2.2 Electrophysiological study
All antiarrhythmic medications except for amiodarone were discontinued at least 5 half-lives before ablation. All patients were on oral anticoagulant therapy which was not interrupted for the procedure. For patients taking vitamin K antagonists an international normalized ratio between 2.0 and 3.0 was a prerequisite for the preoperative period as well as for the day of the procedure. For patients taking direct oral anticoagulants with twice-daily dosing, the morning dose was also given in the majority of the patients, however, in a small minority a single dose was held on the day of the procedure. Transesophageal echocardiography was performed in all patients just before the start of the procedure to exclude left atrial (LA) thrombi. The ablation procedure was performed under deep sedation with propofol, fentanyl and midazolam.
Twelve-lead ECG and intracardiac electrograms were continuously monitored and stored on a computer-based digital amplifier/ recorder system (EP Workmate Recording System; Abbott, St Paul, MN, USA). Intracardiac electrograms were filtered from 30 to 500 Hz. The EnSite Precision three-dimensional system (Abbott, St Paul, MN, USA) was used for mapping of the left and the right atrium if appropriate.
Barium ingestion, before the general anesthesia, was used for real-time fluoroscopic imaging of the esophagus. A 100 IU/kg dose of heparin was administered immediately after the insertion of the femoral sheaths. Subsequent boluses of heparin were administered every 1 hour targeting an activated clotting time >300 s.
The following diagnostic catheters were introduced via the femoral veins: (1) a quadripolar catheter was positioned in the His bundle area; (2) a deflectable decapolar 6F catheter, electrode spacing 2-5-2 mm (Inquiry L, Abbott) was positioned in the coronary sinus (CS), with the distal electrode reaching the 4 o’clock position along the mitral annulus in the 30o left anterior oblique (LAO) radiographic projection.
A transseptal puncture was carried out with the use of an intracardiac echocardiography (ICE) catheter (ViewFlex Xtra, Abbott) connected with a compatible ultrasound console (Philips CX50). A 20-pole, variable radius circumferential mapping catheter (Reflexion Spiral, Abbott) was introduced with the help of a long transseptal sheath (Preface, Biosense Webster, or LAMP 45o, Abbott) to guide PVI, geometry creation, and high-density activation and voltage mapping.
Α contact force ablation catheter (TactiCath Sensor Enabled, Abbott) was inserted into the left atrium (LA) through a steerable transseptal sheath (Agilis 71 cm, Abbott). An anatomical three-dimensional LA model was systematically created by first inserting the ablation catheter in all PVs and the LA appendage (LAA), and then, by precisely delineating the body of the LA with the circumferential mapping catheter.
For the electrophysiological evaluation of Ats, local activation time (LAT) and propagation maps, as well as conventional entrainment mapping were used to clarify the AT mechanism. A focal AT was defined when the activation map was indicative of centrifugal activation from a distinct source, while a macro-reentrant tachycardia was diagnosed with 3D propagation maps when a discrete impulse rotation was evident corresponding to the entire cycle length (CL) of the tachycardia. Conventional entrainment mapping contributed to the diagnosis or was omitted if the propagation map was definitively diagnostic.
Catheter ablation
At the initial AF ablation procedure, a wide antrum PVI was attempted. After placing the 20-polar circumferential PV mapping catheter in each PV, a point-by-point circumferential lesion encompassing the ipsilateral PVs was created aiming at complete electrical PV disconnection. RF energy was applied with an upper power of 30W, a temperature limit of 40Co and saline irrigation flow 17ml / min during RF delivery. A force of 10-30g and a force-time integral (FTI) >400gs was targeted in every ablation lesion. If the ablation catheter was in close proximity to the esophagus, which was fluoroscopically visible with barium, the power was reduced to 25W. In cases of non-paroxysmal AF, after PVI, additional ablation of complex fractionated atrial electrograms or linear lesions were attempted at the discretion of the operators.
At the redo procedures, the PV antra were meticulously re-mapped for conduction recurrence and if observed, additional lesions were administered, using the above ablation settings, to achieve PVI. Previously administered linear lesions were also checked for bidirectional block, and in the case of residual conduction, further lesions were delivered. If the recurrent clinical arrhythmia was persistent AF, beyond the re-isolation of the PVs, box lesion in the LA posterior wall, MI ablation and possibly cavo-tricuspid isthmus (CTI) ablation were performed. If the clinical arrhythmia was AT, the mechanism of the tachycardia was targeted in an individualized manner. For focal tachycardias, the area of origin was ablated, while for macro-reentrant tachycardias, complete linear lesions were performed in anatomical isthmuses (MI, LA roof, CTI).
Mitral isthmus ablation
The MI ablation was preferably performed in sinus rhythm (SR). Special emphasis was given on the accuracy of LA geometry in the MI area, and if there were obvious deficiencies, points were re-collected to correct the 3D model. The MI line started at the 4 o’clock position of the mitral annulus (LAO view) and ended at the lower portion of the circular isolation line of the left PVs. With the ablation catheter supported by the steerable sheath a contact force of 15-35g was applied in every ablation point. If the achieved pressure was less than 15g, the ablation lesion was not attempted to avoid edema which could potentially hinder the formation of a transmural lesion. The radiofrequency (RF) application started from the ventricular aspect of the mitral annulus at the point where the atrial potential was apparent. The RF energy was delivered with an FTI target of 400-1000 gs at each point, until the elimination of local electrogram or its reduction by 90%. After the completion of MI linear ablation, point by point mapping was performed along the MI line and reinforcement ablation was given to any site with residual high-frequency potentials or electrograms of an amplitude >0.05 mV. After elimination of the atrial potentials from the endocardial site, and if complete block had not been achieved, the ablation catheter was inserted through the CS reaching from the epicardium the level of the endocardial MI line. At this point and if discrete atrial potential was recorded, RF energy was delivered for maximum 15 s, with contact force of less than 30g, power of 25W, a temperature limit of 40Co and saline irrigation flow 17-30 ml/min. The energy delivery at the epicardial site was continued until complete block attainment or elimination of the atrial potentials.
The complete and bidirectional MI block was verified by pacing maneuvers. For the implementation and interpretation of the pacing maneuvers, special care was taken to ensure that the pacing and recording catheters were as close as possible to the MI line. By pacing at CL of 500-600ms from the LAA or a point superiorly and close to the line, we sought complete and distinct reversal of the activation sequence in the CS. Additionally, differential pacing from the distal and an adjacent CS bipole would confirm conduction block in the counterclockwise direction (Figure 1 ). When the MI line was made during PMF, the termination of the tachycardia was further confirmatory of the PMF diagnosis, but the complete MI block had to be proven in SR by the pacing maneuvers described above. In all patients, the endocardial MI line length (longitudinal distance from mitral annulus to left inferior PV), and MI line width (maximum transverse distance from the anterior to posterior border of the ablated area) were measured, on the geometry created by the 3-D system. The endocardial and epicardial RF ablation time were also measured.