2.2 Case series
We performed electrophysiological study, catheter ablation and mapping to identify the location of the accessory pathway with velocity map in three patients (2 male, median age 45 yo) with WPW syndrome. First, we started with electrophysiology study to assess the electrical property and the risks of accessory pathway. Then, patients underwent standard local activation time (LAT) mapping with Advisor HD Grid multipolar catheter for localization of AP. Advisor HD Grid was used in order to take advantage of OT and new wave speed map. After AP localization we studied the conduction velocity values registered at the level of the pathway. Normal atrial conduction velocity was found to be 1±0.1 m/s, accessory pathway conduction velocity 2.8±0.02 m/s (Fig 1).
Atrio-ventricular nodal reentrant tachycardia (AVNRT)
Overview
Dual AV node physiology characterizes the normal AV node function, and the presence of dual AV node pathways can be demonstrated in most individuals. Although the potential substrate for AVNRT (dual pathways) is normally available, only a minority of normal individuals develop AV nodal reentry. In fact reentry requires other conditions, first of all refractoriness over the two pathways and the presence of a synchronous trigger. Tipically dual pathways have different capacity of conduction and refractoriness (slow and fast).
Case series
Patients who have AVNRT generally have dual atrioventricular nodal physiology and the ability for a reentrant arrhythmia to occur involving the atrioventricular (AV) node. Patients in general have a fast pathway in which normal conduction proceeds down during sinus rhythm. However, patients with AVNRT have one or more slow pathways or additional circuits near the coronary sinus and connected to the AV node that are capable of electrical conduction. In the most common or “typical form” of AVNRT, patients become stuck in a reentrant loop with conduction proceeding down the slow pathway as the anterograde limb of the circuit and back up the fast pathway as the retrograde limb. Wave speed map can be useful to give numeric value of how fast or slow are the two pathways for patients with dual atrioventricular nodal physiology. We studied two patients presenting to our institution for ablation of AVNRT. First, we started with electrophysiology study to assess the presence of dual nodal pathways and then we used Advisor HD Grid to characterize the conduction velocity of the slow and fast pathways in sinus rhythm. Normal atrial conduction velocity was found to be 1±0.1 m/s and slow pathway 0.9±0.1 m/s. We compared standard voltage map and wave speed map indentifiyng the slow pathway localization (Fig 2).
Atrial flutter
Overview
Atrial flutter are one or the most commons atrial arrhythmia. Atrial flutter are classified in typical, who are cavotricuspid isthmus (CTI)-dependent, and atypical. The electrophysiological substrate under­lying CTI-dependent atrial flutter has been shown to be macroreentry around the tricuspid valve annulus. In most cases typical atrial flutter have counterclock­wise direction around tricuspid valve annulus, in a minority of patients, the direction is clockwise. In both cases the ablation target is bidirectional block through CTI. Atypical or non isthmus-dependent atrial flutter and atrial macroreentry requires fixed or functional block and regions of slow conduction. This is the result in the most cases of catheter ablation or surgery that involves right or left atriotomies.
Case series
We report 6 cases of atrial flutter (3 atypical, 3 typical) mean age 66.67±9 years. Patients underwent catheter ablation and atrial mapping with the new Ensite X system, using the HD Grid. We compared the standard local activation map (LAT) of the critical isthmus (Figure 3a) with the slowest conduction zone identified with OT (Figure 3b). In patients with atypical flutter critical isthmus were identified in LA roof, in mitral isthmus and in LA posterior wall, near left superior pulmonary vein ostium. Mean velocity value for CTI was 1.08 ± 0.3 m/s, mean velocity value for LA atrial flutter critical isthmus was 9.86 ± 7.26 m/s. The conduction velocity map was used to identify areas of slow conduction throughout the isthmus and wave velocity values ​​of 0.45 ± 0.3 m/s were found to discriminate critical areas of the flutter circuits. The mean LAT map area values ​​are 3.89 ± 2.22 cm2 and the slowest conducting zone identified by OT has a mean area of ​​1.26 ± 0.82 cm2. A single RF delivery at the slowest site of critical isthmus resulted in rapid cessation of the arrhythmia in all cases.
Atrial fibrillation
Overview
Pulmonary vein isolation (PVI) represents the primary target of current catheter ablation techniques for the treatment of atrial fibrillation. However, PVI has proven to be effective in paroxismal AF, in patients with persistent and long standing persistent AF this seems not enough to obtain a high efficacy [5,6,7]. Recently, some studies have shown that Bachmann’s bundle plays a significant role in the genesis of AF and its ablation leads to increase efficacy in terms of AF-free survival at follow up [8].