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Magnetic versus manual catheter navigation for mapping and ablation of right ventricular outow tract ventricular arrhythmias: A randomized controlled study Fengxiang Zhang, MD, * Bing Yang, MD, * Hongwu Chen, MD, * Weizhu Ju, MD, * Pipin Kojodjojo, MD, Kejiang Cao, MD, * Minglong Chen, MD * From the *Section of Pacing and Electrophysiology, Division of Cardiology, the First Afliated Hospital with Nanjing Medical University, Nanjing, China, and Department of Cardiology, National University Heart Centre, Singapore. BACKGROUND No randomized controlled study has prospectively compared the performance and clinical outcomes of remote magnetic control (RMC) vs manual catheter control (MCC) during ablation of right ventricular outow tract (RVOT) ventricular premature complexes (VPC) or ventricular tachycardia (VT). OBJECTIVE The purpose of this study was to prospectively evaluate the efcacy and safety of using either RMC vs MCC for mapping and ablation of RVOT VPC/VT. METHODS Thirty consecutive patients with idiopathic RVOT VPC/VT were referred for catheter ablation and randomized into either the RMC or MCC group. A noncontact mapping system was deployed in the RVOT to identify origins of VPC/VT. Conventional activation and pace-mapping was performed to guide ablation. If ablation performed using 1 mode of catheter control was acutely unsuc- cessful, the patient crossed over to the other group. The primary endpoints were patientsand physiciansuoroscopic exposure and times. RESULTS Mean procedural times were similar between RMC and MCC groups. The uoroscopic exposure and times for both patients and physicians were much lower in the RMC group than in the MCC group. Ablation was acutely successful in 14 of 15 patients in the MCC group and 10 of 15 in the RMC group. Following crossover, acute success was achieved in all patients. No major complications occurred in either group. During 22 months of follow-up, RVOT VPC recurred in 2 RMC patients. CONCLUSION RMC navigation signicantly reduces patientsand physiciansuoroscopic times by 50.5% and 68.6%, respectively, when used in conjunction with a noncontact mapping system to guide ablation of RVOT VPC/VT. KEYWORDS Magnetic navigation system; Magnetic catheter; Idiopathic ventricular arrhythmia; Right ventricular outow tract; Noncontact mapping ABBREVIATIONS BO ¼ breakout; EA ¼ earliest activation; LBBB ¼ left bundle branch block; MCC ¼ manual catheter control; MEA ¼ multielectrode array; MNS ¼ magnetic navigation system; NCM ¼ noncontact mapping system; RBBB ¼ right bundle branch block; RMC ¼ remote magnetic control; RVOT ¼ right ventricular outow tract; VA ¼ ventricular arrhythmia; VPC ¼ ventricular premature complex; VT ¼ ventricular tachycardia (Heart Rhythm 2013;10:11781183) I 2013 Heart Rhythm Society. All rights reserved. Introduction Radiofrequency catheter ablation is recommended for the therapy of medically refractory ventricular arrhythmias (VA) including ventricular tachycardia (VT) or ventricular pre- mature complexes (VPC) originating from the right ventricular outow tract (RVOT), which often arises in patients without structural heart diseases. Success rates usually in excess of 80% have been reported. 15 However, catheter navigation within the RVOT can be technically challenging with increased uoroscopic exposure to the patient and operator during mapping and may be compli- cated by the potential risks of perforation. In recent years, remote magnetic navigation systems (MNS) have been successfully used for ablation of various arrhythmias. 68 In the RVOT, MNS could facilitate navi- gation and reduce uoroscopic exposure while reducing risks of perforation due to the soft-tipped nature of the catheter. In this single-center randomized controlled study, we pro- spectively compared the performance and clinical outcomes of remote magnetic control (RMC) vs manual catheter control (MCC) during RVOT VA ablation. The rst two authors contributed equally to this study. This work was supported by grants from the National Natural Science Foundation of China (Grant 81170160), by the Program for Development of Innovative Research Team in the First Afliated Hospital of Nanjing Medical University (Grant IRT-004), by the Six Peak Talents Foundation of Jiangsu Province (Grant 2011-WS-071), and by National Twelfth Five-YearPlan for Science & Technology Support (Grant 2011BAI11B13). Clinical Trial Registration: ChiCTR-TRC-11001550. Address reprint requests and correspondence: Dr. Minglong Chen, Section of Pacing and Electrophysiology, Division of Cardiology, the First Afliated Hospital of Nanjing Medical University, Guangzhou Road 300, Nanjing, 210029, PR China. E-mail address: [email protected]. 1547-5271/$-see front matter B 2013 Heart Rhythm Society. All rights reserved. http://dx.doi.org/10.1016/j.hrthm.2013.05.012

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Magnetic versus manual catheter navigation for mappingand ablation of right ventricular outflow tract ventriculararrhythmias: A randomized controlled studyFengxiang Zhang, MD,* Bing Yang, MD,* Hongwu Chen, MD,* Weizhu Ju, MD,* Pipin Kojodjojo, MD,†

Kejiang Cao, MD,* Minglong Chen, MD*

From the *Section of Pacing and Electrophysiology, Division of Cardiology, the First Affiliated Hospital with Nanjing MedicalUniversity, Nanjing, China, and †Department of Cardiology, National University Heart Centre, Singapore.

BACKGROUND No randomized controlled study has prospectivelycompared the performance and clinical outcomes of remotemagnetic control (RMC) vs manual catheter control (MCC) duringablation of right ventricular outflow tract (RVOT) ventricularpremature complexes (VPC) or ventricular tachycardia (VT).

OBJECTIVE The purpose of this study was to prospectivelyevaluate the efficacy and safety of using either RMC vs MCC formapping and ablation of RVOT VPC/VT.

METHODS Thirty consecutive patients with idiopathic RVOT VPC/VTwere referred for catheter ablation and randomized into either theRMC or MCC group. A noncontact mapping system was deployed inthe RVOT to identify origins of VPC/VT. Conventional activation andpace-mapping was performed to guide ablation. If ablationperformed using 1 mode of catheter control was acutely unsuc-cessful, the patient crossed over to the other group. The primaryendpoints were patients’ and physicians’ fluoroscopic exposureand times.

RESULTS Mean procedural times were similar between RMC andMCC groups. The fluoroscopic exposure and times for both patientsand physicians were much lower in the RMC group than in the MCCgroup. Ablation was acutely successful in 14 of 15 patients in the

The first two authors contributed equally to this study. This work wassupported by grants from the National Natural Science Foundation of China(Grant 81170160), by the Program for Development of Innovative ResearchTeam in the First Affiliated Hospital of Nanjing Medical University (GrantIRT-004), by the Six Peak Talents Foundation of Jiangsu Province (Grant2011-WS-071), and by National “Twelfth Five-Year” Plan for Science &Technology Support (Grant 2011BAI11B13). Clinical Trial Registration:ChiCTR-TRC-11001550. Address reprint requests and correspondence:Dr. Minglong Chen, Section of Pacing and Electrophysiology, Division ofCardiology, the First Affiliated Hospital of Nanjing Medical University,Guangzhou Road 300, Nanjing, 210029, PR China. E-mail address:[email protected].

1547-5271/$-see front matter B 2013 Heart Rhythm Society. All rights reserved.

MCC group and 10 of 15 in the RMC group. Following crossover,acute success was achieved in all patients. No major complicationsoccurred in either group. During 22 months of follow-up, RVOT VPCrecurred in 2 RMC patients.

CONCLUSION RMC navigation significantly reduces patients’ andphysicians’ fluoroscopic times by 50.5% and 68.6%, respectively,when used in conjunction with a noncontact mapping system toguide ablation of RVOT VPC/VT.

KEYWORDS Magnetic navigation system; Magnetic catheter;Idiopathic ventricular arrhythmia; Right ventricular outflow tract;Noncontact mapping

ABBREVIATIONS BO¼ breakout; EA ¼ earliest activation; LBBB ¼left bundle branch block; MCC ¼ manual catheter control; MEA ¼multielectrode array; MNS ¼ magnetic navigation system; NCM ¼noncontact mapping system; RBBB ¼ right bundle branch block;RMC ¼ remote magnetic control; RVOT ¼ right ventricular outflowtract; VA ¼ ventricular arrhythmia; VPC ¼ ventricular prematurecomplex; VT ¼ ventricular tachycardia

(Heart Rhythm 2013;10:1178–1183) I 2013 Heart Rhythm Society.All rights reserved.

IntroductionRadiofrequency catheter ablation is recommended for thetherapy of medically refractory ventricular arrhythmias (VA)including ventricular tachycardia (VT) or ventricular pre-mature complexes (VPC) originating from the right

ventricular outflow tract (RVOT), which often arises inpatients without structural heart diseases. Success ratesusually in excess of 80% have been reported.1–5 However,catheter navigation within the RVOT can be technicallychallenging with increased fluoroscopic exposure to thepatient and operator during mapping and may be compli-cated by the potential risks of perforation.

In recent years, remote magnetic navigation systems(MNS) have been successfully used for ablation of variousarrhythmias.6–8 In the RVOT, MNS could facilitate navi-gation and reduce fluoroscopic exposure while reducing risksof perforation due to the soft-tipped nature of the catheter.In this single-center randomized controlled study, we pro-spectively compared the performance and clinical outcomesof remote magnetic control (RMC) vs manual cathetercontrol (MCC) during RVOT VA ablation.

http://dx.doi.org/10.1016/j.hrthm.2013.05.012

1179Zhang et al Right Ventricular Outflow Tract VT/VPC Ablation

MethodsStudy populationPatients recruited had symptomatic idiopathic VT or VPCwith a left bundle branch block (LBBB) morphology,inferior axis, precordial lead transition zone ≥V4, RVOTVPC burden ≥20% of total daily heart beats, and normal leftventricular ejection fraction on echocardiography. Allpatients had either failed treatment with or could not toleratebeta-blockers and/or Class III or IC antiarrhythmic medi-cations. No patient had previously undergone ablation.Patients with underlying structural heart disease, polymor-phic VA, any concomitant systemic illnesses, ageo18 yearsold, or who were pregnant were excluded from this study.

Consent and randomizationConsecutive patients who fulfilled the inclusion criteria andconsented to the study were randomized to undergo ablationguided by either RMC or MCC. Randomization wasperformed using a random number generator, with sealedenvelopes opened on the day of procedure. All patients gavewritten informed consent. The study was approved by theethical committee review board of Nanjing Medical Univer-sity, China, and prospectively registered with the ChineseClinical Trial Registry (ChiCTR-TRC-11001550).

Patient preparation and noncontact mapping systemsetupAll antiarrhythmic drug therapies were discontinued at least5 half-lives before ablation. Electrophysiologic studies wereperformed with patients in the fasting state. In all patients, aquadripolar diagnostic catheter was positioned in the rightventricular apex. A noncontact mapping system (NCM;EnSite, St. Jude Medical, St. Paul, MN) was used to mapthe origin of RVOT VA. This is our standard clinical practiceas the use of NCM has been previously shown to facilitatemapping, reduce fluoroscopic exposure, and improve suc-cess rates.9–11 Thus, a multielectrode array (MEA) wasinserted via the left femoral vein and deployed in the RVOT.Spontaneous VT or VPC at baseline and during intravenous

Figure 1 The multielectrode array can beseen within the right ventricular outflowtract with a quadripolar right ventricularcatheter. The magnetically enabled catheterhas been navigated to a more anteroseptalposition. The magnetic Navigant screenshows the 2 radiographic views. A: Rightanterior oblique (RAO). B: Left anterioroblique (LAO).

isoprenaline (1–4 mg/min) infusion were recorded. Inpatients without spontaneous VT or VPC, programmedventricular stimulation was performed from the right ven-tricular apex and RVOT at 2 drive cycle lengths with up to 3extrastimuli. In addition, incremental burst pacing at a cyclelength up to 300 ms was performed. The filter settings forintracardiac electrocardiograms were 30 to 300 Hz. Twelve-lead ECGs and bipolar intracardiac ECGs were displayedand recorded at a paper speed of 100 mm/s (Bard LabSystem, CR Bard Inc, Lowell, MA). Recordings were storedon optical disk for offline analysis. During the procedure,intravenous heparin was given to maintain an activatedclotting time between 250 and 300 seconds.

Remote magnetic navigationThe MNS (Stereotaxis Inc, St. Louis, MO) was used inpatients randomized to the RMC group. The MNS used2 large magnets positioned on either side of the proceduretable to generate a composite magnetic field for directionalcatheter orientation, as described previously.6,12 The mag-nets were computer controlled via a workstation (Navigant,Stereotaxis Inc, St. Louis, MO) to effect a change in theorientation of a stable magnetic field within the patient’schest. Combined field strength of 0.08 T was produced innavigation mode. As navigation was best performed with afixed table position, the table position was optimized andisocentered before starting magnetic navigation. While themagnets were positioned next to the patient, only limitedangulation of the C-arm was possible (approximately 281 inthe right and left anterior oblique angulations; Figure 1).

Remote catheter advancement and retraction from thecontrol room were performed using a catheter advancersystem (Cardiodrive, Stereotaxis) positioned on the highanterior thigh. Remote control of the fluoroscopy system wasalso possible from the control room. The 4-mm-tip ablationcatheter (8Fr Helios II, Stereotaxis) contains 3 magnetswithin the distal tip segment, which aligns with the fieldproduced by the external magnets to allow for effectivecatheter orientation. Once the external magnets were in

Heart Rhythm, Vol 10, No 8, August 20131180

position, a physician can leave the fluoroscopic room andperform the rest of the procedure from the control room.

Manual catheter navigationIn subjects randomized to the MCC group, a 7Fr quadripolarcatheter with 4-mm distal electrode (Celsius, BiosenseWebster, Diamond Bar, CA) was used for mapping andablation.

Mapping protocolThe MEA was placed at the optimal mapping position suchthat the earliest activation (EA) and breakout (BO) sites ofVA to the center of the MEA, defined as the R value, werenot more than 35 mm.13 The 3-dimensional geometry of theRVOT was created by remotely or manually navigating theablation catheter within the RVOT around the MEA. Foridentification of the EA and BO sites, a color band settingwith color high set at –0.1 mV and color low set at –2 mVwas used. Virtual unipolar high-pass filter was set at 4 Hz.The EA site was defined by the earliest unipolar deflectionstroke from baseline (Figure 2A), and the BO site was takenas the site along the activation pathway where the localvirtual unipolar electrogram exhibited the maximum dV/dt(Figure 2B).14,15

Endocardial activation mapping at the EA and BO siteswas performed by analysis of contact bipolar electrogramsduring VA. The unipolar virtual electrogram at this site wasreconstructed and analyzed. The presence of QS morphologywas also used as an additional criterion to identify the EAsite. Bipolar pace-mapping was performed with the tip ofablation catheter at the EA and BO sites. Pacing wasperformed at twice diastolic threshold at a cycle length equalto the coupling interval of VPC or cycle length of clinicalVT. Pace-maps were scored (maximum score of 24; a scoreof 1 was acquired for the morphology and amplitude of theQRS complex in each lead if it matched the clinical VPC) by4 experienced physicians who were blinded to this study.16

Figure 2 Identification of earliest activation (EA) and breakout (BO) sites ofmultielectrode array.A: The EA site (white arrow), defined as the earliest unipolar dalong the propagation pathway where the local virtual unipolar electrogram exhib

Ablation protocol and endpointAblation was initiated at either the EA or BO sites of RVOTVA origin identified by the NCM if the following criteriawere met: local activation was at least 10 ms pre-QRS, 11 of12 ECG match during pace-mapping, and virtual unipolarelectrograms with QS morphology. If initial ablation wasunsuccessful at either the EA or BO site in both groups,ablation was redirected toward the other site. If ablation atboth EA and BO sites was unsuccessful in either group,patients were crossed over to the other catheter navigationgroup (RMC to MCC and vice versa).

Ablation was performed in temperature-control mode.Power output was titrated from 30 to 40W to achieve a targettemperature of 401C to 601C for 60 to 120 seconds duringeach delivery. The ablation procedure was consideredsuccessful if the VT or VPC was eliminated during ablationand/or became noninducible with programmed electricalstimulation and isoproterenol infusion.

Fluoroscopic exposure and time measurementsThe entire procedure was arbitrarily divided into 3 stages:achieving access, RVOT geometry creation, and ablation.The first stage comprises the time taken from the firstsuccessful femoral venous puncture to the MEA, rightventricular quadripolar catheter and ablation catheter beingsuccessfully deployed into the RVOT. Patients’ and physi-cians fluoroscopic exposure and times were recorded sepa-rately for each stage.

Follow-upAfter the procedure, ECG monitoring was performed for atleast 24 hours in all patients. Antiarrhythmic medicationswere not restarted after ablation. All patients were reviewedmonthly after the procedure for the first 3 months, followedby 6 monthly visits. During each clinic visit, a 12-lead ECGand 24-hour Holter monitoring were performed. Recurrenceof arrhythmia was defined as either symptomatic recurrence

the clinical ventricular tachycardia/ventricular premature complexes by theownstroke from baseline. B: The BO site (white arrow)was taken as the siteited the maximum dV/dt.

1181Zhang et al Right Ventricular Outflow Tract VT/VPC Ablation

with documented RVOT VT/VPC or asymptomatic frequentVPCs of 45000 per day.17

Study endpointsThe primary endpoint for this study was physicians’ andpatients’ fluoroscopic exposure and times. Secondary end-points were acute ablation success rates, procedural times,and complication rates. Endpoints were determined on anintention-to-treat basis.

Power calculation and statistical analysisIn a prior study using MNS for RVOT VA ablation,fluoroscopic times were 7.5 � 4.3 minutes. Therefore, witha sample size of 30 patients, this study has 92% power todetect a 5-minute difference in fluoroscopic times betweenthe 2 groups at a 2-sided .05 significance level.18 Continuousvariables and categorical variables are given as mean � SDand percentages, respectively. The standard 2-sample t-testwas used to compare continuous variables. The χ2 test wasused to compare discrete variables. All tests were 2-sided,and P o .05 was considered significant.

ResultsPatient characteristicsBetween July 2010 and June 2011, 30 consecutive patients(8 male; mean age 44.1 � 8.5 years) with idiopathic VT orVPC were randomized in 1:1 ratio and underwent ablation.Baseline characteristic parameters were not significantlydifferent between the RMC and MCC groups (Table 1).

Activation and pace-mappingThe prematurity of endocardial activation in relation to QRSonset of VA was similar at the EA and BO sites in bothgroups (Table 2). There was no significant difference in thepace-mapping score at the EA and BO sites.

Acute procedural resultsIn the MCC group, ablation was acutely successful in 14patients; 1 patient was switched to the RMC due tounsuccessful ablation. In the RMC group, ablation wasacutely successful in 10 patients. Five patients with failedRMC ablation crossed over to the MCC group (Table 2).

Table 1 Patient demographics

Variable RMC group

No. of patients 15Gender (male/female) 4/11Age (years) 41.7 � 9.1Weight (kg) 62.9 � 13.0Symptom duration of VT/VPC (months) 33.8 � 30.5No. of VPCs 25,409 � 11,4No. of patients with VPC and VT 5 (33.3%No. of episodes of syncope 5 (33.3%Left ventricular ejection fraction (%) 64.6 � 5.9

Data are given as mean � SD or number (percentage).MCC ¼ manual catheter control; RMC ¼ remote magnetic control; VPC ¼ vent

This difference was not statistically significant. Acuteprocedural success was achieved in all patients who crossedto the other mode of catheter navigation.

Procedural and fluoroscopic timesMean procedural times were 131.8 � 19.4 minutes and115.1 � 27.4 minutes in the RMC and MCC groups,respectively (P ¼ .13). Mean fluoroscopic doses and timesfor the electrophysiologists and patients during differentstages of the ablation are listed in Table 3. Patients’ overallfluoroscopic exposure and times were much lower in theRMC group than in MCC group (Po .05). Use of RMC wasassociated with 50.9% and 50.5% reduction in patients’fluoroscopic exposure and times, respectively. This wasdriven by a significant reduction in the use of fluoroscopyduring geometry creation and ablation. Similarly, physi-cians’ fluoroscopic exposure and times were significantlylower in the RMC group (P o .05). Use of RMC wasassociated with 63.6% and 68.6% reduction in physicians’fluoroscopic exposure and times, respectively.

ComplicationsDuring the procedure, mechanically induced right bundlebranch block (RBBB) occurred in 1 RMC patient and 4MCC patients; all normalized during the first 6 months offollow-up. No severe complications, such as cardiac perfo-ration, occurred in either group.

Follow-upAfter mean follow-up of 22.1� 4.6 months, frequent RVOTVPC recurred in 2 RMC patients in the RMC group. After asecond procedure using manual catheter navigation in bothpatients, long-term success was achieved. The remainingpatients remained free from recurrence.

DiscussionIn the current prospective, randomized study, use of RMCsignificantly reduced fluoroscopic exposure and doses forboth patients and primary operators during NCM-guidedRVOT VA ablation. Although there were a higher number ofpatients who crossed over from the RMC to the MCC group

MCC group P value

15 —4/11 146.5 � 7.4 .1365.9 � 8.5 .4645.4 � 35.5 .36

77 28,280 � 12,083 .62) 6 (40%) .71) 2 (13.3%) .20

65.2 � 4.8 .77

ricular premature complexes; VT ¼ ventricular tachycardia.

Table 2 Mapping and ablation characteristics

Variable RMC group MCC group P value

Activation mapping at EA site (ms pre-QRS onset) 26.4 � 4.6 24.6 � 6.8 .52Activation mapping at BO site (ms pre-QRS onset) 26.2 � 4.3 24.1 � 6.6 .46Pace-mapping score at EA site (out of 24) 23.4 � 0.9 23.3 � 1.6 .88Pace-mapping score at BO site (out of 24) 23.6 � 0.6 23.3 � 1.2 .46Acute ablation success 10/15 14/15 .07Crossover to other group 5 1 .07Ablation energy (W) 40.4 � 9.3 35.7 � 7.5 .01Ablation temperature (1C) 46.7 � 4.0 48.0 � 4.0 .10Ablation duration (seconds) 63.3 � 27.3 72.8 � 35.6 .15Total procedural time (minutes) 131.8 � 19.4 115.1 � 27.4 .13

Data are given as mean � SD.BO ¼ breakout; EA ¼ earliest activation; MCC ¼ manual catheter control; RMC ¼ remote magnetic control.

Heart Rhythm, Vol 10, No 8, August 20131182

compared to vice versa, acute success rates, procedural timesand complication rates were not significantly increased.

The clinical utility of NCM to quickly and accurately mapcardiac arrhythmias has been previously reported. 9,13,14 Theability of the NCM system to determine the site of EA andpropagation pattern in a beat-to-beat manner is especiallybeneficial in patients with infrequent spontaneous VA atelectrophysiologic study. Several small series have demon-strated the feasibility and potential benefits of using theNCM in mapping and ablation of RVOT VA. We have alsoreported that single-procedural success rates of 86.8% with-out the use of antiarrhythmic agents can be achieved byNCM-guided RVOT VA ablation during extended follow-upaveraging more than 36 months.19 Clinical outcomes andcomplications rates were similar to those of a control groupundergoing RVOT VA ablation guided by a 3-dimensionalmapping system.

Our main findings in this study confirm the clinicalbenefits of RMC reported in the literature.6–8,20 RMCsignificantly reduced X-ray exposure times and doses forboth patients and operators. In our study, use of RMCreduced patients’ fluoroscopic times by 50.5% and fluoro-scopic exposure by 50.9% compared with conventionalMCC. For the electrophysiologists, these reductions wereeven greater due to the ability of physicians to perform theablation stage from the control room.

The feasibility of RMC to facilitate ablation within theatria and ventricle has been well publicized, with acutesuccess and complication rates comparable to those ofconventional ablation. This conclusion is drawn largely from

Table 3 Fluoroscopic exposure and fluoroscopic times for every stage

Variables Fluoroscopic exposure (mGym2)

Procedural stage RMC MCCAccess 416.9 � 169.0 446.0Geometry creation 100.7 � 90.1* 474.6Ablation 43.8 � 69.8* 223.6Overall 561.4 � 194.2* 1144.2Physician 416.9 � 169.0* 1144.2

Data are given as mean � SD.MCC ¼ manual catheter control; RMC ¼ remote magnetic control.

*P o .05 vs MCC.

small single-center series. To date, rigorous comparisons ofRMC vs MCC have been performed only in the setting ofcavotricuspid isthmus and supraventricular tachycardia abla-tion. In a single-center study, Vollmann et al20 randomized90 patients undergoing cavotricuspid isthmus ablation toeither conventional manual or RMC-guided ablation. RMC-guided ablation reduced fluoroscopic time by 29% butprolonged overall ablation and procedural times. Althoughacute procedural success rates were similar between the 2groups, long-term success defined as achievement of com-plete bidirectional cavotricuspid isthmus block and freedomfrom atrial flutter recurrence during 6-month follow-up waslower in the RMC compared with the MCC group (73% vs89%). Wood et al21 prospectively randomized 71 patientsundergoing supraventricular tachycardia ablation across 13centers in a 3:1 ratio to either magnetic or manual navigation.In this particular study, magnetic navigation reduced fluoro-scopic time by 34% without adversely impacting totalprocedural times or complication rates. To our knowledge,this study is the first randomized study that prospectivelyinvestigated the clinical benefits of RMC in ablation of VA.

Consensus exists among high-volume users that the soft-tipped nature of RMC catheters is less traumatic, which inprinciple could potentially reduce complications.22 Althoughno serious complication rates occurred in this study,mechanical disruption of right bundle conduction occurredless frequently in the RMC group. In contrast, transientRBBB occurred in 4 of 15 MCC patients, as manualmanipulation of the ablation catheter across the tricuspidvalve into the RVOT not infrequently results in mechanical

of the procedure

Fluoroscopic time (minutes)

RMC MCC� 269.1 3.3 � 1.9 4.0 � 2.5� 456.5 1.4 � 2.3* 3.1 � 2.0� 235.5 0.7 � 1.4* 1.9 � 2.0� 605.9 5.2 � 2.6* 10.5 � 5.0� 605.9 3.3 � 1.9* 10.5 � 4.9

1183Zhang et al Right Ventricular Outflow Tract VT/VPC Ablation

“bumping” of the right bundle. Although conduction blockeventually recovers during follow-up, the development ofRBBB periprocedurally can affect the accuracy of pace-mapping and activation mapping if right ventricular electro-grams were chosen as the fiduciary local activation timingreference in 3-dimensional mapping systems. An additionaladvantage of the soft-tipped magnetic catheter is that it is lesslikely to induce mechanical VPC, which can complicatemapping.18

Conversely, whereas soft-tipped ablation catheter and the0.08-T magnetic force generated by the MNS allow for safenavigation within the cardiac chambers, the inability toprovide sufficient contact force may have resulted in moreRMC patients crossing over to require MCC to achieve acutesuccess, more radiofrequency energy required during abla-tion, and potentially more recurrences during long-termfollow-up. Our study is underpowered to confirm theseobservations.

Study limitationsThis study was performed at a single tertiary center thatperformed relatively high volumes of RMC-guided as wellas VT ablations. Thus, the findings may not be generalizableto less experienced operators or centers. The investigatorshad prior knowledge of the primary endpoints in the conductof this study, which should be considered a potential sourceof bias. The study sample is small. Taking into account2 subjects with recurrences of VPC in the RMC group and5 patients crossing over from the RMC to MCC group duringthe procedure, the medium-term success rates of solely usingthe MNS to complete the ablation procedure is only 8 of 15(vs 14/15 in the MCC group; P ¼ .01). Our threshold forcrossing over to the other treatment arm (both RMC to MCCand vice versa) was relatively low, and it is important to notethat there were no acute treatment failures. Although thestudy was adequately powered for our primary endpoint, thechance of type I error may be very high, particularly whenexamining differences in secondary endpoints such as long-term recurrences. Further studies are required to addressthese questions.

ConclusionRemote magnetic catheter navigation significantly reducespatients’ and physicians’ fluoroscopic times by 50.5% and68.6%, respectively, when used in conjunction with an NCMto guide ablation of RVOT VA.

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