ATRIAL-FLUTTER AFTER LATERAL TUNNEL CONSTRUCTION IN THE MODIFIED FONTAN OPERATION - A CANINE MODEL

Intraatrial reentrant tachycardia, or atrial Butter, is a common posto perative problem after Fontan repair, which involves an atriopulmonary connection, A modification of Fontan repair, total cavopulmonary conn ection, minimizes the portion of the right atrium exposed to stretch a nd hypertension; however, atrial Butter continues to occur after this procedure. We postulated that the intraatrial lateral tunnel suture li ne of total cavopulmonary connection, in the absence of physiologic al terations such as atrial hypertension or stretch, provides the necessa ry electrophysiologic substrate for atrial Butter, The purpose of this study was to produce a canine model of total cavopulmonary connection (1) to establish that the intraatrial suture line alone is sufficient to permit sustained atrial Butter and (2) to characterize the pathway s of resulting reentrant arrhythmias. After induction of general anest hesia, 25 to 30 kg dogs (rt = 17) underwent median sternotomy, cradlin g of the pericardium, and placement of a pacing electrode on the right atrial appendage. Normothermic cardiopulmonary bypass was initiated. The total cavopulmonary connection suture line was placed through a st andard right atriotomy, simulating construction of the lateral tunnel, After closure of the atriotomy, 253 point unipolar atrial endocardial form-fitting electrodes were placed through bilateral ventriculotomie s. By means of atrial burst pacing and programmed extrastimulation, in duction of atrial Butter was attempted. If atrial Butter could not be induced, isoproterenol was infused and the stimulation protocol was re peated. After induction of atrial Butter, mapping of the activation se quence was performed. Before suture line placement, no dog had inducib le atrial Butter. After placement of the suture line, sustained atrial Butter was reproducibly induced in every dog, although isoproterenol was required for this in three (17,6%), The mean Butter cycle length w as 177 +/- 30 msec. In each case, the atrial Butter circuit was limite d to the right atrium, with the left atrium being passively activated. The atrial Butter circuit was dependent on a corridor of myocardium t hat resulted from conduction block on the free wall, created by the la teral margin of the total cavopulmonary connection, In no case was the atriotomy integral to the atrial Butter circuit, This study establish es that the total cavopulmonary connection baffle suture line alone, w ithout alteration in circulatory physiology, creates a sufficient anat omic substrate for atrial flutter in a short-term canine model. Deline ation of the anatomic boundaries of the reentrant circuit raises the p ossibility of targeting areas within the circuit that could be modifie d, potentially reducing the incidence of postoperative atrial flutter after total cavopulmonary connection.