The Boston Circulatory Arrest Study: an analysis

Abstract

1256 The Journal of Thoracic and Card I n their two articles published in the November issue of the Journal, the group from the Children’s Hospital in Boston have provided us with the best clinical data available comparing deep hypothermic circulatory arrest (DHCA) with hypothermic, continuous low-flow bypass (LF)—2 cardiopulmonary bypass (CPB) strategies that are commonly used during the repair of congenital heart defects in infants. It is relevant to provide a brief historical perspective regarding how and why these studies were designed. DHCA became popular after its use was reported by Kirklin and associates in 1961 and later in neonates and infants by Barratt-Boyes and associates in 1970 because it greatly simplified cardiac repair in infants in an era that did not have the sophisticated CPB technology (including thin-walled cannulas with excellent flow characteristics, smaller circuits with membrane oxygenators, and much more) that we enjoy today. By using DHCA, surgeons could repair intracardiac defects in a bloodless field unencumbered by cannulas. Furthermore, surgeons avoided many of the complications created by the more primitive CPB systems, and this most likely produced success in an era when prolonged exposure to CPB was very likely detrimental. Results were generally favorable, and the use of DHCA made cardiac repair in infants reproducibly possible. As technology improved and surgeons began to tackle repair of more complex lesions, DHCA became a staple in the armamentarium of cardiac surgeons. Its use became so ingrained in the practice patterns of cardiac surgeons that it was unusual in the 1980s to find successful pediatric cardiac centers anywhere in the world that did not use DHCA on a routine basis. By the late 1980s, the seeds of concern were germinating regarding the effect of DHCA on the neurologic development of the infants exposed to it. This marked a subtle, but substantial, shift in cardiac surgery for infants—the field was beginning to focus on long-term quality of life rather than just on initial survival. Compared with mortality rates in the earlier days of surgery for congenital heart disease, which were high, mortality after infant heart surgery was becoming less frequent, and rates were comparable with those experienced for adults having more routine procedures (such as coronary artery bypass grafting)—all despite the increasing complexity of defects being repaired by congenital heart surgeons. It was an important era because it heralded the development of so many techniques that we consider commensurate with modern infant heart surgery. Surgeons were shifting to primary repair versus palliation of repairable defects because systems allowed this with predictable survival. Membrane oxygenators; improved methods of myocardial protection; more finely engineered surgical instruments, cannulas, and sutures; and improved prosthetic materials, along with numerous other advances in technology and surgical experience, were enabling surgeons to rethink the systems and techniques that their infant patients were exposed to during surgical reconstruction. Understanding of the “safe” period of DHCA was still evolving. In general, it was considered acceptable to expose infants to circulatory arrest for as long as 45 to 60 minutes at 18°C. Reports appeared in the literature that attempted to characterize the effect of DHCA on neurodevelopmental outcome. For the most part, these reports were retrospective, noncontrolled reviews of neurologic outcomes for widely dissimilar patients, and they generated increasing concern that DHCA might be associated with movement disorders such as choreoathetosis and with 10-17 generalized poor neurodevelopmental outcomes. Against the backdrop of these