Procedural outcomes of fluoroless catheter ablation outside the traditional catheterization lab

Abstract

Aims

Non-fluoroscopic catheter ablation is becoming routine. In experienced centres, fluoroscopy is rarely required. The use of a traditional catheterization lab (cath lab) may no longer be necessary. We began performing catheter ablations at a paediatric centre outside the traditional cardiac cath lab in 2013. The purpose of this study was to compare procedural features of paediatric catheter ablation performed outside the cath lab to those performed within a cath lab.

Methods and results

We prospectively looked at patients presenting to the paediatric centre with supraventricular tachycardia (SVT) undergoing catheter ablation outside the cath lab in a standard operating room (OR group). We compared retrospectively to a control group matched for age, type, and location of arrhythmia who had ablations in a traditional cath lab (CL group). Catheter visualization was exclusively by electro-anatomic mapping. Fifty-nine patients with SVT underwent catheter ablation in the OR from October 2013 to December 2015. Thirty-three patients had accessory pathways, 29 were manifest, and 13 of those were left sided. Twenty-six had atrioventricular nodal re-entrant tachycardia. Transseptal puncture with transoesophageal echocardiography guidance was used for 10 left-sided pathways, whereas the other 3 had patent foramen ovales. Procedure time did not differ significantly between groups (OR group mean 131 min, range 57–408; CL group mean 152 min, range 68–376; P = 0.12). Acute success was similar in both groups [OR group: 58/59 (98.3%) and CL group: 57/59 (96.6%)]. There were no major complications in either group. There was no fluoroscopy used in either group.

Conclusion

Although performing paediatric catheter ablations outside the traditional cath lab is early in our experience, we produced similar outcomes and results without encountering procedural difficulties of performing ablations in a non-conventional setting. Larger multi-centred trials will be essential to determine the feasibility of this practice.

Introduction

Supraventricular tachycardia (SVT) is the arrhythmia most commonly treated in a paediatric electrophysiology (EP) lab.¹ The success rate of catheter ablation of SVT is high, and the complication rate is low.^2,3 With the introduction of electro-anatomic mapping, fluoroscopy times have markedly decreased in all studies reporting outcomes in paediatric patients.^4–12 At our institution, we have performed >600 ablations without fluoroscopy. In the last 500 consecutive procedures, there have been no cases in which fluoroscopy was required that was not anticipated before the start of the procedure. Given the rarity and predictability of fluoroscopy use, in October 2013, we adopted an approach for patients that meet specific requirements to have catheter ablations performed outside the standard catheterization lab (cath lab). Using this approach, portable fluoroscopy was accessible if needed, rather than having a permanently mounted system. This allows more flexibility in the location of a procedure. We report our early experience of cardiac ablation of SVT in a standard operating room (OR) in comparison to a historical control group of rhythm- and age-matched patients undergoing ablation within our cath lab during a similar time frame as the study group.

Methods

Eligible patients

The internal institutional review board approved this study. The study group was prospectively derived from all patients presenting for catheter ablation of routine mechanisms of SVT. This included patients presenting to the paediatric centre with accessory pathway-mediated tachycardia (both manifest and concealed) and atrioventricular nodal re-entrant tachycardia (AVNRT). The study was not randomized or blinded, but all patients were de-identified. The primary determinant of where the procedure was performed was room availability. If the OR was available and the patient met inclusion criteria, then the procedure was performed in the OR. Inclusion criteria for consideration of an OR procedure included the following: weight >15 kg, no significant congenital heart disease, no trans-venous pacemaker or ICD, no mechanical heart valve, and no need for a diagnostic or interventional catheterization during the same procedure.

The historical control group was composed of age- and rhythm-matched patients who had undergone catheter ablation in the cath lab using three-dimensional mapping as the primary imaging modality. We searched our database between the years of 2006 and 2015 to find patients matching the study group for mechanism of tachycardia (manifest accessory pathway, concealed accessory pathway, or AVNRT) as well as location of ablation site (right free wall vs. right septal vs. left sided). Once multiple matching patients had been identified, patients closest in age to the study group were selected for the controls.

Catheter ablation protocol

All procedures in both groups were done under general anaesthesia. All venous access was through the right femoral vein. A steerable octapolar catheter was advanced to the right atrium. Cardiac geometry was then created utilizing the Ensite Velocity system (St. Jude Medical, St. Paul, MN, USA). Initial geometry consisted of superior vena cava (SVC), inferior vena cava (IVC), right atrium, coronary sinus, tricuspid valve, and His bundle location (Figure 1). For manifest pathways and AVNRT, two catheters were used: the octapolar catheter, which was positioned in the coronary sinus, and the ablation catheter. For concealed accessory pathways, a third catheter was added and positioned in the right ventricle apex to allow mapping of retrograde conduction and ablation during ventricular pacing. Cryoablation was used for all typical AVNRT cases. Radiofrequency (RF) energy was used for all right and left free-wall pathways. For septal pathways, cryoablation was used in mid-septal or anteroseptal locations. For posteroseptal pathways, either cryoablation or RF energy was used on the basis of physician judgement.

For left-sided pathways if no patent foramen ovale (PFO) was found, a transeptal puncture was performed using transoesophageal echocardiography (TEE) for guidance. A long J wire was advanced from the femoral vein up to the SVC. This was confirmed on TEE, and then the sheath and dilator were advanced over the wire. The wire was removed, and the needle was inserted. The sheath was then pulled back and positioned on the thin portion of the atrial septum. When the tip of the dilator was shown to be in proper position, the needle was advanced into the left atrium. Saline contrast and pressure tracings were used to confirm left atrial location. The sheath and dilator were then advanced over the needle. For left-sided ablations, IV heparin was given with a target activated clotting time of 250 s. The procedure was then completed according to standard EP protocol at our institution.

For all OR procedures, an ultrasound machine was in the room and turned on for the duration of each procedure. This was felt to offer the quickest assessment of the heart in the event of a significant complication. Portable fluoroscopy was also available for all procedures. After the procedure, patients were transferred from OR or cath lab to recovery. They were discharged the following day. Data collected included patient age, weight, height, gender, mechanism of tachycardia, procedure time (defined as sheath in to sheath out time), energy source used, acute success, fluoroscopy time, and complications.

Statistical analysis

Examination of data included descriptive statistics: mean (standard deviation), median [interquartile range (IQR)], and min/max for all continuous variables and frequencies (percentages) for all categorical variables. Assessments for distributional shape of continuous variables were completed, and subsequent testing utilized appropriate non-parametric tests. Statistical analyses for two-group comparisons were performed to evaluate for statistical difference between the control and the study group based upon age, height, weight, gender, AVNRT, pathway, pathway type, and pathway location. The study and control groups were assessed for differences in clinical variables including total cryoablation time, number of arrhythmias, number of cryoablation applications, number of cryo applications >60 s, procedure time, total RF time, number of RF applications, number of RF applications >30 s, immediate success, major complications, minor complication, PFO crossed, target, and transeptal puncture performed. Statistical analyses were completed using SAS Institute Inc., SAS 9.4/13.2^©. All testing was two-tailed and evaluated at the α = 0.05 level of statistical significance.

Results

There were 59 patients in the study group who underwent catheter ablation of SVT in the OR group and 59 patients in the control group undergoing ablation in the CL group. The baseline characteristics of both groups are detailed in Table 1, whereas clinical characteristics and outcomes are detailed in Table 2. There were no statistically significant differences in the baseline demographics or arrhythmia type between the study and the control groups. The results of the Wilcoxon rank-sum test for non-normally distributed continuous data showed that age (P = 0.44), height (P= 0.53), and weight (P= 0.49) were not significantly different between the two groups. The results of Fisher's exact test for accessory pathway type (P = 1.00) and accessory pathway location (P = 1.00) and the χ² test of independence for gender (P = 0.46) revealed no significant difference in proportions.

The results of the ablation procedure are detailed in Table 2. In the OR group, cryoablation was primarily used in 25/26 (96.2%) AVNRT procedures, and 1/26 (3.9%) received primarily RF energy. With the accessory pathway patients, 27/33 (81.8%) received RF energy, and 6/33 (18.2%) received primarily cryoablation. Acute success was achieved in 26/26 (100%) patients with AVNRT. Acute success was achieved in 32/33 (97.0%) of patients with SVT secondary to an accessory pathway. The patient in whom acute success was not achieved had a posteroseptal manifest pathway with SVT, and at the end of the procedure, she still had antegrade and retrograde conduction without inducible SVT. The pathway was not rapidly conducting, and therefore no further attempts at ablation were made. There were no noted major complications in the study group, but there was a minor complication of transient heart block induced by catheter manipulation near the AV node. This resolved by withdrawing the catheter from the atrial septum.

In the CL control group, cryoablation was primarily used in 26/26 (100%) AVNRT procedures, whereas none received primarily RF energy. With the accessory pathway patients, 18/33 (54.6%) received RF energy, and 15/33 (45.4%) received primarily cryoablation. There was acute success in 25/26 (96.2%) patients with AVNRT. In the patient in whom acute success was not achieved, there was still inducible SVT at the termination of the procedure. Acute success was achieved in 32/33 (97.0%) of the patients with accessory pathways. The case that did not have acute success was a manifest left posterolateral accessory pathway that had persistent antegrade and retrograde conduction without inducible tachycardia; therefore, no further attempts at ablation were made. In the cath lab control group, there were no complications.

No statistically significant difference was observed in the comparison of total procedure time (P = 0.12). The median (IQR) total procedure time was 109 (67) min in the OR group with a range of 57–408 min. In the cath lab control group, the median procedure time was 129 (112) min with a range of 68–376 min. In the cath lab control group, permanently mounted fluoroscopy was available for every case, and in the OR group, portable fluoroscopy was available for every case. However, fluoroscopy was not needed or used in either group. Results of Fisher's exact test indicate no statistically significant difference in proportions between the OR group and the CL group for immediate success (P = 1.00), accessory pathway type, or accessory pathway location (P = 1.00 for both). The Wilcoxon rank-sum test revealed no significant differences between the OR group and the CL group for the following clinical covariates: total cryo time (P = 0.12), number of cryo applications (P = 0.67), number of cryo applications >60 s (P = 0.15), total RF time (P = 0.75), number of RF applications (P = 0.92), and number of RF applications >30 s (P = 1.00). Results of Fisher's exact test revealed no significant difference in proportions between OR and CL for PFO crossed, target arrhythmia, minor complications or transeptal puncture (P = 1.00 for all), or AVNRT type (P = 0.73). There were no major complications reported.

Follow-up

The median follow-up time for the OR study group was 12 months. There has been one recurrence in a patient with Wolff Parkinson White (WPW). That patient was a 14-year-old female with WPW and SVT. She had a mid-septal accessory pathway and underwent cryoablation that was initially successful. At 2-month follow-up, she had recurrence of pre-excitation on electrocardiogram. She has not had recurrence of tachycardia thus far. There have been no recurrences in the patients with concealed pathways or in those with AVNRT. The median follow-up time for the cath lab control group was 48 months. There have been three recurrences: two patients with WPW and one with AVNRT. The first was an 11-year-old male with WPW and SVT. He had a posteroseptal accessory connection and underwent RF ablation. He had recurrence of symptoms and pre-excitation at 1-month post-procedure. The second patient was a 12-year-old male with AVNRT. He had acutely successful cryoablation but recurrence of his tachycardia at 2-month post-procedure. The third patient was a 15-year-old male with WPW and palpitations. He had a right anterior paraseptal accessory pathway and had undergone RF ablation. He had recurrence of pathway conduction noted at 2-month follow-up.

Discussion

Main findings

The principal finding of this study is that catheter ablation of common forms of SVT in patients with structurally normal hearts can be safely performed in settings other than a traditional cardiac cath lab. These findings are from a single institution with over 10 years of experience in catheter ablation without fluoroscopy. The results will not yet be reproducible at most institutions. However, the results are interesting and do raise some intriguing possibilities for the future of paediatric cardiac ablation. Of paramount importance is patient safety. To that end, much planning was involved to anticipate and prevent serious complications or negative outcomes. Patient selection was quite stringent for OR ablations, choosing patients with only structurally normal hearts and common forms of tachycardia. They needed to be of adequate size to make the technical conduct of the procedure not overly challenging. If they had any intracardiac devices that could not be seen by the three-dimensional Ensite system, then the procedure was done in the cath lab. We have found that with advanced planning nearly every case requiring fluoroscopy can be anticipated. However, in the event fluoroscopy is needed when it was not anticipated, we have maintained availability of portable fluoroscopy for every case. In addition, an ultrasound system is in the room and always on during each case, giving us immediate access to evaluate for effusion and function if needed.

An unexpected finding from the study was that the procedure did not take longer in the OR study group compared with the CL control group. In fact, the procedure time was slightly shorter in the OR study group, although not statistically significantly. Because we did not allow for a learning curve in the study group, it was expected that the OR study group would take longer. However, we believe the reason for this lower time was the large number of fluoroless procedures performed (>500) prior to undertaking procedures outside the cardiac cath lab. The level of experience of the electrophysiologists and the entire cath lab staff was significant enough to make the transition essentially seamless.

In addition to the demographic and procedural comparison between the study and the control groups, we also performed a cost analysis to determine if there was a difference between the two groups. After looking at the specific patients in the study and control groups as well as comparing the groups as a whole, we determined that difference in cost was not statistically significant between the two groups. However, when we began performing procedures in the OR, an administrative decision was made to cost and bill the OR procedures, the same as the cath lab. Therefore, a difference would not have been expected. In most institutions, OR procedures are billed at a higher fee than cath lab procedures. This could result in differences between procedures.

Benefits of fluoroless ablation

If there is no compromise of either safety or efficacy, then the benefits and applications of fluoroless procedures are innumerable. The safety of low or no fluoroscopy ablations has been well documented in the literature.^4,5,9 Eliminating the long-term risk of cancer to our patients is by itself a reason to continue the advancement of technology and reduction of fluoroscopy in ablations. That same benefit, however, also accrues to the physician and staff in the cath lab. In addition, if fluoroscopy can be predictably avoided in the majority of cases, lead protective gear does not need to be worn. This is not only a welcome comfort during a case but also decreases the long-term orthopaedic complications associated with its use.¹³

Pregnancy is another situation where fluoroless ablation would be beneficial for patients, as well as staff in the cath lab. Our institution has had nurses, technicians, and anaesthesiologists who have each been able to maintain their position in the cath lab during pregnancy because no fluoroscopy was being used. Finally, we have also faced the clinical scenario of the pregnant patient with incessant tachycardia who failed medical management, ultimately requiring ablation.¹⁴ Previously in this situation, the option of exposing the foetus to potentially toxic anti-arrhythmics was unsettling to both the physician and the family. However, the alternative of exposing the foetus to potentially teratogenic or mutagenic effects of radiation was even more concerning. The option today of performing a procedure without fluoroscopy may make catheter ablation the preferred therapy in the pregnant female with refractory SVT.

Benefits of portable electrophysiology procedures

The ability to have a portable EP lab has many potential benefits. At our own institution, the most immediate improvement noted was the ability to more freely schedule procedures. As is typical in a paediatric institution, the cath lab is shared between EP, diagnostic and interventional catheterization, and often times interventional radiology (IR). Therefore, block time for EP procedures can be competitive. Having a truly portable EP system has reduced the scheduling conflicts immensely. We have also run into the situation where an issue arose at the start of a cardiac surgery, and the patient needed an emergent catheterization. In the past, this would have delayed or cancelled the EP procedure. However, due to the portability of the equipment, we were able to move the EP lab across the hall into a standard OR. In a similar manner, ablations scheduled in the OR make the cath lab open for emergent IR or catheterization procedures. In our cath lab, all EP equipment is on wheels. The registration/stimulation system, pinbox, Ensite system, keyboards, printer, and flat screen monitors are all situated on a single cart. The echocardiographic machine and cryo console are each on their own cart, and the RF generator can be carried. The equipment sits in a storage room within the cath lab. If a case is done in the cath lab, it is wheeled up to the cath table so that the catheters can be connected. If the procedure is in the OR, it is wheeled across the hall. Because it is all permanently situated on mobile carts, it takes <5 min to change rooms.

In an adult EP lab, the room is usually exclusively used for EP procedures. However, adult EP practices tend to be very busy, and there can be competition for the EP lab between physicians. In that case, having a portable lab can allow procedures to be done in more convenient, available rooms when necessary. This is a potential option for those practices that are too busy for a single lab but not busy enough to justify building a second cardiac catheterization suite. For a hospital, it could be a tremendously cost-effective alternative. The cost of building a second lab will be a multi-million dollar project. The cost of purchasing the equipment to allow portable EP procedures would be <1 million. The main EP lab could handle the bulk of procedures, with the portable lab being used as overflow for the more routine studies.

An additional benefit of a portable EP lab is the option to take the lab to the patient when the patient cannot easily get to the lab. Rarely, a patient can present with a tachycardia-induced cardiomyopathy, requiring extracorporeal membrane oxygenation (ECMO) support. Transporting the patient from the intensive care unit (ICU) to the EP lab while on ECMO is both challenging and risky. In that setting, taking the EP lab to the ICU can be a much safer option. With the current technology, it makes this situation a realistic possibility.

Lastly, a portable EP lab could expand the possibilities for electrophysiologists interested in global health. Building a cath lab in a hospital with only basic facilities is unrealistic. However, in the era of a mobile EP lab, the equipment needed would be more easily obtainable, opening up healthcare options for those who have previously had no options for the treatment of cardiac arrhythmias.

Study limitations

Although our study group of OR patients was prospectively enrolled, it was not randomized. Also, the control group was neither prospective nor randomized. However, we believe the results are valid because the procedures performed on both groups were from the same electrophysiologists and the same staff, utilizing the same technology and using the same approach. The CL control group patients were also selected to be as similar as possible to those enrolled in the study OR group. We therefore feel that this retrospective design gives better validity than comparison to published, historical controls. As with any retrospective study, there will be uncontrolled factors that may influence the outcomes. A randomized, multi-centred study would be ideal.

Conclusion

With current technology, it is feasible to perform routine ablation procedures in a non-conventional setting outside of the traditional EP lab, which has many different benefits. As the technology improves and more experience is gained, multi-centred studies will be useful to define which patients are best suited for these ablations and to determine the changes in technology needed to make the approach more broadly accepted and easily implemented.

Acknowledgements

We would like to thank the Rebecca D. Considine Research Institute for their administrative support as well as Stephanie Chambers, MHA, for her assistance in financial analysis.

Conflict of interest: J.M.C. has received a consulting fee from St. Jude Medical.

References