81 PITFALLS IN LATERAL ACCESSORY PATHWAY ABLATION: THE IMPORTANCE TO RECOGNIZE MITRAL ISTHMUS CONDUCTION BLOCK DURING REDO PROCEDURES


 
 
 Inaccurate mapping and ablation of left-lateral concealed AP can result in mitral isthmus conduction block, mimicking concentric retrograde activation. AVRT recurrences are frequent because ablation leaves the conduction through the AP intact.
 
 
 
 A 50-years-old patient with history of previous ablations of concealed left-lateral AP underwent third redo procedure due to reoccurrence of SVT. Quadripolar catheters were placed in the His bundle and RV apex; a decapolar catheter was placed in the CS. Retrograde conduction during ventricular pacing was non decremental. CS activation was concentric during AVRT. Mitral anulus was mapped via transeptal approach, showing mitral isthmus block, justifying the “concentric” atrial activation appearance, due to a left counterclockwise activation circuit and short VA interval distally to the previous ablations site. Single RF application of 1.9 sec interrupted the AP conduction. Effective ablation was confirmed by failure to induce tachycardia and by induction of AV dissociation using adenosine during ventricular pacing.
 
 
 
 Change of retrograde activation pattern during AVRT reoccurrences may be referred to iatrogenic atrial conduction block achieved during ablation, rather than to the presence of a concomitant misdiagnosed AP.
