When patients with congenital heart issues have an operation, surgeons have to proceed with an “eye of faith” as they work around conduction tissue - a network of cells and electrical signals that control the beating of a heart. Not visible to the naked eye, conduction systems vary person to person, but they’re particularly difficult to pinpoint in patients with complex congenital heart defects (CHD). When surgeons can’t locate conduction tissue during surgery, they risk accidentally injuring it. This can cause heart block, a form of arrhythmia that often creates the need for a pacemaker and more operations. Surgeons have long wanted to “see” the conduction system. Now, a promising technique provides that vision and could lead to consistent identification of conduction tissue in complex cases of CHD.

The innovation is a collaboration between surgeons from the Department of Cardiac Surgery and cardiologists from the Electrophysiology Service in the Department of Cardiology at Boston Children’s Hospital (Boston, MA, USA). The new technique updates an approach not often used: A catheter collects electrical signals on open, beating hearts during surgical repair. The technique lets surgeons mark the spot of conduction tissue with a marker or small suture so they can avoid injuring it.

For the team of cardiologists who spearheaded the effort, preventing heart block is a much-preferred alternative to implanting a pacemaker after a child has developed a postsurgical arrhythmia related to scarred conductive tissue. As far back as the 1970s, clinicians attempted to use electrophysiology (EP) tools to map the conduction system during surgery, but it didn’t become a standardized practice for a variety of reasons. With cardiac surgeons performing more complex CHD operations each year, leading to an increase in heart block, the cardiologists took another look at the tools of their trade to prevent injuring conduction tissue.

After some testing, they found that an FDA-approved grid-mapping catheter that is often used by electrophysiologists to treat arrhythmias could quickly and accurately pinpoint conduction tissue during surgery. The team likens this EP tool to a metal detector that helps beachcombers find objects buried in sand. In many complex CHD cases, surgeons previously had to estimate where conduction tissue was. Now, the EP tool allows surgeons to improve surgery in the moment and create a catalog of findings that can be further studied. For instance, they are finding that anatomical variables, such as the position of ventricles or the heart itself, can influence the location of the conduction system.

The EP tool has aided more than 150 surgeries at Boston Children’s in the past two years and has prevented heart block in many patients - especially those with heterotaxy who need complex biventricular repair. In that patient group, heart block has decreased from over 14% to less than 3% when conduction mapping is performed during surgery. The team is now working on several fronts to share the insight they have gained from EP mapping and advance its mainstream use in complex CHD surgeries. The team is creating 3D models of the heart of every CHD patient who benefits from EP mapping. Ultimately, those models will be available in a digital library so clinicians can review the influences that different anatomies have on conduction and take a more personalized approach to a surgery.

“For certain types of CHD, it’s already been a major game-changer,” said Eric Feins, MD, a surgeon in the Benderson Family Heart Center’s Department of Cardiac Surgery. “We’re understanding where conduction tissue is - and sometimes finding out it’s in a location we didn’t expect.”

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