Background-Gaining anatomic information about the posterior isthmus is not generally part of flutter ablation procedures. We postulated that right atrial (RA) angiography could rationalize the ablation approach by revealing the conformation of the isthmus. Methods and Results-In 100 consecutive patients, biplane RA angiography was performed before ablation to guide catheter contact with the isthmus along its length. Angiography showed a wide variation in the width of the isthmus (17 to 54 mm; 31.3Ϯ7.9), its angle with the inferior vena cava in the right anterior oblique projection (68°to 114°; 90.3Ϯ9.0°), and its lateral position relative to the inferior vena cava in the left anterior oblique projection. A deep sub-Eustachian recess was revealed in 47%, with a mean depth of 4.3Ϯ2.1 mm (1.5 to 9.4). A Eustachian valve was visualized in 24%. Ablation resulted in bidirectional conduction block (which could be transient) in all, with a median of 2 dragging radiofrequency (RF) applications (2.3Ϯ2.5 RF applications; 57°C, Յ99 seconds each). Permanent block was achieved in 99%, with a median of 3 RF applications (3.4Ϯ3.0). The presence of a Eustachian valve or concave isthmus was associated with statistically more RF applications; the same trend was seen for patients with deep pouches. The number of RF applications decreased statistically throughout the study, indicating a learning curve. No patient had a recurrence after a follow-up of 13Ϯ11 months. Conclusions-Right atrial angiography reveals a highly variable isthmus anatomy, often showing particular configurations that can make ablation more laborious. Rational adaptation of the ablation approach to these anatomic findings may contribute to successful ablation.

Knowledge of anatomical predilection sites and mapping the right (and/or left) atrium with a 'sweeping Halo technique' allow for effective ablation of most post-surgical atrial tachycardias. Severely damaged atria with multiple arrhythmias may require 'preventive' ablation of all recognizable channels.

Effective creation of linear lesions is difficult. Pliable catheters that conform to the endocardial contour give the best results. The only endpoint that reliably predicted histological transmural continuous necrosis was development of split potentials indicating conduction block.