811 Conduction Properties of the Crista Terminalis in Patients with Typical Atrial Flutter: Basis for a Line of Block in the Reentrant Circuit CHING-TAI TAT, M.D., SHIH-ANN CHEN, M.D., YI-JEN CHEN, M.D., WEN-CHUNG YU, M.D., MING-HSIUNG HSIEH, M.D., CHIN-FENG TSAI, M.D., CHIEN-CHENG CHEN, M.D., YU-AN DING, M.D., and MAU-SONG CHANG, M.D. From the Division of Cardiology, Department of Medicitie. National Yang-Ming University. School of Medicine. Veterans General Hospilal-Taipei. Taiwan, Republic of Chitia Conduction Properties of the Crista Terminalis. Introduction: Previous mapping studies in patients with typical atrial flutter have demonstrated the crista terminalis to he a posterior harrier of the reentrant circuit forming a line of hlock. However, the functional role of the crista terminalis in patients with or without a history of atrial flutter is not well known. The aim of this study was to determine whether the conduction properties of the crista termi- nalis are difl'erent hetween patients with and those without a history of atrial flutter. Methods and Results: The study population consisted of 12 patients with clinically docu- mented atrial flutter (group 1) and 12 patients with paroxysmal supraventricular tachycardia as well as induced atrial flutter (group 2). A 7-French, 20-pole, deflectahle Halo catheter wa»i posi- tioned around the tricuspid annulus. A 7-French, 2U-pole Crista catheter was placed along the crista terminalis identified hy the recording of douhle potentials with opposite activation se- quences during typical atrial flutter. After sinus rhythm was restored, pacing from the low pos- terior right atrium near the crista terminalis was performed at multiple cycle length to 2:1 atrial capture. No douhle potentials were recorded along the crista terminalis during sinus rhythm in hoth groups. In group 1, the longest pacing cycle length that resulted in a line of hlock with dou- hle potentials along the crista terminalis was 638 ±119 msec. After infusion of propranolol, it was prolonged to 832 ± 93 msec without change of the interdeflection intervals of douhle poten- tials. In group 2, the longest pacing cycle length that resulted in a line of block with douhle po- tentials along the crista terminalis was 214 ± 23 msec. After infusion of procainamide, it was prolonged to 306 ± 36 msec with increase of interdeflection interval of double potentials. Conclusion: The crista terminalis forms a line of transverse conduction block during typical atrial flutter. Poor transverse conduction property in the crista terminalis may he the requisite suhstrate for clinical occurrence of typical atrial flutter. (J Cardiovasc Electrophysiol, Vol. 9, pp. HN-819, August I99H) atrial flutter, crista terminalis, double potentials Supported in part by Grants NSC 87-23I4-B-OIO-O58. 87-2314-B- 010-059. 87-23I4-B-075-070. and 87-2314-B-075-071 from the National Science Council and Grants VGHYM-S4-3O and VGHYM-S4-31 from the Tzou's Foundation, Taipei. Taiwan. Re- public of China. Address for correspondence: Shih-Ann Chen, M.D.. Division of Cardiology. Department of Medicine, Veterans Generai Hospital- Taipei. 201 Sec 2. Shih-Pai Road. Taipei, Taiwan, Republic of China. Fax: 886-2-2873S656. Manuscript received 24 February 1998; Accepted for publication 26 May iy98. Introduction Previous mapping studies in patients with typ- ical atrial flutter have demonstrated a macroreen- trant circuit in the right atrium supported by anatomic barriers such as the crista terminalis, eu- stachiati ridge, and tricuspid annulus.' '" Olgin et al."^ used intracardiac echocardiography to place a multipolar catheter along the length of the crista terminalis and found split potentials along this