Ann Thorac Surg 2006;82:1091-1093
© 2006 The Society of Thoracic Surgeons
Case report
Intraoperative Electro-Anatomical Mapping and Beating Heart Ablation of Ventricular Tachycardia
Sekar S. Bhavani, MDa,
Patrick Tchou, MDb,
Mina Chung, MDb,
Tamer Fahmy, MDb,
A. Marc Gillinov, MDa,*
a Department of Thoracic and Cardiovascular Surgery, The Cleveland Clinic Foundation, Cleveland, Ohio
b Department of Cardiovascular Medicine, The Cleveland Clinic Foundation, Cleveland, Ohio
Accepted for publication December 8, 2005.
* Address correspondence to Dr Gillinov, Department of Thoracic and Cardiovascular Surgery, The Cleveland Clinic Foundation/F24, 9500 Euclid Ave, Cleveland, OH 44195 (Email: gillinom{at}ccf.org).
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Abstract
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In most cases ventricular tachycardia is responsive to antiarrhythmic drug therapy. If antiarrhythmic drugs fail, then percutaneous, endocardial ablation guided by electro-anatomical mapping is usually curative. Occasionally neither of these therapies is successful and surgical ablation is required. Challenges encountered in surgical ablation include application of reliable intraoperative real-time electro-anatomical mapping to identify the focus of ventricular tachycardia and the need for technology that enables ablation on the beating heart. We present a case demonstrating the feasibility of surgical cryoablation of ventricular tachycardia arising from the right ventricle using intraoperative real-time epicardial and endocardial electro-anatomical mapping and argon-based cryoablation.
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Introduction
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Ventricular tachycardia (VT) usually responds to antiarrhythmic drug therapy. If medical therapy fails, percutaneous, endocardial ablation guided by electro-anatomical mapping is the next step. When neither of these therapies is successful, surgical ablation is an option. Challenges associated with surgical ablation of VT include the needs for reliable intraoperative real-time electro-anatomical mapping to identify the focus of VT and for technology that enables ablation on the beating heart. We present a case demonstrating the feasibility of surgical cryoablation of VT arising from the right ventricle using intraoperative real-time epicardial and endocardial electro-anatomical mapping and argon-based cryoablation.
A previously healthy and physically active 45-year-old man presented with recurrent episodes of palpitations. Cardiac monitoring demonstrated multiple runs of VT. A 12-lead electrocardiogram revealed a tachycardia with left bundle branch block and superior axis. Because of the frequently recurrent nature of the tachycardia, an ablation was recommended. However, with endocardial delivery of radiofrequency lesions to the right ventricular early activation site, the tachycardia became incessant. A second percutaneous ablation was then attempted using both an endocardial approach and an epicardial approach. Earliest activation sites were identified at the inferoseptal portion of the right ventricular endocardium. However, radiofrequency applications at those sites could not eliminate the VT. The patient was then transferred to the Cleveland Clinic Foundation with the diagnosis of idiopathic VT arising from the right ventricle. A third percutaneous ablation using a saline cooled catheter was attempted. Mapping confirmed the right ventricular source of VT and ablation was temporarily successful at suppressing the arrhythmia. Figure 1
shows the endocardial map of the VT and a segmented 3-dimensional computed tomographic image of the ventricles, demonstrating the region from which the VT arose. However, within 1 week the patient returned to incessant VT. Because the focus was not amenable to a percutaneous approach to ablation, the patient was offered surgical ablation.
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Fig 1. CARTO (Biosense-Webster, Diamond Bar, CA) and segmented 3-dimensional computed tomographic images of the left and right ventricles. The image to the left is a CARTO endocardial electro-anatomical map (Biosense-Webster); the red color on the map denotes the site of earliest activation in the right ventricle and is the area targeted for ablation. The image on the right is a 3-dimensional computed tomographic image of the left and right ventricles. Both images are oriented to show an inferior view of the ventricles with the right ventricle on the left and the left ventricle on the right; the apex of the heart is pointing up.
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The operating room setup included a special bed with a large, metal-free space to enable mapping with an electro-anatomical system (CARTO [Biosense-Webster, Diamond Bar, CA]). After induction of general endotracheal anesthesia, a median sternotomy was performed and epicardial mapping commenced. Two epicardial temporary pacing leads were placed on the anterior-lateral surface of the left ventricle to provide an electrical activation reference. The epicardial surface of the right ventricle was then mapped in a point-by-point fashion using a standard 4-mm electrode mapping catheter (Navistar [Biosense-Webster]). This system consists of an external magnetic field emitter on which the patient lays, a miniature magnetic field sensor on a deflectable catheter tip, and an external processing unit. The external magnetic field emitter generates three different ultra-low magnetic fields. The miniature magnetic field sensor is used to acquire information regarding the position of the catheter tip on the heart and the local activation time in relation to the fixed epicardial ventricular electrogram. As the catheter is moved from point to point along the epicardial surface, the local activation time at each site is recorded. This electro-anatomic information is then displayed on a computer generated map showing the 3-dimensional location of each point, color coded for activation time. Using this technique, the epicardial site of earliest VT activation was identified; it corresponded to previous maps created in the electrophysiology laboratory and confirmed the ablation target for the surgical team.
A 25-mm cryoprobe (Cooper Surgical, Shelton, CT) was placed on the right ventricular epicardium in the region with the earliest activation. After 2 minutes with this nitrous oxide based cryo system, the temperature reached –30°C to –50°C and sinus rhythm was restored; however, during thawing VT recurred. This cycle was repeated several times. Because of the inability to terminate the arrhythmia permanently, we elected to perform endocardial cryoablation on cardiopulmonary bypass.
After bi-caval and ascending aortic cannulation, the patient was placed on cardiopulmonary bypass. The caval snares were tightened and the right atrium was opened. The mapping catheter was then advanced into the right ventricle under direct vision and an endocardial electro-anatomical map was created. The site of earliest activation was identified; this corresponded to epicardial maps generated preoperatively and in the operating room. Visual observation of the area of endocardial early activation showed that it was located at the base of the septal papillary muscle in a region with unusually deep trabeculations. Sites of prior endocardial radiofrequency lesions were visually identifiable during mapping of the right ventricular endocardium. These lesions seemed to be mostly near the surface of the trabeculations. The location of early activation at the base of the papillary muscle and the deeper than usual trabeculations at that site may have been factors rendering the catheter ablation unsuccessful.
Endocardial cryoablation at –30°C to –50°C temporarily terminated the VT, which recurred each time the tissue thawed. At this point we elected to change ablation technology in order to create a deeper lesion. Using an argon-based cryoablation system (CryoCath Technologies, Montreal, Canada) we performed endocardial ablation at –160°C. At this temperature the patient converted to sinus rhythm in 15 seconds. A 2-minute, oval-shaped lesion measuring 3 cm in greatest diameter was created surrounding the endocardial region of earliest activation. After thawing, the patient was weaned from cardiopulmonary bypass and the heart rhythm was monitored for 30 minutes. Sinus rhythm was maintained.
The patient recovered from surgery without difficulties and with no recurrence of VT. He was discharged on postoperative day 4 taking only a low dose of beta-blocker. At 1-month follow-up the patient reported no symptoms and an electrocardiogram confirmed normal sinus rhythm.
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Comment
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In most cases suppression of frequently occurring or incessant VT can be achieved with antiarrhythmic drugs or percutaneous endocardial or epicardial ablation [1]. Occasionally these modalities fail and surgical ablation is necessary [2]. Surgical ablation provides direct visualization of the sites of early activation. At surgery, high-powered cryoablation tools can be applied to these regions facilitating deeper ablation. To optimize success, surgical ablation of VT should incorporate electro-anatomical mapping and ablation on the beating heart using a technology that enables creation of a deep lesion. The Biosense-Webster CARTO system can be adapted for operating room use with minor effort; this requires use of an appropriate surgical table that does not interfere with the magnetic fields of the mapping system. This mapping technology generates anatomic information that easily guides the surgeon to the target for ablation. Argon-based cryoablation facilitates treatment [3]. Although we did not attempt epicardial, off-pump ablation with the argon-based system, it is possible that such a procedure would ablate the arrhythmia, particularly with the lower temperatures achieved with argon-based cryoablation. This approach, with some modification of ablation and mapping catheters, may also facilitate minimally invasive or percutaneous epicardial ablation of VT [4].
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References
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- Joshi S, Wilber DJ. Ablation of idiopathic right ventricular outflow tract tachycardiacurrent perspectives. J Cardiovasc Electrophysiol 2005;16:S52-S58.
- Braun MU, Knaurt M, Rauwolf T, Strasser RH. Microwave ablation of an ischemic sustained ventricular tachycardia during aortocoronary bypass, mitral valve and tricuspid valve surgery guided by a three-dimensional nonfluoroscopic mapping system (CARTO) J Interventional Card Electrophysiol 2005;13:243-247.
- Doll N, Kiaii BB, Fabricius AM, et al. Intraoperative left atrial ablation (for atrial fibrillation) using a new argon cryocatheterearly clinical experience. Ann Thorac Surg 2003;76:1711-1715.[Abstract/Free Full Text]
- Sosa E, Scanavacca M. Epicardial mapping and ablation techniques to control ventricular tachycardia J Cardiovasc Electrophysiol 2005;16:449-452.[Medline]
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Abstract
Introduction
