Upper turnaround point of the reentry circuit of common atrial flutter-three-dimensional mapping and entrainment study

Although the anterior and posterior boundaries of cavotricuspid isthmus-dependent atrial flutter (AFL) are reported to be located at the tricuspid annulus and sinus venosa region or crista terminalis, the exact upper turnaround point of the AFL circuit remains unclear. The aim of this study was to determine the upper turnaround site of the AFL circuit by means of three-dimensional (3D) mapping and entrainment pacing. Subjects were 21 patients with counter-clockwise AFL in whom high-density mapping of the high right atrium (RA) and superior vena cava (SVC) orifice was performed with an electroanatomical or non-contact mapping system. Entrainment pacing was performed around the SVC-RA junction. In 20 of the 21 patients, the wavefront from the septal RA split into two wavefronts: one that traveled anterior to the SVC and another that traveled to the posterior RA where it was blocked. In the remaining patient, the wavefront from the septal RA split into two wavefronts: one that propagated through the anterior portion of the SVC orifice and another that propagated transversely across the posterior portion of the SVC orifice. The two wavefronts joined in the lateral RA. Entrainment pacing from the SVC-RA junction demonstrated that the anterior boundary was within the circuit in all patients, but the posterior boundary also constituted a circuit in four patients. We surmise that the upper turnaround site of the AFL circuit is located in the anterior portion of the SVC-RA junction in the majority of patients with AFL.