Anatomic and electrophysiologic differences between chronic and paroxysmal atrial flutter: intracardiac echocardiographic analysis.

Background: It remains unknown why atria] flutter (AFL) occurs as either a chronic or paroxysmal arrhythmia. Purpose: The aim of the study was to compare intracardiac echocardiographic (ICE) images of the crista terminalis (CT) and transverse conduction properties of the CT between chronic and paroxysmal forms of common AFL. Methods: Chronic AFL (n = 7) was defined as non-self-terminating AFL lasting > 1 month, and paroxysmal AFL (n = 8) was defined as an intermittent arrhythmia with symptomatic episodes of 24 hours maximum duration. ICE images of the right atrium were recorded with a 9 F 9-MHz intracardiac ultrasound catheter during pullback at 0.5-mm intervals from the superior vena cava to the inferior vena cava triggered by electrocardiogram and respiration. The two-dimensional image of the right atrium was reconstructed into a three-dimensional (3-D) image. Results: Three-dimensional images from patients with chronic AFL showed the CT to be thick and continuous, and conduction across the CT was blocked at a pacing rate just above sinus rhythm in all seven patients. In contrast, 3D images from paroxysmal AFL showed the CT to be thin and discontinuous, and conduction across the CT during midseptal pacing was observed in five of the eight patients. Conclusion: The nature of AFL is deter-mined, at least in part, by anatomic and electrophysiologic characteristics of the CT.