Characterization and surgical ablation of acute atrial flutter following the mustard procedure: A canine model

Background. A high incidence of refractory atrial flutter has been reported as a late postoperative complication of the Mustard procedure. The objective of this study was to reproduce experimentally the long-cycle-length atrial flutter that occurs in these patients and attempt to ablate the arrhythmia surgically. Methods and Results. Nine dogs underwent a simulated Mustard procedure, which included a longitudinal right atriotomy, a septectomy, and a continuous suture line placed in the usual baffle location. All animals were subsequently inducible into sustained atrial flutter after surgery. Activation-time electrophysiological maps of the various pathways of atrial reentry were determined using atrial endocardial molds containing 252 bipolar electrodes. Four distinct reentrant circuits were observed in the following locations: (1) around the tricuspid valve annulus (n=5; cycle length, 175±5 milliseconds), (2) around the atriotomy incision (n=2; cycle length, 208±3 milliseconds), (3) in a pathway involving both atria (n=1; cycle length, 180 milliseconds), and (4) around the mitral valve (n=1; cycle length, 135 milliseconds). A common pathway for eight of the nine reentrant circuits included the free-wall segment of the right atrium (excluding the mitral valve circuit). In the first three animals, surgical ablation of the atrial flutter was not attempted, but an incision made perpendicular to the atriotomy down to the tricuspid valve annulus resulted in termination of the atrial flutter in the other six animals. One of these animals was subsequently inducible into an atrial flutter of different morphology (cycle length, 125 milliseconds) that involved an isolated left atrial reentrant circuit. Conclusions. The Mustard procedure creates several anatomic substrates that increase the probability of the heart to develop atrial flutter, and these may be amenable to subsequent surgical correction.