Comparative electrophysiological evaluation of atrial activation and sinoatrial node function following Senning and Mustard procedures: an experimental study

Intermediate outcome after Mustard and Senning procedures: A study by the Congenital Heart Surgeons Society

Although atrial switch is rarely performed today except as part of a "double switch" operation, there continues to be interest in the long-term outcome of the procedure because of the many Mustard and Senning survivors who are in follow-up. In contrast to most other reported series on atrial switch, this study by the Congenital Heart Surgeons Society (CHSS) is a prospective multiinstitutional study of patients encountered in a relatively short time frame during the late 1980s. Between 1985 to 1989, 20 centers with surgeons belonging to the CHSS prospectively registered patients <15 days of age presenting with simple or complex transposition of the great arteries (TGA). The patients were assigned to protocol groups based on intent to treat (arterial switch, Mustard, or Senning). Data were abstracted in the Data and Analysis Center, which in most cases, conducted the annual follow-up. Among the 281 patients who had an atrial switch, there were 108 Mustard and 173 Senning procedures. For the combined atrial switch population, the survival at 1 month, 5 years and 10 years was 90%, 85%, and 84%, respectively. Results for the Mustard were better than for the Senning with survival at 1 month, 5 years, and 10 years being 96% versus 86%, 95% versus 80%, 93% versus 78%; (P <.001) for Mustard versus Senning. While the major mortality risk occurred in the first postoperative month for both groups, thereafter, the late rate of death from 1 to 10 years after operation was 0.78%/year Senning versus 0.23%/year Mustard (P <.05). TGA/ventricular septal defect (VSD), lower weight, younger age, cardiac positional anomalies, and procedures on the left ventricle (LV) outflow all correlated significantly with poor outcome. There were 19 reoperations including 2 for right ventricle (RV) failure, 12 for pathway obstruction, and 5 for baffle leak with a 36% overall mortality. Freedom from any pathway obstruction at 10 years was 95%. A permanent pacemaker was required in 21 patients with the significant risk factors including TGA/VSD and a Senning, and previous atrial septectomy. Freedom from a pacemaker insertion at 10 years was 91%. For both Mustard and Senning, 60% of patients were in New York Heart Association (NYHA) functional Class I with the remaining in Class II. This study of atrial switch outcomes by the CHSS suggests that the subgroup undergoing a Mustard procedure had better early and late survival than those undergoing a Senning operation. The overall incidence of baffle pathway obstruction was low though reoperation for this complication carried high risk. Serious arrhythmia requiring medication and the need for a permanent pacemaker were both relatively uncommon. The incidence of severe right heart failure was very low, although only 60% of patients are unrestricted in their activity. Copyright 2000 by W.B. Saunders Company

Arrhythmias and intracardiac conduction after the arterial switch operation

Intraatrial baffling procedures such as the Mustard or Senning repair of transposition of the great arteries have been associated with a high incidence of cardiac arrhythmias. These abnormalities are thought to arise from trauma to the sinus node and atrial muscle during the procedure. In the arterial switch operation, there is little intraatrial manipulation other than the repair of the atrial septal defect. In theory, rhythm disturbances after the arterial switch operation should be less prevalent. From January 1, 1983, to December 31, 1990, 390 patients (230 with intact ventricular septum and 160 with a coexisting ventricular septal defect) underwent an arterial switch operation. Electrocardiograms and 24-hour Holter monitor studies were obtained in the 364 survivors at hospital discharge and during follow-up. Limited intracardiac electrophysiologic studies were performed 6 to 12 months after the operation.

RESULTS

Atrioventricular node function was preserved in most patients; seven patients (2%) had first-degree, two (0.7%) second-degree, and five (1.7%) had complete atrioventricular block (all with coexisting ventricular septal defect). All five patients with complete heart block received a permanent pacemaker. In those patients not having a permanent pacemaker, sinus rhythm was present in 96% on the surface electrocardiogram and 99% during 24-hour Holter monitor studies (1 month to 8.5 years, mean 2.1 years after the operation). Intracardiac electrophysiologic studies (n = 158) demonstrated normal corrected sinus node recovery times and AH intervals in 97% of patients. Atrial ectopy was present in 152 of 172 (81%) patients, with the majority (64%) of patients having only occasional premature beats without repetitive forms. Ventricular ectopy was a frequent finding during 24-hour monitoring. At hospital discharge 70% had ventricular ectopy; these values fell to 57% (in patients with intact ventricular septum) and 30% (in patients with a coexisting ventricular septal defect) at follow-up. In the early postoperative period, there were 25 episodes of supraventricular tachycardia (14 of which required therapy), 6 episodes of junctional ectopic tachycardia, and 9 episodes of ventricular tachycardia. The incidence of supraventricular tachycardia had fallen to 5% at follow-up, with no atrial flutter or fibrillation noted. Three patients had ventricular tachycardia on follow-up Holter studies. In summary, our results confirm the theoretical advantages of anatomic correction over atrial level correction of transposition of the great arteries with respect to preservation of sinus node function and low incidence of clinically significant tachyarrhythmias.