Anatomical landmarks are mostly used in the catheter ablation of the sluggish route in individuals with atrioventricular nodal reentrant tachycardia (AVNRT). We investigated whether the mapping of slow route potentials for AVNRT ablation might be facilitated by a novel ablation catheter fitted with mini-electrodes. Patients who were referred to our centre for AVNRT were prospectively included. An irrigated catheter with 3 insulated mini-electrodes on the distal tip was used for mapping and ablation. There were 13 consecutive cases (85% female, median age 46) included. On mini-electrode bipolar tracings, slow route potentials could be found in 77% of cases compared to 15% on traditional bipolar tracings (p = 0.0009). At the conclusion of the procedure, all patients had double potentials on the ablation line, but only on the mini-electrode.

The most common junctional tachycardia is atrioventricular (AV) nodal reentrant tachycardia (AVNRT). In symptomatic individuals, catheter ablation of the slow route may be advised because it is an effective, long-lasting treatment with a success rate of more than 90% [1]. During the technique, anatomical landmarks (at the basal portion of the Koch triangle, prior to coronary sinus ostium) rather than electrophysiological criteria are primarily used to delineate the area of interest. To be more precise, the slow pathway is not typically targeted using the discrete sharp or discrete potentials that Jackman and Haissaguerre, respectively, first defined. These signals are difficult to recognise, and it is still unknown what role they play in pathophysiology.

We wanted to determine if using a fresh ablation catheter with a distal.

2.1. Patient Population We prospectively included individuals who had received an AVNRT diagnosis and had been seen for an electrophysiological investigation in our department. Patients under the age of 18 were excluded.

The study protocol was approved by the regional human research ethics committee. Before inclusion, each patient signed an informed consent form.

Data on demographics, the presence of structural cardiac disease, clinical presentation, and antiarrhythmic therapy were also gathered.

On a dedicated electrophysiological recording platform, surface and endocardial tracing recordings were made (LabSystem Pro 9900 with dedicated software version 2.7a, Bard Electrophysiology, Boston Scientific, Lowell, MA, USA). The filter was set at 30-250 Hz (notch filter 50 Hz). A quadripolar catheter was placed at the His bundle, a quadripolar catheter was relocated either at the high right atrium or at the right ventricular apex, and a decapolar deflectable catheter was positioned inside the coronary sinus (CS) by a right femoral vein approach.

Extrastimuli and atrial and ventricular incremental pacing were utilised to elicit sustained AVNRT and to determine the electrophysiological characteristics of the AV nodal sluggish route. Finally, a 1 milligramme bolus of atropine injection and/or an isoproterenol infusion.

Extrastimuli and atrial and ventricular incremental pacing were utilised to elicit sustained AVNRT and to determine the electrophysiological characteristics of the AV nodal sluggish route. Finally, a 1 milligramme bolus of atropine injection and/or an isoproterenol infusion.

Two skilled electrophysiologists reviewed all of the tracings (NC and DB).

At one year, all patients had a telephone interview to evaluate their clinical state.

JMP analysis software was used for the analyses (version 9.0, SAS Institute, Cary, NC, USA). The median, range, and mode were used to express quantitative variables.

the population The prospective inclusion included 13 consecutive patients who were treated for symptomatic AVNRT ablation. Table 1 lists the initial characteristics. Other than one patient, they were all index procedures.

Reports specific electrophysiological features. The median length of the entire procedure (including ablation) was 66 minutes (range 51–131, IQR 41). Baseline values for the anterograde atrioventricular block, HV interval, and median AH were 108 (range 72–164, IQR 25), 50 (range 32–72, IQR 13), and 333 (range 26–600, IQR 71), respectively. Eight patients underwent the induction of typical AVNRT (slow-fast type in all patients) without the requirement for any medication, three patients under isoproterenol alone, and two patients under isoproterenol and atropine. The median (interquartile range) tachycardia cycle length (TCL) was 350 ms.

Three patients on mini-electrodes with bipolar signals and one patient on conventional electrodes each had a sharp potential, as first noted by Jackman and colleagues (Figure 2) [3]. Eight patients on mini-electrode signals and only two patients on traditional bipolar signals had a low dV/dt potential, as first documented by Hassaguerre and colleagues [2]. Overall, on mini-electrode bipolar tracings particular potentials, defined as potential slow route potentials, were found in 77% of cases versus 15% on traditional bipolar tracings (p = 0.0009).

The average number of 60-second RF applications was 4, with a range of 2 to 21. A 45 °C maximum temperature was specified for the irrigation rate, which was set at 15 mL/min. During the first 10 s, power was set at 20 W, then during the remaining application time, it was increased to 30 W. In 69% of cases, an escape junctional rhythm was noted during application. When the surgery was finished, no patient was inducible. One consistent, isolated echo beat was present in just one patient.

Without any complications, all patients were discharged the same day. After a year, there was no sign of a recurrence.

Double Potentials (3.5)

Only on mini-electrode bipolar signals: in 6 cases, was it possible to identify a double potential prior to ablation in 69% of cases.

The results of this study demonstrate for the first time that: (1) mini-electrode bipolar mapping during AVNRT ablation may improve the clarity of identification of so-called slow pathway potentials; and (2) visualisation of a significant increase in double potentials interval on the ablation line following RF application, typically 15% of baseline TCL, is associated with non-inducibility.

There have been two distinct slow route potentials identified in the past. At the expense of extremely time-consuming techniques, Jackman and colleagues [3] found a sharp potential, typically in sinus rhythm or retrogradely. The fact that such sharp potentials were only discovered in one-fourth of the cases in our investigation suggests that we were only looking for rapidly detected slow route potentials in sinus rhythm. This fast-sloping potential was consistently created during ablation.

Conduction block in a number of arrhythmias, particularly atrial flutter, has been linked to the discovery of a double, split potential on an ablation line, but never with AVNRT [4,5]. Prior to ablation, double potentials have been thoroughly explored in the AV nodal slow route region [6,7]. As opposed to being specific to the slow pathway itself, they would be "caused by asynchronous activation of two large muscle bundles separated by the mouth of the coronary sinus and thought to be a marker for the region between the coronary sinus orifice and the tricuspid annulus, where the slow pathway is frequently found" [6]. Thanks to the mini-electrodes placed directly on the distal (RF-delivering) electrode of our series, we were able to observe double potentials after RF ablation for the first time in a consistent manner.

Furthermore, contrary to what has previously been proposed [9], double potentials may not be related to a delay in activation in the slow route. However, ablation in the slow pathway region would continue to increase the spacing of these double potentials and hence, inadvertently, indicate ablation success. The location of the ablation site may also affect the length of the delay between double potentials. A more proximal ablation site along the slow pathway would be linked to a longer retrograde activation after ablation and a longer delay. More tests with larger samples are required to pinpoint the double potential delay's cutoff and describe the observable mechanisms.