심방세동 중 정방향 좌측 방실부전도의 도자절제술

International Journal of Arrhythmia 2011;12(2): 50-53.

ECG & EP CASES

심방세동 중 정방향 좌측 방실부전도의 도자절제술
Jun Kim, MD Department of Internal Medicine, Pusan National University School of Medicine, Pusan National University Yangsan Hospital, Yangsan, Korea

Case

A 23-year-old man with Wolff-Parkinson-White syndrome and atrial fibrillation was referred for catheter ablation. He had recurrent paroxysmal palpitations since childhood. He underwent direct current cardioversion of preexcited atrial fibrillation (AF) 15 months before admission. Past medical history was unremarkable. Physical examination was normal. A 12-lead electrocardiogram shows delta waves with negative polarity in lead aVL and positive polarity in lead V₁, suggestive of left free wall accessory pathway (Figure 1A). Echocardiography was normal.

   After an informed consent was obtained, a cardiac electrophysiologic study was performed under fasting conditions. Sedation and analgesia was administered using propofol and morphine. Multipolar electrode catheters were advanced into the femoral veins and positioned in the right atrium, His-recording region, right ventricular apex and coronary sinus. Preexcited AF occurred spontaneously. During preexcited AF, the shortest RR interval was 214 ms (Figure 1B). Immediate recurrence of AF by an earlier atrial ectopy at the high right atrium was noted after each attempt of 3 successful direct current cardioversion (Figure 2). Based on the clinical history of preexcited AF, short RR interval during AF and atrial vulnerability during the study, catheter ablation of the bypass tract was performed.
   After successful transseptal catheterization and heparinization (100 units/kg), a 7-Fr conventional ablation catheter with a 4 mm distal tip was advanced through the transseptal sheath. Earlier ventricular activation was noted at the lateral mitral annulus where ventricular electrograms, preceding the onset of delta wave by 25 ms, and QS pattern on unipolar electrograms were noted (Figure 3A, B). Application of radiofrequency energy (50 W, 60 °C) at the site abolished the ventricular preexcitation in 4 seconds (Figure 3C). Total energy delivery time was 140 seconds.
   After restoration of sinus rhythm by an electrical shock, there was no antegrade and retrograde conduction via the bypass tract. There was only retrograde nodal conduction without antegrade dual AV node physiology. AF was induced by a single atrial extrastimulation (A₁A₁ 500 ms, A₁A₂ 220 ms) and was electrically cardioverted to sinus rhythm. During infusion of isoproterenol up to 20 mcg/min, there was no atrial ectopic beat or AF. Procedure was finished without complication. Total procedural time, fluoroscopic time was 80 and 6 minutes, respectively.
   He had no recurrence of ventricular preexcitation or AF during 1- year-follow-up period.

   Discussion

   We report a successful catheter ablation of antegrade accessory pathway during AF guided by intracardiac electrogram analysis.
   Catheter ablation of bypass tracts is established treatment for symptomatic patients with manifest or concealed bypass tracts.¹ Targeting of the ablation site is determined by local AV interval, local V-QRS onset interval during sinus or atrial pacing or local VA interval during ventricular pacing or VA interval during AV reentrant tachycardia.^2,3
   If AF complicates the ablation procedure of ventricular preexcitation, electrical or pharmacologic cardioversion can be tried. As in this case electrical cardioversion requires deep sedation and even immediate recurrence of AF may complicate the procedure. Pharmacologic cardioversion can be tried. However, amiodarone, the only available intravenous antiarrhythmic drug effective in AF in Korea is not useful because it has a delayed onset compared with other class IV drugs and may block accessory pathway conduction.
   Hindricks et al. reported that mapping of a,site with Kent bundle potential and analysis of unipolar electrogram recorded at the mapping catheter was useful in targeting the optimal target sites in preexcited AF.⁴ We could not record Kent bundle potential at the target site. However, a unipolar electrogram was used for determining the optimal target site. Multiple AF waves can distort the local ventricular electrogram and hamper the analysis of local activation time especially in the distal bipolar electrogram. Because there was no atrial signal in the unipolar electrogram, unipolar electrogram can be invaluable to determination of local activation time. To obtain noise-less unipolar electrogram, an independent electrode in the inferior vena cava should be used as an indifferent electrode rather than the Wilson central terminal.
   Regarding the origin of atrial fibrillation in this patient, the right superior pulmonary vein or the superior vena cava is the probable site of origin. Because ① ablation of the bypass tract is sufficient in eliminating atrial fibrillation, especially in young patients with preexcited atrial fibrillation and ② atrial ectopy was noted only transiently after electrical cardioversion, mapping and ablation of triggering sites was not attempted.^5,6
   In conclusion, ablation of the atrioventricular bypass tract during atrial fibrillation can be successfully done by analysis of intracardiac bipolar and unipolar electrogram.

References

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