Slow Conduction or Block of the Cavotricuspid Isthmus—Treat or Trick?

Abstract

Editorial CommentIn the earlier experience of atrial flutter ablation, up to 50% of patients had a recovery of cavotricuspid isthmus conduction during 1-12 months of follow-up with a cumulative recurrence of atrial flutter after the radiofrequency ablation for right atrial typical flutter of 5-10%. 1,2 An incomplete conduction block with a residual slow-conduction gap, as small as 8 mm, in the ablation line accounts for most acute or late recurrences of atrial flutter. 3 The radiofrequency application may slow the conduction velocity to 0.3 m/sec, which can mimic a complete isthmus block even when meticulous pacing and mapping are performed. 4 The identification of complete bidirectional isthmus conduction block still remains as the best predictor of the long-term success for the ablation of typical atrial flutter. 5,6 Vigorous attempts had been made to differentiate complete isthmus block from the slow conduction of the isthmus (Table 1). A change in the activation sequence recorded from a duodecapolar catheter positioned parallel to the tricuspid annulus, if the ablation is performed during septal pacing, indicates bidirectional block of the isthmus conduction. RV pacing was also used successfully to monitor continuously the atrial activation sequence during the ablation in cases in which it was difficult to achieve constant septal pacing. 7 The transisthmus activation time measured as the separation between the components of the double potentials has been used to identify complete block. A positive predictive value of 100% has been proposed for a separation of 110 ms and a specificity of 80% for a 50% increase in the transisthmus conduction time from baseline. 8-10 A change in the terminal P-wave from negative to positive in leads II, III, and aVF when pacing from the low RA could reflect cavotricuspid isthmus block due to the loss of the ascending activation along the RA wall opposite the pacing site, but it did not help differentiate between complete block and very slow conduction. 11,12 Further, a change in the unipolar electrogram from an RS configuration to a single positive R-wave and a polarity change in the initial deflection of the

An Alternative Method of Assessing Bidirectional Block for Atrial Flutter

“…As with virtually any method of differentiating CTI conduction from block, this method may not have discerned extremely slow conduction across the CTI 1 . Our study method performed at least as well as our standard method.…”

“…Several methods are available to assess the presence or absence of bidirectional block across the CTI 1–6 . These include assessing the tricuspid annular activation sequence during both coronary sinus (CS) and low lateral right atrial pacing, measuring the separation between the double potentials across the CTI, and by using differential pacing maneuvers 1–6 . A CS catheter is commonly used to sense and pace the interatrial septum.…”