Detailed Electrode Catheter Positioning is Important for the Ablation of Outflow Tract Origin Ventricular Arrhythmias

1Division of Cardiology, Heart center, Konyang University Hospital, Daejeon, Korea 2Division of Cardiology, Department of Internal Medicine, College of Medicine, The Catholic University of Korea, Seoul St. Mary’s Hospital 3Division of Cardiology, Department of Internal Medicine, College of Medicine, The Catholic University of Korea, Uijeongbu St. Mary’s Hospital 4Department of Cardiology, Pohang St. Mary’s Hospital 5Division of Cardiology, Department of Internal Medicine, College of Medicine, The Catholic University of Korea, Incheon St. Mary’s Hospital 6Division of Cardiology, Department of Internal Medicine, College of Medicine, The Catholic University of Korea, Daejeon St. Mary’s Hospital 7Division of Cardiology, Department of Internal Medicine, College of Medicine, The Catholic University of Korea, St. Vincent’s Hospital 8Division of Cardiology, Department of Internal Medicine, College of Medicine, The Catholic University of Korea, St. Paul’s Hospital 9Division of Cardiology, Department of Internal Medicine, College of Medicine, The Catholic University of Korea, Yeouido St. Mary’s Hospital

To control this kind of PVC or VT, catheter ablation is known to be an effective treatment modality. [2][3][4] However, localization of the origin of OT PVC/VT relevant to procedural success is not always guaranteed in the ventricular OT of a three-dimensional (3D) narrow tubular structure. To enhance mapping accuracy, ablation guided by a 3D system or a body surface electrocardiographic mapping system as a noninvasive technique is quite safe and effective for the ablation of OT PVC/VT. 5,6 However, these modalities carry considerable economic burden.
The efficacy of multielectrode catheter mapping methods has been reported in some studies but these methods have the limitations of small group sizes and uncertain statistical significance. 7,8 Our study sought to evaluate the efficacy of circular and multielectrode diagnostic catheters without 3D system mapping (detailed catheter positioning group) for the ablation of OT PVC/VT compared to that of the conventional 3D system mapping method.

Study population
This retrospective non-randomized study compared different mapping methods used for the ablation of OT PVC/VT. Between June 2012 and February 2017, a total of 92 patients who were admitted for an electrophysiology (EP) study and ablation due to OT PVC/VT were consecutively enrolled in this study. All patients had documented 12-lead electrocardiography (ECG) of the OT PVC/VT with symptoms including dizziness, palpitation, dyspnea, or chest discomfort and had problems using antiarrhythmic medications due to drug inefficacy or intolerance.
Patients underwent 24-hour Holter monitoring before the EP study and again 3-6 months after the procedure.

Mapping and ablation procedure
The EP study was performed in a fasting and non-sedated state.
All antiarrhythmic medications were stopped for five half-lives before the procedure. The EP study and ablation were performed using two different mapping methods. In the group of patients who underwent detailed diagnostic catheterization without 3D system mapping (Group 1), linear multielectrode catheters

Follow-up
After the procedure, the patients visited the outpatient department and were examined using a Holter monitor or serial ECG. Symptoms of PVC were evaluated together. Chronic success was defined as >80% PVC reduction in follow-up Holter monitoring compared to the baseline study or more than two serial PVC-negative ECG at least 1 week apart. Primary outcomes were acute and chronic success. Secondary outcomes were need for medication for symptom relief, duration of total procedure time, fluoroscopy time, ablation time, and presence of procedure-related complications.

Statistical analysis
Continuous variables are expressed as mean ± standard deviation and were compared using Student's t-test. Categorical variables were compared using the χ 2 test or Fisher's exact test or Cox regression analysis. The survival result was compared using Kaplan-Meier analysis. Statistical significance was considered when the P value was <0.05. The statistical analysis was performed using SPSS statistical software (SPSS version 18; SPSS, Chicago, IL, USA).

Results
A total of 92 de novo OT PVC/VT cases and six repeat cases were consecutively enrolled. The mean follow-up period was 17.7±14.5 months. The baseline demographic and clinical characteristics of the study population are shown in Table 1.
Patients were younger in group 1, but the follow-up period was similar between the two groups. Group 1 had a shorter total procedure time, fluoroscopy time, and ablation time than group 2.
However, the medication requirement including beta blockers, 29% in group 2, p<0.01) ( Table 2). Cox regression analysis showed that the use of 3D mapping did not significantly affect procedural success (Table 3). Long-term arrhythmia-free survival did not differ significantly between the two groups ( Figure 3). In group 2, two patients had VT that originated from the left ventricle (LV) summit; ablation was attempted in the target area but was insufficient.
Six patients underwent a repeat ablation procedure due to PVC recurrence (two in group 1, four in group 2). Among the three patients in group 1, one underwent a repeated ablation procedure using the same initial detailed catheter mapping system, whereas the other patient opted for a 3D mapping system. Similarly, in group 2, one patient used the detailed catheter mapping system and the other three patients used a same initial 3D mapping system. Four patients were free from OT PVC/VT and other ventricular arrhythmias, but two patients experienced recurrence during the remaining follow-up period.
There were no major complications in this study group. In group 1, one patient developed a puncture site hematoma after the procedure that was managed conservatively with eventual selfresolution.
* Recurrence means at least one of low PVC reduction, symptom, or anti-arrhythmic medication need FU, follow up; PVC, premature ventricular complex; min, minute; sec, second In our detailed mapping practice, our main concern is the potential risk of circular multielectrode catheter entrapment in cardiac valves or subvalvular structures. Circular multielectrode catheter entrapments have been reported, especially in the ablation of atrial fibrillation. 16 As described previously in another study, we used pre-shaped guiding introducers for the delivery and placement of circular multielectrode catheters to avoid catheter entrapment 8 ; in this study, we did not note this complication. Previous studies showed an 85-100% acute success rate of OT PVC/VT ablation. 12   seemed to be relatively high, but it might have been overestimated because we could not confirm that their recurrent symptoms were truly related with the recurrence of targeted PVC.
This study has some limitations in that the number of patients with non-sustained VT-and LV-outflow tract origin PVC/VT were significantly higher in the 3D mapping group than in the detailed catheter group. We thought that a non-sustained VT is more complex arrhythmia than PVC, while LVOT-origin PVC/ VT is also more difficult to ablate than RV-outflow origin PVC/ VT, so 3D mapping methods may be used more frequently in non-sustained VT or LV-outflow origin ventricular arrhythmia ablation procedures.

Conclusions
Detailed electrode catheter positioning is a safe and costeffective method for the ablation of OT PVC/VT.