Intraatrial re-entrant and focal atrial tachycardias are often seen after surgeries of CHD. Corrective atrial incisions and sutures performed during surgery lead to subsequent myocardial fibrosis, which can contribute to the development of intraatrial re-entrant tachycardias. Reference Bouchardy, Therrien and Pilote1,Reference Walsh and Cecchin2 This complication is more common in complex CHD. Reference Lundqvist, Potpara and Malmborg3 In patients with CHD, sustained atrial tachycardias and impaired ventricular function are important risk factors for sudden cardiac death. Reference Gatzoulis, Balaji and Webber4 Isolated focal atrial tachycardias cause also left ventricular dysfunction if left uncontrolled.
Treatment of these arrhythmias is crucial as they are associated with increased morbidity and mortality in these patients. Transcatheter ablation is the most effective treatment for atrial tachycardia compared to pharmacological therapy.
The use of high-density mapping system provides reliable data in ablation of intraatrial re-entrant tachycardia and focal atrial tachycardia in a shorter time by collection of more points during mapping. This facilitates the identification of critical ablation targets. Reference Balt, Klaver, Mahmoodi, van Dijk, Wijffels and Boersma5
In this study, we describe our experience utilising Advisor™ High Density (HD) Grid mapping catheter in transcatheter ablation of intraatrial re-entrant and focal atrial tachycardias in patients with palliated CHD.
Materials and methods
Patient population
All patients who underwent a first ablation procedure for focal atrial tachycardia and intraatrial re-entrant tachycardia at our centre from January 2017 to January 2023 were included. Clinical and periprocedural data were collected from the electronical medical records and the database of the electrophysiology laboratory. A follow-up was performed either by inpatient or outpatient planned visit or by phone with no prescheduled follow-up period. The study was approved by local ethics committee.
Electrophysiologic study
Electrophysiologic study and ablation were performed by a single operator. The procedure was performed under local anaesthesia and conscious sedation using propofol or under general anaesthesia. Antiarrhythmic medication was discontinued at five half-lives prior to electrophysiologic study. In patients taking warfarin, the drug was discontinued before the procedure to maintain an international normalised ratio between 1.5 and 2. Vascular access was obtained via femoral vessels for all patients. Heparin was administered as a bolus infusion of 100 U/kg to achieve and maintain an activated clotting time > 350 ms throughout the procedure.
Three-dimentional electroanatomic mapping was performed in all patients using EnSite™ precision system (Abbott, St Paul, MN, USA). A deflectable decapolar catheter was used as reference electrode for activation mapping and pacing. Electrophysiology catheters were placed in the coronary sinus, right ventricular apex, and His bundle positions. The decapolar catheter was either introduced into the coronary sinus in most of the patients or alternatively placed within the left atrial appendage in subjects after atrial switch procedure for d-transposition of great arteries.
The Advisor™ HD Grid Catheter (Abbott Technologies, Minneapolis, MN) was used for mapping (Fig. 1). This catheter is a 16-electrode, flexible diagnostic catheter with 3 mm equidistant electrode spacing and can record not only parallel but also perpendicular to the splines allowing rapid assessment of voltage, activation, and directionality of conduction as well as omnipolar electrogram assessment. Reference Frisch6 The bidirectionality feature of HD Grid catheter allows it to reach up to 35 mm in D curve and up to 42 mm in F curve flexion. HD Grid catheter is 8-Fr and 110 cm long. Long sheaths (Agilis-Abbott) were used to manoeuvre the HD Grid catheter.
Pacing was performed either using the ablation catheter or a coronary sinus catheter. Whenever possible, bipolar voltage maps in sinus rhythm and/or activation maps of the present arrhythmia were created at the discretion of the operator. Voltage values were also recorded at each point and represented in colour scale (grey < 0.1 mV, purple > 0.5 mV). Scar area was defined as tissue with voltage < 0.1 mV, intermediate tissue as voltage of 0.1–0.5 mV, and healthy tissue as voltage > 0.5 mV. Reference Namboodiri7 Isoproterenol infusion (1–5 microgram/min) was used as needed for tachycardia induction. Patients with a clinically documented baseline cardiac rhythm of atrial tachycardia underwent complete activation mapping. Based on the results of activation sequence mapping by the electroanatomical system and entrainment mapping from multiple disparate sites during atrial tachycardia, the arrhythmia mechanism and type were determined. A tachycardia was classified as intraatrial re-entrant if a macro-re-entry circuit with coverage of > 90% of cycle length mapped around an anatomical structure or scar. Reference Mantziari, Butcher and Shi8 The entrainment site where pacing resulted in local concealed fusion and the post-pacing interval was < 30 ms was considered the "critical isthmus." The mechanism was classified as focal if the activation sequence mapping revealed centrifugal spread from a single source and if the spread of local activation times was < 70 % of the cycle length of the atrial tachycardia.
Ablation procedure
Intraatrial re-entrant tachycardia
Ablation was performed using the open 7-Fr irrigated ablation catheter (FlexAbility, Abbott Park, IL) in all patients. Generator settings were 30 W with target temperature of 45 °C. Ablation was continued until there was at least 90% reduction of electrogram amplitude along the ablation line. Radiofrequency lesions were applied point by point in order to induce a complete conduction block across the isthmus. In patients with both cavotricuspid isthmus and scar circuits, inducibility was assessed after ablation of each circuit.
Focal atrial tachycardia
Ablation was performed at the site of earliest endocardial activation by using 7-F irrigated ablation catheter (FlexAbility, Abbott Park, IL). Cryoenergy was preferred in patients with foci close to atrioventricular node using a steerable 7F Freezor Xtra 6-mm tip catheter (Freezor Xtra, Medtronic, Minneapolis, MN, USA). Cryoablation was performed with a target temperature of –75 °C for 240 s.
A procedure was considered to be acutely successful when achieving sinus rhythm with non-inducibility of any tachycardia in focal atrial tachycardias and bidirectional block in intraatrial re-entrant tachycardias after for a waiting period of 30 minutes.
Statistical analysis
SPSS 22.0 (IBM Corporation, Armonk, New York, USA) was used to analyse all data. Quantitative data were expressed as mean ±standard deviation and median range (minimum-maximum) values. Categorical values were stated as n (number) and % (percentage).
Results
Between 2017 and 2023, a total of 45 patients underwent catheter ablation procedures for the treatment of documented intraatrial re-entrant and focal atrial tachycardia in our centre. Patient characteristics were shown in Table 1.The mean weight and age of the patients were 48.3 ± 16.2 kg (22–83 kg) and 14.2 ± 7.3 years (6–32 years), respectively. Before the ablation procedure, 26 patients were being treated with antiarrhythmic drugs. Of these 26 patients, 12 were taking beta blockers, four sodium channel blockers, six calcium channel blockers, three amiodarone, and one sotalol. Twenty of the patients were intraatrial re-entrant tachycardia. The CHD diagnosis of the patients are listed in Table 1, with most being tetralogy of Fallot or atrioventricular septal defect. Of these patients, 14 had complex and 6 had simple heart disease. Of the 21 re-entrant circuits, 15 were classified as cavotricuspid isthmus-dependent and 5 were non-cavotricuspid isthmus-dependent (lateral wall suture). In one patient, two re-entrant circuits were identified. In the four non-cavotricuspid isthmus-dependent re-entrant circuits (Fig. 2), the scar was near the right anterior atriotomy scar and the final scar was in the pulmonary venous atrium. Three of the patients had focal atrial tachycardia in addition to intraatrial re-entrant circuit. Of these three patients, two were Ebstein’s anomaly and one was atrioventricular septal defect. In all these three patients, the foci was in the right atrium. In two patients with Ebstein’s anomaly, the foci was crista terminalis and in one patient with atrioventricular septal defect the foci was in the coronary sinus ostium. In two patients with Ebstein’s anomaly, additional ablation of an accessory atrioventricular pathway was performed during the same procedure. Tachycardia locations were shown in Table 2 and flowchart.
Table 1. Patients characteristics
AVSD = atrioventricular septal defect; ASD = atrial septal defect; DILV = double-inlet left ventricle; F = female; FAT = focal atrial tachycardia; HLHS = hipoplastic left heart syndrome; IART = intraatrial re-entrant tachycardia; kg = kilogram; LV = left ventricle; M = male; PPVRA = partial pulmonary venous return anomaly; TGA = transposition of great arteries, TA = tricuspid atresia; VSD = Ventricular septal defect.
Values are n (number) mean ± SD (min-max).
Table 2. Procedural data
CL = cycle length; CS = coronary sinus; CTI = cavotricuspid isthmus; FAT = focal atrial tachycardia; IART = intraatrial re-entrant tachycardia; LUPV = left upper pulmonary vein; min = minutes; ms = milliseconds; mm = millimetre; mGy = miligray; PV = pulmonary venous; RUPV = right upper pulmonary vein; RAAS = right atrial anatomy scar; s = seconds.
Values are n ( %) mean±SD (min-max).
Of the total 45 patients, 25 were isolated focal atrial tachycardia. Nineteen of them had right atrium foci with nine crista terminalis, five coronary sinus ostium, four atrial appendage, and one midseptal area. Six of the patients had left atrium foci with two left upper pulmonary vein ostium, two mitral annulus, one left atrial appendage, and one right upper pulmonary vein ostium. Of the 45 patients, 9 had left ventricular dysfunction (left ventricule ejection fraction < 50%). Of these nine patients; five of them were intraatrial re-entrant tachycardia and four were focal atrial tachycardia.
Mean age during the first operation was 16.8 ± 7.5 months. The mean time between surgery and radiofrequency ablation was 12.4 ± 9.1 years (range 5–34 years). Preprocedural complaints were palpitations in 20 patients, fatigue in 12, and presyncope in 6. Seven patients were asymptomatic.
A transbaffle ablation was successfully performed in the left atrium in one patient. Radiofrequency ablations were performed in the left atrium as well as in the right atrium in this patient. Mean procedure duration was 180.2 ± 64.3 min, and mean fluoroscopy time was 5.2 ± 4.6 min. Radiofrequency ablation was performed using a mean of 14 ± 10 irrigated radiofrequency applications per tachycardia isthmus. One cryoablation was performed in midseptal region. Procedural success was achieved in 43/45 (95.5%) subjects. Procedural data are given in Table 2.
On transthoracic echocardiography after the procedures, no pericardial effusions were detected. No major complications occurred.
After 1 month from the procedure, there were recurrence in two cases. One with cavotricuspid isthmus-dependent tachycardia and the other with focal atrial tachycardia originating from the crista terminalis. A succesful second ablation was performed in both.
Discussion
Traditional mapping catheters have limitations as they can only record bipolar signals in one direction. Patients with CHD often have multiple inducible arrhythmia mechanisms and circuits. High-density mapping is useful in atrial tachycardias as it can determine successful sites for ablation and mechanism of tachycardia. It can assess the gap during cavotricuspid isthmus ablation and holds promise for addressing mapping gaps in other lesion sets during the ablation of other arrhythmias. Reference Frisch6 In our study, the experience of Advisor™ HD Grid mapping catheter to guide atrial arrhythmias in patients with CHD and in isolated focal atrial tachycardia was described.
Advisor™ HD Grid mapping catheter successfully records continuous, low-amplitude, fractionated electrogram. It provides a clear target for ablation by visualising the low-voltage isthmus. The unipolar mapping feature of HD Grid catheter offers greater mapping sensitivity, regardless of direction of wavefronts’ activation. The catheter can simultaneously record bipolar electrograms along and across the splines (orthogonal-bipolar electrograms) at the same location. This allows creation of high-definition map by selecting the best electrogram with the best highest peak-to-peak voltage. Reference Paymard and Chakrabarti9 Approaching the anatomic substrate in patients with complex anatomy in shorter time is feasible because of the bidirectionality feature of HD Grid that allows the catheter to reach up to 35 mm in D curve and up to 42 mm in F curve flexion. Reference Paymard and Chakrabarti9 Collecting numerous points to create the maps in relatively short period of time is an advantage of HD Grid catheter. These advantages reduces ablation time, fluoroscopy time, and radiation dose.
Other high-density mapping catheters, such as the PentaRay catheter and IntellaMap Orion™, are also available. Each has its own electrode arrangement and mapping system. PentaRay catheter has 20 electrodes arranged in 5 soft radiating splines (1 mm electrodes seperated by 2 mm interelectrode spacing) laid out flat to cover an area with a 3.5 cm diameter. It can only be used with the CARTO mapping systems. Reference Nedios, Sommer and Bollmann10 The IntellaMap Orion™ (Boston Scientific) multipolar catheter has 64 electrodes. This system comprises eight splines with eight electrodes per spline, 0.4 mm2 electrode size, and 2.5 mm interelectrode spacing and is used in combination with the Rhythmia mapping system. Reference Nakagawa, Ikeda and Sharma11 High-density mapping with new multipolar HD mapping catheters has changed the way we can look at cardiac arrhythmias, especially atrial tachycardia and ventricular arrhythmia.
In our experience, we found high-density mapping with HD Grid mapping catheter to be safe and feasible in the paediatric/CHD population. Our recurrence rate was 4.4%, and we collected 3800 (1950–8500) points. In another study by Ulrich et al., patient population were adults with CHD who underwent catheter ablation for atrial arrhythmias with high-density mapping. The recurrence rate was also low (12.5%), and the number of collected points were 14.814 ± 10.140 and 2319 ± 1244 that were finally used to characterise the tachycardia. Reference Krause, Müller, Stellmacher, Backhoff, Schneider and Paul12 In the study of Johannes et al., the number of collecting points was 2634 (1767–7654) per map. Reference Von Alvensleben, Sandhu and Chang13
HD Grid catheter is also commonly used in ablations of patients with ventricular tachycardia. Johannes et al. used HD Grid catheter in patients with other tachycardias like atrioventricular nodal re-entrant tachycardia, ventricular tachycardia. They also found the Advisor™ HD Grid mapping catheter safe and effective in the paediatric and CHD patients. Reference Von Alvensleben, Sandhu and Chang13 Sergio et al. used HD Grid catheter in patients with ventricular tachycardia, and they found shorter radiofrequency and mapping time during ventricular tachycardia but longer procedural and mapping times in sinus rhythm. This longer time in sinus rhythm may be due to the greater amount of information collected by the mapping catheter and the more elaborate post-processing analysis of acquired points. Reference Conti, Sabatino, De Blasi, Di Stabile and Sgarito14 HD Grid catheter views low-voltage areas successfully and is less sensitive to far-field signals. This feature provides for viewing scar areas in sinus rhythm.
Giulio et al. compared ablations made by multielectrode catheters and ablations by mini-basket catheters in their study, and they found high-density mapping after cryoballoon ablation using the fourth-generation cryoballoon and the new spiral mapping catheter identifies incomplete pulmonary vein isolation, not detected by the new catheter, in a significantly lower proportion of veins compared to high-density mapping performed after the other generation cryoballoon ablation. Reference Conte, Soejima and de Asmundis15
Success rate of focal atrial tachycardia might be improved by high-density mapping. The success can be improved in this population due to the risk of significant atrial scars from prior heart surgeries/incisions. In our experience, acute success of high-density mapping in focal atrial tachycardia was 96%. In the study of Antonia et al., they compared ultrahigh-density mapping with conventional electroanatomical mapping, and acute success was significantly higher in the ultrahigh-density mapping cohort (89.6%). Reference Kellnar, Fichtner and Mehr16
Newlon et al performed a retrospective cohort study of children and CHD patients undergoing electrophysiology study and ablation to determine the effect of HD Grid catheter use on outcomes including complications, fluoroscopy use, procedure duration, acute ablation success, and arrhythmia recurrence. They found acute success was lower and recurrences higher in HD Grid catheter compared to non-HD Grid catheter cases. They also found HD Grid catheter use in children and CHD patients is safe and not associated with higher complication rates. Reference Newlon, Asaki and Pilcher17
Limited data is available regarding the utility of the Advisor™ HD Grid catheter in CHDpatients with atrial tachycardia. In our study, Advisor™ HD Grid mapping catheter was used in catheter ablation of atrial arrythmias in patients with CHDe and recurrence rates was found to be quite low.
Some difficulties were experienced in mapping with HD Grid mapping catheter of patients with foci near pulmonary vein and coronary sinus ostium due to size of mapping catheter. Expanding options of sizes of the catheter may overcome these difficulties.
Study limitations
The study was limited due to the small number of patient groups and its retrospective design. Larger sample size and having direct comparison to conventional mapping catheters with similar operators would provide more accurate and quantifiable comparisons. This single-centre experience also may not be generalisable to other programmes and electrophysiology labs due to the specific patient population.
Conclusion
Advisor™ HD Grid mapping catheter was found to be safe and achieved an acceptable success in transcatheter ablation of patients with intraatrial re-entrant tachycardia and focal atrial tachycardias.
Figure 1. Advisor™ HD grid catheter was shown.
Figure 2. Advisor™ HD grid catheterised mapping of a patient with intraatrial re-entrant tachycardia originating from the right atrial scar area. Scar areas and isthmus were observed. Diagram of the tachycardia location was shown.
Acknowledgements
None.
Financial support
This research received no specific grant from any funding agency, commercial, or not-for-profit sectors.
Competing interests
None.
