CONDUCTION-VELOCITY IN THE TRICUSPID VALVE-INFERIOR VENA-CAVA ISTHMUSIS SLOWER IN PATIENTS WITH TYPE-I ATRIAL-FLUTTER COMPARED TO THOSE WITHOUT A HISTORY OF ATRIAL-FLUTTER

Slower Conduction in the TV-ITC Isthmus, Introduction: In human type I atrial nutter, the electrophysiologic substrate is unclear, In order to determine if slow conduction is mechanistically important, we evalu ated conduction velocity in the tricuspid valve-inferior vena cava (TV -IVC) isthmus, right atrial free wall, and interatrial septum in patie nts with and without a history of atrial flutter undergoing electrophy siologic study. Methods and Results: Nine patients with (group 1) and nine without a history of type 1 atrial flutter (group 2) were studied , Conduction time (msec) in the right atrial free wall, TV-IVC isthmus (bidirectional), and interatrial septum was measured during pacing in sinus rhythm at cycle lengths of 600, 500, 400, and 300 msec from the low lateral right atrium and coronary sinus ostium, Conduction veloci ty (cm/sec) was calculated by dividing the distance between pacing ele ctrodes and sensing electrodes (cm) by the conduction time (sec), Cond uction velocity was slower in the TV-IVC isthmus in group 1 (range 37 +/- 8 to 42 +/- 8 cm/sec) versus group 2 (range 50 +/- 8 to 55 +/- 9 m sec) at all pacing cycle lengths (P < 0.05), However, conduction veloc ity was not different in the right atrial free wall or interatrial sep tum between groups 1 and 2, Conduction velocity was also slower in the TV-IVC isthmus than in the right atrial free wall and interatrial sep tum in group 1 patients, at all pacing cycle lengths (P < 0.05), Atria l flutter cycle length correlated with total atrial conduction time (r greater than or equal to 0.832, P < 0.05). Conclusion: Slow conductio n in the TV-IVC isthmus may be mechanistically important for the devel opment of human type I atrial putter.