ThreeDimensional CT Overlay in Comparison to

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2, visualization of all pulmonary vein (PV) ostia was done by PV angiography, followed by merging of the CT image and .... proper visualization of catheters, and low energy levels and low frame rate .... when there is a large time delay between CT acquisition and ... of a point-by-point map can be omitted and the process of.
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Three-Dimensional CT Overlay in Comparison to CartoMerge for Pulmonary Vein Antrum Isolation JEROEN STEVENHAGEN, M.D.,∗ ,§ PEPIJN H. VAN DER VOORT, M.D.,∗ ,§ LUKAS R.C. DEKKER, M.D., Ph.D.,∗ ROLAND W.M. BULLENS, Ph.D.,† HARRIE VAN DEN BOSCH, M.D.,‡ and ALBERT MEIJER, M.D., Ph.D.∗ From the ∗ Department of Cardiology, Catharina Hospital, Eindhoven, the Netherlands; †Philips Health Care, Best, the Netherlands; and ‡Department of Radiology, Catharina Hospital, Eindhoven, the Netherlands

CT Overlay for PV Antrum Isolation. Introduction: Three-dimensional (3D) navigation systems are widely used for pulmonary vein antrum isolation (PVAI). To circumvent left atrial (LA) mapping, 3D CT reconstructions of the LA can be superimposed directly (CT overlay) on the fluoroscopy image to guide ablation catheters and to mark ablation sites. Methods and Results: Sixty-eight patients (pts) with symptomatic AF refractory to medical therapy were randomly assigned to CT overlay (group 1, n = 38) or CartoMerge (group 2, n = 30). In group 1 registration of the CT image was performed with contrast injections in 2 orthogonal projections. In group 2, visualization of all pulmonary vein (PV) ostia was done by PV angiography, followed by merging of the CT image and the Carto shell. We compared procedural success, procedure time, fluoroscopy time and radiation burden, measured as dose area product (DAP). Baseline characteristics were comparable in both groups. Procedural success, defined as disappearance of PV potentials in all PVs, was achieved in 37/38 (97%) of group 1 patients and 27/30 (90%) patients in group 2 (P = NS). Total procedure time was significantly shorter in group 1 compared to group 2 (129 ± 34 vs 181 ± 30 min, P < 0.0001). Although fluoroscopy time tended to be longer in the CT overlay group (47 ± 16 vs 40 ± 13 min, P = 0.06), proper use of diaphragmation resulted in comparable radiation values for both groups (DAP 53 ± 27 vs 56 ± 35 Gy cm2 , P = 0.76). Conclusions: CT overlay for PV isolation is feasible and may, in comparison to conventional LA navigation systems, shorten procedural time without increases in radiation burden. (J Cardiovasc Electrophysiol, Vol. 21, pp. 634-639, June 2010) atrial fibrillation, catheter ablation, image integration, electroanatomic mapping, computed tomography Introduction Currently, electroanatomic mapping systems are widely used to assist in catheter ablation for pulmonary vein isolation in atrial fibrillation (AF).1 Compared to techniques using fluoroscopy only, 3-dimensional (3D) imaging may facilitate the creation of wide circumferential lesions,2 in order to prevent RF application inside the pulmonary veins and subsequent PV stenosis. In addition, wide circumferential ablation using electroanatomic mapping may be associated with better outcomes3,4 and a reduction of the radiation burden.5,6 Merging of preacquired 3D MRA or CT reconstructions with electroanatomic maps7,8 leads to further decreases in radiation

§Both authors contributed equally to this work. R. Bullens is employed by Philips Health Care; and A. Meijer received fellowship support from Philips Health Care. No other disclosures were made. Address for correspondence: Pepijn van der Voort, M.D., Department of Cardiology, Catharina Hospital, P.O. Box 1350, 5602 ZA Eindhoven, The Netherlands. Fax: +31 40 2447885; E-mail: [email protected] Manuscript received 20 July 2009; Revised manuscript received 21 October 2009; Accepted for publication 26 October 2009. doi: 10.1111/j.1540-8167.2009.01665.x

burden,7 procedural duration,5,9 and improved outcomes.9 Despite its advantages, the use of electroanatomic mapping systems increases procedural costs and the choice of ablation catheters may be limited.6 Furthermore, the creation of an electroanatomic map is time-consuming.10 Recently some reports have been published on the clinical utility of the superimposition of a semitransparent 3D reconstruction over the fluoroscopic image.11-13 These 3D reconstructions are derived from contrast CT or MRA and are subsequently imported into and registrated to the realtime fluoroscopy system. The value of these techniques for PV isolation has been demonstrated, resulting in good procedural outcomes and reduced radiation doses compared to conventional ablation.12,13 However, there are still limitations to these techniques such as the requirement for biplane fluoroscopy13 and the incapability to mark the ablation sites.12 A novel application has been developed to superimpose a semitransparent CT image of the left atrium over commercially available fluoroscopy (CT overlay, EP Navigator prototype, Philips Healthcare, Best, The Netherlands). In contrast to previous systems, this application can be used on monoplane fluoroscopy and carries the possibility to tag ablation sites by points on the 3D surface of the reconstructed left atrium superimposed on fluoroscopy. The aim of this prospective study was to evaluate the feasibility of this technique for PV antrum isolation and to compare this new application with a proven electroanatomic mapping system

Stevenhagen et al. CT Overlay for PV Antrum Isolation

for procedural success, procedural duration, and radiation burden.

Methods Study Population and Procedural Aspects Sixty-eight patients with drug refractory paroxysmal (n = 49) or persistent (n = 19) atrial fibrillation were enrolled in the study. Prior to ablation all patients underwent cardiac transthoracic echocardiography; transesophageal echocardiography was performed according to the guidelines.1 The patients were randomly assigned to either CT overlay or CarR toMerge (CartoMerge Image Integration Software Module, Biosense Webster, Inc., Diamond Bar, CA, USA). All patients gave informed consent for the procedure. Oral anticoagulation was continued at INR levels between 2.5 and 3.5, while antiarrhythmic drugs were stopped at least 5 half-lives, except amiodarone. The catheter ablation was performed in patients in a fasting state; local anesthetics and conscious sedation were used. A 5 Fr sheath was introduced in the left femoral artery for continuous blood pressure monitoring. A 6 Fr sheath was positioned in the left femoral vein for coronary sinus access with a quadripolar catheter for stimulation. Transseptal access was obtained by 2 separate punctures of the right femoral vein for introduction of SL0 8.5 Fr sheaths (St. Jude Medical, St. Paul, MN, USA), continuously flushed with heparinized saline. After transseptal access, systemic heparinization was started and titrated to an activated clotting time above 300 seconds. For catheter ablation, we used irrigated 3.5 or 4.0 mm RF-ablation catheters, at a maximum power of 30–35 W and an irrigation rate of 20 mL/min. PV isolation was performed by wide circumferential ablation, encircling all ipsilateral PVs. Isolation of a PV was defined as complete disappearance of PV potentials, demonstrated by a multipolar circular diagnostic catheter. To reduce the radiation burden, a fluoroscopy dose setting was chosen that was tuned to a low dose that still allowed proper visualization of catheters, and low energy levels and low frame rate (7.5 fr/s) were used for fluoroscopy. In addition, operators were encouraged to maximize diaphragmation whenever possible.

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CT Overlay An Allura FD10 Xper monoplane X-ray system (Philips Healthcare) was used in combination with a prototype version of EP navigator (Philips Healthcare), allowing superimposition of a segmented 3D image of the LA on the X-ray image (“CT overlay”). The acquired MSCT data set was imported in the software, followed by an automatic segmentation of the different chambers of the heart. This computerderived segmentation was checked manually and corrected if necessary. After correct segmentation of the CT slices, a 3D reconstruction of the LA and proximal PV was constructed. Registration of the 3D CT image to the X-ray image was achieved in a standardized protocol. First, the position of the CT image was adjusted to the superior border of the LA and the superior PV ostia in an anterior-posterior projection (AP, 0◦ ), as the borders of the LA and PVs can be assessed easily by contrast injections into both superior pulmonary veins simultaneously (Fig. 1). Second, in an orthogonal projection (right lateral, RAO 90◦ ) the table height was adjusted until the LA was centered again. A repeated contrast injection in the left upper PV was performed to further adjust the CT image. Last, correct position of the CT image was confirmed by selective contrast injections in both inferior pulmonary veins. After registration and locking, the prototype software offers additional options during the ablation procedure. The 3D CT image will be depicted always in the same angle as the fluoroscopy. In addition, the 3D image can be clipped manually, allowing internal views. Finally, tags can be placed on the surface of the 3D image to mark ablation sites and other sites of interest (Fig. 2). CartoMerge For preparation of the CT images for CartoMerge, Cartosegmentation software was used (Biosense Webster, Inc.). Initially, selective contrast injections were given in all PVs, and each PV ostium was defined by at least 3 tags. Following delineation of the PV ostia, point by point mapping was performed to construct the body of the left atrium. After completion of the LA reconstruction, merging of the CT image and Carto-reconstruction was performed by initial registration of 3 landmarks points, followed by optimization using surface registration.7,14 Endpoints

CT Acquisition CT data were acquired using a 256-slice CT scanner (Brilliance iCT, software version 2.5.1, Philips Health Care, Best, The Netherlands). Slice thicknesses of 0.7–1.0 mm were achieved in all patients. A bolus of 85 mL of contrast (iomeR prol, 400 mg iodine/mL, Iomeron , Bracco, Milan, Italy) was administered intravenously in all patients. A biphasic injection protocol was used: 50 mL at a rate of 5 mL/s, and 35 mL/s at a rate of 2.5 mL/s. Bolus tracking technique was used to monitor the appearance of contrast material in the descending aorta. Images were acquired during inspiratory breath-hold using retrospective ECG gating. Image reconstruction was performed at 40% RR interval and 75% RR interval to receive images in end-systole and mid-diastole, respectively. Time interval between CT acquisition and ablation procedure was 17 ± 16 days.

Procedural success and complications were compared between groups. For additional comparisons, the procedure was divided into (1) mapping/registration time, the time between transseptal puncture and start of ablation, and (2) the ablation time, the time between start of ablation and end of the procedure. The total procedural time was defined as the sum of mapping/registration time and ablation time. Radiation burden was not only measured as fluoroscopy time, but also as Air Kerma (AK), which is a measure for the skin dose, and dose area product (DAP), which reflects the body dose. These estimates were provided by the X-ray system. Statistics All quantitative data are expressed as mean ± SD. For comparison of continuous data, a 2-sided Student’s t-test was used. Comparisons of categorical data were performed

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Figure 1. Registration of 3D CT reconstruction and fluororoscopy. (A) Simultaneous contrast injection in both superior pulmonary veins (AP 0◦ ). (B) Unregistered position of 3D image. Registration in the frontal plane is performed manually. (C) Clipped 3D CT image after registration. (D) Confirmation of registration by contrast injection in the right inferior pulmonary vein (RAO 40◦ ). The multipolar catheter is positioned in the right superior pulmonary vein.

using Fisher’s exact or chi-square test. A P-value < 0.05 was considered to be statistically significant. Results Patients The CT overlay group (Group 1) consisted of 38 patients, and 30 patients were included in the CartoMerge group (Group 2). Baseline characteristics were not different between groups (Table 1). In Group 1, adequate registration of the 3D image to the fluoroscopy could be achieved in all patients. Ablation Procedure Procedural success, defined as isolation of all PVs, could be achieved in 37 patients in Group 1 (97%) and 27 (90%) patients in Group 2 (P = NS). PV isolation could not be achieved in 2 (ipsilateral) veins in 1 CT overlay patient and in a single PV in 2 CartoMerge patients; in 1 Group 2 patient, 2 veins remained unisolated after cessation of the procedure due to a tamponade (Table 2).

The total procedural time in the Group 1 was significantly shorter than Group 2 (129 ± 34 vs 182 ± 30 min, P < 0.0001). Reductions in procedural time were found both for mapping/registration-time (20 ± 8 vs 53 ± 14 min, P < 0.0001) and for ablation-time (109 ± 32 vs 128 ± 25 min, P < 0.01) (Fig. 3A). Radiation Burden Cumulative duration of fluoroscopy tended to be longer in Group 1: 47 ± 16 vs 40 ± 13 min, P = 0.058. While fluoroscopy for mapping/registration was significantly shorter in Group 1 (4 ± 2 vs 14 ± 6 min, P < 0.0001), this was counterbalanced by increased fluoroscopy time during ablation (43 ± 16 vs 25 ± 10 min, P < 0.0001) (Fig. 3B) Measurements of Air Kerma and DAP were comparable between both groups. Total Air Kerma 480 ± 196 vs 440 ± 228 mGy (P = 0.43) and DAP: 53 ± 27 vs 56 ± 35 Gy. cm2 (P = 0.76) (Fig. 3C and D). Complications Two major complications occurred in 2 Group 2 patients (P = 0.31 vs Group 1). In 1 patient, after isolation of the left

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Figure 2. Additional features of the system. Panels (A) and (B) show the instantaneous position of an ablation catheter in 2 fluoroscopic directions, respectively, LAO 23◦ and RAO 39◦ , essential for accurate placement of ablation tags at the surface of the 3D CT reconstruction. (C) By extensive use of diaphragmation a keyhole view can be created to reduce radiation burden, while the complete 3D CT is shown. (D) Complete set of lesions around the right pulmonary vein antrum (LAO 45◦ ).

PVs a cardiac tamponade occurred, with full recovery after surgical intervention. In a second patient, after successful PV isolation a transient stroke occurred. No other major complications were observed.

TABLE 1 Baseline Characteristics

Age, years Male (%) AF history, years Failed AAD LA pslax , mm CHADS, 0/1/>1 AF classification Paroxysmal (%) Persistent (%) BMI, kg/m2

Group 1 CT Overlay (n = 38)

Group 2 CartoMerge (n = 30)

57 ± 11 29 (79) 5±5 2.4 ± 0.6 44 ± 5 20/12/6 71/29 27 (71) 11 (29) 27 ± 3

61 ± 7 22 (73) 6±5 2.4 ± 0.7 43 ± 4 12/14/4 73/27 22 (73) 8 (27) 27 ± 3

Discussion This study shows that a technique of superimposition of a 3D CT image of the left atrium over real-time fluoroscopy is feasible for PV antrum isolation. This application permits fluoroscopy-directed guiding of an ablation catheter and diagnostic catheters in a virtual 3D model of the left atrium, and subsequent tagging of ablation sites, facilitating the operator to create continuous lines and to return to critical ablation sites. Compared to an established and widely used electroanatomic mapping technique for PV antrum isolation, procedural duration can be shortened significantly without concomitant increase in radiation burden.

P-Value 0.10 0.10 0.59 0.99 0.62 0.69 0.84

0.86

Data are given as mean ± SD. AF = atrial fibrillation; AAD = antiarrhythmic drug; LA pslax = left atrium dimension measured at parasternal long axis; BMI = body mass index (kg/m2 ).

TABLE 2 Acute Results and Complications

Complete isolation (%) Isolated PVs/Total PVs (%) Complications Tamponade Stroke Other major

Group 1 CT Overlay (n = 38)

Group 2 CartoMerge (n = 30)

37 (97) 148/150 (99) 0 0 0 0

27 (90) 112/116 (97) 2 1 1 0

P-Value 0.31 0.41 0.19

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Figure 3. Procedural results for both groups. Procedures are divided into mapping/registration time (black bars) and ablation time (white bars). Data are shown as mean + SD. (A) Procedural time. (B) Fluoroscopy time. (C) Air Kerma. (D) Dose area product.

Registration Adequate registration of the 3D CT image to the real-time fluoroscopy could be achieved in a relatively short time in all patients. The sequential alignment in 2 orthogonal directions allows this technique to be used with monoplanefluoroscopy, whereas other techniques require use of biplane fluoroscopy.13,15 Compared to this latter technique,13 manual calibration of images was not necessary, as this was done by software automatically. Also, rotational adjustments were not necessary, provided the patient was in the same supine position as during the CT acquisition. Ector et al.13 found that registration improved after matching certain landmarks, such as PV bifurcations, between 3D image and fluoroscopy; this technique requires detailed angiography and 3D reconstruction of the more distal PVs beyond the ostia. However, we found that good registration could be achieved by matching the borders of the LA and the proximal PVs only. It may be questioned whether a perfect match between the 3D CT image and the fluoroscopy can be achieved. There always will be inaccuracies due to differences in heart rate and rhythm,7 volume status, and changes over time particularly when there is a large time delay between CT acquisition and procedure.14 An additional source for discrepancies between fluoroscopy and 3D mages is respiratory motion, as CT is usually acquired during inspiratory breath-hold, while ablation is performed during all phases of normal respiration. As the left atrium shows only minor changes with respiration, we feel that registration to the borders of the left atrium and proximal PVs will be more reliable than matching landmarks more distally in the PV branches.16,17 New methods for registration include the use of intracardiac ultrasound, which may improve designation and definition of intracardiac landmarks.18 As an alternative to CTderived 3D images, rotational 3D reconstructions of the left atrium can be used for overlay, minimizing the time delay between image acquisition and procedure and coming closer to real-time 3D imaging.19

A major advantage of the current technique is the ability to tag ablation sites on the 3D image, facilitating the creation of a narrow, continuous ablation line and allowing the operator to return to critical ablation sites. In previous overlay studies, simultaneous use of an electroanatomic mapping system was required to mark these sites.12 Comparison to Electroanatomic Mapping Electroanatomic mapping systems are widely used for ablation of atrial fibrillation.1 Comparison of these techniques to conventional ablations shows no unequivocal results: while procedural duration and radiation dose tend to decrease in some reports,5,6 increases of these parameters have been showed by other investigators.20 Merging catheter-based LA reconstructions with previously acquired CT or MRA images may further improve AF ablation, also resulting in better outcomes.7-9,20 In our study, we observed a reduction in procedural time, both in mapping time and ablation time, without concomitant increase in radiation burden. The reduction in mapping time may be attributed to fact that the construction of a point-by-point map can be omitted and the process of registration involves matching of PV ostia and LA borders only. The difference in ablation time is more striking and we can not explain this difference. An additional advantage of the overlay technique, particularly when used for patients under conscious sedation, is the ability to perform a quick reregistration in case of major changes in the patients’ position. However, unlike the Carto system that is giving an alert for patient movements, the operator needs to be alert on discrepancies between catheters and anatomy, and check registration in case of suspected movement. Radiation Burden Long, complex ablation procedures expose both patients and medical workers to high radiation burden. Radiation dose is related to fluoroscopy duration, but is influenced also by

Stevenhagen et al. CT Overlay for PV Antrum Isolation

frame rate during fluoroscopy, radiation beam energy, area of the beam (diaphragmation), beam angulation and patient characteristics, such as body mass.21 Although in our CT overlay group the fluoroscopy duration was longer than in the Carto group, the other measures for radiation burden (Air Kerma and DAP) were comparable. The observed relative low radiation burden in the CT overlay group is explained by the ability to show the entire CT image around diaphragmated area, allowing more extensive use of diaphragmation (“keylock” imaging) to locate the ablation catheter (Fig. 2). In addition to the radiation burden of the ablation procedure, CT acquisition also adds to the total radiation burden for the patient. As an alternative to CT, MRA can be used, both for CartoMerge procedures and for overlay, although, at present, the optical resolution is less than in CT.

6. 7.

8.

9.

Limitations Although patients were randomized between CartoMerge and CT overlay, operators were not blinded and bias cannot be excluded. A disadvantage of both EP navigator and CartoMerge is the reliance on a previously acquired CT image. Although it has been shown that differences in size between these CT images and the actual LA size are minor, major differences may occur; in Carto, one can return to the catheter-based LA reconstruction without Merge, which may be more accurate than the CT image. New versions of EPnavigator will allow for intraprocedural rotational scanning of the LA.19

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11.

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Conclusion 14.

This study shows that integration of a 3D CT reconstruction of the left atrium with conventional fluoroscopy is feasible for PV antrum isolation. In comparison to an established and widely used electroanatomic mapping technique, procedural duration can be shortened without a concomitant increase in radiation burden.

15.

16.

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