Materials and methods

Observational retrospective study of consecutive patients with CHD referred for catheter ablation from 01 January, 2016 to 31 December, 2021 in a tertiary referral centre. Procedural endpoints and mid-term outcomes were assessed.

Data required for cohort characterisation was collected from the patient’s clinical records. Arrhythmias were divided into the following groups: cavotricuspid isthmus-dependent atrial flutter, intra-atrial re-entrant tachycardia, focal atrial tachycardia, atrioventricular re-entrant tachycardia, atrial fibrillation, and ventricular tachycardia. The CHD complexity was divided into simple, moderate, and severe as defined by the 2014 Paediatric and Congenital Electrophysiology Society/Heart Rhythm Society expert consensus statement.^{Reference Khairy, van Hare and Balaji9}

All patients provided written informed consent and the study complied with the Declaration of Helsinki and was approved by the local institutional ethics committee.

Patients were eligible for inclusion in the study if they presented any CHD according to the International Paediatric and Congenital Cardiac Code and the Eleventh Iteration of the International Classification of Diseases 11,^{Reference Franklin, Béland and Colan10} and were submitted to catheter ablation.

Exclusion criteria were less than 6 months of follow up and patients that only performed a diagnostic electrophysiological study without ablation.

In patients under vitamin K antagonists, the medication was continued in the periprocedural period with an international normalised ratio within 2.0–3.0 range. In patients taking non-vitamin K antagonists, the last drug dose was omitted. Patients interrupted anti-arrhythmic drugs at least 5 half-lives before the procedure, except for amiodarone, which was suspended 1 month prior to the procedure. Whenever necessary, the procedures were performed under general anaesthesia. The use of transesophageal or intracardiac echocardiographies was left to the physician’s discretion.

In the setting of left atrial arrhythmias, unfractionated heparin was administered immediately after transseptal puncture and adjusted to achieve a target-activated clotting time above 300 s. In dextro-transposition of the great arteries corrected with Senning procedure, access to the pulmonary venous atrium was achieved by transbaffle puncture (Fig. 1).^{Reference Palma, Sousa, Silva and etal11}

Figure 1. Dextro-transposition of great arteries, after senning procedure. CT scan images were merged with real-time 3D electroanatomical mapping (CARTO 3, biosense webster, inc) allowing the reconstruction of the the systemic (SVA) and pulmonary venous atria (PVA) and the visualisation of the needle tip during transbaffle puncture. Posterior view, the senning baffle is highlighted in blue. The white arrow indicates the transbaffle puncture. PVA = pulmonary venous atrium, SVA = systemic venous atrium.

Anatomical mapping data was collected using a 3D mapping system (CARTO3®, Biosense Webster) and integrated with a CT imaging reconstruction, when available. Ablation was performed with point-by-point radiofrequency energy with a Thermocool SmartTouch® irrigated tip contact force-sensing catheter, in a power-controlled mode with temperature limited to 43°C. Power settings varied according to the targeted region.

Whenever the patient was in tachycardia at the beginning of the procedure (clinical tachycardia), the first objective was to identify the electrophysiological mechanism and perform ablation to interrupt that circuit. If there was a doubt concerning the interpretation of the activation map, entrainment manoeuvre was performed to confirm the suspected tachycardia mechanism. An additional activation map was carried out to confirm bidirectional block along any de novo linear lesion, followed by attempts to induce other tachycardias, which were mapped accordingly. The goal was to terminate all induced tachycardias and to achieve absence of inducibility at the end of the procedure.

If the patient was in sinus rhythm at the beginning of the case, pacing manoeuvers and isoprenaline were used for tachycardia induction. If induced, the procedure would continue as described above. If an arrhythmia was inducible but not maintained despite several attempts, an ablation guided by substrate was performed. A bipolar voltage mapping was obtained (criteria for healthy and scarred tissue were > 0.5mV and < 0.2mV, respectively). If no arrhythmia was inducible and no ablation was performed, the case was excluded from the study.

If the patient was in atrial fibrillation at the start of the case, and as the goal was to treat other tachycardia, electrical cardioversion was performed. Once in sinus rhythm, we followed the steps above mentioned. However, if our goal was to perform atrial fibrillation ablation, after reconstruction of the left atrium, wide pulmonary vein isolation was performed. If patients maintained atrial fibrillation, an electric cardioversion was performed. A bipolar voltage mapping was subsequently performed and low-voltage areas were ablated to achieve tissue homogenisation. If necessary, lines were performed connecting these scarred areas. Bidirectional block was confirmed after these lines were performed. If atrial fibrillation persisted or was still inducible at the end of the procedure, an electric cardioversion was performed.

The primary endpoint focused on the mid-term arrhythmia recurrence rate in patients with CHD referred for catheter ablation. Recurrence was defined by documenting at least 30 sec of arrhythmia during follow up, irrespective of symptoms.^{Reference Khairy, van Hare and Balaji9}

The secondary endpoints were acute success and safety. Acute success was defined as disappearance of the arrhythmia immediately after catheter ablation, despite induction manoeuvres. Safety was defined as any of the following events occurring within the first month after the index ablation: death, major bleeding as defined by the International Society on Thrombosis and Hemostasis,^{Reference Schulman and Kearon12} occurrence of a thromboembolic event, atrio-oesophageal fistula, phrenic nerve palsy, pulmonary valve stenosis, pericarditis, and vascular access complications.

We also evaluated predictors for arrhythmia recurrence during follow up.

Patients were evaluated before discharge, as well as at 3, 6, and 12 months after the procedure and thereafter yearly. Transthoracic echocardiography and 24-hour Holter monitoring were performed before discharge. Information collected during follow up included a 12-lead electrocardiogram and a 24-hour Holter in each appointment. A 7-day Holter monitoring was performed at least once yearly. At discharge, anti-arrhythmic drugs were prescribed according to patient characteristics and operators’ decision. The first three months post-procedure were considered as a blanking period. Anti-coagulation strategy was based on the CHA2DS2Vasc Score.

Statistical analysis was performed using IBM SPSS Statistics version 25 (IBM, Chicago). Categorical variables are expressed in frequencies and percentages and continuous variables are expressed as mean ± standard deviation or median and interquartile range for variables with or without normal distribution, respectively. The X² test was used to assess differences between categorical variables and the Student t-test or the Wilcoxon test was used to compare continuous variables with or without normal distribution, respectively. The Kolmogorov-Smirnov test was used to test for normality of distribution of continuous variables. Kaplan-Meier curve was performed to illustrate freedom from atrial arrhythmia recurrence during follow up. Cox regression was used to identify predictors of atrial arrhythmia during follow up. Statistical significance was accepted for p values<0.05.