Successful Ablation of Resistant Left Lateral Accessory Pathway and Coexisting Atypical Atrioventricular Nodal Reentrant Tachycardia
A 41-year-old man had a 5-year history of palpitations with exertion, due to a paroxysmal supraventricular tachycardia. The paroxysmal supraventricular tachycardia was intractable to medical treatment, and he was referred for electrophysiological study and RF ablation. The documented electrocardiography of supraventricular tachycardia revealed a heart rate of 168 bpm and no definitive P waves. After obtaining an informed consent, all antiarrhythmic medications were discontinued, and an electrophysiological study was performed. Under local anesthesia and using sterile technique, two quadripolar electrode catheters (St. Jude Medical, Inc., Minnetonka, MN, USA) were positioned to record the activity of the His bundle and right ventricular (RV) apex. The high right atrium (RA), low RA, and coronary sinus (CS) were mapped with a deflectable duo-decapolar catheter (St. Jude Medical, Inc., St. Paul, MN, USA), inserted via the left femoral vein. Intracardiac electrograms were recorded using a Prucka CardioLab™ electrophysiology system (General Electric Health Care System, Inc., Milwaukee, WI, USA).\nThe retrograde conduction pattern was eccentric and the earliest retrograde atrial activation was recorded in the distal CS during RV pacing (). A narrow QRS tachycardia was repeatedly inducible with programmed atrial and ventricular stimulation (). The mechanism of tachycardia was confirmed to be AVRT, based on the advancement of atrial activation, induced by the ventricular extra-stimulation at the time of the refractoriness.\nAblation of the left lateral AP, during a sinus rhythm, was first attempted via a transseptal approach. RF energy was delivered to this site at a temperature of 55℃, but it did fail to eliminate the bypass tract. Despite the repeated RF applications around the left lateral region, the tachycardia remained inducible with programmed atrial stimulation. Extensive RF applications from the left lateral to the posterolateral region were ineffective, as well. After injection of the contrast medium under fluoroscopy in left anterior oblique 45° and right anterior oblique 30° projections, the ablation catheter was positioned in the intra CS (). RF energy delivered at this site, using a maximum power of 30 Watts () and a maximum electrode-tissue interface temperature of 50℃ eliminated the retrograde conduction over the AP ().\nUpon programmed atrial stimulation, atypical AVNRT was initiated with antegrade conduction through the fast pathway and retrograde conduction through the slow pathway (fast-slow type) (). The induced tachycardia had a tachycardia cycle length (TCL) of 340 msec, a short AH (140 msec) interval, a long HA interval (210 msec), AH/HA ratio <1, and a long VA interval, over 60 msec (185 msec). Single ventricular extra stimuli with a coupling interval of 360 msec were unable to reset the tachycardia. Following a cessation of ventricular entrainment pacing, the tachycardia resumes with a V-A-V response, and the values of post-pacing interval minus TCL were greater than 115 msec (). Thus, a fast-slow type AVNRT was confirmed. The tachycardia was reproducibly induced upon a decremental atrial pacing and terminated with atrial overdrive pacing. A 7-Fr, 4-mm-tip deflectable ablation catheter (Boston Scientific Corp., Natick, MA, USA) was positioned at the roof of the CS ostium, and slow pathway ablation was attempted in the inferior region of the Koch's triangle, where the local A/V was <0.5. An accelerated junctional rhythm was immediately observed and AVNRT could not be induced with either decremental atrial pacing or programmed atrial stimulation. A post-RF ablation electrophysiology study with isoproterenol did not induce any supraventricular tachycardia. The patient remained asymptomatic three years later.