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ORIGINAL ARTICLE
Year : 2014  |  Volume : 3  |  Issue : 1  |  Page : 9-14

Safety and efficacy of three-dimensional mapping systems in idiopathic ventricular tachycardia ablation


Department of Cardiac Arrhythmia Research Centre, Centro Cardiologico Monzino IRCCS University of Milan, Milan, Italy

Date of Web Publication9-Apr-2014

Correspondence Address:
Nadeem A Raja
Cardiac Arrhythmia Research Centre, Centro Cardiologico Monzino IRCCS, Via Carlo Parea 4, 20138 Milan
Italy
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2278-0521.130199

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  Abstract 

Background: Idiopathic ventricular tachycardia (VT) accounts for approximately 10% of all patients referred for evaluation of VT. 3-D mapping system has proved very useful in ablation of complex arrhythmias e.g. atrial fibrillation and VT in structural heart disease. The aim of the current study is to evaluate safety and efficacy of new 3-D mapping system in idiopathic VT ablation and comparison of between contact (Carto™) and noncontact (EnSite Array™ Catheter) mapping systems. Materials and Methods: Study population included 62 patients with idiopathic VT. (27 female 35 male, mean age 43.5 ± 22.4 years). Six patients had previously undergone unsuccessful ablation in other centers using conventional method. Site of VT/PVCs origin was RVOT in 44 (70.9%), LVOT in 4 (6.5%) and LV cavity 14 (22.6%) patients. VT was successfully ablated in 54/62 (87.1%) patients and ablation was not successful in 8/62 (12.9%) patients. VT was successfully ablated in all (6/6) patients who had previous failed ablation with conventional methods. Four (6.4%) patients developed procedure related complications. No patient with successful ablation had recurrence at six months follow up and 6/8 patients in whom ablation failed had recurrence during follow up. There was no difference in safety and efficacy of two mapping systems (success rate was 90.9% in EnSite and 82.5% in Carto (p 0.6)). Conclusion: New 3-D mapping systems (Carto™, EnSite Array™ Catheter) are very useful in ablation of idiopathic VTs with good acute success and short-term follow up. These systems are particularly useful in patients with failed ablation by conventional methods. There is no difference the two systems with regards to acute success, recurrence and complications rate.

Keywords: Idiopathic VT, 3-D mapping system, catheter ablation


How to cite this article:
Raja NA, Carbucicchio C, Bartoletti S, Tondo C. Safety and efficacy of three-dimensional mapping systems in idiopathic ventricular tachycardia ablation. Saudi J Health Sci 2014;3:9-14

How to cite this URL:
Raja NA, Carbucicchio C, Bartoletti S, Tondo C. Safety and efficacy of three-dimensional mapping systems in idiopathic ventricular tachycardia ablation. Saudi J Health Sci [serial online] 2014 [cited 2022 Jan 22];3:9-14. Available from: https://www.saudijhealthsci.org/text.asp?2014/3/1/9/130199


  Introduction Top


Idiopathic ventricular tachycardia (VT) accounts for approximately 10% of all patients referred for evaluation of VT. [1] Outflow tract VT is the most common form of idiopathic VT. [2] Outflow tract VT typically originates from the free wall of the right ventricular outflow tract, but can also occur along multiple sites of the septum, the left ventricular outflow tract, above the pulmonic valve, the aortic sinus of Valsalva, near the His bundle, and the epicardial surface of the ventricles. [2],[3],[4],[5] Radiofrequency catheter (RF) ablation results in a high short-term success rate of 90% in the right ventricular outflow tract VT and 76% in the left ventricular outflow tract VT. [1] Activation mapping and pace mapping are mainly used to localize the site of origin of VT. Activation mapping is based on detecting the earliest endocardial activation time during tachycardia. Pace mapping relies upon single-point mapping under fluoroscopic guidance to obtain ≥11/12 morphologic match of the 12-lead ECG paced QRS complex to the tachycardia QRS complex.

Main reason for failure of catheter ablation of idiopathic VT is non-inducibility of ventricular tachycardia/premature ventricular contraction (VT/PVC) during VT ablation. Because RF energy produces relatively smaller lesion sizes, precise localization of the site of origin is required. Non-fluoroscopic localization of ablation catheter is done by magnetic (Carto0™) or electrical fields (EnSite Array™ Catheter). These technologies allow the construction of a three-dimensional (3-D) geometry to localize the site origin of VT and guide catheter navigation.

Radiation exposure during catheter ablation is associated with an increased lifetime risk of malignancy, and all possible measures should be taken to minimize exposure. [6],[7] Use of non-fluoroscopic 3-D mapping systems reduce radiation exposure. [8],[9] Non-fluoroscopic mapping technology has been of great value in the ablation of complex arrhythmias such as atrial fibrillation, atypical atrial flutter, and structural heart disease VT; however, its effectiveness has not been demonstrated for more straightforward cases. [10]

The aim of the current study is to evaluate safety and efficacy of new 3-D mapping system in idiopathic VT ablation and comparison of the Carto™ and EnSite Array™ catheter mapping systems.


  Materials and Methods Top


Study population includes patients who underwent ablation for idiopathic VT at our center during January 2011 to December 2011. History, ECG, echocardiography, exercise stress test, magnetic resonance imaging (MRI), and coronary angiography, when indicated, were used to exclude structural heart disease. Electronic patient records were reviewed to determine the 3-D system used, acute outcome, periprocedural complications, and recurrence during the six-month follow-up. Three- and six -month 24-hour Holter recordings or when the patient had symptomatic tachycardia monitored recurrence.

Electrophysiological study and electro-anatomical mapping

All patients provided written informed consent to invasive procedures. Ablations were performed under mild sedation, after discontinuation of all anti-arrhythmic drugs for at least five half-lives. Three quadripolar electrode catheters were inserted percutaneously and advanced under fluoroscopic guidance to the high right atrium, RV apex, and AV junction for recording of the His bundle electrogram. Bipolar intracardiac recordings were filtered at 30-500 Hz and displayed simultaneously with three surface ECG leads on a multichannel oscilloscope or digital monitor. Data were stored on optical disk (Prucka Engineering).

Carto0™ system (Biosense-Webster) [Figure 1] electro-anatomic voltage mapping was performed in sinus rhythm. An 8-F ThermoCool (Biosense-Webster) catheter, with a 4-mm distal-tip electrode and a 2-mm ring electrode with an inter electrode distance of 1 mm, was introduced into the chamber of interest under fluoroscopic guidance and used as the mapping/ablation catheter. The catheter was placed at multiple sites on the endocardial surface to record bipolar electrograms and construct a 3-D geometry. Bipolar electrogram signals (filtered at 10-400 Hz and displayed at 100 mm/s speeds on the Carto system) were analyzed with regard to amplitude, duration, relation to the surface QRS, and presence of multiple components. A recording was accepted and integrated into the map when the variability in cycle length, local activation time stability, and maximum beat-to-beat difference of the location of the catheter were <2%.
Figure 1: Contact mapping (Carto) with Carto sound image of LVOT tachycardia ablation

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EnSite Array catheter (St Jude Medical, St Paul, MN, USA) [Figure 2] utilizes a non-contact mapping catheter that contains 64 filaments with 0.025-in insulation breaks at specified sites to form a multi-electrode array. This array was advanced through the vasculature in low profile to the chamber of interest over a guidewire. With the multiple electrode arrays in position, sweeping a mapping/ablation catheter along the endocardium created a 3-D geometry of the chamber of interest. The location of the mapping catheter relative to the multiple electrode arrays was determined by the system using a low-current "locator" signal. Location positions were automatically acquired 10 times per second. In case of right ventricular outflow tract (RVOT) mapping, an ablation catheter was placed in the pulmonary artery and slowly withdrawn until sharp bipolar electrograms were recorded on the distal electrodes, signifying the pulmonary valve RVOT junction. Using this position as a fluoroscopic landmark, the non-contact array was then deployed at least 1 cm below the valve.
Figure 2: Non-contact mapping (EnSite Array) Isopotential map of the right ventricular outfl ow tract activation and virtual electrograms at the site of earliest activation

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Once the 3-D geometry was constructed, a standard protocol of programmed electrical stimulation (PES) was performed (500- and 400-ms cycle lengths, up to three extra stimuli from two different RV sites and burst pacing at different cycle lengths, given the characteristics of the arrhythmia. In addition, isoprenaline (2-10 μg/min) was infused to promote ventricular tachyarrhythmia either alone or with concurrent burst pacing.

Detailed activation mapping was performed if clinically stable VT was induced. In case of non-inducibility, the optimum ablation site was determined mostly by pace mapping. When isolated PVC was not recorded, the first beat of VT was selected as a template. The origin of PVC or VT was defined as the ablation site where the best pace mapping score was obtained and the targeted VT/PVC disappeared by a single energy delivery. For VT from the left ventricular outflow tract (LVOT), the origin was defined as the site where the best pace mapping score was obtained and the endocardial activation time during VT was the shortest. Pace mapping was performed during sinus rhythm with bipolar cathode stimulation at an output just greater than the diastolic threshold. The ventricle was paced at a slow rate of 120-140 per minute, according to the coupling interval of the PVC selected as a template. If the QRS morphology and amplitude of 12 ECGs of the paced beat was perfectly similar to that of PVC, the pace mapping score was calculated as (0.3 × 3 + 0.1)×12 = 12 points. This was considered the best point for ablation. Ablation was performed with a 4-mm irrigation tip catheter.

Ablation and acute outcome

A 4-mm irrigated-tip catheter was used for ablation in all cases. After completing ablation, the acute procedural outcome was defined as a success if clinical VT/PVC no longer occurred spontaneously (in a 30-minute observation period) and could not be induced by standard PES (as described above). The acute procedural outcome was instead defined as a failure if clinical VT/PVC still occurred and/or could be induced by PES. The occurrence of non-clinical VT/PVC morphologies was also a pre-specified outcome possibility, although this did not happen in our study.

Follow-up

All patients visited outpatient clinic at the third and sixth months post ablation with 24-hour Holter recording to monitor for VT or PVC recurrence. All patients were instructed to attend an emergency department for immediate ECG should they experience recurrent tachycardia.

Statistical analysis

Continuous variables were expressed as mean ± SD. Comparisons between groups were made using one-way analysis of variance after determining normality of distribution. Categorical variables, expressed as numbers and percentages, were compared using Fisher's exact test or Chi-square test, depending on the number of variables. All tests of significance were two-tailed, and P < 0.05 was considered statistically significant.


  Results Top


Study population

[Table 1] summarizes the main presenting features of our study population. Between January 2011 and December 2011, 62 patients (27 female and 35 male; median age: 43.5 ± 22.4 years) who were referred to our institution for ablation of VT or frequent PVCs in the absence of any known heart disease and with a normal left ventricular ejection fraction constituted our study population. The presenting arrhythmia was sustained monomorphic VT in 34/62 patients (54.8%), non-sustained monomorphic VT in 20/62 (32.3%) and frequent monomorphic PVCs (defined as >1000/24 h on Holter ECG monitoring) in the remaining 8/62 patients (12.9%). VT/PVC morphology was left bundle branch block with inferior axis in 40/62 patients (64.5%) or with superior axis in 9/62 (14.5%), while it was right bundle branch block with inferior axis in 4/62 patients (6.5%) or with superior axis in 9/62 (14.5%).
Table 1: Clinical characteristics

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All patients had history of VT for 5.4 ± 3.5 years and had failed 3 ± 1 anti-arrhythmic medications. Syncope/presyncope was the presenting complaint in 8/62 patients (12,9%), palpitations in 45/62 (72.6%), and chest pain in 9/62 (14.5%). Six patients (9.7%) had previously undergone unsuccessful ablation elsewhere.

Acute outcome and complications

VT/PVCs either occurred spontaneously or were induced by ventricular pacing maneuvers in 38/62 patients (61.3%). In 24 (38.7%) patients, no VT was inducible or occurred spontaneously in electrophysiology laboratory. Induced VT/PVC was terminated during RF delivery in 31/38 (81.6%) patients. VT/PVCs were successfully ablated in 54/62 (87.1%) patients; ablation was not successful in 8/62 (12.9%) patients. There was no statistically significant difference in the rate of acute success between right- and left-sided VT/PVCs (P = 0.3). Ablation was successful in all (6/6) patients who had undergone a previous failed ablation using conventional methods. Site of origin of VT/PVC was RVOT in 44 (70.9%), LVOT in 4 (6.5%), and LV cavity 14 (22.6%) patients. No clinically significant association was found between different clinical and electrophysiological parameters with regard to acute success. [Table 2]
Table 2: Association of clinical and electrophysiological characteristics with acute success

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Procedure-related complications occurred in 4/62 patients (6.5%). Groin hematoma was observed at the site of femoral puncture, femoral arterio-venous fistula, moderate pericardial effusion (treated conservatively), and LBBB during ablation (which persisted at 6 months).

Recurrences during follow-up

Six (9.7%) patients had recurrence during six months of follow-up. Recurrence occurred only in patients in whom either VT/PVCs were not inducible or were not successfully ablated. Four out of 24 (16.6%) in whom no VT was induced or occurred spontaneously during electrophysiology (EP) study had recurrence, whereas 2 out of 38 (5.3%) in whom VT/PVC was induced or occurred spontaneously during EP study, but could not be ablated, had recurrence. There was no statistically significant difference in the recurrence rate between patient gender, presenting symptoms, ECG morphology, or right- versus left-sided ablation site. [Table 3] presents the relationship of different clinical and electrophysiological parameters with recurrence rates.
Table 3: Clinical and electrophysiological characteristics in carto and EnSite array

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Comparison between Carto and EnSite Array catheters

[Table 4] outlines patient and procedural data as related to the choice of mapping system used. Carto™ mapping system was used in 40/62 (64.5%) patients and EnSite Array catheter in 22/62 (35.5%) The EnSite Array catheter was used in significantly higher numbers in right-sided arrhythmias (P < 0.001). There was no statistically significant difference between the two systems in terms of mean fluoroscopy time, acute success (P = 0.4), or recurrence rate (P = 0.4).
Table 4: Association of clinical and electrophysiological characteristics with recurrence

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  Discussion Top


Carto™ and EnSite Array catheters are two main 3-D mapping systems used in cardiac electrophysiology laboratory. Each system has its own advantages and disadvantages. Carto™ is good in generating voltage maps, which helps define the anatomy of the chamber very well, and it is easy to shift from one chamber to another; moreover, it can be used in smaller spaces such as coronary sinus and sinus of Valsalva and helps differentiate scared myocardium from normal myocardium in very early stage of arrhythmogenic right ventricular dysplasia. EnSite Array is very useful in cases where it is difficult to induce tachycardia as it can use single PVC to map the focus.

Main findings

We found the new 3-D mapping to be a useful adjunct to guiding ablation in a consecutive series of patients with idiopathic VT. VT/PVC was not inducible in almost 24 (38.7%) patients despite the fact that 3-D guided ablation was acutely successful in 85.5% of this population, with recurrence rate of 9.7% during a follow-up of 6 months; of this, 16.6% in whom VT/PVC was not induced or occurred spontaneously during EP study had recurrence, whereas 5.3% in whom VT/PVC was induced or occurred spontaneously during EP study had recurrence. Complication rate was low (6.4%), and there was no mortality associated with the procedure. Fluoroscopy time was less as compared to conventional methods. [11],[12],[13] Both systems ( EnSite™ and Carto™) were equally effective and safe.

Catheter ablation has become an early therapeutic option for idiopathic VT because of high success and low complication rates; [11],[12],[13],[14] however; catheter ablation is limited when the arrhythmogenic site is located epicardially or when tachycardia is not inducible during the EP study. [15] Two major ways to identify target site for ablation in the conventional approach are activation mapping and pace mapping. Activation mapping is based on detecting the earliest endocardial activation time during tachycardia. Pace mapping relies upon pacing at a single site to obtain ≥11/12 morphologic match to the clinical tachycardia on the 12-lead ECG. Activation mapping requires induction of sustained and stable VT during ablation. VT is non-inducible in a significant proportion of patients, as shown in this study (23%). Initial endocardial activation away from the site of origin is rapid. In a recent series of patients undergoing 3-D electro-anatomical mapping during RVOT VT, the mean area of myocardium activated within the first 10 msec was 3.0 ± 1.6 cm 2 , ranging from 1.3 to 6.4 cm 2 . [4] Given an inter-observer variability of up to 5 msec or more in the manual assignment of activation time, it is not surprising that electrogram timing alone has been reported to have a relatively limited utility as a predictor of successful ablation sites.

Several studies have suggested that pace mapping may be superior to endocardial activation time mapping as endocardial activation time was not found to be significantly different at successful versus unsuccessful ablation sites. [3],[16] This is likely due to early activation occurring over a broader area than a "single point." Even pace mapping may only have a resolution of 5-10 mm. [17] Green et al. [18] reported that identical 8-lead ECG pace maps might occur at a distance of up to 8 mm from the stimulus site. Wen et al. [19] found that the use of pace mapping alone for ablation site selection was a predictor of tachycardia recurrence in patients with idiopathic RVOT VT. Given that typical RF lesions are approximately 5 mm in diameter, [20] the imprecision of both activation and pace mapping may be limiting factors and require broader areas of ablation. One potential advantage of the 3-D mapping system is that it enables targeting areas of interest more specifically for ablation and cataloging ablation sites. The 3-D localization abilities associated with these systems is superior to the use of 2-D fluoroscopy. Given the high reported success rate for idiopathic VT ablation using even single-point mapping, [13],[14],[15] the purported advantages of these systems are to make the procedure more efficient and reduce radiation exposure. By quickly identifying the earliest site of activation, pace mapping focused on this region may be facilitated.

Mark et al. [21] have used Carto™ and NavX™ in their study, and concluded that in catheter ablation of the commonly ablated SVTs (ie, AVNRT, AVRT, WPW, and typical atrial flutter), both systems were equally effective and safe. Both techniques, however, reduce X-ray exposure, with NavX producing a significantly greater effect than Carto. Although this benefit is achieved at a greater cost, there may be long-term benefits to the community and catheter laboratory staff.

The main disadvantage of using contact and non-contact mapping systems is cost of the equipment.

Study limitations

This is a retrospective study that included a relatively short follow-up and few patients with failed previous ablation. The numbers in each group were smaller, thus the power of this study to demonstrate differences between Carto™ and EnSite Array catheter was reduced.


  Conclusion Top


New 3-D mapping systems (Carto™ and EnSite Array™) are useful in the ablation of idiopathic VT, with good acute success and short-term follow-up. These systems are particularly useful in patients with failed ablation by conventional methods and those in whom VT/PVC is not inducible in EP laboratory. There is no difference between the two systems with regard to acute success, recurrence, and complication rate.

 
  References Top

1.Bunch TJ, Day JD. Right meets left: A common mechanism underlying right andleft ventricular outflow tract tachycardias. J Cardiovasc Electrophysiol 2006;17:1059-61.  Back to cited text no. 1
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3.Coggins DL, Lee RJ, Sweeney J, Chein WW, Van Hare G, Epstein L. Radiofrequency catheter ablation as a cure for idiopathic tachycardia of both left and right ventricular origin. J Am Coll Cardiol 1994;23:1333-41.  Back to cited text no. 3
    
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9.Kirchhof P, Loh P, Eckardt L, Ribbing M, Rolf S, Eick O, et al. A novel nonfluoroscopic catheter visualization system (LocaLisa) to reduce radiation exposure during catheter ablation of supraventricular tachycardias. Am J Cardiol 2002;90:340-3.  Back to cited text no. 9
    
10.PackerDL. Three-dimensional mapping in interventional electrophysiology: Techniques and technology. J Cardiovasc Electrophysiol 2005;16:1110-6.  Back to cited text no. 10
    
11.Kim RJ, Iwai S, Markowitz SM, Shah BK, Stein KM, Lerman BB. Clinical and electrophysiological spectrum of idiopathic ventricular outflow tract arrhythmias. J Am Coll Cardiol 2007;49:2035-43  Back to cited text no. 11
    
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14.Zhu DW, Maloney JD, Simmons TW, Nitta J, Fitzgerald DM, Trohman RG, et al. Radiofrequency catheter ablation for management of symptomatic ventricular ectopic activity. J Am Coll Cardiol 1995;26:843-9.  Back to cited text no. 14
    
15.Friedman PA, Asirvatham SJ, Grice S, Glikson M, Munger TM, Rea RF, et al. Noncontact mapping to guide ablation of right ventricular outflow tract tachycardia. J Am Coll Cardiol 2002;39;1808-12.  Back to cited text no. 15
    
16.Rodriguez LM, Smeets JL, Timmermans C, Wellens HJ. Predictors for successful ablation of right- and left-sided idiopathic ventricular tachycardia. Am J Cardiol 1997;79:309-14.  Back to cited text no. 16
    
17.Kadish AH, Childs K, Schmaltz S, Morady F. Differences in QRS configuration during unipolar pacing from adjacent sites: Implications for the spatial resolution of pace-mapping. J Am Coll Cardiol 1991;17:143-51.  Back to cited text no. 17
    
18.Green LS, Lux RL, Ershler PR, Freedman RA, Marcus FI, Gear K. Resolution of pace mapping stimulus site separation using body surface potentials. Circulation 1994;90:462-8.  Back to cited text no. 18
    
19.WenMS, Taniguchi Y, YehSJ, Wang CC, Lin FC, Wu D.Determinants of tachycardia recurrences after radiofrequency ablation of idiopathic ventricular tachycardia. Am J Cardiol 1998;81:500-3.  Back to cited text no. 19
    
20.Haines D. Determinants of lesion size during radiofrequency catheter ablation: The role of electrode-tissue contact pressure and duration of energy delivery. J Cardiovasc Electrophysiol 1993;2:509-15.  Back to cited text no. 20
    
21.Earley MJ, Showkathali R, Alzetani M, Kistler PM, Gupta D, Abrams DJ, et al. Radiofrequency ablation of arrhythmias guided by non-fluoroscopic catheter location: A prospective randomized trial. Eur Heart J 2006;27:1223-9.  Back to cited text no. 21
    


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