RESUMO
BACKGROUND: Differences in the duration of the excitable gap along the reentry circuit during typical atrial flutter are poorly known. AIM: To prospectively evaluate and compare the duration and composition of the excitable gap during typical counterclockwise atrial flutter in different parts of the circuit all around the tricuspid annulus. METHODS: The excitable gap was determined by introducing a premature stimulus at various sites around the tricuspid annulus during typical counterclockwise atrial flutter in 34 patients. Excitable gap was calculated as the difference between the longest resetting coupling interval and the effective atrial refractory period. RESULTS: The duration of the excitable gap, the effective atrial refractory period and the resetting coupling interval differed significantly along the tricuspid annulus. Duration of excitable gap was significantly longer at the low lateral right atrium (79±22 ms) than at the cavotricuspid isthmus (66±23 ms; P=0.002). The effective atrial refractory period was significantly longer at the cavotricuspid isthmus (160±26 ms) than at the high lateral right atrium (149±29 ms; P=0.004). Other locations, such as coronary sinus ostium, right atrial septum and atrial roof displayed intermediate values. CONCLUSION: The duration of the excitable gap differed significantly along the tricuspid annulus, with a larger excitable gap at the lateral right atrium and a shorter excitable gap at the cavotricuspid isthmus, because of longer refractory periods at the isthmus.