Using intracardiac catheter recordings from the his and proximal coronary sinus to distinguish isthmus conduction block during catheter ablation of type I atrial flutter

Isthmus conduction block, demonstrated with the use of multipolar catheter recordings, is considered the preferred endpoint for ablation of type I-atr ial flutter. This study investigated the feasibility of using recordings fr om the His-and coronary sinus (CS) td document isthmus conduction block. Is thmus conduction block was produced with Linear radiofrequency (RF) ablatio n in 27 patients with type I atrial flutter. In 13 patients [group I), RF w as delivered until bidirectional isthmus conduction block was demonstrated with multipolar Halo catheter recordings. In 14 patients (group II), RF was delivered during pacing front the lateral isthmus at 600 ms until a revers al in activation of the proximal CS and I-lis occurred, At this point, data from the Halo recordings were reviewed to see if reversal correlated with conduction brock; if nod further ablation was performed until block was dem onstrated. The initial reversal in His and CS activation during RF energy d elivery correlated with isthmus block in only 4 (28.6%) of 14 patients in g roup II; Additional RF delivery produced isthmus block in the other ten pat ients resulting in a further increase in the St-CS interval of 35 +/- 20 ms . A His-CS interval of at least -40 ms signified isthmus block with a sensi tivity and specificity of 48% and 100%, respectively. Reversal in His-CS ac tivation during pacing from the lateral margin of the isthmus is not specif ic for the creation of isthmus block. While activation of the proximal CS b ipole > 40 ms after activation of the His appears specific for isthmus bloc k, the low sensitivity of this finding limits its clinical use.