Mechanism and location of atrial flutter in transplanted hearts: Observations during transient entrainment from distant sites

Objectives. This study was designed to elucidate the location and mechanism of typical atrial Butter in the transplanted heart. Background. Although the F wave morphology in atrial Butter is similar in nontransplanted and transplanted hearts, the surgical incision needed for the atrial anastomosis may create a distinct electrophysiologic substrate of atrial Butter. Methods. Entrainment from the lateral wall of the right atrium and interatrial septum was used to determine the location of atrial Butter in five patients with a transplanted heart and six patients with a nontransplanted heart. The difference between the first postpacing interval (FPPI) and the Butter cycle length (FCL) was used as an index of proximity to the circuit. Results. In the transplant group, the FPPI was equal to the FCL at sites located close to the tricuspid annulus (TA); the mean differences (+/-SD) were 1 +/- 5 and -1 +/- 2 ms at the lateral wall and interatrial septum, respectively. However, from sites close to the surgical incision at the lateral wall and at the interatrial septum, these differences were significantly longer (29 +/- 12 and 27 +/- 9 ms, respectively, p < 0.05). In the nontransplant group, the FPPI was similar to the FCL at points in the lateral wall and interatrial septum close to the TA (mean difference 7 +/- 6 and 6 +/- 11 ms, respectively) and at sites close to the crista terminalis (CT) in the lateral wall (mean difference 1 +/- 4 ms). However, in sites separated from the TA at the interatrial septum the difference was markedly longer (35 +/- 11 ms, p < 0.05). Conclusions. Atrial Butter in transplanted hearts may best be explained by macroreentry around the tricuspid ring. In nontransplanted hearts a different structure (perhaps the CT?) may be the basis for atrial Butter at the lateral wall. (C) 1997 by the American College of Cardiology.