EP Lab Digest - October 2007 - (Page 15)

OCTOBER 2007 EP CASE STUDY 15 mapping was used to map the earliest local activation of APCs with respect to the atrial electrogram from electrodes 5 and 6 on the coronary sinus. Activation mapping was performed using the CARTO mapping system. The earliest activation was 82 msec earlier than the surface P-wave, and was located along the mid portion of the crista terminalis in the posterolateral right atrium. Atrial pacing failed to demonstrate entrainment, and the activation map was consistent with a focal source. High output pacing revealed no evidence of phrenic nerve stimulation. Application of a single radiofrequency (RF) lesion with 50 watts of power and a temperature limit of 60 degrees for 60 seconds to this area resulted in acceleration of the tachycardia followed by complete cessation of the arrhythmia and normal sinus rhythm. Five additional RF lesions were empirically placed in a circular pattern around the initial lesion; none of these resulted in atrial premature beats of tachycardia. At threemonth follow-up, the patient had no recurrence of his palpitations. the clinical morphology, followed by abrupt termination of the patient’s arrhythmia. A second lesion was empirically applied in the same region, but did not induce PVCs. At two-month follow-up, the patient had no evidence of recurrence of his PVCs or monomorphic VT. Discussion These cases demonstrate the utility of magnetically-guided robotic navigation for mapping and ablation of focal tachycardias. In the first case, Stereotaxis allowed us to map in precise 1° deflections and 1-mm steps, which allowed for accurate and reproducible activation and pace mapping. By creating a stored magnet orientation for the site of earliest activation, we could return to the location of interest with remarkable precision, in this case, the crista terminalis. Tissue contact is affected only by the direction of magnetic field and reach of the soft, floppy catheter. As a result, application of a magnetic vector allows the ablator tip to remain fixed to the endocardium and is largely unaffected by respiratory and cardiac motion. Finally, because the position of the soft, floppy magnetic catheter is not dependent on catheter stiffness, guiding sheath, or operator pressure, there is virtually no risk of perforation. In the second case, we were interested in mapping the right ventricular outflow tract for focal VT. With a conventional steerable catheter, the right ventricular outflow tract is difficult to navigate with a catheter that only deflects in a single plane. To compensate, the operator must rotate the system and rely on torque transmission to guide the ablation catheter. This strategy makes navigation and dense contact mapping difficult, particularly in large or hyperdynamic ventricles, where catheter reach can be compromised.3 During ablation, cardiac systolic motion may cause the ablation catheter to slide, leading to inadequate lesion formation and increased perforation risk. By using 1-mm and 1-degree magnetic navigational increments, we were able to form a dense and complete activation map. At the point of earliest activation, we reproduced a perfect surface ECG pace map. However, in our experience, even small 1-degree or 1-mm movements from the VT focus led to imperfect pace maps, which emphasize the importance of fine mapping for precise localization.4 In both cases, a single RF lesion with a 4 mm ablation tip resulted in apparent elimination of the clinical arrhythmia. Figure 2. Posteroanterior and right lateral views of the CARTO™ activation map of the right atrium. The right plane shows the electrogram of the site of earliest activation. Case Report #2 A 44-year-old man with a history of myocarditis presented with frequent monomorphic premature ventricular complexes (PVCs) and wide complex tachycardia documented by ambulatory ECG monitoring. His ejection fraction was normal. He was taken to the electrophysiology lab, where frequent monomorphic PVCs were present in the baseline state. The PVCs had left bundle branch block morphology with an inferior axis, consistent with origin from the right ventricular outflow tract. Programmed ventricular stimulation did not induce sustained VT or VF. Electroanatomic mapping was performed using a 4 mm NaviStar RMT catheter. The Stereotaxis system was used to navigate the catheter for contact mapping. After creating a three-dimensional anatomic shell of the right ventricular with the tricuspid and pulmonary valves, contact mapping was used to create an activation map in reference to the surface maximum intrinsicoid deflection of the QRS of the PVC on surface lead II.The earliest activation was 101 msec earlier than the reference deflection, and was mapped to the posterior aspect of the septal mid right ventricular outflow tract (Figure 3). Pacing at this spot resulted in a perfect morphologic match to the PVC in all 12 ECG leads. Application of a single RF lesion (50 watts and 60 degree limit) resulted in a flurry of PVCs identical to Figure 3. Anteroposterior and right anterior oblique views of the CARTO™ activation map of the right ventricle. The right plane shows the electrogram of the site of earliest activation (-101 msec). In a thirteen-month period, 108 ablations were performed at our institution using the Stereotaxis system, including nine accessory pathways, ten slow pathway modifications, nine right ventricular outflow tract tachycardias, 60 atrial fibrillation ablations, and twelve atrial tachycardias (focal and macroreentrant). In six cases (two accessory pathways; three left atrial ablations; one right ventricular dysplasia), the operators switched to a manual catheter system in order to use an 8-mm electrode tip (when previously not available for use with Stereotaxis), an irrigated tip ablation catheter, or because of the concern of insufficient catheter contact. In all 108 cases, there were no perforations or Stereotaxis equipment malfunctions. In summary, the use of magnetic navigation is a feasible and effective approach for treatment of focal tachycardias. Although the technology has primarily been used for atrial fibrillation ablation, it can be successfully used for focal right atrial and right ventricular ablations.While there are no randomized trials evaluating the benefits of remote magnetic navigation for focal tachycardias, the technology may be useful when dense activation or pace mapping is required, or when handheld catheter manipulation is difficult due to the patient’s anatomy or cardiorespiratory motion. References 1. Ernst S, Ouyang F, Linder C, et al. Initial experience with remote catheter ablation using a novel magnetic navigation system: Magnetic remote catheter ablation. Circulation 2004;109:1472–1475. 2. Di Biase L, Fahmy T, Patel D, et al. Remote magnetic navigation: Human experience in pulmonary vein ablation. J Am Coll Cardiol 2007;50:868–874. 3. Thornton A, Jordaens L. Remote magnetic navigation for mapping and ablating right ventricular outflow tract tachycardia. Heart Rhythm 2006;3:691–696. 4. Gumbrielle T, Bourke J, Doig J, et al. Electrocardiographic features of septal location of right ventricular outflow tract tachycardia. Am J Cardiol 1997;79:213–216. Editor’s Note: This article was peer reviewed by one or more members of EP Lab Digest’s editorial board.

Table of Contents Feed for the Digital Edition of EP Lab Digest - October 2007

Finally! The New Registered Cardiac Electrophysiology Specialist (RCES) Credential: Interview with Christopher M. Nelson, RN, RCIS, FSICP ECG 101: Closing the Gap Phenomenon Contents Letter from the Editor ICD Patient Support Group: St. Peter’s Hospital Spotlight Interview: Community Healthcare System Use of Magnetic Catheter Navigation for Ablation of Focal Tachycardias Echocardiography: The Preeminent Front Line Screening and Diagnostic Tool for Cardiovascular Imaging and Physiological Assessment First Annual EP Lab Digest Salary Survey: Last Chance! Clinical Trial Update: 2007 Email Discussion Group Adopting and Implementing the AF Ablation Consensus Statement Electrophysiology in the West Summit Events Calendar The Sustained Treatment of Paroxysmal Atrial Fibrillation (STOP AF) Clinical Trial: Interview with Kevin Wheelan, MD Industry News and Products

EP Lab Digest - October 2007

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