CONDUCTION PROPERTIES OF THE INFERIOR VENA-CAVA TRICUSPID ANNULAR ISTHMUS IN PATIENTS WITH TYPICAL ATRIAL-FLUTTER

Conduction Properties of the Annular Isthmus. Introduction: A function al region of slow conduction located in the inferior right atrium has been postulated to be critical to the induction and maintenance of typ ical human atrial flutter, We reexamined the potential role of functio nal conduction delay in the annular isthmus between the tricuspid valv e and the inferior vena cava; it is within this region that such delay s have been postulated to occur, and where interruption of conduction by radiofrequency energy application has been shown to eliminate typic al flutter, Methods and Results: Thirty patients with type I atrial fl utter (30 counterclockwise, 14 clockwise) were studied. Counterclockwi se and clockwise isthmus activation times adjacent and parallel to the tricuspid valve were measured during three conditions: (1) atrial pac ing in sinus rhythm, (2) atrial flutter, and (3) entrainment of atrial flutter. During pacing in sinus rhythm at progressively shorter cycle lengths, both counterclockwise and clockwise isthmus activation times remained unchanged; decremental conduction prior to flutter induction or loss of capture was not observed. Counterclockwise isthmus activat ion time did not significantly differ during flutter (68 +/- 23 msec), inferolateral tricuspid annulus pacing (71 +/- 23 msec), or entrainme nt of flutter (72 +/- 23 msec), Similarly, clockwise isthmus activatio n times did not significantly differ between flutter (65 +/- 22 msec), proximal coronary sinus pacing (73 +/- 21 msec), or entrainment of fl utter (64 +/- 15 msec). Conclusion: Decremental conduction is not char acteristic of activation through the isthmus when activation is assess ed parallel and adjacent to the tricuspid annulus. Functional slowing or conduction delay does not develop in this region during typical atr ial flutter.