The Use of Remote Magnetic Navigation in Catheter Ablation of Atrial Arrhythmias

Jeffrey A. Tice, MD



In This Article

Technology Assessment (TA)

TA Criterion 1: The Technology Must Have Final Approval From the Appropriate Government Regulatory Bodies

The NIOBE Remote Magnetic Navigation system first received FDA 510(k) approval in January 2003. It is categorized as a Class 2 device under the product code DXX. NIOBE is integrated with Siemens' and Phillips' digital x-ray fluoroscopic imaging systems and Biosense Webster's three dimensional catheter location sensing technology and ablation catheter technology. The list of FDA 510(k) approvals is shown below.

TA Criterion 1 is met.

TA Criterion 2: The Scientific Evidence Must Permit Conclusions Concerning the Effectiveness of the Technology Regarding Health Outcomes

The procedure time and complication risk during catheter ablation vary dramatically by the type of arrhythmia. This assessment will focus on atrial arrhythmias because they were initially the primary type of arrhythmia treated with catheter ablation and because a recent systematic review of remote magnetic navigation for catheter ablation of ventricular tachycardias concluded that additional comparative and randomized trials were needed.[46] The Medline database, Embase, Cochrane clinical trials database, Cochrane reviews database and the Database of Abstracts of Reviews of Effects (DARE) were searched using the key words "remote navigation" OR "remote magnetic navigation" OR "Niobe" OR "Stereotaxis." The search was performed for the period from 1945 through December 2011. The bibliographies of systematic reviews and key articles were manually searched for additional references. References were also solicited from the manufacturers and local experts. The abstracts of citations were reviewed for relevance and all potentially relevant articles were reviewed in full. We excluded studies of ventricular arrhythmias.[47–57]

The search identified 425 potentially relevant studies (Figure 1). After elimination of duplicate and non-relevant references including reviews and animal studies the search identified 25 articles describing seven case series,[58–64] 16 comparative studies[65–80] and two small randomized trials.[81,82] An additional 11 early case series were excluded because they were too small to provide reliable estimates for the outcomes of interest.[83–93]

Figure 1.

Selection of studies for inclusion in the assessment

Level of Evidence: 2, 3, 4 and 5.

TA Criterion 2 is met.

TA Criterion 3: The Technology Must Improve Net Health Outcomes

The most important outcome for catheter ablation is long-term freedom from recurrence of the arrhythmia. Patients need to be followed for a relatively long time to be sure that they are free from the arrhythmia. Randomized trials that demonstrated the value of catheter ablation for the treatment of atrial fibrillation followed patients for a minimum of nine to twelve months[94,95] and one ongoing trial comparing different techniques for catheter ablation plan to follow more than 240 patients for twelve months in order to have adequate power to demonstrate the equivalence of the two techniques.[96]

Other important outcomes are primarily safety outcomes: freedom from adverse events such as cardiac tamponade, permanent heart block, myocardial infarction (MI), stroke, major vascular complications, radiation exposure, and death.

Case Series

The seven case series of catheter ablation for atrial arrhythmias were all small: there were only a total of 338 patients described in these series.[58–64] The characteristics of the studies are described in Table 1. Most reported on the results from a single type of atrial arrhythmia, but the largest case series described results of treating six different arrhythmias including ventricular tachycardia.[62]

The outcomes and adverse events are summarized in Table 2. The acute procedural success rate for AVRT and AVNRT was generally high (81% to 100%) and similar to the experience in manual catheter navigation.[58,59,61,62] However, the outcomes in studies of atrial fibrillation were more variable. In the study by Di Biase and colleagues, a 4 mm non-irrigated tip catheter for ablation[60] resulted in a substantial proportion with charring (33%), and an extremely low incidence (8%) of pulmonary vein electrical isolation.[60] While they reported a low incidence of adverse events, the charring could pose a significant risk of TIA/stroke; in fact, recent data suggests that asymptomatic cerebral thromboembolism during (or shortly after) AF ablation is common, demonstrating that a lack of acutely evident events does not exclude the possibility that this technology in fact increased such events.[97–99] Chun and colleagues used a RMN open-irrigated catheter on 56 (37 paroxysmal and 19 persistent AF) patients and reported that 70% of their patients were in sinus rhythm after a mean follow-up of 426 +/- 213 days; this is comparable to the success rate for manual catheter navigation.[64] However, this study failed to report details of how many patients were on antiarrhythmic medications and whether or not they performed systematic ambulatory monitoring to detect asymptomatic AF. In subsequent study of AF ablation patients, Miyazaki et al. observed similar success rates between their initial RMN-guided procedure (N = 30, 69% efficacy at one year) and a group of historical controls that had undergone manual ablation (N = 44, 61% efficacy at one year).[73] However, their fluoroscopy, procedural, and ablation times were significantly longer in the RMN group; it is difficult to know if these longer times were due to lack of operator familiarity that would improve with more experience or if they represented something inherent to the RMN procedure.[73]

There are two notable findings from these case series. First, the complication rate was low. Five of the case series reported no significant complications[58–61,63] and there were a total of five complications in the other two series.[62,64] As expected, the complication rate for the treatment of atrial fibrillation was greater than that of the other arrhythmias.[64] Second, in the three studies that reported operator exposure to fluoroscopy, the operator exposure was much shorter than the total fluoroscopy time. This is one of the benefits of remote navigation, though it does not have direct impact on patient outcomes

Comparative Studies

The search identified sixteen studies that compared the outcomes for 945 patients treated using remote magnetic navigation to 1582 controls.[65–80] The majority were single site studies that used historical controls from their local experience to evaluate the impact of remote magnetic navigation. Only a handful of the studies carefully matched the characteristics of patients treated with manual navigation to those of the patients treated with remote magnetic navigation. None of the studies used more sophisticated statistical techniques, such as instrumental variables or propensity scores to account for differences between the two groups of patients. The vast majority of the studies had fewer than 50 patients in each group, so that sophisticated modeling was not feasible.

It is remarkable that seven of the first eleven studies reported 100% success rates for both the manual and magnetic navigation groups.[65,66,69,71,73–75] Only one of the studies reported a nominally higher success rate with remote magnetic navigation and the difference was not significant.[79] The recurrence rates were also low, except for studies of atrial fibrillation, which is more difficult to treat with catheter ablation than other atrial arrhythmias.

The average total procedure time varied from 45 minutes to 340 minutes, depending on the arrhythmia, but was consistently longer for remote magnetic navigation. Fluoroscopy time, on the other hand, was consistently shorter for remote magnetic navigation. None of the studies reported operator fluoroscopy time.

The overall complication rate was remarkably low: less than two percent in both the remote and manual navigation groups. Pericardial effusions and tamponade tended to occur less often in the remote navigation group, but the numbers were so small in each study that the differences were not significant.

Learning Curve

Seven of the observational studies provided data on changes in outcomes with increasing experience with remote magnetic navigation.[61,63,66–68,70,79] Five studies compared the outcomes for their first 10 to 27 patients treated using remote magnetic navigation to those of later patients in the study (Table 3).[61,63,66,68,79] All reported significant decreases in both total procedure time and fluoroscopy time with greater experience. Two other studies performed linear regression to evaluate the effect over all procedures in their studies.[67,70] The largest study reported that both the procedure time and fluoroscopy continued to decrease even after 75 cases.[70] In that study, the total procedure time for the ablation of atrial fibrillation decreased by an average of 51 minutes and the fluoroscopy time decreased by 44 minutes. Across all studies, there was clearly a significant learning curve to the use of remote magnetic navigation that may require more than 75 cases to achieve optimal efficiency.

Summary of Observational Studies

Several things are clear from the observational data. First, as expected, the operator exposure to radiation from fluoroscopy is markedly reduced. This may translate into less occupational cancers among staff working in electrophysiology laboratories. Second, catheter ablation procedures are longer when magnetic navigation is used, although the extra time tends to decrease with increasing experience. Third, it is likely that the total time that patients are exposed to radiation from fluoroscopy is decreased, but the comparisons were not randomized, so the differences could be due to secular trends in the success rate of catheter ablation or to selection bias. In general the success rate was high, but no higher than that obtained with manual navigation. Similarly, the complication rates were low and appeared comparable to manual navigation. The individual studies were small, so the confidence intervals around each of the estimates of procedural success and complications were wide. In addition, the same concerns about secular trends in outcomes and selection bias increase the uncertainty about the reliability of these findings. Randomized trials are needed to demonstrate equivalence. Given expected differences in the success rate and complications based on the type of arrhythmia, randomized trials should either focus on one type of arrhythmia or stratify randomization by arrhythmia. Studies addressing similar questions in atrial fibrillation suggest that the trials should randomize 250 to 300 patients and follow them for at least one year.[94–96]

Randomized Clinical Trials

The Helios Electrophysiology Ablation Remote Treatment (HEART) Trial The Helios Electrophysiology Ablation Remote Treatment (HEART) trial randomized patients with supraventricular tachycardia in a 3:1 ratio to ablation with remote magnetic navigation or manual navigation.[81] The study included patients at least 18 years of age who had a documented episode of SVT in the prior year and were scheduled for ablation of either AVNRT, an accessory pathway, or AV junctional ablation. The study excluded patients with any of the following: contraindications to magnetic resonance imaging; recent MI or cardiac procedure; intra-cardiac thrombus, or unstable angina. The primary outcome was total fluoroscopic time. Secondary outcomes included the acute success rate, the success rate at 90 days, total procedure time, and adverse events. Based on power calculations, the study was designed to randomize 256 patients. The study was stopped after 71 patients (28% of goal) when a magnetic catheter became commercially available. Follow-up at three months was also low at only 65%. The randomization procedures, allocation concealment, and blinding were not described. In addition, one patient randomized to the remote magnetic navigation group was excluded because ablation was not attempted, a violation of the intention to treat principle. Thus, the overall quality of the trial was poor.

The study required physicians to perform a minimum of five and a maximum of twenty procedures using remote magnetic navigation before randomizing any patients. The study reported outcomes on the 73 patients treated during this skill-building phase in addition to the 56 patients randomized to magnetic navigation and 15 patients randomized to manual navigation. There were no statistically significant baseline differences between the remote magnetic navigation group and the manual navigation group, but some of the differences were large. For example, the average age in the remote navigation group was 53 years compared to 43 years in the manual navigation group (p=0.17). Similarly, there were more men in the remote magnetic navigation group (41% versus 27%, p=0.49) and all of the patients receiving AV junction ablation were in the remote magnetic navigation group (9% versus 0%, p=0.91). In a larger trial, these differences would have been statistically significant.

Total fluoroscopy time, the primary outcome, was shorter in the remote magnetic navigation group (17.8 minutes versus 27.1 minutes, p<0.003). The total procedure time was identical in the two groups (151 minutes). The acute success rates were similar for the two groups (91% versus 87%, p>0.05). Among the 65% of patients who returned for the three month follow-up, the chronic success rates were also similar and favored the remote magnetic navigation group (95% versus 87%, p>0.05). Finally, the major adverse event rates were also similar (5.4% versus 6.7%, p=1.0). The adverse events in the remote magnetic navigation group were two repeat ablations for treatment failure within one week of the initial ablation and one pulmonary embolism. The adverse event in the manual navigation group was chest pain that resolved with antacid therapy. Given the small sample size, baseline differences between the two groups, and poor follow-up, it is impossible to make any firm conclusions about the acute or chronic success rate or the adverse event rate. The differences in fluoroscopy time are large enough, that they are likely to be real, though the differences in case mix (more AV junction ablations) and the lack of blinding could explain some of the difference in fluoroscopy time.

Atrial Flutter Trial – Vollmann 2009 The second trial randomized 90 patients with documented typical atrial flutter to catheter ablation with either remote magnetic navigation or manual navigation.[82] The study excluded patients with prior ablations and those with a device at risk for magnetic interference (pacemaker, implantable cardioverter defibrillator). The primary endpoints were total fluoroscopy time and the duration of radiofrequency application duration. Secondary outcomes included total procedure time, patient radiation exposure, the acute success rate, long-term success through six months, and adverse events.

The study randomized 45 patients to each group. The two groups were reasonably similar in age (69 versus 68 years) and sex (80% versus 73% male), though there were fewer patients with coronary artery disease in the remote magnetic navigation group (40% versus 51%) and fewer taking statins (33% versus 47%). The study did not report p values for these baseline characteristics and did not comment on statistical significance.

Both fluoroscopy time (10.6 versus 15.0 minutes, p=0.043) and total patient radiation exposure (3274 versus 4304 microGrey, p=0.032) were significantly lower in the remote magnetic navigation group. Total procedure time (113.5 versus 77.2 minutes, p<0.0001) and radiofrequency application duration (17.1 versus 7.5 minutes, p<0.0001) were significantly longer in the remote magnetic navigation group. There were no significant differences in the acute procedural success rate (84% versus 91%, p=0.52) or in the six-month success rate (73% versus 89%, p=0.063), although there was a trend towards more recurrences in the remote magnetic navigation group (13% versus 2%, p=0.073).

Summary The observational data demonstrated that operator exposure to radiation is decreased with remote magnetic navigation at the expense of longer total procedure time. The observational data also suggested that remote magnetic navigation reduced patient exposure to radiation. This finding was confirmed in the two randomized trials. However, both randomized trials were underpowered to demonstrate the equivalence of remote magnetic navigation to manual navigation for the two most important clinical outcomes: long-term freedom from arrhythmia recurrence and major complications. In the HEART trial, the acute success rate was higher by 4.2% in the remote navigation group, but the 95% confidence interval ranges from 15% worse to 23% better.[81] For the other randomized trial, the 95% confidence interval for the difference in success rates ranges from 20% worse to 6.8% better.[82] These confidence intervals contain absolute differences in success rates that would be clinically unacceptable. It is unfortunate that the HEART trial was of poor quality and was terminated early because the planned sample size should have been sufficient to confirm the equivalence of remote magnetic navigation to manual navigation within reasonably narrow confidence intervals.

TA Criterion 3 is not met.

TA Criterion 4: The Technology Must Be as Beneficial as Any Established Alternatives

Manual navigation is the established alternative to remote magnetic navigation. As noted above, remote navigation clearly reduces both operator and patient exposure to ionizing radiation from fluoroscopy. These are clear benefits compared to manual navigation. However, there is too much residual uncertainty about the magnitude of difference in the acute and long-term success rate. In the HEART trial, the acute success rate with remote magnetic navigation was higher, while in the other randomized trial it was lower. In both studies, the confidence intervals were wide. The situation was reversed for recurrence rates: in the HEART trial the recurrence rate was higher in the remote magnetic navigation group, while in the other randomized trial it was lower. Finally the confidence intervals surrounding the major complication rates were also wide. In the HEART trial, there was only a 1.2% difference in the complication rate and it favored remote navigation, but the confidence interval ranged from13% worse to 15% better. Larger, better quality trials are needed to clearly demonstrate equivalence in clinical effectiveness and safety.

TA Criterion 4 is not met.


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