An observational study was conducted with the first 62 consecutive patients to undergo Rhythmia-guided ablation of paroxysmal or persistent symptomatic AF (n = 37 and n = 25, respectively) at our center between July 2015 and July 2016. The results were compared with those obtained in a retrospective cohort of consecutive patients who underwent AF ablation as the sole intervention with a conventional navigation system (Ensite Velocity, St. Jude Medical, St. Paul, Minnesota, United States); procedures in the control group were conducted between July 2015 and July 2016 by the same senior system operator who performed the Rhythmia procedures. Mean participant age was 63 years, 46% of the patients were women, and 17 patients had undergone a previous AF ablation procedure, 2 with Rhythmia and 15 with another navigation system. All patients were under anticoagulant therapy for at least 21 days before the procedure. Vitamin K antagonist therapy was maintained without interruption, whereas treatment with new anticoagulants was suspended for 12 to 24hours before ablation and reinitiated on the same day as treatment with no bridging therapy.

The study was approved by the local ethics committee and conformed to the ethical principles of the Helsinki Declaration. All study participants gave informed consent before the procedure.

In the control group, we followed our usual ablation protocol based on published methodology.7,8 In brief, patients underwent double transseptal puncture followed by electroanatomic mapping guided by the Ensite Velocity system (St. Jude Medical, St. Paul, Minnesota, United States); the other catheters used were a TactiCath irrigated ablation catheter and a Reflexion Spiral variable radius circular diagnostic catheter. The Ensite Verismo software package was used to fuse electrical maps with 3-dimensional reconstructions derived from segmented left atrium contrast CT images. Protocols and techniques for sedation, anticoagulant therapy (intraprocedural and periprocedural), and ablation were the same as those used in the Rhythmia group.

Quantitative variables are presented as means ± standard deviation. Categorical variables are presented as number and percentage. Differences between 2 patient groups were analyzed by the Student t test for independent samples. Qualitative variables were compared by the chi-square test or the Fisher exact test. In bilateral tests, statistical significance was assigned at P < .05. Statistical analysis was conducted with SPSS for Windows, version 22 (SPSS Statistics, IBM Software Group).

Our series confirms the ability of the Rhythmia system to create a very high point-density map of the left atrium and PV without interfering in the AF ablation procedure workflow. This allowed us to achieve reasonable procedure times even in an initial study that included learning how to operate the system. In all patients, maps obtained with Rhythmia were comparable with those obtained by CT. When used together with the multipolar Orion catheter, the Rhythmia system allows rapid generation of complete activation and voltage maps without the need for manual correction. Using Rhythmia in automatic mode, we obtained maps with 12 125 electrograms on average in a mean mapping time of 18minutes. In most instances, manual correction is unnecessary because the system compares each point with its neighbors and corrects discordances due to poorly recorded isolated points. This feature ensures that a small number of erroneously annotated points will not affect overall map interpretation. In our series, the high resolution of the Rhythmia activation maps was especially useful in redo proceures because it enabled more accurate identification of reconnection gaps than the conventional navigation system (gaps detected in 67% of reconnected PV with Rhythmia vs 40% withVelocity; P = .042) (Figure 1). Similarly, after apparently complete circumferential ablation around a vein in a patient undergoing an index ablation, the Rhythmia system could generate a new activation map of a single vein within 2minutes, providing a guide for focal ablation. For several patients in our series who underwent redo ablation, we created “exit maps” of reconnected PV by in-vein stimulation with the ablation catheter and deployment of the Orion catheter in the venous ostium, followed by withdrawal toward the atrium (Figure 2 and video of the supplementary material). This maneuver takes only a few minutes and is very useful for delimiting reconnection gaps; however, its value is limited when stable capture within the PV cannot be achieved.

Figure 1.

Example images from an atrial fibrillation patient undergoing redo ablation, in whom atypical atrial flutter was induced mechanically. An 18 579-point activation map was created in 13 minutes. A block line made in the previous procedure can be seen on the roof of the left atrium, with a conduction gap where it joins the right superior pulmonary vein. The arrhythmia resolved after focal ablation at this level. Beats, beats captured for map creation; EGMs, electrograms captured for map creation; Time, mapping time; Volume, map volume.

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Figure 2.

Left superior pulmonary vein exit map from a posterior viewpoint in an atrial fibrillation patient undergoing redo ablation. During pacing from the ablation catheter inside the pulmonary vein, the maximally deployed Orion catheter was withdrawn slowly with rotation. A clear conduction gap can be seen in the PV antrum. Electrical isolation was achieved by focal ablation at this point. Beats, beats captured for map creation; EGMs, electrograms captured for map creation; Time, mapping time; Volume, map volume.

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In our view, the combination of the Orion catheter with a deflectale sheath creates a very versatile tool for left atrium and PV mapping, allowing adequate navigation even in patients with a variant anatomy and providing a number of advantages over conventional circular mapping catheters (Figure 3). For example, the number of selectively catheterized PV was significantly higher than that achieved with a conventional circular catheter, and the Orion catheter adapted to a wide range of venous anatomies in acceptable mapping times. Another advantage of the Orion catheter is its aptness for exploring the septal region close to the inferior portion of the right inferior PV, a site that presents difficulties for both mapping and ablation due to the risk of displacement to the right atrium. By smoothly withdrawing the fully-deployed catheter until consistently encountering resistance from the interatrial septum, the resulting map is left with an approximately 3 mm diameter zone lacking recorded potentials, corresponding to the transseptal puncture site (Figure 4). The shape of the Orion catheter also facilitates mapping of the venous ostia by the simple maneuver of deploying it within the vein and withdrawing it slowly until a typical “spike” is observed on passing into the left atrium. Finally, the pairing of electrodes both longitudinally and radially on the Orion catheter splines allows left superior PV potentials to be distinguished, without catheter manipulation, from signals due to far-field potentials from the left atrial appendage; this is possible because impulses propagate from proximal to distal in the PV, whereas far-field signals are simultaneous (Figure 5).

Figure 3.

Posterior views of variant pulmonary vein anatomy revealed by electroanatomic mapping (left) and 3-dimensional computed tomography reconstruction (right) of the left atrium. A left superior pulmonary vein opens in the atrial roof, showing evidence of dilatation and a proximal curvature that could interfere with multipolar catheter mapping. The Orion catheter allowed exploration of the 4 veins observed. Mapping time, 24minutes.

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Figure 4.

Electroanatomic map of the left atrium from a right anteroinferior viewpoint. By smoothly withdrawing the Orion catheter until encountering resistance, it was possible to map part of the interatrial septum and mark the transseptal puncture site.

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Figure 5.

A: Example electrograms recorded with the Orion catheter inside the left superior pulmonary vein; with no need for catheter manipulations or stimulation maneuvers, recordings from a single spline can distinguish pulmonary vein potentials, which propagate from proximal to distal (yellow arrows), from “far-field” potentials originating in the left atrial appendage, which are simultaneous (white arrows). B: Electrograms from far-field ventricular potentials (red arrow) are also simultaneous, allowing them to be distinguished from pulmonary vein potentials.

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Many unresolved questions remain. For voltage mapping, there is a need to define the optimal cutoffs for distinguishing between healthy and scar tissue. The values used in the present series satisfactorily revealed lines made in previous procedures; however, we cannot be sure that these values are optimal for characterization of atrial tissue.

Volumes measured with Rhythmia were smaller than those measured by CT, indicating that Rhythmia did not explore the whole left atrium. It should be borne in mind that these Rhythmia maps were made in the clinical setting of AF ablation procedures; areas not explored systematically in this series might be covered by a more detailed mapping procedure of the kind used in patients with left atrial flutter, thus producing values closer to the true atrial volume. Even with this caveat, the recorded volumes were 84.14% of values measured by CT, indicating adequate adaptation by the Orion catheter to the different left atrium regions.

Inclusion of a magnetic sensor significanly improved the introduction of the ablation catheter, but there is room for further improvement in vision-guided catheter placement. It would also be useful to have a magnetic catheter with a resistance sensor. Finally, given the high cost of the Rhythmia system, a cost-benefit analysis is warranted to help prioritize selected patient subgroups for this procedure.

The obvious limitations of this study are the lack of randomization in the control group and the lack of long-term follow-up. However, rather than evaluate long-term clinical outcomes, this study aimed to describe experience and acute outcomes obtained with Rhythmia-guided AF ablation procedures. Further, randomized studies will be needed with larger samples in order to evaluate long term clinical efficacy.