QRS morphology and prolonged RP intervals. Europace. 2013;15:969.)


The tachycardia was interrupted by ventricular extrastimulation and an A-V response or with single ventricular extrastimuli that were not conducted to the atria, while His-synchronous ventricular extrastimuli failed to reset the tachycardia. Thus the differential diagnosis is between atypical AVNRT and AVRT because of a concealed midseptal accessory pathway. For differential diagnosis, entrainment by ventricular pacing attempted both from the RV apex and RV base was necessary. After entrainment maneuvers as indicated in Figs. 15.10 and 15.11 , an accessory pathway was mapped and ablated at the midseptal area near the His bundle.


Fig. 15.12 presents a rare case of an orthodromic AVRT caused by a concealed nodoventricular pathway and AV dissociation.


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Jun 26, 2021 | Posted by in CARDIOLOGY | Comments Off on Wolff-Parkinson-White syndrome and atrioventricular reentrant tachycardias

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