Study population
This was a prospective single-center study which included 80 consecutive patients who underwent radiofrequency catheter ablation (RFCA) of symptomatic PAF at our Department in Ain Shams University Hospitals during the period from 2013 till 2016.
PAF was defined according to the recommendations of the 2012 HRS/EHRA/ECAS Expert Consensus Statement on Catheter and Surgical Ablation of Atrial Fibrillation [6]. Structural heart disease (SHD) was defined as having hypertensive heart disease, coronary artery disease, cardiomyopathy, and grown-up congenital heart disease as described by Hoffmann BA et al. [7].
All patients were divided into two groups according to age at the time of the index ablation procedure. Young population group included 34 patients aged < 35 years while the old group included 46 patients ≥ 35 and ≤ 70 years old.
Trans-esophageal echocardiography was performed in all patients to rule out left atrial (LA) thrombus before ablation. In patients on vitamin K antagonists, anticoagulation was stopped 3 days prior to ablation and replaced by intravenous heparin to maintain a partial thromboplastin time of 2–3 times of the normal value or bridged with low molecular weight heparins. Ablation was performed under therapeutic INR values of ≤ 2. The study was performed under general anesthesia after obtaining informed written consent. All patients consented for the procedure and the study protocol.
Mapping
First, we evaluated patients for the presence of supraventricular tachycardia (SVT) and inducibility of AVNRT/AVRT in young patient’s cohort. In case of AVNRT/AVRT, slow pathway ablation or ablation of the accessory pathway (AP) was performed and those patients were excluded from the study.
Trans-septal access to the left atrium was obtained with standard techniques followed by the introduction of the long vascular sheath (PREFACE® Sheaths, Biosense Webster, USA).
Repetitive intravenous heparin was administered to maintain an activated clotting time of 300 to 350 s. Mapping and catheter ablation of AF was performed using 3D electro-anatomical (3D EA) mapping system (CARTOR 3 System, Biosense Webster, Diamond Bar, CA, USA)
Simultaneous surface ECG and bipolar intracardiac electrogram (EGM) recordings (filtered between 30 and 500 Hz) were amplified and displayed using the Prucka CardioLab System (GE Medical Systems, Milwaukee, WI, USA).
Mapping was performed during sinus rhythm using a 3.5-mm-tip catheter (ThermoCool Navi-Star, Biosense Webster Inc., Diamond Bar, CA, USA) to create a voltage map. In each case, we tried to obtain an evenly distributed map throughout the left atrium.
Voltage was measured from the peak-to-peak bipolar signal filtered at 30–400 MHz with the ablation catheter using an interpolation threshold of 10 mm. Bipolar voltage amplitudes > 0.5 mV were considered “normal,” whereas amplitudes ≤ 0.5 mV were defined as “diseased” (0.1–0.5 mV) or “scar” (< 0.1 mV). A low-voltage area (LVA) was defined by ≥ 3 adjacent mapping points that each had a voltage of ≤ 0.5 mV. In order to characterize regional voltage distribution, the LA shell was divided into seven distinct anatomic segments: septum, anterior wall, floor, lateral wall, posterior wall, roof, and peri-mitral annular (MA) region [8]. Activated clotting time (ACT) measurement was performed every 20–30 min, and heparin dose was adjusted to the desired target ACT.
After the 3D reconstruction of the LA, each pulmonary vein (PV) ostium was tagged on the map.
Lasso catheter was positioned across the ostium of each PV aiming at recording pulmonary vein potentials (PVPs).
RF ablation protocol
RF ablation approach chiefly involved pulmonary vein isolation (PVI) in all patients plus individually tailored substrate modification guided by endocardial voltage mapping in the event of encountering identifiable scars or low-voltage areas.
PVI was performed first at the antrum of left PVs followed by the right-sided PVs using RF energy of 25–30 W with an external irrigation flow rate of 15–17 ml/min. RF current was applied continuously with repositioning of the catheter tip every 30–60 s. Special caution was done at the posterior wall near the esophagus as power was reduced to 25 W with continuous repositioning of the catheter tip every 20 s. Disappearance or dissociation of PV potentials on Lasso catheter was defined as acute PVI success. Then, in case of detection of low-voltage areas, additional substrate modification was performed by placement of strategic linear lesions connecting non-excitable tissue or electrical isolation of the LVA depending on the location, the shape, and the extent of an LVA. In LVAs located in the posterior wall, substrate modification was achieved by creating box lesions including the LVAs electrically isolating the posterior wall and verification of entrance or exit block. Other LVA ablation strategies depended on the size of the scar; if the LVA was small, ablation aimed at encircling the LVA with ablation lesions aiming at electrically isolating the area, and if the LVA was large, isolation from the remainder myocardium was achieved by linear ablation lesions that were connected to non-conducting atrial structures. Then, conduction block across linear lesions (entrance and exit block) and electrical isolation of circumscribed areas were confirmed.
After ablation, patients who had AF during the study underwent electrical cardioversion (CV) in order to verify PVI in SR, and PVI was reassessed in all patients after a 30-min waiting period. Confirmation of PVI was defined by the absence of PVPs on the Lasso catheter during pacing from a coronary sinus or an LA catheter (entrance block) and failure of capturing the atrium through pacing from all poles of Lasso catheter inside each PV (exit block).
Post AF ablation, all patients were followed up every 3 months for a period of 1 year as regards AF recurrence. The primary endpoint was freedom from AF recurrence during a 12-month follow-up period after a single ablation procedure. Arrhythmia recurrence was defined as any episode of AF > 30 s documented beyond a 90-day post ablation blanking period (BP) on 12 lead surface ECG or 24-h Holter recording that was obtained every 3 months during the period of follow-up.
Statistical analysis
All data were revised and statistically analyzed using IBM SPSS software package version 20. Continuous data are expressed as mean and standard deviation. Population proportions were presented as a percentage. Comparisons between groups for categorical variables were assessed using chi-square test (Fisher or Monte Carlo). Mann-Whitney test was used to compare two groups for abnormally distributed quantitative variables. Student t test was used to compare two groups for normally distributed quantitative variables. Significance of the obtained results was judged at the 5% level. P value < 0.05 was considered significant, and P value < 0.01 was considered highly significant.