Ann Thorac Surg 2003;75:1189-1193
© 2003 The Society of Thoracic Surgeons
Original article: cardiovascular
Cardioscopic guidance of linear lesion creation for radiofrequency ablation
Yoshito Inoue, MDa*,
Ryohei Yozu, MDb,
Katsuhisa Onoguchi, MDc,
Nobuyuki Kabei, PhDc,
Shigeyuki Takeuchi, MDc,
Shiaki Kawada, MDb
a Department of Cardiovascular Surgery, Saiseikai Utsunomiya Hospital, Tochigi, Japan
b Department of Surgery, Keio University School of Medicine, Tokyo, Japan
c Saitama Cardiovascular and Respiratory Center, Saitama, Japan
Accepted for publication October 29, 2002.
* Address reprint requests to Dr Inoue, Department of Cardiovascular Surgery, Saiseikai Utsunomiya Hospital, 911-1 Takebayashi, Utsunomiya, Tochigi 321-0974, Japan
e-mail: yosito_inoue{at}saimiya.com
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Abstract
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BACKGROUND: The broad use of catheter ablation of atrial fibrillation is limited by the difficulty inherent in creating transmural linear lesions under fluoroscopy. Therefore, we evaluated cardioscopy as a more accurate method of guiding the catheter for the placement of linear lesions.
METHODS: Nineteen swine underwent endocardial ablation to create linear conduction block lesions in the right atrium under cardioscopy (group I, n = 13) or fluoroscopy (group II, n = 6). In both groups, the linear lesion was created between the superior and inferior vena cava, perpendicular to hexapolar electrodes placed on the epicardial surface. Each swine received two pairs of epicardial hexapolar electrodes: one pair to measure the conduction delay time across the ablated line and another pair for pacing. The time spent to complete the ablation, number of trials and effective ablations, ratio of effective ablations to trials, length of the lesion, conduction delay under pacing, and postmortem pathology were compared between the two groups.
RESULTS: Statistically significant differences were found for the time required for ablation, ratio of effective ablation to total number of trials, and conduction delay. Histologic analysis revealed more homogenous, continuous lesions in group I.
CONCLUSIONS: Cardioscopy facilitated the placement of a conduction block line more efficiently than ablation performed under fluoroscopy. Landmarks of tissue relevant to ablation are readily visualized by cardioscopy. Moreover, cardioscopy can be useful for the development of a guiding catheter for the ablation of atrial fibrillation.
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Introduction
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Radiofrequency (RF) ablation is widely used for the treatment of cardiac arrhythmias in both medical and surgical fields. For the nonpharmacologic treatment of atrial fibrillation (AF), RF ablation is used not only for catheter-based ablation but also for intraoperative ablations concomitant with cardiac operations [1–4].
Catheter-based treatment is less invasive than surgical treatment, but in the case of AF the success rate of treatment is lower than with maze surgery, and complications such as pulmonary vein stenosis are of concern [5]. Postprocedural recurrence of AF sometimes requires additional catheterizations. These disadvantages are related to the limited visibility of anatomic landmarks under fluoroscopic guidance, the difficulty in confirming electrode–tissue contact, and discontinuity of the conduction block line.
In an attempt to solve these problems, other methods of anatomic guidance for endocardial linear ablation, such as intracardiac ultrasonography, have been reported [6, 7]. Despite these studies, however, no breakthrough has been made. Confirming the ablation line during RF ablation under suboptimal anatomic guidance is difficult and takes a long time, leading to AF recurrence and increased occurrence of thromboembolic events. To overcome these current difficulties, optimal anatomic guidance is essential for a catheter-based treatment of AF.
Intracardiac endoscopy [8, 9] is still an experimental procedure, which enables direct vision of intracardiac structures and electrode–tissue contact. We compared cardioscopy with fluoroscopy as a guide for the placement of linear lesions.
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Material and methods
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Animals
Nineteen domestic swines underwent endocardial ablation to create a linear lesion of the conduction block in the right atrium (RA) under cardioscopy (group I, n = 13) or fluoroscopy (group II, n = 6). The swines (weighing 16 to 46 kg) were premedicated with ketamine hydrochloride (500 mg) and atropine sulfate (2 mg) administered by intramuscular injection. Anesthesia was maintained with 5% pentobarbital sodium and pancuronium bromide administered by intravascular injection every 30 minutes. The animals were ventilated mechanically with room air. The level of anesthesia and limb-lead electrocardiogram were monitored throughout the procedure. Through cutdowns, the right jugular vein was dissected to allow the introduction of the ablation and endoscopic catheters. All animals received humane care in compliance with the "Guide for the Care and Use of Laboratory Animals" (National Institutes of Health publication 85-23, 1996).
Procedures
Linear lesions were created with a 7F 4-mm steerable ablation catheter (Cerabrate, OSYPKA GMBH Medizintechnik; NEC Medical Systems Co, Ltd, Tokyo, Japan). After positioning the catheters, RF energy was delivered by an RF generator capable of delivering up to 50 W. The generator was set to deliver energy for as long as 30 seconds and achieve a temperature of 70°C. The power was regulated by feedback from the two thermocouples mounted on each ablation coil. Temperature, impedance, and power were monitored for each delivery of energy.
For cardioscopy, a newly developed catheter consisting of a spindle-shaped latex balloon to create bloodless visual fields was used for intracardiac endoscopic imaging (5.6-mm flexible end-viewing endoscope: Pentax Co, Ltd, Tokyo, Japan) (Fig 1).
These cardioscopic catheters have a tip-mounted ablation catheter connected to an ablation generator (HAT300S, OSYPKA GMBH Medizintechnik). Images were viewed in real time and recorded on videotape. The cardioscopic catheter was positioned in the RA through the right jugular vein. Before each delivery of energy, the cardioscopic catheter was manipulated to obtain an optimal view of the electrode. The catheter was withdrawn or advanced to ensure that the entire coil–tissue connection was visualized.
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Fig 1. The cardioscopy device is a 5.6-mm flexible endoscope provided with a spindle-shaped balloon filled with saline and a tip-mounted ablation catheter.
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In each swine, two pairs of hexapolar electrodes were placed on the epicardial surface of the RA through median sternotomy. Linear lesions were created perpendicular to the hexapolar electrodes, between the superior and inferior vena cavas (Fig 2).
The catheter contains six flexible coil electrodes with thermocouples embedded in each coil.
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Fig 2. Scheme of the experimental ablation line (thin dotted line). The conduction block line was made at the endocardial side, which was perpendicular to the epicardial hexapolar lead. (Ao = aorta; IVC = inferior vena cava; PV = pulmonary vein; RA = right atrium; RV = right ventricle; SVC = superior vena cava.)
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Cardioscopic guidance imaging was performed in group I (n = 12), whereas the catheter locations and stability were determined under fluoroscopic guidance alone in group II (n = 7). In group I, the ablation operator used the cardioscopic images to guide placement of the ablation coils and optimize coil–tissue contact. In this group, energy was not delivered if the coil–tissue contact was thought to be poor, based on the cardioscopic image. The ablation catheter was positioned at the desired region in contact with the endocardium. Linear lesions were created by applying energy to the ablation coils. In some regions, the linear lesion could not be completed with a single catheter placement. In these cases, the catheter was repositioned, under either fluoroscopic or cardioscopic guidance, to extend the lesion from the location of the previous energy application. Cardioscopy was used in group I to optimize completion of each linear lesion by ensuring a successful delivery of energy along the entire endocardial length of the desired target region.
In both groups, one pair of the epicardial hexapolar electrodes was used to measure the conduction delay time across the ablated line and the other pair was used for pacing. We compared the time spent to complete the ablation, number of trials and effective ablations, ratio of effective ablations to total number of trials, length of the lesion, and conduction delay during pacing. An application of RF energy was considered successful if the energy was delivered for a full 30 seconds and the tissue attained a temperature of more than 60°C. The procedure was completed when a linear transverse lesion was created on the right atrial free wall that was sufficient to cause conduction block.
After completion of the procedure, the animals were killed humanely and the ablated lesions of the RA were examined. The RA tissue was stained with hematoxylin-eosin, and the lesions were bisected longitudinally to assess the continuity and depth of the lesions and to determine whether they were linear or transmural.
Statistical analysis
Values are presented as the mean ± SD. Variables were compared using Mann-Whitney’s U test. Differences were considered significant if the p value was less than 0.05.
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Results
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Right atrial endocardial anatomy was well visualized in all animals under cardioscopic guidance, and the ablation coils were easily identified (Fig 3).
The course of linear ablation and level of thermal degeneration of the ablated tissue could also be observed and coil–tissue contact was easily evaluated for each of the 133 energy applications attempted by cardioscopic imaging during the procedure (Fig 4).
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Fig 3. Cardioscopic image of radiofrequency endocardial ablation. Two prior lesions are observed as dents filled with blood surrounded by heat-degenerated atrial tissue (arrows).
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Fig 4. A continuous lesion was created by an additional ablation placed next to the previous lesion. The area of heat degeneration is identified by the difference of tissue color at the lower portion of this figure (arrowheads).
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Cardioscopic guidance resulted in a higher rate of successful energy application, with shorter procedural time and the formation of a firmer conduction block line, compared with fluoroscopic guidance alone (Table 1).
The time to complete the procedure was 11.3 ± 4.72 minutes in group I and 27.8 ± 19.9 minutes in group II (p = 0.03). The number of applications of ablation energy was 10.2 ± 2.87 in group I and 15.8 ± 4.50 in group II (p = 0.03). Although the difference between the groups in the number of effective ablations was not significant (9.38 ± 2.77 in group I and 9.25 ± 5.38 in group II, p = 0.96), the difference was significant in the ratio of effective ablations to total number of trials: 0.92 ± 0.11 in group I and 0.58 ± 0.34 in group II (p = 0.02). In other words, 92% of cardioscopy-guided attempts were successful compared with only 58% of the fluoroscopy-guided attempts. The conduction delay time was 38.8 ± 17.4 ms in group I and 13.3 ± 4.27 ms in group II (p = 0.01). The length of the created lesion, which was measured at the endocardial site of RA, was not statistically significant (34.7 ± 17.4 mm in group I and 18.0 ± 6.06 mm in group II; p = 0.10).
Pathologic evaluation revealed that cardioscopic guidance improved the continuity, completeness, and placement of linear right atrial lesions. Although transmural linear heat degeneration was observed in both groups in the same anatomic region previously observed on cardioscopy, the extent of heat degeneration was more homogenous (linear) in group I (Fig 5A),
compared with group II (Fig 5B). Discontinuous segments (gaps) were observed between the ablated lesions in group II. No heat-induced perforations were observed under the experimental conditions (70°C and 30 seconds) in either group. Examination of the RA endocardium revealed no thrombus formation inside the RA cavity.
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Fig 5. Microscopic photographs of the ablated lesion showing heat degeneration in the same anatomic region as previously observed by cardioscopy. (A) In group I, the extent of heat degeneration was more homogenous and linear. (B) In group II, discontinuous segments (gaps) were observed between the ablated lesions. (Hematoxylin and eosin; x25 before % reduction.)
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Comment
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The purpose of this preliminary experiment was to compare cardioscopy with fluoroscopy for anatomic guidance during intraatrial RF ablation. Our results have demonstrated the superiority of cardioscopy over fluoroscopy for this purpose. Cardioscopy allowed us to obtain real-time anatomic landmarks for RA endocardial ablation under direct vision, which in turn allowed the creation and confirmation of continuous linear lesions in a shorter time than with fluoroscopy. The accuracy of RF ablation was also reflected by the higher rate of successful energy application, accompanied by shorter procedural time and the formation of a firmer conduction block line.
Haissaguerre and colleagues [1] reported that the spontaneous initiation of AF due to ectopic beats originates mostly from the pulmonary veins, and application of RF energy at these focal sources is effective to terminate the AF. Their findings appear to have affected the treatment of AF, which changed from involving the production of multiple linear conduction block lines inside the atria [10] to a minimal number of ablations for electrical disconnection of pulmonary veins [11, 12]. Although our experiment was performed in the right atria, cardioscopic guidance is also useful for electrical isolation of pulmonary veins under direct anatomic guidance, for which we do not need to spend time for left atrial mapping.
The main limitations of our study are that we did not attempt to visualize the left atrium and we did not evaluate the effectiveness of lesion creation for controlling AF. Further studies are necessary to evaluate whether our device is useful for controlling AF in humans.
Despite its limitations, this study provides the basis for overcoming problems inherent with catheter-based treatment and surgical invasion by virtue of its advantages, which include easy production of a conduction block line and direct video image. These factors are important to overcome problems associated with RF catheter ablation at present. Cardioscopic guidance may also allow us to treat other arrhythmias besides AF.
Based on our results, we conclude that the landmarks of tissue relevant to ablation are readily visualized under cardioscopy, and that this technique is more efficient than fluoroscopy for the placement of a conduction block line. Cardioscopy may be useful for developing a guiding catheter for the ablation of AF in humans.
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References
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Abstract
Introduction
