Ablation of Supraventricular Tachyarrhythmias
Erik Wissner, .. Karl-Heinz Kuck, in Cardiac Electrophysiology: From Cell to Bedside (Sixth Edition), 2014
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Accessory Pathway Localization
Accessory pathways are commonly located along the tricuspid or mitral annulus or within the subepicardial pyramidal space in the inferoseptal region (Figure 123-1), forming connections between atrial and ventricular tissue. Rarely, an accessory pathway spans from the atrium (atriofascicular), AV node (nodofascicular or nodoventricular), or His bundle (His-fascicular) to a more distal branch of the His-Purkinje system or the ventricular musculature. The 12-lead surface electrocardiogram (ECG) will aid in pathway localization and preparation for the best ablation strategy. Arruda et al.20 developed an algorithm for accessory pathway localization correlating the surface 12-lead ECG pattern with the successful ablation site in 135 patients with manifest anterogradely conducting pathways.20 In a prospective evaluation of 121 patients, the authors could demonstrate that the vector of the initial portion of the surface delta wave in leads I, II, aVF, and V1, as well as the R-to-S ratio in lead III and V1 accurately predicted 1 of 10 sites around the atrioventricular annuli or subepicardial region with a sensitivity of 90% and a specificity of 99%.20
Following successful catheter ablation, the 12-lead surface ECG commonly demonstrates repolarization changes in the direction of the delta wave. These alterations in repolarization are caused by cardiac memory and require no further treatment resolving spontaneously over time.21
Multiple accessory pathways can occur in up to 13% (see Figure 123-1) of patients with the WPW syndrome and its prevalence is as high as 52% in patients with Ebstein anomaly.22 The presence of additional accessory pathways may be evident only after ablation of the first, or it might be suggested during intracardiac mapping by variations in the activation sequence because of simultaneous or alternating conduction across multiple pathways.
Accurate localization of an accessory pathway will require careful intracardiac mapping during the electrophysiology study. Ventricular myocardium is relatively thick at the atrioventricular groove, resulting in an atrial-to-ventricular-signal amplitude ratio less than 1, whereas a position at the atrial insertion site has a ratio of approximately 1 and a position at the ventricular insertion site a ratio of 1/2 to 1/6. Catheter stability is verified by less than 20% variation in the atrial potential amplitude.23
The most reliable mapping criterion is the recording of an accessory pathway potential. In manifest pathways, the distal bipolar recording at the successful ablation site will demonstrate a discrete, low-amplitude accessory pathway potential between the local atrial and ventricular electrogram that precedes the onset of the delta wave on the surface ECG (Figure 123-2). Generally, pacing maneuvers at atrial and ventricular sites are used to dissociate the pathway potential from the atrial and ventricular electrograms. Importantly, the number of RF energy applications necessary for successful pathway ablation is lower if an accessory pathway potential can be identified.3
In clinical practice, the earliest local ventricular or atrial activation will identify the accessory pathway insertion site. In anterogradely conducting accessory pathways, the timing of the preexcited local ventricular electrogram on the bipolar recording during sinus rhythm, atrial pacing, or antidromic AVRT in reference to the earliest onset of the delta wave on the surface ECG is used to localize the ventricular insertion site of the accessory pathway accurately.24 At this site, the unipolar electrogram demonstrates a QS pattern indicating spread of activation from the insertion of the accessory pathway toward local ventricular tissue (see Figure 123-2).
In concealed accessory pathways or retrogradely conducting manifest pathways, the site of earliest atrial activation during orthodromic AVRT or ventricular pacing identifies the atrial insertion site. Ipartition 3.4.5 serial.
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The local atrioventricular or ventriculoatrial intervals are insufficient parameters to predict the successful ablation site, because pathway conduction in most patients will follow an oblique course or the local activation wavefront recorded on the distal mapping electrode will vary in direction.
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