Intraoperative mapping of atrial activation before, during, and after the Mustard operation.

Thirty-eight patients with transposition of the great arteries underwent intraoperative mapping of atrial epicardium and endocardium during various stages of the operative procedure. The purpose was to determine the electrophysiological basis of the postoperative supraventricular arrhythmias associated with this operation. Comparisons were made between atrial activation patterns and times before and after each of the following stages: (1) cannulation, (2) atriotomy, (3) excision of atrial septum and coronary sinus, and (4) placement of intra-atrial baffle. The first stage produced no significant changes in atrial activation times or patterns but did demonstrate a shift of the functional pacemaker to the sulcus terminalis in 8 of 14 patients studied. Longitudinal atriotomy did not significantly lengthen atrial activation. Transverse atriotomy did not alter activation times of the His bundle but did significantly change patterns of epicardial and endocardial activation. Excision of the septum and coronary sinus always produced block in the posterior crista terminalis, and placement of a baffle worsened this block. Four patients developed nodal rhythm on the operating table and had both a posterior crista terminalis block and anterior septal block. Suggestions for modification in the surgical techniques were advanced to help prevent rhythm disturbances in paitients undergoing transvenous correction of transposition of the great arteries.