Atrial tachycardias in patients with congenital heart disease: a minimally invasive simplified approach in the use of three-dimensional electroanatomic mapping

Abstract

Aims

Atrial tachycardia (AT) is a common complication after repair of congenital heart disease (CHD). This two-centre prospective study evaluated the ability of three-dimensional electroanatomic mapping (EAM) to guide ablation of ATs in this particular population with a minimally invasive simplified approach.

Methods and results

Thirty-one consecutive patients (mean age 26 ± 17 years) with AT after repair of CHD were treated with a very limited number of intracavitary catheters and a specific setting of the Window of Interest (WoI) for the ablation of post-surgical ATs. A single-intracavitary catheter approach was performed in 22 patients, whereas an overall use of two intracavitary catheters in the other nine patients. Thirty-one patients exhibited 41 ATs. Seventy-six per cent of these were macro-reentrant ATs (MRATs), and 24% were focal ATs (FAT). The mid-diastolic isthmus (MDI) was located in the right atrial free wall (RAFW) in 82.8% of MRATs. Also in FATs, the RAFW was the most common site (77.8%) of the ectopic focus. Fifty-eight per cent of MRATs showed a double-loop reentry, with both loops sharing the same MDI in all cases. In 87% of cases, the abolition of the MRAT was obtained by applying radiofrequency energy to the MDI. Ninety per cent of FATs were successfully ablated. Mean conduction velocity and voltage amplitude had significantly lower values in successfully treated than in unsuccessfully treated MRATs.

Conclusion

Three-dimensional EAM, performed with a minimally invasive simplified approach and by using a specific parameter setting of the WoI, showed to be very effective to guide ablation of ATs in CHD patients.

Introduction

Atrial tachycardia (AT) is a common early and late complication after surgery for congenital heart disease (CHD).

Due to atriotomy and to the cannulation of the great veins or the right atrial appendage, the formation of scar tissue creates a complex arrhythmogenic substrate for multiple reentrant circuits or, less frequently, for abnormal automaticity.

Haemodynamic factors due to abnormal pressure–volume load, and, consequently, electrical and anatomical remodelling of the atria, have also been associated with the development of AT.^1,2

In previous reports, the combined approach using both three-dimensional electroanatomic mapping (EAM) and entrainment mapping was shown to be very effective in these patients with complex anatomy and presence of multiple reentrant loops.^3–8 Nevertheless, this approach might require long-lasting procedures and multiple catheters, which is not always possible in CHD patients.

Recently, a specific setting of the window of interest (WoI)—used to perform EAM so to identify the mid-diastolic isthmus (MDI) of the macro-reentrant atrial tachycardia (MRAT) without the compulsive need for entrainment validation—has been reported in the literature.⁹ Using this method, radiofrequency (RF) ablation of the MDI allowed good results in the general patient population.⁹

In this study, we report a two-centre experience in the application of a simplified minimally invasive approach based on a very limited number of intracavitary catheters and a specific setting of the WoI for the treatment of post-surgical ATs in patients with CHD.

Methods

Patient population

From July 2006 to June 2010, 31 consecutive CHD patients (mean age, 26 ± 17 years; range, 6–73 years) referred for the ablation of spontaneous or inducible post-surgical ATs were considered. The clinical characteristics of these patients are reported in Table 1. Seventy-seven per cent of patients had a complex congenital heart defects.

Simplified minimally invasive approach and electroanatomic mapping

In all cases, attention was paid to use a minimally invasive venous approach. Whenever it was possible, an intra-oesophageal quadripolar catheter was positioned and the atrial deflection recorded from the distal electrodes was used as a reference for EAM; therefore, in these cases, a single-intracavitary catheter approach was performed. Alternatively, a multipolar catheter was positioned in the coronary sinus and used as a reference for EAM with an overall use of two intracavitary catheters.

Three-dimensional EAM was used (CARTO XP, Biosense-Webster Inc., Diamond Bar, CA, USA). Recently, the XPress module has been integrated and used. This allows three-dimensional fast anatomical mapping (FAM) of the atrial chamber with generation of a surface anatomic reconstruction, based on the volume data recorded continuously during manipulation of the mapping catheter. During FAM, single electroanatomic points are acquired and projected onto the anatomic surface reconstruction. In patients with very complex anatomy, EAM was performed using the CARTO-Merge module¹⁰ with integration of pre-acquired magnetic resonance imaging.

In all cases, a specific setting of the WoI, with the onset fixed in mid-diastole between two consecutive P-waves, was used, as previously described.⁹ When a macroreentrant activation pattern was present, mapping was continued until a complete electroanatomic reconstruction was obtained, and the interval between the earliest and latest activated sites was >90% of the total cycle length (CL). Using the specific setting of the WoI, each colour in the colour-coded activation scale represented a specific chronology, with red and orange identifying mid- and late diastolic activations, respectively; dark blue and purple identifying early and mid-diastolic activations, respectively, and the remaining colours identifying areas of systolic activation. As a consequence of this WoI setting, the MDI is identified at the interface between the red and purple colours, and highlighted by the dark red band automatically interposed by the system. Reentry was defined as double-loop when activation along each loop spanned at least 90% of the CL. It was planned to use entrainment mapping only when the reentry course and the MDI were not clearly identified by EAM. Mapping sites were homogeneously distributed in the atrial chamber, and high-density mapping was performed in and around the MDI in order to define precisely its limits and width. The width of the MDI was calculated by using the electronic calliper of the system. The average peak-to-peak bi-Volt in the MDAI was calculated for each MRAT. Conduction velocity (CV) in the MDAI was manually calculated for each morphology, as previously described (Figures 1–3).¹¹

When a centrifugally spreading activation pattern was present, EAM was continued until a complete electroanatomic reconstruction of the atrial chamber was obtained and the earliest activated area precisely identified. Areas with bipolar voltage (bi-Volt) ≤0.05 mV were considered electrically silent. Sites with double potentials separated by >50 ms of isoelectric line were considered areas of local conduction block and activation detour.

In patients with limited tolerance of the AT, EAM was performed during sinus rhythm (SR) and remapping during AT focused on areas abnormal conduction and/or voltage identified in SR.

Ablation and procedure endpoints

According to operators’ preference, either a 4 or 8 mm tip or a 3.5 mm irrigated-tip catheter (Navistar, Biosense Webster Inc., Diamond Bar, CA, USA) was used. When 4 or 8 mm tips were chosen, a target temperature of 50°C was selected, and a power cut-off of 60 or 70 W, respectively, was used. Ablation with an irrigated-tip catheter was performed with a target power of 30–40 W, a temperature cut-off of 43°C, and a flow rate of 30 mL/min for target power.

For the MRAT, the ablation was directed to the MDAI. The aim of the ablation was to achieve arrhythmia termination and conduction block in this area, as demonstrated by the double potentials separated by an isoelectric line, with a consistent change of propagation during SR or atrial pacing from an appropriate site, and/or disappearance of electrical potentials in the target isthmus and the surrounding areas.

For focal AT (FAT), the ablation aimed at the earliest activated site. The procedure was considered successful if spontaneous or induced tachycardias were abolished by RF delivery and organized atrial arrhythmias were not inducible with three extrastimuli and burst pacing at baseline and during isoproterenol infusion administered 30 min after the end of the last RF application.

All patients were evaluated at 1, 3, 6, and 12 months after ablation by clinical evaluation, standard ECG, and Holter monitoring. Symptoms suggestive of tachycardia recurrence were recorded in patient diaries and referred to the physician in charge of follow-up.

Statistics

Continuous variables are expressed as mean ± SD, while categorical variables are expressed as percentages. Non-parametric tests were used to compare continuous variables. The correlation between non-normal variables was evidenced by Spearman's rank test. A value of P < 0.05 was considered statistically significant.

Results

Procedure and type of arrhythmias

Thirty-one patients exhibited 41 AT morphologies. All ATs were mapped and ablated in the right atrium. As shown in Table 1, 31 morphologies (76%) were MRATs (CL 282 ± 53 ms; range 200–430 ms), and the remaining 10 (24%) were FATs (CL 353 ± 119 ms; range 230–575 ms). In 22 patients (71%), the procedure was performed with a single intracavitary catheter. Whereas, in the remaining nine patients (29%), two catheters were used. The mean procedure duration was 293 ± 104 min (range 120–500) and the mean fluoroscopy time was 38.4 ± 23.4 min (range 2–119).

Electroanatomic mapping

The mean number of annotated points used for the reconstruction of the electroanatomic map was 109 ± 52 (range 47–280) for MRAT and 79 ± 30 for FATs (range 33–114).

In MRATs, EAM reconstructed 95 ± 4.7% of the circuit and identified in all the MDI, with no need for entrainment mapping validation. In the vast majority of MRAT cases (26/31; 84%), the MDI was localized in the right atrial free wall (RAFW), whereas in the remaining five cases (16%), it was located in the cavotricuspid isthmus. The mean width of the MDI was 22.6 ± 15.6 mm (range 2–69 mm). The mean CV across the MDI was 30 ± 17 cm/s (range 8–77 cm/s) and the average voltage of the MDAI was 0.50 ± 0.58 mV (range 0.10–2.4 mV). Eighteen out of 31 morphologies (58%) were a double-loop reentry, with both loops sharing the same MDI in all cases. The central obstacle of the reentrant circuit (including both single and dual loops) was an electrically silent area in 27, the tricuspid annulus in 15, and the inferior vena cava in 7.

In FATs, the site of origin of the tachycardia was localized in the right atrial septum in 2 out of 10 (20%) cases, and in the RAFW in 8 out of 10 (80%) cases.

Procedural outcome

A 4 mm tip catheter was used in 11 patients, an 8 mm tip catheter in 2 patients, and an irrigated-tip catheter in 18 patients.

The abolition of the MRATs was obtained by applying RF energy to the MDI in 27 out of 31 (87%) mapped morphologies. In successfully ablated double-loop reentry morphologies with both loops sharing the same MDI, ablation at this site resulted in all cases in termination of the arrhythmia without conversion in another morphology sustained by persistence of one of the two loops.

In the last two patients, with limited tolerance of the AT, the remapping during AT showed that the MDAI was exactly located in the lower CV area during SR. Radiofrequency applications to this site were successful in both these patients.

Mean CV and bi-Volt had significantly lower values in successfully treated MRATs than in unsuccessfully treated MRATs (24.2 ± 9.2 vs. 66.2 ± 14.7 cm/s, P = 0.001; and 0.32 ± 0.27 vs. 1.65 ± 0.8 mV, P = 0.003, respectively), whereas the MDI width (22.6 ± 15.4 vs. 22 ± 18.8 mm) was comparable in both groups.

The ablation of FATs was successfully in 9 out of 10 (90%) cases.

Follow-up

During a mean follow-up of 12 ± 4.5 months, no recurrence of tachycardia was observed in any of successfully ablated patients, nor was any suggestive clinical feature recorded in patient diaries.

Discussion

In previous reports, the incidence of atrial arrhythmias in patients with CHD was ∼20% preoperatively and increased by 10% after surgery. The incidence was higher in patients who underwent Mustard or Senning operations (20–60%) and Fontan operation (30–60%). On the contrary, it was lower in those who underwent atrial septal defect repair (12%), anomalous PV drainage repair (5%), ventricular septal defect closure (2.6%), and Tetralogy of Fallot repair (<2%). In patients with a poor haemodynamic results, such as residual shunts, atrioventricular valve regurgitation, or ventricular dysfunction, the incidence of AT was higher.¹²

Radiofrequency ablation is a good treatment option; however, with conventional approaches, the acute success rate is only between 68% and 90%, with a high percentage of recurrence (12–60%).^13–16 This is due to the fact that in patients with complex anatomy and presence of multiple reentrant loops, it may be difficult to clarify the atrial activation during AT in order to define a rational ablation strategy.^1,17–23 Recently, the combined use of conventional and three-dimensional EAM to this purpose has shown very good results.^3–8,20

In this study, we report our experience with a three-dimensional EAM system using a minimally invasive simplified approach which implies a very limited number of catheters (maximum two intracavitary catheters), a specific setting of the WoI for activation mapping sparing entrainment mapping validation, and ablation at the MDI in MRATs that in double-loop reentry results in simultaneous abolition of both reentrant loops. In our series of post-surgical patients, more than 70% are with complex CHD.

This approach was both possible and effective for mapping and ablation of ATs in this particular patient setting. In fact, by the use of such strategy, we achieved an acute RF ablation success rate similar to those reported in previous studies in which the combined approach with three-dimensional EAM and entrainment mapping was used.^3–7 Actually, in 22 out of 31 (70%) patients, we performed EAM by the use of only one endocavitary catheter, and achieved successful ablation in 25 out of 29 (86.2%) mapped ATs. All these single-catheter procedures were performed at the same institution where using a minimally invasive approach in paediatric patients has always been a major goal.²⁴ These results are even more important when considering that, in CHD patients, particular anatomy, previous transcatheter interventional procedures, or surgery might hinder the venous or atrial approach with multiple catheters (such as Glenn operation, Mustard operation, procedures for left atrial isomerism, etc.).

In MRATs, moreover, ablation aimed at the MDI was shown to be especially beneficial in the morphologies with a typical double-loop figure-of-8 reentry pattern, in which both loops share the same MDI. In this pattern, observed in 58% of morphologies in our series, ablation of the MDI was able to simultaneously abolish both loops and this spares the time spent for further mapping and ablation when the two loops are targeted independently at the identified narrowest anatomic isthmus. Furthermore, we found a correlation between unsuccessfully treated morphologies, and significantly higher CV and bipolar voltage in the MDAI, which confirms the results reported recently.¹¹

All ATs were mapped in the right atrium, and the central obstacle of MRAT circuits was mainly a scar, both in simple and in complex CHDs, as already described.⁶ Interestingly, both MDIs and ectopic foci were mainly localized in the RAFW in 88% of cases. An explanation could be that the RAFW is the site more stretched by both volume and pressure overloads due to haemodynamic sequelae, and furthermore is the usual site of surgical incision.

Finally, it is important to note that, in the last two procedures performed in two very complex CHD patients, FAM allowed us to record a fluoroscopy time of 108 and 25 s, respectively, much shorter than in the other procedures. Considering this, we can reasonably expect that, in the near future, we will be able to perform a single-catheter ablation of ATs in CHD patients with minimal or even no use of fluoroscopy.

Limitations

We can only available a mid-term follow-up because of about half of patients was sent to us from other centres who have returned after our pre-endpoint.

A statistical comparison between patients treated with single- vs. double-intracavitary catheter approach has not been developed due to the statistically small number of patients.

Conclusion

Based on our experience using the described minimally invasive simplified approach in patients with ATs after surgical correction of CHD, we can conclude that:

• The use of a single intracavitary catheter is possible for mapping and ablation in this patient setting.

• The specific setting of the WoI allows reconstruction of the whole activation pattern in MRATs with easy identification of the target site for ablation with no use of entrainment; this can be used even in cases, in which the AT nature is unclear before mapping, since it does not alter mapping of FAT cases.

• In these particular patients, the arrhythmogenic substrate responsible of ATs is more commonly localized in the RAFW.

Conflict of interest: none declared.

References