Personalized Left Atrium Wall Thickness-Based Radiofrequency Ablation for Paroxysmal Atrial Fibrillation
Circumferential pulmonary vein isolation (PVI) has become a mainstay in the treatment of atrial fibrillation (AF), particularly in symptomatic patients with paroxysmal AF (PAF) intolerant or refractory to medical treatment.1
Dormant conduction and pulmonary vein reconnections are responsible for AF/atrial tachycardia (AT) recurrences owing to incomplete nontransmural ablation lesions that generate gaps on ablation lines.2-4
In recent years, advances have been made in the ablation technique with the introduction of contact force (CF) catheters and the development of complex weighted formulas such as the ablation index (AI), which allow for more efficient lesion creation and durable PVI.5 AI is a novel marker of ablation lesion quality that incorporates power, CF, and time in a weighted formula; it has been found to accurately estimate ablation lesion depth in preclinical studies.6 Radiofrequency (RF) power, delivery duration, baseline impedance, and CF have all been shown to be determinants of lesion formation.
The development of other advances in the ablation technique, such as tailoring the AI to the left atrial wall thickness (LAWT), has allowed for more efficient lesion creation and durable PVI.7
The LA wall is a thin structure with heterogeneous thickness, ranging from <1 mm to >5 mm, with significant interpatient and intrapatient variability.8 Durability of PVI can be limited by the inability to create transmural lesions in certain anatomical sites where LAWT is greater.
The application of AF ablation protocols in general for all patients, without considering the anatomical variability that each patient may present (among other clinical characteristics), led us to propose a personalized LAWT-based method for RF ablation of PAF. In this article, we present a brief case that illustrates use of this personalized approach.
Case Presentation
We report the case of a 66-year-old female with a past history of high blood pressure and symptomatic, drug-refractory PAF and no associated structural heart disease. The patient was under antiarrhythmic treatment with flecainide and beta-blockers, and was anticoagulated with edoxaban (CHA2DS2-VASc=3). The patient was referred for point-by-point RF ablation, which was performed by tailoring the local AI targets to the LAWT. Oral anticoagulation was uninterrupted and periprocedural anticoagulation was managed to achieve an activated clotting time >300 sec.
A preprocedural multidetector computed tomography (MDCT) was performed with a 256-slice CT scanner. The images were acquired during an inspiratory breath-hold using a retrospective electrocardiogram (ECG) gating technique with tube current modulation set between 50% and 100% of the cardiac cycle. Angiographic images were acquired during the injection of a 70-mL bolus of iopromide 370 mg/mL at a rate of 3 mL/s. Axial images were reconstructed in the workstation with a slice thickness of .625 mm. Further postprocessing, which was performed using the ADAS 3D imaging platform (ADAS3D Medical), obtained a color-coded 3D LAWT map as well as a color-coded isodistance map of the esophagus in relationship with the posterior LA wall (Figure 1). Both maps were imported into the navigation system. LAWT was classified into 5 incremental categories of 1 mm each (Figure 2). Ablation lines around the PV ostia were manually traced on the imported maps, avoiding regions thicker than >3 mm or the closest points (<1 mm) to the esophagus as much as possible. An additional carina line was always performed for the right PVs, since there is anatomical and electrophysiological evidence for the presence of epicardial connections and interconnections of the ipsilateral veins in up to two-thirds of the patients referred for AF ablation.9-12
General anesthesia and “high rate-low volume” ventilation (with 50 rpm and 4.0 mL/Kg tidal volume) were used to provide greater precision and stability of the ablation catheter. Since a single-catheter approach was used, single right femoral venous access was performed.13 Transseptal puncture was guided with transesophageal echocardiography using no fluoroscopy. A multithermocouple esophageal temperature probe (SensiTherm, Abbott) was introduced after performing the transseptal puncture. Access to the LA was obtained with the ablation catheter using a pressure sensor on the Preface sheath (Biosense Webster, Inc, a Johnson & Johnson company). Reconstruction of the LA and PVs as well as postprocessing was performed with ADAS 3D and fusion with MDCT to show the LAWT was integrated into the navigation system (Figures 3 and 4). Ablation of the PVs was achieved with AI adapted to the LAWT, considering the isodistance map of the esophagus with the posterior wall of the LA to avoid thicker regions and the path of the esophagus (Figures 5 and 6).
PVI was performed point-by-point using a nonsteerable sheath and a ThermoCool SmartTouch (Biosense Webster) 3.5-mm irrigated tip CF-sensing RF ablation catheter. The number of RF points was 32 for the left PVs and 38 for the right PVs, with a RF time of 6.5 min on the left PVs and 8.8 min on the right PVs. Maximal interlesion distance was 6 mm. Visitag (Biosense Webster) settings were as follows: catheter position stability: minimum time 3 seconds; maximum range: 3 mm; force over time: 25%, minimum force: 3 g; lesion tag size: 3 mm (Videos 1 and 2). The irrigation flow rate was set to 2 mL/min during mapping and 30 mL/min during ablation. The flow was constant irrespective of power output chosen for ablation.
Video 1
Video 2
Videos 1 and 2. PVI was performed point-by-point using a non-steerable sheath and a ThermoCool SmartTouch 3.5 mm irrigated tip contact force-sensing RF ablation catheter (Biosense Webster). Maximal interlesion distance was 6 mm. Visitag settings were as follows: catheter position stability: minimum time 3 s; maximum range: 3 mm; force over time: 25%, minimum force: 3g; lesion tag size: 3 mm.
Table 1 resumes the AI targets by local LAWT on the thickness color map: thickness <1 mm (red): 300; 1-2 mm (yellow): 350; 2-3 mm (green): 400; 3-4 mm (blue): 450; and >4 mm (purple): 500. These AI were chosen based on the “Ablate by-LAW” study.7
To reach these AI values, the power output was set at 35W for the posterior wall. For the anterior wall, power was set at 40W for LAWT between <1 and 2 mm; and at 50W wherever LAWT was >3 mm (green, blue, and purple on the thickness map).
The circumferential PV line was thicker in the left PVs compared with the right PVs. The anterior segments (roof, anterosuperior, anterior carina, and anteroinferior) were thicker than the posterior (posterosuperior, posterior carina, posteroinferior, and inferior). Four applications were necessary in areas of 3-4 mm and only 2 applications in areas of >4 mm. All were located at the anterior segments of the left PVs.
In this case, we did not observe any significant rise in temperature during ablation. It remained below 37.5 ºC at all sites of RF application along the ablation line, with variations of 0.1-0.4 degrees above baseline esophageal temperature at sites closer to the esophageal footprint.
We achieved “first pass” PVI in all PVs without complication, with a total fluoroscopy time of 2 seconds (needed for placing the esophageal temperature probe) and a total (skin-to-skin) procedure time of 54 minutes. Acute PVI was confirmed after first pass with the single-catheter method of demonstrating entry block with the absence of PV potentials inside the vein, with the ablation catheter placed sequentially in each segment inside the circumferential PV line; exit block was demonstrated by proving absence of conduction to the LA when pacing from inside the circumferential PV line at each segment sequentially.13,14
The patient passed to the monitoring unit awake and without complications. After 4 hours, no pericardial effusion was found on echocardiogram. We restarted oral anticoagulation with 60 mg of edoxaban. At 24 hours, the patient was reevaluated and discharged from the hospital without antiarrhythmic drugs.
The patient was scheduled for follow-up at the outpatient clinic at 1, 3, and 6 months, and every 6 months thereafter, or in case of symptoms. Each evaluation included an ECG and 24-hour Holter monitoring. Recurrence was considered as any documented arrhythmia (ie, AF, atrial flutter, or AT) lasting longer than 30 seconds off antiarrhythmic medication or symptoms suggesting clear recurrence as identified by the patient (symptoms that had been associated with a documented arrhythmia episode before the ablation procedure). In our personalized AF ablation protocol, antiarrhythmic drugs are stopped after ablation unless nonsustained AT/frequent atrial ectopic beats during in-hospital ECG monitoring. After the procedure, we did not repeat imaging with the ADAS software, since it allows only for evaluation of the myocardial thickness at each point and not an assessment of the “quality” of the lesion performed. In addition, since only the local thickness could be evaluated and not the characteristics of the tissue where the lesions were made, repeating the CT scan would imply an extra dose of radiation for the patient. At 1-year clinical follow-up, no recurrences of AF were observed in this patient.
Discussion
The personalized LAWT-based ablation approach described here can potentially allow for safer and likely more efficient AF ablation procedures by allowing a reduced RF dose to be administered. Moreover, this case describes a single-catheter approach that simplifies ablation. This comprehensive approach could result in shorter procedure (skin-to-skin), fluoroscopy, and RF times, while providing efficacy results that may be comparable to more demanding ablation protocols. Larger studies are needed to confirm these hypotheses. Some problems regarding thermal ablation, such as excessive overheating of the tissue or the potential to injure extracardiac structures, remain an unresolved concern of RF ablation of AF.
Conclusion
A personalized approach adapting the AI to the LAWT allowed PVI with low RF energy delivery, fluoroscopy, and procedure time, while also obtaining first-pass isolation using a single-catheter technique and adapting the ablation line considering the isodistance map of the esophagus projected into the posterior LA wall. LAWT permits the operator to deliver the proper amount of energy at any given point without doing it randomly, since the strategy of dichotomizing into the anterior/posterior atrial wall for RF delivery is an oversimplification that does not take into consideration the complex anatomical reality of the LA.
We also highlight the importance of adapting ablation protocols to each individual patient. Personalized AF ablation is feasible, and above all, likely safer and more efficient.
Disclosures: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. Dr Berruezo reports grants or contracts from Biosense Webster, Biotronik, and Galgo Medical; he reports payment or honoraria for lectures, presentations, speakers bureaus, manuscript writing or educational events from Circle Cardiovascular Imaging and Biosense Webster.
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