Commentary: Time to take a stroll around the block?

Abstract

Central MessageThis is a major foray into intraoperative mapping of the conduction system. The goal is to guide surgeons around the conduction system and reduce the incidence of postoperative complete AV block.See Article page XXX. This is a major foray into intraoperative mapping of the conduction system. The goal is to guide surgeons around the conduction system and reduce the incidence of postoperative complete AV block. See Article page XXX. Despite the considerable advances in pediatric heart surgery, complete atrioventricular (AV) block has remained a stubborn and frustrating complication. Feins and colleagues1Feins E.N. O'Leary E.T. Davee J. Gauvreau K. Hoganson D.M. Schulz N. et al.Conduction mapping during complex congenital heart surgery: creating a predictive model of conduction anatomy.J Thorac Cardiovasc Surg. 2023; (XXX:XXX)Google Scholar report their experience attempting to define the His bundle locations in various forms of complex congenital heart disease to provide surgeons with a roadmap to avoid conduction tissue. Since the anatomy of the normal conduction system was defined in the 1800s,2Cavero I. Holzgrefe H. Remembering the canonical discoverers of the core components of the mammalian cardiac conduction system: Keith and Flack, Aschoff and Tawara, His, and Purkinje.Adv Physiol Educ. 2022; 46: 549-579Crossref Scopus (1) Google Scholar significant advancements have been made to delineate its expected course in various cardiac anatomies.3Anderson R.H. Yen Ho S. Becker A.E. The surgical anatomy of the conduction tissues.Thorax. 1983; 38: 408-420Crossref PubMed Scopus (67) Google Scholar Despite these advances, the incidence of pacemaker requirement remains in excess of 15% in some complex anatomy subgroups.4Liberman L. Silver E.S. Chai P.J. Incidence and characteristics of heart block after heart surgery in pediatric patients: a multicenter study.J Thorac Cardiovasc Surg. 2016; 152: 197-202Abstract Full Text Full Text PDF PubMed Scopus (32) Google Scholar Although there have been many histology-based studies defining conduction tissue anatomy as well as functional studies assessing His bundle locations during transcatheter procedures, each has is limitations for surgeons faced with complex repairs while trying to avoid injuring conduction tissue that is invisible to the naked eye. This is the first large-scale attempt to fully define the functional His bundle location in various complex cardiac anatomies while the heart is in an open, decompressed but beating state. With this strategy they were able to successfully identify His signals in 96% of patients. There were no complications encountered related to mapping, including no patients developing an air embolus. They report the surgical results as well as create a model to explore the His bundle relationship to various anatomic variables and ventricular septal defect locations. A main finding is that despite their effort there was still a 10.5% incidence of complete AV block requiring pacemaker placement, although the incidence of block was only about 3% in heterotaxy patients, compared with a prior report from their center where 14% required pacemakers. There are several potential reasons for the incidence of block remaining high. Although they are able to map the His bundle in a majority of patients, they comment on the inability to map the His bundle in a select few as a limiting factor, which they believe was due to the limitations of using catheters designed for a transcatheter approach. Another issue is that while mapping identified the His bundle, it did not delineate the anatomy of the entire conduction system, so despite preserving His bundle function, the surgeon may injure the compact AV node or conduction tissue distal to the His bundle. There is also the potential that despite identifying the His location one may find that the only feasible place to anchor a patch may be in close proximity, and although extra care may be taken there may be conduction damage nonetheless. Overall, this is novel work and represents a significant addition to current knowledge. One question that remains is whether or not the conduction system location is consistent enough to truly be predictable, or if there is enough variability to preclude a confident prediction in patients with certain types of anatomy. Simply put, would we consider routinely adding this step to a complex congenital repair, or will these studies provide a master atlas such that a roadmap need not be created on each patient? Conduction mapping during complex congenital heart surgery: Creating a predictive model of conduction anatomyThe Journal of Thoracic and Cardiovascular SurgeryPreviewThe study objectives were to report on a growing experience of conduction system mapping during complex congenital heart surgery and create a predictive model of conduction anatomy. Full-Text PDF