Functional characterization of the crista terminalis in patients with atrial flutter: implications for radiofrequency ablation. 
The aim of the study was to investigate the conduction properties and anisotropy of the crista terminalis (CT) in patients with atrial flutter (AFL) using non-contact mapping.  The CT is a posterior barrier during typical AFL.  However, the CT has transverse conduction capabilities in patients with upper loop re-entry (ULR).  Twenty-two patients (16 males, 63 +/- 15 years) with typical AFL and ULR were included.  Non-contact mapping of the right atrium during AFL and pacing from coronary sinus (CS) and low anterolateral right atrium (LARA) was performed to evaluate transverse conduction across the CT.  During ULR, the longitudinal (CV(L)) and transverse (CV(T)) conduction velocity along and across the CT were measured.  The width of the CT conduction gap was evaluated to guide radiofrequency ablation (RFA).  No transverse CT gap conduction was found during typical AFL.  Transverse CT gap conduction was found in three patients during CS pacing and in three patients during LARA pacing.  During ULR, CV(L) was greater than CV(T) (1.28 +/- 0.43 vs. 0.73 +/- 0.30 m/s, p < 0.001).  The CV(L)/CV(T) ratio was 1.95 +/- 0.77, which was inversely related to the CT gap width (15.7 +/- 6.8 mm) (p < 0.001).  The RFA of the CT gap was successful in 18 patients.  Four patients had recurrence of arrhythmias during the follow-up of 11 +/- 3 months.  Most of the CT conduction gaps were functional and only appeared during ULR.  The width of the CT gap was inversely related to the anisotropic ratio of the CT.  The RFA of the CT gap was effective in eliminating ULR.